Great article by Scientific American about reading scientific papers!
After a long respite on this blog due to limited access to a computer while my laptop was being fixed, I’m happy to make the belated announcement that I’ll be joining the Population Biology graduate group as a first-year PhD student at UC Davis in Fall 2017!
My primary advisor will be Jennifer Gremer, a new plant ecologist in the Evolution and Ecology department. I’ve been working closely with her during my time as a Research Assistant in Johanna Schmitt’s lab, the position I currently hold, because she is co-leading a project that takes up the majority of my responsibilities as a tech.
I’m even thinking about doing some of my own PhD research on the project I’ve been working on for the past year – we are studying life history variation and local adaptation in the native California wildflower Streptanthus tortuosus in the context of its potential ability to adapt to climate change.
S. tortuosus is an ideal study organism for these questions because it displays a wide range of morphologies and adaptations across its range, which encompasses most of California and elevations from about 500-12,000 feet. It’s also classified as a biennial or perennial in many field guides, but we’ve seen it display an annual life history as well. In fact, we think we’ve found a trend in life history: increasing perenniality with increasing elevation. It also responds differently to vernalization treatments, flowers at different times, and grows at different rates in a common garden, providing some evidence for genetic differences in these traits.
I am especially interested in finding out whether this species is locally adapted to snowmelt timing on mountainsides. I have tentative plans to explore this question further this summer at Lassen Volcanic National Park, where I have observed plants displaying very different phenologies dependent on snowmelt timing across very short physical distances. These plants are bad at selfing, which means they rely on outcrossing by pollinators to reproduce, so I also want to study the landscape genetics of the species at Lassen – are there different “genetic cohorts” reproducing with each other every year because they consistently have open flowers at the same time as a consequence of when they emerge from the snow?
Hopefully, I can equip myself with the conceptual, statistical, and methodological tools to begin answering these questions during my first year of classwork as a PhD student. Whether or not this ends up being my dissertation project, I’m learning a lot about plants, genetics, and conducting long-term independent research in the meantime!
This paper comes from an open-access journal, Ecosphere! Woohoo! You can read the whole paper yourself for free here: Effects of climate change on phenologies and distributions of bumble bees and the plants they visit I encourage you to read both the scientific paper and my summary to get the most complete picture of the story – this paper is more comprehensible than most!
Shameless plug for native bees:
Honey bees get a lot of attention from the media because they help to pollinate the food we eat, but in terms of their conservation, agriculture is really the only reason we would focus on protecting honey bees. They are actually a non-native species from Europe, are not in any danger of dying out as a species, and in the wild, they often outcompete native bee species for floral resources, potentially causing harm to ecosystems overall. The following paper is about native or naturalized bumblebee species and describes one of the problems native bees are facing in nature due to climate change. Read on to learn more!
In this paper, the authors are focusing on bee and plant phenology, which is the timing of life events like birth, death, and peak activity, and in plants specifically, events like sprouting, budding, flowering, fruiting, and senescing (pre-programmed partial or complete death of plant parts, like when oak trees shed their leaves in the fall). Bees and plants interact with each other in a mutualistic relationship, meaning they help each other out with functions necessary to survival. This occurs primarily through pollination, whereby bees collect nectar and pollen to eat and feed their young, and the plants receive fertilization so they can produce successful offspring. But this mutualism can only occur when the bees and plants are operating on the same timeline – bees need to be buzzing around searching for food at the right time of the season, namely, when flowers are open on plants, for pollination to proceed. With changes in climate, bees and plants may need to shift their phenologies to coincide with optimal weather conditions – but a big question in ecology right now is, will they shift their phenologies in the same way so that they stay matched up with each other? This potential phenological mismatch between bees and plants, or asynchrony, is what Pyke and his colleagues explore in this paper.
- Organisms are expected to respond to changing climate by shifting geographical ranges and phenology toward remaining in their compatible climate zones
- Such changes may result in spatial or temporal mismatches between interacting species (asynchrony)
- This study examines mismatches arising from climate-induced shifts in plants and their pollinators
- Surveyed bumble bees and the plants they visit in 1974 and 2007 at the Rocky Mountain Biological Laboratory in Colorado (33 years)
- Tested hypotheses arising from observed climate change
The Rocky Mountain Biological Laboratory (RMBL) has been providing scientists with a natural outdoor laboratory since 1928. Many famous studies have been conducted there, and an author on the paper, David Inouye (below), has spent summers performing experiments on pollination ecology at RMBL since 1971.
RMBL is a great place to study shifts in phenology due to climate change, because changes in temperature occur very rapidly with changes in altitude on the slopes of mountains. In the 33-year intervening period between their two study years, for example, monthly spring and summer temperatures have increased 2 degrees C on average, which means that for plants and bees to experience the same temperature conditions they had in 1974, they must move 317 meters up the mountain by 2007.
- H1: Species distributions have shifted upwards by about 317 m to match the change in temperature with elevation
- H2: Phenologies have shifted earlier in the season, but not identically, resulting in asynchrony (mismatching)
- H3: Bumble bee abundance was lower in 2007 than in 1974 (due to asynchrony)
- Study encompassed an elevation range of 1000 m and spatial range of 16 km
- 47 study sites – dominated by grasses and herbaceous plants
- Surveyed every 8 days (1974) or 6 days (2007)
- Transects or “circle sites” (covering circular areas on roadsides)
- ID’d bumble bees observed and flowers visited
- 12 perennial plant species ID’d as important to bumble bees (represented 74.5% of visits)
- 8 bumblebee species (represented 97% of bumble bees observed)
Did bees shift up?
- H1A: Bees shifted up but not necessarily 317 m
Did plants shift up?
- H1B: Plant species did not show significant change in upwards distribution (expect one species)
Did bee phenology shift earlier?
- H2A: Phenological differences were partially consistent with hypotheses
- Workers shifted in peak recording rate ~17 days earlier in transect sites
Did flowering phenology shift earlier?
- H2B: Flowering phenology was significantly earlier in 2007 compared with 1974
Was there asynchrony (mismatching) between bees and plants?
- H2C: Found expected reduction in synchrony between bees & plants
- However, the authors assume that the bees and plants were synchronous in the first place in 1974
Was there lower bee abundance in 2007?
- H3: Found lower bee abundance in 2007 compared with 1974
Summary of results
- Shifts towards higher elevations for most bumble bee species, but not for most plant species
- Phenology shifted earlier for plants but not bees
- Bees and plants were mismatched in 2007
- Bee abundance was lower in 2007
We discussed this paper in a seminar on the phenological consequences of climate change that I’m auditing this quarter at UC Davis. Here are some of the points our discussion centered around:
- Only 2 years of data – are their conclusions justified?
- Why are upward shifts in bees inconsistent with the expectation (317 m)?
- Their surveys in 2007 ended before bumble bee workers declined, making it difficult to accurately estimate dates for peak recording rates – how might this affect their results?
- Can’t draw a causal link between reduced synchrony & reduced bee abundance, but how convinced are we that they’re related?
- Could not support the hypothesis that phenologies coincided seasonally in 1974 but not 2007 – do we think this reduces the power of their results?
- How can we better incorporate both spatial and temporal changes due to climate change when considering mismatch, especially for mutualisms occurring on steep environmental gradients?
Particularly if you read the paper in full, I encourage you to think carefully about these potential issues with the paper. It took me six years of reading scientific papers to feel comfortable with questioning methods, statistics, results, and claims that authors make, but learning to approach science with a healthy degree of skepticism is an important part of the your development as a critical thinker and the scientific process as a whole and. Always remember that correlation does not imply causation, and that each paper is only a small part of the bigger picture that science will eventually paint on particular issues as evidence builds over time. Certain parts will inevitably be wrong, and it’s our job as researchers to figure out which bits are wrong, and which bits are right, so we can eventually discover the mechanisms and processes that drive natural phenomena over the long term.
Regardless of the potential problems with the paper, I found it most interesting because while phenological mismatch is a hot topic to study in ecology right now, this is the first paper I’ve seen that studies several bumble bee species and several plant species at once, or the whole plant-pollinator community occurring in the study area. It is also the only paper I’ve come across that considers both the temporal and spatial components of mismatch: it’s easier to quantify phenology in ecological studies, so the temporal component has been overstudied in comparison to the spatial component, but both are equally important – think about it, if the bees and plants aren’t in the same physical location, it will be harder for pollination to proceed normally.
Why should you care?
Mismatch between all different kinds of interacting species around the world can have potentially devastating consequences for ecosystem functioning, and in turn, the provisioning of ecosystem services to humans. Nature consists of highly interconnected systems where organisms interact both directly and indirectly with each other in tandem: take the famous example of wolves having cascading effects on the ecosystems in Yellowstone National Park. When wolves were reintroduced, deer began avoiding parts of the park, which allowed plants to grow back. Willow and aspen trees sprang up, and with them came more berries and insects, attracting more bird species to the park. Beavers came back and created dams with wood from the trees, and the dams attracted otters, muskrats, and other reptiles. Wolves also killed coyotes, so the mice and rabbit population grew, attracting weasels, red foxes, badgers, and hawks. The wolves even indirectly changed the rivers — with increased plant growth now that deer were not munching everything in sight, the vegetation decreased erosion and stabilized river banks. Channels narrowed, more pools formed, and the rivers stayed more fixed in their course. In this ecosystem, everything is functioning properly and imposing balance on its individual components. But what if the timing was all off? What if the deer were giving birth before the plants started to grow in the spring time and the babies didn’t have enough food to survive? What if the berries didn’t grow on the trees at the same time as birds were foraging for food? What if the deer moved to a climate they preferred because the climate was warming, but the wolves didn’t move as quickly and the deer started to eat all the vegetation again because their populations weren’t being held in check by predators? These are the kinds of questions ecologists are asking about phenological mismatch due to climate change, and finding the answers will be of paramount importance in understanding how to conserve nature and protect intact ecosystems.
Pyke, G.H. et al. 2016. “Effects of climate change on phenologies and distributions of bumble bees and the plants they visit.” Ecosphere 7(3). (Published under a Creative Commons license).
Read the abstract of this paper yourself here: Conflicting selection on the timing of germination in a natural population of Arabidopsis thaliana
In this paper, the authors explore how seeds sprouting early versus sprouting late in the season can be good or bad for the plant’s overall fitness (its ability to survive and reproduce) depending on the effect that sprouting time has on the plant’s fitness at different stages in its life cycle.
