Ecological processes may diffuse through evolutionary time: an example from Equidae

Body mass evolution and diversification within horses (family Equidae). Lauren Shoemaker, Aaron Clauset. 2013. Article first published online: 5 DEC 2013. Ecology Letters. DOI: 10.1111/ele.12221

One of the things that community phylogenetic approaches have tended to overlook is that how we interpret phylogenetic relationships depends on a model of evolution. For example, the assumption that closely related species also are similar in their traits is implicitly relying on a particular model of trait evolution. One downside to this approach is that different models of evolution may provide different conclusions about macroecological patterns and processes (competition, environmental filtering, facilitation). 

For example, a new paper in Ecology Letters provides an example of how patterns of trait divergence and adaptive radiation can evolve as a result of diffusion evolution, rather than from a single strong ecological pressure. The paper by Shoemaker and Clauset focuses on the Equidae (horse) family, which underwent an adaptive radiation 56 million years ago, resulting in massive increases in diversity and in trait variation, particularly in body size, habitat type and range size, diet, life span and reproductive traits. Several explanations have been proposed for this radiation and in particular the great increase in body size variation (species are estimated to have ranged between 10-1200 kg). A diversity-focused model explains body size divergence as the result of macroecological competition for niches. A limited number of niches at a given size are assumed to be available, and these niches vary in quality or attractiveness. Increasingly extreme body sizes (and presumably less desirable niches) evolve as niches are filled at more desirable sizes. The result is a correlation between diversity and body size variation, much like the one seen in Equidae. The alternative model considered suggests that trait space is filled via diffusion or a random walk, with the only assumption being that there are some physiological constraints – here a hard limit on minimum size, and an assumption of increasing extinction risk as maximum size increases.

From Shoemaker + Clauset, 2013.

Using mathematical models of Equidae body size evoluation, the authors’ results were very clear (figure below): “Using family Equidae as a model system, we found that macroevolutionary ‘diffusion’, in which selective effects on species body size vary independently of the occupation status of nearby niches, explains substantially more of the observed changes in the Equidae body mass distribution over 56 Myr (Fig. 5) than does a diversity-driven mechanism...”. The results are interesting because they are a reminder that the relationship between macroecological patterns (for example, of traits like body size) may be related to evolutionary history in a much more nuanced way than ecophylogenetic studies sometimes assume. Rather, Shoemaker and Clauset suggest that the better performance of the diffusion model--rather than indicating that competition is *not* important--may be effective at capturing many independent ecological interactions and selective effects all driving body size evolution. A macroevolutionary model of competitive effects on trait divergence is may simply be unrealistic, since competition and ecological interactions may be more localized and less generalized in their effects across the entire Equidae family.

From Shoemaker and Clauset, 2013. Left - competition model, Right - diffusion model

“A large role for diffusion does not undermine the general ecological importance of competition, but rather clarifies its role in generating broad-scale patterns for horses in particular, and for evolving systems in general. Macroevolutionary diffusion is an effective large-scale description of many roughly independent ecological interactions and evolutionary constraints on species size variation. Short-term selective effects on size for a particular species can stem from any number of specific mechanisms, including but not limited to competition over ecological niches. So long as the magnitude and direction of these effects, as defined at the species-level, are roughly independent across the taxonomic group, the large-scale pattern will be well described by diffusion. Ecological competition may thus be crucial for individual species, but its effects are more diffuse at the large scale because competition is typically a local process.”

This is a reminder that many phylogenetic hypotheses (trait divergence or convergence in communities, etc) are too simplistic in their assumptions that broad macroecological processes dominating, and instead need to recognize that ecological processes are often numerous, independent, and local, making outcomes more nuanced than usually assumed. 

The European Ecology Federation Congress, day 2

Day two of the conference, and still many great talks. I mainly stayed in the session on synthesizing community ecology, phylogenetics and macroecology. This has turned out to be a great conference and Avila is a great venue.

Carsten Rahbek. His talk is on merging the fields of macroecology to better understand patterns of diversity. Different models explain variation differentially at different scales. For example, climate models do well for wide-ranging species but not for scarce species. A model of evolution may do much better for scarce species, but not for wide-ranged species. Statistical tests confirm a correlation, but not necessarily a mechanism. One could get different conclusions if one were to compare to a null model. He advocates a spatially explicit species assembly model that integrates macroecological models with community assembly. It is scale invariant and can explain spatial and temporal variation in assemblages. In an example, he shows that, based on small scale sampling, species distribution models will over-predict richness. Need to combine macroecological models with distribution models, because acroecological models do well to predict richness but not composition while distribution models predict composition but not diversity.

Jens-Christian Svenning. He talked about paleoclimatic influences on ecological patterns and function across scales. Past climates have shown masive changes and different groups of species have evolved during these events, while other species have gone extinct. The velocity of climate change was highest in northern Europe and North temperate North America, and higher velocity results in lower endemism since it is quicker for species to migrate than diversify. Higher velocity results in lower specialization in hummingbirds. He finishes with a note about current regions undergoing fast climate change; these are not necessarily those same regions that had the most change in the past.

Adreas Prinzing. His talk was about how niche conservatism can inform our potential solutions for changing environments. Specialists are declining in changing environments and how does this apply to specialist clades of closely related species? Specialist species tend to occur in