To understand what they’re studying, it is important to know what “conflicting selection” is. First, plain old selection is the process by which more adapted individuals (i.e., those with better fitness) survive and pass on their genetic information to the next generation. Many many instances of natural selection over time cause evolution to occur.
Conflicting selection is a slightly more complicated version of regular selection. Jose Gomez (2004) describes a basic example in which producing bigger acorns can be advantageous for an oak plant to make because they contain more nutrients for the sprouting plant to use, but they can also be disadvantageous because animals that eat acorns, like squirrels, prefer to collect larger acorns. In cases like this, you might expect that because the smallest acorns die without enough nutrients and the largest acorns are eaten by squirrels, the only acorns left that actually survive long enough to make more oak trees are the medium-sized ones. That’s conflicting selection at work!
In Akiyama and Agren’s paper, the researchers study conflicting selection on the timing of germination, or sprouting, of a small flowering plant in the mustard family called Arabidopsis thaliana.
In order for plants to contribute genetic material to the next generation, they need to survive, and they need to reproduce. In this study, plants that sprouted early experienced lower survival as seedlings, but if they did survive to become adult plants, the adults had better survival and produced more offspring. On the other hand, plants that sprouted later experienced higher survival as seedlings, but out of the survivors, the adults had lower survival and produced fewer offspring than the plants that sprouted early.
In a situation like this where there are complicated pros and cons associated with sprouting early or late, which plants win the fitness game?
To find out, the authors measured overall fitness of the plants that sprouted at different times and found that the advantages of sprouting early outweighed the disadvantages: plants that sprouted earlier had higher overall fitness.
A word of caution from the authors: this study only took place over one year, which is not enough time to generalize these results as a consistently winning strategy for this population of plants. For example, during the year of this study, the fall and winter were fairly cool. This means that the plants that sprouted earlier may have had two advantages related to that year’s weather: 1) even though the early-sprouting seedlings were small and delicate in the fall, they may have survived drought conditions better than they usually would at that size because the fall was cooler than normal, and 2) because the early-sprouting plants had more time to grow big before winter came, they may have had an advantage over the smaller, later-sprouting plants because winter was cold and larger plants have a better chance of surviving the winter.
This is why it’s important to replicate studies – in this case, repeat it with different plants, in different places, over multiple years, etc. – before assuming all plants of the same species or even the same population employ the same early-sprouting strategy all the time. If the fall and winter had been warmer, the researchers may have found completely different results!
Why should you care?
This paper illustrates an important point about the complexity of nature – often, what’s really going on isn’t what seems initially obvious, or even what seems obvious after the second or third or fiftieth time an experiment has been done on it! Science is a slow process, and each paper like this one is a small brick added to a wall of knowledge that will always have gaps in it. Only with much rigorous science can we make the gaps smaller and smaller and the wall sturdier over time.
Akiyama, R. & Agren, J. 2013. Conflicting selection on the timing of germination in a natural population of Arabidopsis thaliana. Journal of Evolutionary Biology 27:193-199.
Gomez, Jose M. 2004. Bigger is not always better: Conflicting selective pressures on seed size in Quercus ilex. Evolution 58(1):71-80.
The latitudinal diversity gradient describes the phenomenon in which the diversity of species inhabiting biomes is higher near the equator and lower near the poles. Read on to learn more about existing hypotheses that attempt to explain why this gradient exists, and how scientists may benefit from considering more than one hypothesis at a time when approaching ecological questions of this scale and magnitude.
A standardized, multipronged approach to studying the Latitudinal Diversity Gradient
One of the most fundamental objectives of the field of ecology is to determine how species are assembled in space and time and why they are assembled in such ways, or in other words, whether and why there are patterns in species composition and diversity over varying spatial scales (Witman & Roy 2009). Globally relevant patterns are often difficult to study because of their inherently – indeed, literally – all-encompassing and therefore highly complex nature. However, global patterns can facilitate the elucidation of fundamental ecological processes because they promise generality.
One such pattern is the decline of biodiversity with low latitudes; a phenomenon termed the “latitudinal diversity gradient” (LDG) (Connolly 2009). This gradient, which has been observed with varying intensity throughout Earth’s history, is hypothesized to extend back through the Mesozoic and into the Paleozoic (Jablonski et al. 2006, Jansson et al. 2013, Crane & Lidgard 1989). First observed by Alexander von Humboldt during his travels to South America in the mid-18th century, the LDG has become one of the biggest unresolved challenges of biogeography and macroecology, for there remains much debate and controversy over which of the many hypotheses – or which combination of said hypotheses – best explains the LDG.
There has been a recent push in the endeavor to explain global patterns of diversity, partly due to the “increasingly urgent need to prioritize regions for conservation on a global scale” (Connolly 2009). As humans increasingly alter the Earth, conservationists grapple with the issue of how to conserve a high level of global diversity. Learning as much as possible about how and why the LDG arose could be key to informing conservation and management of biodiversity in the future.
Over the past several decades, a body of emerging evidence has suggested that many very different taxa exhibit similar species richness gradients; namely, the LDG (Connolly 2005). However, is the LDG a generalizable pattern of species diversity? Is the LDG even accurately designated as a gradient? Here, I explore these and similar questions, focusing not on whether the LDG exists, but whether scientists are utilizing the appropriate methodology and language to most effectively ascertain the truth about patterns of species richness observed in nature.
As I explore the above queries, I couch my analysis within a hypothetical situation in which the LDG is assumed to exist, and the goal of macroecology and other sciences regarding the LDG is to determine which combination of hypotheses explains the LDG best. Put aside the uncertainty and controversy over the existence of the LDG for the next fifteen minutes or so while you read. I argue that we enact environmental policy and move forward with conservation plans now, using the knowledge we already have about species diversity patterns, rather than delay action until we have more information and/or a confirmed scientific consensus over the existence and generality of the LDG, because global biodiversity is under threat now.
Caveats of studying the LDG
Studying global patterns across large temporal and spatial scales is a challenging and often daunting task. There are more interactions and variables to consider at large scales, at which the computing and processing abilities of computers, and indeed, our brains, is limited. In his 1989 Robert MacArthur Awards Lecture, Simon Levin stated, “the problem of pattern and scale is the central problem in ecology, unifying population biology and ecosystems science, and marrying basic and applied ecology” (Levin 1989). It is this very problem with which scientists grapple when studying global patterns such as the LDG. However, as Levin alludes, solving the problem of scale when tackling a given scientific question can yield immensely valuable insights into the way our world works. The key to prediction and understanding, and the essence of science, lies in the elucidation of the mechanisms and processes that underlie and produce patterns (Levin 1989), and the concepts of scale and pattern are indelibly intertwined (Hutchinson 1953).
When we probe into a scientific inquiry, we observe the environment on a limited range of scales. This means that our perception of events and therefore our science provides us with only a “low-dimensional slice through a high-dimensional cake” (Levin 1989). When we scale up in study scope, “we must understand how information is transferred from fine scales to broad scales, and vice versa” (Levin 1989). Presently, ecologists do not fully understand why and how patterns of diversity exist on local or regional scales; therefore, we are necessarily limited by our lack of understanding at smaller scales when we attempt to scale up to study global patterns of diversity. Large-scale studies of global biodiversity also fall prey to the trade-offs between studying ecological patterns at small or at large scales. At small scales, we are able to pay closer attention to detail, but stochasticity plays a larger role and the patterns and interactions being studied are more unpredictable. At large scales, which display more regular statistical behavior, we trade off the loss of detail for the gain of predictability and generalizability (Levin 1989).
These considerations lead to another important question: is the LDG general? If the LDG holds true for the majority of Earth’s species, then yes. However, what is the magnitude at which a clade of organisms must follow the LDG in order for it to be considered displaying the LDG, or cited as evidence for the LDG’s existence? What proportion of Earth’s biodiversity must follow the LDG for it to be considered a global phenomenon? One of the main assumptions of the LDG is that Earth’s biodiversity is completely described. Scientists know this is certainly not the case. In fact, today, centuries after explorers and naturalists like Humboldt and Darwin first observed incredible biodiversity in the tropics, we do not even know within an order of magnitude the full extent of biodiversity on Earth: current estimates range from 3 to 30 million species (Gullan & Cranston 2010). Although our knowledge regarding global biodiversity is not complete, we can still study phenomena like the LDG using inference and the knowledge we currently have. This being said, scientists should also think carefully about caveats surrounding the LDG and studying global patterns, including the assumptions underlying the LDG and the incompleteness of our understanding of species diversity, distributions, and interactions at smaller scales.
In light of the tradeoff between studying science at large versus small scales, Levin reasons that there is no “correct” scale on which to describe populations or ecosystems; instead, when studying a particular scale, one should recognize that change is taking place on many scales simultaneously and consider that interactions occur across scalar boundaries (Steele 1978, Levin 1989, Wiens 1989). Consider this: organisms respond to their environment at an individual level, meaning that what we call a community or ecosystem is really just an “arbitrary subdivision of a continuous gradation of local species assemblages” (Whittaker 1975, Levin 1989). Globally, communities and ecosystems are not well-integrated units that move and evolve en masse; rather, they are assemblages of organisms responding individually to spatial and temporal variation. Thus, although a pattern like the LDG is observed globally, it arose through the individualistic ecological and evolutionary responses of much smaller constituents of the world’s biodiversity, rather than through evolution at the community or ecosystem level (Levin 1989). Many hypotheses seeking to elucidate the mechanisms underlying the LDG (see below for an overview of these hypotheses) refer to the evolution of entire clades of organisms; however, it is key to consider that the accuracy of analyses is reduced when considering evolutionary processes at higher taxonomic levels.
Once mechanisms underlying a pattern have been described and determined, the key to understanding the pattern lies in separating the mechanisms which theoretically could give rise to the observed pattern from the mechanisms which actually did give rise to the observed pattern. As Levin wisely points out, “there are many roads to Rome” (Levin 1989). Below I describe the various hypotheses explaining how the LDG arose. While each mechanism is supported by evidence that it contributed to the existence of the LDG, it is important to recognize that theory alone can only ever create a catalogue of possible mechanisms. Without performing experiments, or without support for highly risky predictions associated with one or more of the proposed hypotheses explaining the LDG, distinguishing among said hypotheses can be done only to a certain extent.
Because there are so many factors to consider when studying the LDG, there are also many different ways in which people can study it, with emphasis on varying factors depending on a person’s particular perceptions of the world, biases, and knowledge base. One of these factors is the concept of an appropriate resolution at which to study the LDG. For example, general circulation models were once performed in 10-degree grids, and current models allow for much higher resolution as the grids become smaller and smaller, similar to a picture including more and more pixels. This concept of resolution can also be applied to studying ecological concepts: as we scale up to include larger temporal and spatial scales, our resolution necessarily becomes coarser. The finer the resolution at which we study the world, the more accurate an interpretation of the world we are able to obtain. In many studies of the LDG, the world is parsed into latitudinal bands into which information on species diversity is separated. Presumably, the more finely one parses latitude while studying the LDG, the more accurately one interprets observed patterns of global species diversity, albeit in a necessarily asymptotic fashion. I explore this concept further below by performing a literature review to determine how finely studies of the LDG parse the globe into latitudinal bands. Ultimately, I ask: at what minimum resolution of observation is the LDG accurately termed a “gradient?”
One last caveat of studies of the LDG involves the dangers of correlation: most studies seeking to explain the LDG utilize simple correlations (Connolly 2009). Perhaps it has been repeated so often that it is now met with some impatience, but I will repeat it again because no matter how many times it is said, its relevance will not dwindle: “correlation does not imply causation.” Hypotheses pertaining to the LDG are intrinsically correlative. Furthermore, there is a cautionary tale amongst statisticians that when performing studies with a very large sample size n or very large number of observations i, the correlation in question (i.e. the relationship between latitude and species diversity) becomes increasingly likely to become significant as an artifact of that large amount of data. For example, the more people sampled from a given population, the more significant a correlation will become between people who have mustaches and people who smoke cigars, not because these two events are dependent upon each other in any way, but because the calculation of the significance level indirectly depends on the sample size. It is important to be cognizant of these and other caveats while studying the LDG because the elucidation of the mechanisms and processes underlying the LDG has the potential to shed much light on important scientific questions and inform global conservation and management of biodiversity in the future.
Hypotheses explaining the LDG
Exactly what proportion of Earth’s identified species display patterns matching the LDG? Although studies have been biased towards well-studied, larger-bodied organisms such as vertebrates and higher plants, and the majority of studies originated from the Americas, overall evidence suggests that most clades generally follow the LDG (Hillebrand 2004). Hillebrand (2004) performed a meta-analysis of nearly 600 observations of the LDG in the literature and found strong evidence for the existence of a generally applicable LDG. Notable exceptions include macroalgae (Kerswell 2006), fish parasites (Rohde 1998), seabirds (Proches 2001), and ichneumonid wasps (Janzen 1981). Major hypotheses regarding the LDG can be categorized into 1) spatial/area hypotheses 2) historical/evolutionary hypotheses, or 3) biotic hypotheses. Below, I provide a brief overview of these hypotheses. This overview is necessarily incomplete due to the sheer number of hypothesis in the literature endeavoring to explain the LDG, but I attempt to touch upon the major perspectives regarding the LDG, both currently and throughout history, and provide an accurate representation of all types of hypotheses and the level of support those hypotheses have received in the ecological community.
Spatial/area hypotheses include the mid-domain effect (MDE), the geographical area hypothesis (GAH), the species-energy hypothesis (SEH), the climate harshness hypothesis (CHH), and the climate stability hypothesis (CSH).
The mid-domain effect (MDE) was first described by Colwell and Hurtt (1994) and Willig and Lyons (1998), who used computer simulations to show that when species ranges are randomly placed in a domain (Earth) with boundaries at the poles, species ranges tend to overlap at the center of the domain, creating an MDE of low-latitude peak in species richness. Mid-domain models have been suggested to contribute to the LDG; however, these models do not include any ecological or environmental influences on species richness; therefore, they have been argued to be null models (Colwell et al. 2004, 2005). This means that if latitudinal gradients of species richness were determined by the MDE, the LDG would be indistinguishable from patterns produced by the random placement of observed species ranges (Colwell & Lees 2000). Some tests have found mid-domain models to have high predictive power, especially on large spatial scales (Jetz & Rahbek 2001, Dunn et al. 2007), while others claim it has low predictive power (Bokma & Monkkonen 2001, Kerr et al. 2006).
Connolly (2009) points out that the MDE assumes that the frequency distribution of range size displayed by a particular clade depends on the domain’s size and shape but not on characteristics of the clade. This approach, Connolly argues, ignores the fact that “rates of origination, colonization, or local extinction may differ among clades in the absence of geographical gradients of those rates,” meaning that “frequency distributions of ranges sizes may well differ among taxa, independent of any effects of environmental gradients” (2009).
Mid-domain models are the only ones that use latitude as a geometric constraint imposed on species’ ranges. All other models attempt to elucidate the relationship between latitude and one or more factor co-varying with latitude. Connolly believes this is a flaw in our approach to studying biogeographical patterns, because regression-based approaches can only assess a model’s predictive power, not its explanatory power (2009). Because analyses of species richness like those studying the LDG seek to explain how much a certain environmental factor has influenced species richness patterns over time and space, Connolly argues that the types of methodologies used to study macroecological patterns should be shifted from those better able to predict to those better able to explain (2009).
The geographical area hypothesis (GAH) suggests that the LDG arose through the ability of the tropics to contain more species because of their large contiguous geographic extent (Terborgh 1973). As the largest biome, the tropics can support species with larger range sizes, and larger range sizes impart lower extinction rates and increased speciation rates upon tropical species, leading to increased diversity in the tropics (Rosenzweig 2003). However, critics point out that successive biomes north of the tropics are similar in area, and should therefore contain similar levels of species richness according to the GAH, but they do not (Gaston & Blackburn 2000). Others argue that the terrestrial tropics are not the largest biome, and that it is erroneous to define the tropics as a single biome (Rohde 1997, Hawkins & Porter 2001). Additionally, area-dependent hypotheses such as the GAH are generally better able to predict species richness patterns for species with smaller ranges than those with larger ranges (Mora & Robertson 2005).
The species-energy hypothesis (SEH) (also called the “energy-richness hypothesis” or the “more individuals hypothesis”), posited in the mid-20th century by Hutchinson (1959) and later elaborated by Brown (1981) and Wright (1983), postulates that increased energy availability in the tropics boosts net primary productivity, allowing more individuals to exist, and therefore more species to evolve, in the tropics. Critics question the validity of the statement that increased productivity leads to increased numbers of individuals which in turn leads to increased numbers of species (Cardillo et al. 2005). Currie and colleagues (2004) tested the SEH and found that the relationship between productivity and the density of individuals at large spatial scales is weak. They further concluded that extant evidence is inconsistent with the mechanism proposed for the SEH.
The climate harshness hypothesis (CHH) states that the LDG exists because more species can physiologically tolerate the wetter, warmer environmental conditions of the tropics. Cardillo et al. (2005) and Currie et al. (2004) criticize this hypothesis by providing evidence that species are not present within every area whose climate they are able to tolerate.
The climate stability hypothesis (CSH) suggests that areas with stable environments like the tropics, which do not have as variable conditions as higher-latitude areas like temperate regions, allow species to specialize into narrow niches, decreasing resource overlap between species and therefore increasing speciation (Kaustuv et al. 1999, Lima-Ribeiro et al. 2009). Critics point out that climate stability does not always lead to higher species diversity, and that high species diversity exists in non-stable climates (Brown & Lomolino 1998).
Hypotheses invoking historical or evolutionary processes to explain the LDG include the historical perturbation hypothesis (HPH), the diversification rate hypothesis (DRH), the evolutionary time hypothesis (ETH), and the out of the tropics model (OTM).
The historical perturbation hypothesis argues that historical perturbations such as glaciation disproportionately affect global species richness levels, and that increased historical perturbations have dampened species richness levels at higher latitudes (Brown & Lomolino 1998, Gaston & Blackburn 2000). Further, the HPH suggests that temperate regions are not yet saturated with species due to moderate levels of disturbance over geologic time; therefore, diversity in temperate regions will continue to increase until it reaches an equilibrium number of species (Clarke & Crame 2003).
The diversification rate hypothesis proposes that higher ambient temperatures lead to shorter generation times, higher mutation rates, and faster physiological processes which contribute to higher diversification rates in the tropics (Rohde 1992, Currie et al. 2004, Cardillo et al. 2005). More research is needed to determine whether speciation rates are indeed higher in the tropics.
The ETH advocates that the long period of time under which the tropics have existed in a stable state has contributed to the generation and maintenance of the LDG, in combination with increased evolutionary rates in the tropics via mechanisms similar to those proposed by the DRH. This hypothesis accepts that other factors may contribute to the LDG, and assumes that the environment does not saturate as richness increases (it is a non-equilibrium hypothesis). Several studies have found evidence supporting this hypothesis (Allen et al. 2006, Wright et al. 2006, Jansson et al. 2013).
The OTM states that many taxa originate in the tropics and expand towards the poles while still remaining present in the tropics. Jablonski et al. (2006) found that a global analysis of marine bivalves supports this model and emphasizes a key implication of the OTM: if the tropics experience reduced biodiversity due to disturbance or human impacts, then after an ensuing time-lag, global diversity will also experience a similar reduction in biodiversity.
Proponents of biotic hypotheses argue that the increased intensity of biotic interactions like competition, predation, and parasitism at low latitudes caused the formation of the LDG (Pianka 1966). However, these hypotheses do not provide evidence that biotic interactions increase towards the equator, and additionally fail to explain why the biotic interactions cited as contributing to the LDG would increase towards the equator. Recent studies have found that changes in the intensity of biotic interactions with latitude are inconsistent (Lambers et al. 2002, Hillebrand 2004).
Reviews/multiple contributing mechanisms:
While some ecologists seek one primary mechanism driving the LDG, a growing number of ecologists argue that several mechanisms contribute to the LDG (Gaston & Blackburn 2000, Willig et al. 2003, Rahbek et al. 2007, Hawkins et al. 2003, Colwell & Lees 2000). Several recent studies (published in the past decade) have also performed reviews of the literature to determine whether one or more the above hypotheses are supported by data on observed species richness patterns.
For example, Currie and colleagues (2004) attempted to derive and test the predictions of the SEH, the CHH, the DRH, and biotic hypotheses. Their study yielded little support for the SEH, mixed results for the CHH, and neither support for nor evidence against the DRH and biotic hypotheses due to a lack of evidence available to test the predictions of these hypotheses. Currie et al. (2004) emphasize the need for more research on the LDG in general and express a hope for the ability of science to make more conclusive statements about the DRH and biotic hypotheses as the field of molecular-based evolutionary biology advances.
Jansson et al. (2013) performed a review of over 100 phylogenetic studies and mapped the latitudinal ranges of all taxa in order to test the relative importance of the OTM, a variation of the ETH called the tropical conservatism hypothesis (TCH), and the DRH. Like the OTM, the TCH argues that most clades originate in the tropics, but unlike the OTM, the TCH maintains that transitions of lineages from tropical to temperate latitudes are rare, resulting in increased species diversity in the tropics compared to higher latitudes (Jansson et al. 2013). Jansson and colleagues (2013) found that while most clades originated in the tropics and peaked in the zone of origin, transitions between latitudinal zones occurred frequently – at 16-22% of nodes – with the most common transitions occurring between tropical and temperate zones. Their results supported the ETH and the OTM, but contradicted the TCH and the DRH. Jansson et al. (2013) also suggest that the OTM is actually a special case of the ETH.
In Hillebrand’s review (2004), the LDG was found to be ubiquitous but varying in strength by scale, organism body mass, and trophic level. The LDG was weaker in freshwater habitats and also differed significantly between continents and habitat types. Fine and Ree (2006) found that a time-integrated area of biomes is positively correlated with species richness. They use this and other evidence to argue that area and time determine species richness.
While data evidencing the LDG is necessarily and sometimes woefully incomplete, there is enough evidence to support the statement that the LDG exists across geologic time, space, and the majority of the taxa we have documented to date. After performing a literature review of 25 studies of the past century supporting, contradicting, and/or comparing the major hypotheses regarding the LDG, I conclude that many of the competing hypotheses regarding the LDG can be reconciled because 1) the way the LDG is studied throughout the literature is inconsistent due to differences in assumptions underlying various hypotheses and methodologies, 2) apparent controversy over the hypotheses regarding the LDG may be an artifact of subjective biases and differences in worldviews between scientists, and 3) the LDG exists due to a combination of driving mechanisms of varying importance.
Across the 10 hypotheses and 25 papers I reviewed, there exists no standard definition for what is statistically, mathematically, or taxonomically considered an LDG. The hypotheses and studies define no standard minimum steepness at which the relationship between latitude and diversity must be observed, nor do they define a standard fit to a standard curve at which the relationship must be observed, for the relationship to “count” as a single observation of the LDG.
While some studies consider a “single” LDG, or the existence of a general latitudinal gradient of species richness incorporating the entirety of the Earth’s biodiversity, others speak of multiple latitudinal diversity gradients for given clades of organisms. Of those studies that consider multiple LDGs, the definition of an LDG is not constricted to a specific taxonomic level; rather, any observation of the decline of diversity with latitude in any taxonomic level from the lowest classification (species) to much higher-level classifications is counted simply as one instance of the LDG being observed. This is problematic because it skews the results of the study towards being more general for some groups of organisms and more specific for other groups of organisms.
Further, the studies and hypotheses I reviewed do not follow a standard minimum resolution at which the relationship between latitude and diversity can be deemed a “gradient:” in other words, the hypotheses and studies attempting to explain the LDG separate the globe into inconsistent numbers of latitudinal bands when performing analyses. For example, several hypotheses, although supported by studies that include much finer resolutions of species diversity gradients, make their arguments based on the difference between mechanisms operating in “the tropics” and “everything else,” such as the DRH and biotic hypotheses. Perhaps the most gradient-oriented hypothesis is the OTM, which, despite comparing the rates of diversification in the “tropics” to “everything else,” refers to a mechanism of range expansion underlying the LDG that is by definition truly gradating. Perhaps differences in resolution between studies of the LDG could be reconciled quantitatively through a type of data transformation that has not yet been described.
Clearly, the authors of these hypotheses and studies have varying assumptions about what defines an occurrence of the LDG and/or regarding what an LDG actually is. While scientists are still able to glean information about the LDG despite these differences, it is crucial that these differences are either eliminated or at least minimized by the creation of standard definitions surrounding the LDG, or that these differences are understood and/or better communicated by scientists so as to decrease any controversy that may arise as an artifact of these differences in assumptions rather than due to actual differences in interpretation of the data.
A related issue with studies of the LDG is that, without experimental evidence to back up a given hypothesis, as scientists offer differing ideas about various hypotheses, controversy could be a product of subjective differences in worldviews and theory dependency rather than evidence supplied by objective data, of which there is a serious lack. For example, Jansson et al. (2013) assume that migration is important, while Fine and Ree (2006) assume that it is not. Fine and Ree (2006) further suggest that the species-energy hypothesis is unlikely to be important. Ultimately, when grappling with complex patterns over large scales with little evidence at their disposal, scientists can make hand-waving claims and find nuggets of data backing up their work without receiving much criticism because in truth, there is a certain amount of guesswork and inference involved. When breaking down the different hypotheses regarding the LDG, one can ask, what is more fundamental: area, time, or energy? It is mere differences in worldviews that will sway scientists towards one or another. Even meta-analyses performing what are considered to be large-scale reviews on the LDG like those studying observations of LDGs numbering in the hundreds, the data included in these studies is patchy and incomplete, and I could even say, at risk of sounding hyperbolic, “a drop in the bucket” compared to the amount of data that would be needed to fully understand the mechanisms and processes driving the LDG.
Considering the complexity of the world and its interacting components, it seems likely that multiple mechanisms contributed to the origination and continued existence of the LDG. Even at regional scales, very rarely if never is a single mechanism responsible for an observed ecological pattern in nature – there are too many variables at play acting both singly and in tandem. At global scales, this should be even less likely. Many of the 10 hypotheses outlined above can coexist without contradicting each other. Each hypothesis can vary in importance with factors such as temporal and spatial scale, place, time, taxa, biome, and sets of environmental conditions.
Declining diversity towards the equator can be considered a general phenomenon, insofar as it is generally observed across clades and species that have been described by scientists thus far. Several caveats of the LDG include the issue of studying patterns at large spatial and temporal scales; the inherent incompleteness of the data used to study the LDG; and human biases, inconsistency, and lack of standardization when studying the LDG. There are many different hypotheses explaining the LDG, some of which can be reconciled. Here, we find an instance in which a lack of risky predictions for hypotheses explaining the LDG may actually be helpful in that this deficit can reveal what may be the truth: that no one hypothesis is more important than any other. The normal rules of ecological research may not apply when studying very large scales, and why should they? For example, the idea that many hypotheses interact with each other to explain the LDG at varying degrees flies in the face of the rule of parsimony, which when applied may otherwise erroneously force ecologists to choose one hypothesis to cling to and provide evidence for, or unhelpfully cause the scientific community to be inclined to determine one primary mechanism driving the LDG. Scientists must exercise creativity, open-mindedness, and fluid thinking in order to successfully study complex, large-scale patterns.
I argue that equal consideration should be given to each hypothesis and that the key to solving the mystery of the LDG will not be to determine which one hypothesis is correct above all others, but to determine how each hypothesis can vary in importance in relation to various intrinsic and extrinsic factors. The implications of the solution to this enigma are imperative to the conservation and maintenance of the most diversity possible in a rapidly changing, increasingly warming world. Understanding the processes underlying global patterns in species diversity will allow conservationists to conduct more effective triage as biodiversity dwindles. This is a rather grim yet practical outlook; for example, if the OTM explains a large proportion of the LDG, conservationists may consider prioritizing the tropics and building corridors to allow species to extend their ranges beyond the tropics. However, if the OTM explains less of the LDG than the GAH, conservationists may instead focus more time and energy on the protection and maintenance of large expanses of contiguous tropical habitats.
It is a great irony that the results of research lead scientists to conclude that more research should be done; alas, I too am forced to concur with this sentiment. There is an urgent need for more numerous and creative studies attempting to elucidate the causes, mechanisms, and processes underlying the LDG. In the meantime, I implore scientists to use the knowledge we already have – namely, that the LDG exists and that some combination of existing hypotheses likely tells us why – to create policy to protect the Earth’s biodiversity before it disappears.
Allen, A. P., J. F. Gillooly, V. M. Savage, and J. H. Brown. 2006. Kinetic effects of temperature on rates of genetic divergence and speciation. Proceedings of the National Academy of Science 103:9130-9135.
Bokma, F. J., and M. Monkkonen. 2001. Random processes and geographic species richness patterns: why so few species in the north? Ecography 24:43-49.
Brown, J. H., and M. V. Lomolino. 1998. Biogeography. Sinauer Associates, Sunderland.
Brown, J.H. 1981. Two decades of homage to Santa Rosalia: toward a general theory of diversity. American Zoologist 21:877-888.
Cardillo, M., C. D. L. Orme, and I. P. F. Owens. 2005. Testing for latitudinal bias in diversification rates: An example using New World birds. Ecology 86:2278-2287.
Colwell, R. K., and Hurtt, G. C. 2004. The American Naturalist 144:570–595.
Colwell, R. K., and Lees, D. C. 2000. The mid-domain effect : geometric species richness. Trends in Ecology and Evolutionary Biology, 15:70–76.
Connolly, S. R. 2009. Macroecological theory and the analysis of species richness gradients. Pages 279-309 in J. D. Witman and K. Roy, editors. Marine Macroecology. The University of Chicago Press, Chicago, IL, USA.
Crane, P. R., and Lidgard, S. 1989. Angiosperm diversification and paleolatitudinal gradients in cretaceous floristic diversity. Science 246:675–678.
Currie, D. J., G. G. Mittelbach, H. V. Cornell, D. M. Kaufman, J. T. Kerr, T. Oberdorff, J. F. Guegan, Hawkins, B. A., Dawn, M. K., Kerr, J. T., Oberdorff, T., O’Brien, E., and J. R. G. Turner. 2004. Predictions and tests of climate-based hypotheses of broad-scale variation in taxonomic richness. Ecology Letters 7:1121-1134.
Fine, P. V. A., & Ree, R. H. 2006. Evidence for a time-integrated species-area effect on the latitudinal gradient in tree diversity. The American Naturalist 168:796–804.
Gaston, K. J. 2000. Global patterns in biodiversity. Nature 405:220–227.
Gaston, K. J., and T. M. Blackburn. 2000. Pattern and processes in macroecology. Blackwell Scientific, Oxford.
Gullan, P.J. and P.S. Cranston. 2010. The Insects. Ed. 4. Wiley-Blackwell, UK.
Hawkins, B. A., and E. E. Porter. 2001. Area and the latitudinal diversity gradient for terrestrial birds. Ecology Letters 4:595-601.
Hawkins, B. A., Field, R., Cornell, H. V, Currie, D. J., Guégan, F., Kaufman, D. M., Kerr, J. T., Mittelbach, G. G., Oberdorff, T., O’Brien, E. M., Porter, E. E., and J. R. G. Turner. 2003. Water, and broad-scale geographic patterns of species richness. Ecology 84:3105–3117.
Hillebrand, H. 2004. On the generality of the latitudinal diversity gradient. The American Naturalist 163:192–21l.
Hutchinson, G. E. 1950. Homage to Santa Rosalia, or why are there so many kinds of animals? The American Naturalist 93:145-159.
Hutchinson, G. E. 1953. The concept of pattern in ecology. Proceedings of the National Academy of Sciences 105:1-12.
Jablonski, D., Roy, K., and J. W. Valentine. 2006. Out of the tropics: evolutionary dynamics of the latitudinal diversity gradient. Science 314, 102–6.
Jansson, R., Rodríguez-Castañeda, G., and L. E. Harding. 2013. What can multiple phylogenies say about the latitudinal diversity gradient? A new look at the tropical conservatism, out of the tropics, and diversification rate hypotheses. Evolution; International Journal of Organic Evolution 67:1741–55.
Janzen, D.H. 1981. The peak in North American Ichneumonid species richness lies between 38 degrees and 42 degrees N. Ecology 62:532-537.
Jetz, W., and C. Rahbek. 2001. Geometric constraints explain much of the species richness pattern in African birds. Proceedings of the National Academy of Sciences 98:5661-5666.
Kerswell, A. 2006. Global biodiversity patterns of benthic marine algae. Ecology 87:2479-2488.
Lees, D. C., and R. K. Colwell. 2007. A strong Madagascan rainforest MDE and no equatorward increase in species richness: Re-analysis of ‘The missing Madagascan mid-domain effect’, by Kerr J.T., Perring M. & Currie D.J (Ecology Letters 9:149-159, 2006). Ecology Letters 10:E4-E8.
Levin, Simon A. 1989. The Problem of Pattern and Scale in Ecology. The Robert H. MacArthur Award Lecture: Toronto, Ontario, Canada.
Lima-Ribeiro, M., Diniz-Filho, J. A. F., and M. Barberi. 2010. Climate stability and the current patterns of terrestrial vertebrate species richness on the Brazilian Cerrado. Quaternary International 222:230-236.
Mora, C., and D. R. Robertson. 2005. Causes of latitudinal gradients in species richness: a test with fishes of the Tropical Eastern Pacific. Ecology 86:1771-1792.
Pianka, E. R. 1966. Latitudinal gradients in species diversity : A review of concepts. The American Naturalist 100:33–46.
Proches, S. 2001. Back to the sea: Secondary marine organisms from a biogeographical perspective. Biological Journal of the Linnean Society 74:197-203.
Rahbek, C., Gotelli, N., Colwell, R.K., Entsminger, G.L., Rangel, T.F.L.V.B., and G. R. Graves. 2007. Predicting continental-scale patterns of bird species richness with spatially explicit models. Proceedings of the Royal Society of London Series B 274:165-174.
Rohde, K. 1992. Latitudinal gradients in species diversity: The search for the primary cause. Oikos, 65: 514–527.
Rohde, K. 1998. Latitudinal gradients in species diversity: area matters, but how much? Oikos 82:184-190.
Rosenzweig, M. L. 1992. Species diversity gradients: We know more and less than we thought. Journal of Mammalogy 73:715–730.
Rosenzweig, M. L. 2003. How to reject the area hypothesis of latitudinal gradients. Pages 87–106 in T. M. Blackburn and K. J. Gaston, editors. Macroecology: Concepts and Consequences. Blackwell Publishing, Oxford.
Roy, K., Jablonski, D., and J. W. Valentine. 1999. Dissecting latitudinal diversity Gradients: functional groups and clades of marine bivalves. Proceedings of the Royal Society of London Series B 267:293-299.
Steele, J. H. 1978. Some comments on plankton patches. Pages 1-20 in J. H. Steele, editor. Spatial pattern in plankton communities. Plenum, New York, New York, USA.
Terborgh, J. 1973. On the notion of favorableness in plant ecology. The American Naturalist 107:481-501.
Whittaker, R. J., Willis, K. J., and Field, R. 2001. Scale and species richness: towards a general, hierarchical theory of species diversity. Journal of Biogeography 28:453–470.
Whittaker, R.H. 1975. Communities and ecosystems. Macmillan, New York, New York, USA.
Wiens, J. A., J. T. Rotenberry, and B. Van Horne. 1986. A lesson in the limitations of field experiments: shrubsteppe birds and habitat alteration. Ecoloy 67:365-376.
Willig, M. R., and S. K. Lyons. 1998. An analytical model of latitudinal gradients of species richness with an empirical test for marsupials and bats in the New World. Oikos 81:93-98.
Willig, M. R., Kaufman, D. M., and R. D. Stevens. 2003. Latitudinal gradients of biodiversity: Pattern, process, scale, and synthesis. Annual Review of Ecology, Evolution, and Systematics 34:273–309.
Witman, J. D. and K. Roy. 2009. Marine Macroecology. The University of Chicago Press, Chicago, IL, USA.
Wright, D. H. 1983. Species-energy theory: an extension of species-area theory. Oikos 41:496-506.
Wright, S., J. Keeling and L. Gillman. 2006. The road from Santa Rosalia: a faster tempo of evolution in tropical climates. Proceedings of the National Academy of Science 103:7718 –7722.
 The DRH is also a climate-related hypothesis, but I have included it here as a historical/evolutionary hypothesis because it more directly relates to evolutionary rates which are hypothesized to be caused by climate-related factors.
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Hi there! I am starting to get back into blog writing in the months leading up to starting grad school in the Fall of 2017 (don’t ask me where, I haven’t decided yet). One of the things I’d like to use this blog for is summarizing papers I’m reading. I hope it’ll give people a chance to access some science, even if it’s only a little bit at a time, without paying $20 for a pdf. Plus, it’ll give me some practice at translating science to a general audience. Here goes try number one!
Paper of the day: Dudley and Schmitt 1996, “Testing the adaptive plasticity hypothesis: Density-dependent selection on manipulated stem length in Impatiens capensis”
Untangling some mumbo-jumbo jargon for you first – if you decide to read the paper yourself (which I highly recommend, if you can access it for free!), you would need to understand at least these terms:
Plasticity: the ability of an organism to change its phenotype in response to changes in the environment. (i.e. human bodybuilders changing their muscle mass and distribution)
Phenotype: the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment. (i.e. eye color, height)
Genotype: the genetic constitution of an individual organism. (i.e. all that DNA stuff that makes you uniquely you)
This paper tests the hypothesis that organisms adapt to the environment where they live, and therefore perform better than organisms that aren’t originally from that environment. Or in other words, “the phenotype evoked by each environment results in higher relative fitness than the alternative phenotype.” In biology, this is often referred to as the “home court advantage.” In this paper, the authors study the plant Impatiens capensis and how it responds to different environments.
In nature, Impatiens sometimes has to compete with fellow Impatiens plants or with other neighboring plant species for sunlight. How does a plant compete with other plants? Since plants can’t move, they have evolved many strategies to adapt to the environment where they’re stuck when they sprout from a seed. Many people have heard about the strategies that occur on a species-level, like cacti being able to draw on the water they hold in their bodies during dry spells in the desert. But, some species have populations spread across highly variable environments, and changes in the conditions plants face can occur from the top of a mountain to the bottom, or one football field-sized patch to the next, or at even smaller spatial scales, like one plant being next to a river and another stuck wedged between two rocks two feet away. To deal with this on an individual level, plants have evolved to be highly plastic – this means that each individual plant has the ability to adapt to its specific environment, and even if you put four genetically identical plants in different places, they could all end up looking and behaving totally differently.
That’s the basic premise of plasticity. BUT, the big question the authors ask in this paper is: is plasticity adaptive? In other words, is it a good strategy for that plant to adapt to its environment, or not? The overall goal of a species is to continue existing, so scientists determine adaptiveness by figuring out whether the adaptation contributes to that individual plant’s potential for future offspring (or “fitness”) – for example, by allowing the plant to grow bigger, make more flowers, and/or make more seeds that will grow to become the next generation of plants.
So, how does Impatiens compete with other plants for sunlight? It grows taller by elongating its stem and growing leaves higher than other plants. That way, it avoids being shaded by other plants. In this study, the authors manipulated the plants in two treatments by mimicking 1) an environment where the plants were shaded by other plants, and 2) an environment with full sunlight (not shaded by other plants). When plants were placed in the “shaded” treatment, they elongated their stems, and when they were placed in the full “sunlight” treatment, they did not elongate their stems.
Then, the scientists put the plants from each treatment, shaded or sunlight, into two different environments in nature: (1) plots where there were already lots of other plants present (high-density), and (2) plots where few other plants were present (low-density). In doing so, they were able to determine whether there was a home-court advantage, and they found that there was: plants with elongated stems performed better (or had higher “fitness”) in high-density plots than those without elongated stems. In other words, taller plants were more fit when there were other plants around for them to compete with, because they were able to reach the sunlight, whereas the shorter plants didn’t do as well because they were shaded by the other competing plants. On the other hand, plants withOUT elongated stems performed better than those WITH elongated stems in low-density plots. Why? The taller, more spindly plants tended to fall over if they were not physically held up by other plants crowding in on them (like in the high-density plots), so in the plots with only a few other plants, they were less fit than the short, squat plants that didn’t have any problem staying upright on their own.
The difference in fitness between the two environments (high or low density) that the tall vs. short plants displayed is an example of the “home court advantage.” The plants did better in the environment in which they adapted to live. But plasticity isn’t always adaptive! In a different study, some of the same researchers studied whether it was more adaptive for Impatiens to display this stem elongation type plasticity in sunny versus woodland habitats (Donohue et al. 2000). They did this because in a sunny environment, the plant can either experience sun when there are aren’t competitors, or shade when there are competitors – but in a forested area, the plants may experience shade from the tree canopy. As you can imagine, it’s not very useful for the plants to try to grow taller than the trees to reach the sun – so in this circumstance, their plastic response of elongating their stems was not as adaptive.
Why should you care about all this? It seems like it’s not important to the way people live their lives every day, but if we want to conserve and protect nature, we also have to understand all the nitty gritty messy complicated details that go along with nature. Understanding the fundamentals of plasticity itself could have enormous benefits to people when applied to medicine: imagine if you could trigger genes that activated increased production of melanin in your skin, getting a tan AND an effective sun blocker without having to expose yourself to harmful UV radiation at the same time? That’s a plastic response we could induce in humans if we knew how it all worked at a mechanistic level.
Thanks for reading! This was my first go at explaining a science paper to a relatively naive audience – my intended audience is anyone with high school-level biology or above. Send me a message or leave a comment if you have any constructive criticism!
Donohue, K., D. Messiqua, E. Hammond Pyle, M.S. Heschel, and J. Schmitt. 2000. Evidence of adaptive divergence in plasticity: density- and site-dependent selection on shade avoidance responses in Impatiens capensis. Evolution 54: 1956-1968.
The metaphor that one’s personal and cultural history is a plant that extends roots into the land or into the past pervades across various cultures and times. An individual’s, a country’s, or a people’s history is something that is strongly embedded into said entity’s core identity and is an ever-present, almost living yet simultaneously intangible concept to be nurtured; grown leaf by leaf. Continuity and change in Igbo culture is a complex topic to approach, partially because of a remarkable Igbo receptivity to change and their tradition of adaptation that blurs the distinction between what is organic or introduced in Igbo society. However, the Igbo do resist change – the most significant Igbo traditions do persevere, especially when Igbo ideals clash with European ones. Chinua Achebe depicts these issues in his novels. The Igbo are particularly receptive to change due to certain aspects of their tradition; however, they have difficulties adapting to situations that clash with their most steadfast beliefs. In particular, the Igbo have difficulties expanding and lessening their identification with place and handling those within society who hold dissimilar moral codes than the majority of society.
Several general concepts dictate Igbo tradition and culture and apply to all of its aspects: identification with place, ancestral ties, egalitarianism, individuality, and duality. Only within this framework can the Igbo’s worldview and actions be understood.
Historically, identification with place is largely a universal held by African peoples. An apt example arising not from the Igbo, but applicable to the Igbo worldview, is the well-known anthropological case study of “S.M.,” the Kenyan man whose burial place was hotly debated due to the conflicting wishes of his widow and brother. This case was significant because the debate did not center on the simple idea of respecting a widow’s versus a brother’s wishes, but raised issues about the importance of traditional practices and worldviews-including identification with place—in the modern age. Richard Kwach, counsel for the Luo clan defending Luo burial customs, referred to the poetry of Okot p’Bitek, quoting one part of his Song of Lawino: “The ways of your ancestors/ Are good, / Their customs are solid/ And not hollow/ They cannot be blown away/ Because their roots reach down into the soil” (Cohen 55).
Again the metaphor of one’s history as having roots crops up, this time indicative of a strength and substance in one’s history that cannot be ignored. Perhaps history is intangible, but it is certainly strong. The traditional Luo practice of burying people where they were born emphasizes the African’s identification with his home and with the physical land he cherishes and is born and raised upon. Traditions, as Okot p’Bitek portrays them, are physically connected to the earth, rooted in the land. The metaphor of ancestral ties as roots bespeaks a strong identification with place as a symbol of group identity, history, and culture. Clearly, cultural identity has unavoidable ties with place, and “home” is a concept that is interwoven tightly into the fabric of the people’s cultural and individual identities.
Igbo people are no exception – their identification with place and ancestral ties are strong, and I would argue that African peoples’ identification with place is stronger than Westerners’ for reasons I will outline later. It is for these reasons that the Igbo are less receptive to change when it comes to identification with place and find it more difficult to expand their definition of “their people” and “home” when it became paramount to build a sense of nationality at the eve of Nigeria’s declaration of independence.
Igbo people are highly individualistic, which lends the population an egalitarian set of values—as Uchendu remarks, “all Igbo share the same egalitarian ideology: the right of the individual to climb to the top, and faith in his ability to do so” (71). Ottenberg explains further, “The possibilities of enhancing status and prestige are open to virtually all individuals…. Ibo society is thus, in a sense, an ‘open’ society in which positions are largely achieved” (186). Igbo propensity for an egalitarian mindset is intertwined with the idea of duality.
The precept of duality is an Igbo universal. As Uchendu says, “Existence for the Igbo… is a dual but interrelated phenomenon involving the interaction between the material and the spiritual, the visible and the invisible, the good and the bad, the living and the dead” (12), which mandates “‘the element of balance by virtue of which the relationship of the two terms of duality is complementary rather than contrary (Nwodo 15)’” (Ndibe, History and Memory). Achebe remarks that duality makes the Igbo world “an arena for the interplay of forces…” (Foreword, Igbo Arts) which lends its people and society a “dynamism, multidimensionality, and nonlinear character” of thought (Cole 216).
The implications of duality on Igbo society are both deep and broad. Aspects of Igbo life impacted by duality include cosmology, religion, social relations, government, and the Igbo worldview in general. Within Igbo cosmology is the idea that balancing complementary opposites forms the basis for maintenance of harmony between worlds: “In his role as mediator, the priest became both man and spirit (Basden: 1938, 132-133)” (Kalu 140). Similarly, when it comes to government, the same principle of balance of forces is seen at work in Igbo legal procedures. In an example elucidating the Igbo ways of governing (the Aro), Uchendu explains, “The principle of equal sharing of rights and privileges is sacred. To be effective decisions must be unanimous” (45-6). Achebe depicts this in Things Fall Apart when Umuofia and all its inhabitants come together in meetings to make important decisions in a highly democratic way (Achebe). As aforementioned, Igbos prize an egalitarian government where “political cohesion is achieved by… consensus rather than by dictation” (46). Democracy reaches new heights in Igbo society at least partially due to duality, which safeguards against imperialism, which Igbo people detest. This principle is expressed in the statement “Igbo enwe eze (the Igbo do not have kings)” (Okafor 68). In Things Fall Apart, Okonkwo, a man who hopes to excel in society, ultimately fails because of his imperialistic mindset (Achebe).
As Ndibe points out, the “‘thing that stands besides’ encodes alternatives, embodies possibilities, and offers a harvest of blueprints and departures” (History and Memory). Duality allows for a high receptivity to change in Igbo society because so many options are available to the Igbo people, who are not barred by the singular mode of thought so common in Western societies. Ottenberg elucidates Igbo tradition of change more thoroughly in his essay “Igbo Receptivity to Change.” Ottenberg states, “The Ibo are probably most receptive to culture change, and most willing to accept Western ways, of any large group in Nigeria” (179). Ottenberg makes the paradoxical statement that “of all Nigerian peoples, the Ibo have probably changed the least while changing the most” (142). The premise of this argument is that the Igbo, with their dualistic worldview that makes them so receptive to change, have a “tradition” of adaptation. Ergo, at their roots, they have changed their fundamental principles very little by transforming their society when adaptation becomes necessary. Others have added to this concept with their own opinions and observations. Isichei agrees, stating: “To understand Igbo history in the colonial era it is essential to understand that for many, perhaps most Igbo, life was not changed very fundamentally” (19). Uchendu also describes the Igbo world as one “…in which change is constantly expected. Its contractual character makes it a constantly changing world” (Uchendu 15). Okafor points out: “the democratic nature of Igbo society… has enabled its people to adapt rapidly to the modern, Western way of life” (Okafor 69).
Afigbo goes so far to say, “‘basically’ colonialism did not change the Igbos because they maintained Igbo identity and cultural soul. He states:
While changing they were able to preserve their ‘ethnic essence’ because they were astute enough to use in their own way, the new institutions and values introduced by colonialism (283-4)
Upon European intrusion, the Igbo used British influence to their advantage and incorporated them into their traditional system of values. The Igbo wanted independence in order to become westernized more quickly: “Ibo politicians tend to be anti-colonial but not pro-traditional or antagonistic to western European culture; they believe that they can become westernized more rapidly if freed from British rule” (Ottenberg 180). As for religion, generally “…belief in ancestral spirits [gave] way to Christianity” and “missionaries have had considerable success in converting Ibo to Christianity” (Ottenberg 181). Igbo adaptive propensities facilitated this forced societal change by the British colonial administration. Chinua Achebe’s works show a progression of Christian penetration into Igbo society. Beginning in Things Fall Apart, Christian converts consist mainly of outcasts from society, like women who bore twins or slaves and “lazy children” (Achebe 102). However, in Arrow of God, Ezeulu, a chief priest, gives a son to Christianity. In No Longer at Ease, set on the eve of Nigerian independence in the 1950s, the main character’s father, Isaac, is such a religious zealot (a Christian catechist) that he condones a sacred traditional Igbo act – kola nut “sacrifice to idols” (59) – and refuses even to allow his wife to tell his children folk stories or allow his children to eat in the houses of heathens (66-7).
Social constructs also morphed within the confines of traditional social norms in Igbo society. Ottenberg explains that after British conquest, the Igbo recognized the superior strength of the intrusive forces, but instead of rejecting or accepting it, “the acquisition of this power and authority became one of their important goals. The task was not merely to control the British influence but to capture it” (187). The adaptability and flexibility of Igbo society allowed Igbo people to transform something that could have been highly destructive into a positive force: “Villages compete to build the first or the best school, village groups to improve their markets… Many social groups strive to push some of their ‘sons’ ahead in schooling and to obtain scholarships in competition with other groups” (Ottenberg 187). The highly individualistic mindset of Igbo peoples meshes well with the introduction of new ideas and practices, and the shifting African landscape became a veritable mine of opportunities for the intelligent, innovative individual in Igbo society: “the alternatives open to the individual have been increased by… culture change” (Ottenberg 188).
Uchendu argues another important ideological factor contributes to Igbo adaptability: “Igbo ideas about change. A people who fear change and are ideologically opposed to experimentation might not react in the same way…” (104). Uchendu is correct about a crucial point: other ethnic groups have not reacted nearly as well as Igbo people have to situations in which change is necessary. As Ottenberg warns, “The Ibo—traditionally accustomed to thinking, acting, and making decisions in terms of a range of alternatives—are more at home in the culture contact situation than members of other societies with different orientations” (188). Other societies, evidently, did not fare as well under the new regime and many fervently struggled to maintain their traditional ways, often in futility.
In fact, a number of ethnic groups in Africa responded with vehement outcries that their traditional practices would be stampeded to dust in the aftermath of British colonization. In one community, “young boys receive training and instruction in traditional lore and morality… Education is designed to instill an appreciation of the value of their way of life” (Schneider 157). Another people, the Pakots, believe that “the traditional way of life is most acceptable to Tororut, that he created it and desires it to continue, in fact, that it is the best conceivable life” (Schneider 158). Furthermore, “magic may also be used by the community to punish a deviant, so that most persons are careful not to transgress the accepted ways even if they should so be inclined” (159). To this day, the Pakot have “found almost nothing in Euroamerican culture that will entice them to abandon their old ways” (Schneider 160).
Even in Igbo culture, receptivity to change can fail. One example in which tradition trumps new ideas is where identity is tied irrevocably to place. Everyone has ties with home, and places, but in Western societies, especially the United States of America, people cannot typically stand in their houses and say “my ancestors have lived and died on this very land for hundreds or thousands of years,” mainly because the majority of US citizens have immigrated to the land in recent history. African peoples, however, have a much richer history that has been preserved in the memories of society’s members and passed down through the generations orally.
For example, Davidson discusses that when a Bushongo tribe elder was asked to recall the legend of their past, he “traversed the list of their kings, a list of one hundred and twenty names, right back to the god-king whose marvels had founded their nation” (6). Again the metaphor of one’s history as having roots crops up, this time indicative of a strength and substance in one’s history that cannot be ignored. Perhaps history is intangible, but it is certainly strong, and is irrevocably tied to the land upon which it was played out.
For Igbo people, specifically, land holds significant meaning to them. As Uchendu says, “Land means many things to the Igbo. It is the domain of the earth-goddess, a burial place for the ancestors, a place to live on and make a living. Land is therefore the most important asset to the people” (Uchendu 22). Clearly, land is an important aspect of Igbo identity, and even with their highly adaptable and amorphous mindset, ties to land are one facet of the set of traditional Igbo values that cannot be altered as easily as other aspects of Igbo society. As I outline later, this can be problematic when a sense of national identity is crucial to obtaining independence because Igbo ties to land are very localized and difficult to expand to larger spatial scales.
One cannot possibly hope to build a sense of identity without a basis of history on which to begin. History makes us who we are, and without it, we would be lost. A key aspect of many cultures’ histories is the idea that one’s ancestors are still with one, guiding one, watching over one, or even influencing or interfering with the future or actions of one, even if these ancestors have long since passed out of the world of the living. One’s ancestry is a vital part of one’s history that allows one to feel as if, through one’s self or one’s ancestors, the actions of those who share one’s blood – one’s genes – have made a lasting impact on this earth, and it is something one can be proud of and revel in. One’s ancestors’ existence provides a substance of character and identity rarely matched by any other force.
Such is the connection with one’s ancestors that the Igbo even believe that the living are spirits reincarnated from dead ancestors: “In the Igbo view, there is a constant interaction between the dead and the living: the dead are reincarnated, death making the transition from the corporeal to the incorporeal life of the ancestors possible” (Uchendu 12). The Igbo incorporate their ancestors into their identity so much that they believe that the spirit of the ancestors lives on within them, fully reincarnated.
Although having such strong ties with place is an enviable quality of Igbo society, it does not come without its hindrances. As aforementioned, the Igbo people found it difficult to expand their worldview to include a “nation” or a unified people when the collective unit of peoples who dubbed themselves “Nigeria” was fighting for independence in the late 1950s. As Phoebe Ottenberg elucidates, “Though they share many linguistic and cultural traits, the Ibo have only recently begun to think of themselves as a unified people” (205-6). Phoebe Ottenberg further attests, “There were no large political groupings—no states or kingdoms—to unite these groupings and provide them will an over-all unity of social structure and culture” (179). Thus, it was difficult to unite without a cohesive social structure and culture that was lamentably lacking on the eve of Nigeria’s independence.
Achebe provides examples of the struggles of Igbo people to expand identity to include a “place” of larger spatial scale in his novels. In the Igbo world, everyone knows where his or her place is, and where everything and everyone in that place exists. Such is the small spatial scale of the Igbo world that to an Igbo person, the familiarity of everything and everyone important to him is heightened to the extreme and opening up to the unfamiliar can be highly daunting. In Arrow of God, the British administration built a road to “connect Okperi with its enemy, Umuaro.” This opens up contact between communities that had previously been antagonists and inevitably changes the landscape of both communities and causes some distress within them.
Isichei argues that “A sense of Igbo identity came only when its people left Igbo-land” (19), and indeed this is evidenced by Obi’s viewpoints in Achebe’s No Longer at Ease. Obi, the main character, receives a scholarship given to him by the people of Umuofia to go to England to become educated as a doctor or lawyer. As Obi states, “It was in England that Nigeria became more than just a name to him” (14). To those who never leave their villages, “Nigeria” is a word without meaning—not a place, nor a collection of people the Igbo ostensibly belong to, but an empty title holding a sense of nationality that was foreign to Igbos. As Isichei aptly reiterates, “There was…no sense of pan-Igbo identity. The Igbo villager’s view of external reality was a sharp dichotomy, ‘they and us’ with sense of attachment to us growing weaker as the unit grew larger – the family, the village, the village-group. Invariably he felt a strong local patriotism” (19). This local patriotism is reduced when Obi leaves Umuofia. However, his people condemn him for lack of respect when he does not return for his mother’s funeral: “He was told that his mother died and he did not care” and “he forgets his home and his people” (181). Obi’s perspective, however, is different: “What was the point in going to Umuofia? She would have been buried by the time he got there, anyway. The thought of going home and not finding her!” (183). He separates the idea of place with his identity and with that of his mother. Now, he thinks only of his mother—his home is not part of those feelings anymore. It is not place, but intangible bonds between people, that constitutes community for Obi. This difference between Obi and his people bars the uniting of all Igbo people needed to form a national identity.
Another situation that the Igbo find difficult is when an individual within society has an ethical code that does not mesh well with traditional Igbo values or when differences in individual’s ethical codes arise. When the British administration took over, they introduced new morals, ideas, values, and practices in society. Inevitably, different people incorporated different aspects of European society into their own lives, and suddenly, the Igbo people did not share all of the same traditional views and moral code. Each Igbo individual is pulled in different directions under the influence of tradition, his family, his own beliefs, and now, under European influence. How, then, does one determine ethical values in a society where the grounds shift considerably; where a citizen must negotiate between several conflicting deities and codes? Achebe explores these struggles and conflicting ethical codes in depth throughout his novels.
In No Longer at Ease, when Obi goes to England, his people expect him to become a doctor or lawyer and return to Nigeria to provide services to and repay his people. However, Obi neither becomes a doctor nor a lawyer, and instead of helping his people, finds a position in Lagos and subsequently attempts to woo an “osu” woman named Clara, who, due to her ancestry, is considered unacceptable for marriage by Igbo society. Umuofians are confused and disappointed, saying, “He runs after sweet things, dances breast to breast with women and forgets his home and his people. Do you know what medicine that osu woman may have put into his soup to turn his eyes and ears away from his people?” (181). Obi left Umuofia before the Igbo ways could become entrenched in his worldview and at the time during which his young, impressionable mind could be influenced by what he sees and experiences during his time in England. Achebe’s experiences as a child may have influenced his depiction of Obi’s character:
The young African boy enthusiastically opened his heart and mind to the exciting, wider world unfolding around him. I did not see myself as an African to begin with. I took sides with the white men… The white man was good and reasonable and intelligent and courageous. The savages arrayed against him were sinister and stupid. I hated their guts” (A Celebration 7).
Indeed, upon return to Umuofia, Obi, while aware of the stigma associated with osu women, believes that he can convince his parents that his marriage to Clara is acceptable. His equally educated friend, Joseph, wisely warns that although they have been educated, not all of Igbo society has: “In future, when we are all civilized, anybody may marry anybody. But that time has not come. We of this generation are only pioneers” (86). However, Obi stubbornly persists on the same path, saying, “What is a pioneer? Someone who shows the way. That is what I am doing” (86). As Achebe warns, however, “…stories are not innocent…they can be used to put you in the wrong crowd, in the party of the man who has come to dispossess you” (Achebe A Celebration 7). Obi has been placed in the “wrong crowd” by spending time in England. He faces pressures that pull him in opposite directions-toward his roots or towards educated, high society. Obi views himself as a pioneering modernist, but ultimately, the pressures of his people’s displeasure overwhelm his love for Clara, and Obi is unable to follow through with the marriage.
Similarly, Obi’s father Isaac sees himself as a rejecter of tradition, but ultimately sticks to traditional values when he forbids his son from marrying Clara, an osu: “Osu is like leprosy in the minds of our people. I beg of you, my son, not to bring the mark of shame and of leprosy into your family. If you do, your children and your children’s children unto the third and fourth generations will curse your memory” (152). Isaac faces difficulty with the changing landscape of African thought that provides multiple conflicting alternatives, both traditional and new, that one must combine into a cohesive worldview. He is a zealous Christian, but prohibits marriage to an osu, a highly pagan view, because his traditional values conflict with his new religion.
In Achebe’s Things Fall Apart, Okonkwo, a warrior and secular figure fascinated by personal power and obsessed with excelling, believes he is a defender of tradition. However, he is too imperialistic and extreme to uphold Igbo tradition, which is dualistic and more focused on finding balance. Okonkwo’s sins in the eyes of Igbo society are all of a moral nature because of his dissonant ethical code. Where Obi fails to act, Okonkwo acts too quickly or too violently. For example, during the week of peace when no one may raise a hand against another, Okonkwo beats his wife. When people tell him to stop because he is committing a moral injustice by beating his wife during the week of peace, Okonkwo does not cease because he “was not the man to stop beating somebody half-way through, not even for fear of a goddess” (19). Beating someone during the week of peace was “unheard of” (19) and no one knows how to deal with it, because Okonkwo’s moral code differs from that of the majority of Igbo society. He is a man of profound moral misconceptions, and in attempting to preserve the tradition of manly power over women, he in fact rebukes a much more sacred tradition.
Okonkwo’s desire to appear strong is one that is traditionally shared and considered important by many male members of society, but unlike other Igbo men, Okonkwo places this desire above the communal good and desires. Near the end of Things Fall Apart, Umuofia holds a village meeting for the people to discuss how to deal with impending war against their clanmates. The decision-making process is lengthy and consists of many steps including consulting the oracle, deciding as a whole village, and hearing from the elders of the village. However, Okonkwo goes to the meeting having already decided how he is going to act, no matter what the village decides: “If Umuofia decided on war, all would be well. But if they chose to be cowards he would go out and avenge himself” (113).
This is an extreme view clashing with Igbo morals for two important reasons. First, it is unheard of that a man would go against the wishes of his entire village. However, Okonkwo does not abide by the universal Igbo principle of duality. He is singular: his will stands and nothing stands beside it, not even a god’s, as evidenced by his lack of fear of godly wrath when he beats his wife during the week of peace. Okonkwo’s beliefs are, according to him, not only central, but also the only set of values worthy of respect, a concept that is foreign to the dualistic mindset pervasive in Igbo society. As Onuekwusi explains, “He relies on old strategies and old yard-sticks such as show of brute force and rashness, fiery temper, resistance to change and rigid show of ‘manliness’ complex to acquire excellence” (75).
Second, if Okonkwo did single-handedly go to war against his clanmates, the punishment would be death. This issue is what Umuofia is deciding upon-how to go about warring with clanmates if part of their law states that this is morally unjust. At the end of the meeting, Okonkwo kills the messenger representing the British administration who had come to break up the meeting. Other Umuofians ask, “Why did he do it?” (116), unable to wrap their minds around the fact that Okonkwo’s worldview and moral code clashes with their own. Ultimately, Okonkwo, who sees himself as a preserver of tradition, commits the epitomic sin in Igbo eyes: suicide. As one Umuofian states, “It is against our custom… It is an abomination for a man to take his own life” (117). The people throw him into the Evil Forest where only the abominable are left to rot in “a final show of revulsion from the clan, which is unable to accommodate Okonkwo’s inability to change with the times” (Onuekwusi 75). Okonkwo, a believer in the preservation of tradition, has such a warped ethical code that he condemns himself to a tragic end and becomes an infamous figure in Igbo folklore because of it.
In Achebe’s Arrow of God, Ezeulu is a priest obsessed with contemplating the nature and scope of his power whilst perceiving himself as, primarily, a moral agent. Ezeulu is the chief priest of Ulu, a war god that was created by the villagers to secure the future of six villages which all came together to stand as one: Umuaro. However, time and time again Ezeulu’s actions have the potential to break apart the villages. Ezeulu bears witness against his own community, Umuaro, when the white administration is deciding whether to give disputed land to Umuaro or Okperi: he says, “the land belongs to Okperi. It was Okperi who gave us a piece of their land to live in” (15). Ezeulu defends his actions by arguing it is his duty to speak the truth, but in Igbo society, when the truth that you tell leads to a fracturing in society, you shouldn’t tell the truth. Ulu is the god that brought together the six villages; but now, due to Ezeulu’s love of the power and influence he holds, Ulu’s priest is tearing the villages asunder.
As Ulu’s priest, Ezeulu also dictates the changing of the seasons, an important task because if he does not count the seasons, the people cannot plant or harvest when it is time to do so. Therefore, Ezeulu essentially regulates the people’s access to food, both for subsistence and economic value. Ezeulu should be obsessed with the success of the community, but from the very beginning of the novel he is contemplating his power and is obsessed with it in an intellectual, abstract way:
“Whenever Ezeulu considered the immensity of his power over… the people he wondered if it was real… No! The Chief Priest of Ulu was more than that, must be more than that. If he should refuse to name the day there would be no festival—no planting and no reaping. But could he refuse? No Chief Priest had ever refused” (3).
Eventually, Ezeulu does refuse to name the changing of the seasons, and condemns his people to death by starvation. However, Ezeulu eventually descends into utter madness and dies an insane old man. Ezeulu views himself as a faithful priest who must stay fast to the stipulations of his deity, but he is ultimately unable to carry out Ulu’s wishes and tears the villages apart when Ulu was in fact created to bring them together. His conflicting morals—obsession with power and the wish to please his deity—drive him to extreme action, insanity, and eventually, death.
The Igbo people are remarkably receptive to change, and their society has fared better because of it, adapting quickly to European intrusion and using Western ways to their advantage to “get up” in society. However, people like Obi and Okonkwo face difficulties adapting to change, whether it be identifying with place on a national scale or forming a cohesive moral code that does not contradict itself or that of society at large. Despite these difficulties, the Igbo people were able to unite to form Nigeria. Although they face hardships as a developing country, they are independent and continue to use Western civilization to their advantage, with increasing numbers of Nigerians becoming educated, prominent members of society every year. It is my hope that we of the United States can learn a lesson or two from these receptive, unique people by interacting with and learning about them and better ourselves because of it.
Achebe, Chinua. “African Literature as Restoration of Celebration.” Chinua Achebe: A Celebration. Eds. Kirsten Holst Petersen and Anna Rutherford. Oxford and Portsmouth, NH: Heinemann, 1991. 1-10. Print.
Achebe, Chinua. Arrow of God. New York: Anchor Books, 1969. Print.
Achebe, Chinua. Home and Exile. New York: Anchor Books, 2001. Print.
Achebe, Chinua. No Longer at Ease. New York: Anchor Books, 1995. Print.
Achebe, Chinua. Things Fall Apart. New York: Anchor Books, 1994. Print.
Afigbo, Adiele. Ropes of Sand: Studies in Igbo History and Culture. Ibadan: University Press Limited and Oxford University Press, 1981. Print.
Cohen, David William, and E.S. Otieno Adhiambo. Burying SM: The Politics of Knowledge and the Sociology of Power in Africa. Portsmouth: Heinemann, 1992. Print.
Cole, Herbert M, and Chike Cyril Aniakor, eds. Igbo Arts: Community and Cosmos. Los Angeles: Museum of Cultural History, 1984. Print.
Davidson, Basil. “The Discovery of African History.” Africa Today, 7.1 (1960): 5-6. Print.
Isichei, Elizabeth. A History of the Igbo People. London: Macmillan, 1976. Print.
Kalu, Anthonia C. “Achebe and Duality in Igbo Thought.” Emerging Perspectives on Chinua Achebe. Eds. Ernest N. Emenyonu and Iniobong I. Uko. Vol. 2. Trenton, NJ and Asmara, Eritrea: Africa World Press, 2004. Print.
Ndibe, Okey. History and memory in the fiction of Chinua Achebe, John Edgar Wideman, and Zakes Mda. Diss. Electronic Doctoral Dissertations for UMass Amherst, 2009. Electronic. October 27, 2012.
Okafor, Clement. “Igbo Cosmology and the Parameters of Individual Accomplishment in Things Fall Apart.” Chinua Achebe’s Things Fall Apart: A Casebook. Ed. Isidore Okpewho. New York: Oxford University Press, 2003. 67-81. Print.
Omiegbe, Odirin. “Chinua Achebe and Igbo (African) Traditional Religion.” Emerging Perspectives on Chinua Achebe. Eds. Ernest N. Emenyonu and Iniobong I. Uko. Vol. 2. Trenton, NJ and Asmara, Eritrea: Africa World Press, 2004. Print.
Onuekwusi, Jasper. “Archetypes and the Quest for Excellence in Chinua Achebe’s Early Novels.” Emerging Perspectives on Chinua Achebe. Eds. Ernest N. Emenyonu and Iniobong I. Uko. Vol. 2. Trenton, NJ and Asmara, Eritrea: Africa World Press, 2004. Print.
Ottenberg, Phoebe. “The Changing Economic Position of Women Among the Afikpo Ibo.” Continuity and Change in African Culture. Eds. William Bascom and Melville Herskovits. Chicago, IL: University of Chicago Press, 1970. Print.
Ottenberg, Simon. “Ibo Receptivity to Change.” Continuity and Change in African Culture. Eds. William Bascom and Melville Herskovits. Chicago, IL: University of Chicago Press, 1970. Print.
Schneider, Harold. “Pakot Resistance to Change.” Continuity and Change in African Culture. Eds. William Bascom and Melville Herskovits. Chicago, IL: University of Chicago Press, 1970. Print.
Uchendu, Victor C. The Igbo of Southeast Nigeria. Belmont: Thomson, 2004. Print.
This week, I’ve been a college graduate for one year. I’m thinking a lot about what I’ve done in the intervening year, what I could do better, and how my first “adult decisions” have shaped my life.
I’m thinking about self-worth as defined by society and fighting against subconscious usage of that definition as my own. I’m strategizing how to better use my time, and working hard to disabuse myself of the notion that I have plenty of it. I’m reflecting on taking risks and how going against my instincts to play it safe has led me to some of the best people, places, and opportunities Of my life. I’m pontificating on fear and the debilitating effect it can have, and how to recognize and work through it rather than deny it exists or run away from it. I’m constantly thinking about change, growth, and self-improvement, but also about acceptance, self-care, and self-love.
I’m exploring ways to be a better ally to various human rights movements, and wondering how to be outspoken without overstepping my bounds and flaunting my various flavors of privilege, something I’m terrified of doing. I’m prioritizing interacting with people who bring positivity into my life and avoiding people who bring negativity into it. I’m thinking about mindfulness, meditation, and living in the moment. I’m striving to choose love and empathy over anger and animosity when people treat me poorly.
What is it that I have that I can translate into bettering the world? How can I make positive change through my work as a scientist and a writer? How can I live my life as the example I want to set for others? As I “settle” into adulthood, how can I maintain an open mind and avoid stagnation? How can I continue to better myself and prioritize seeking new experiences?
These are the things I’m thinking about, and have thought about over the past year. I’m looking forward to taking action on these thoughts in the future!
Check out this diagram to which I contributed drawings; it’s recently been published in a paper in Ecology: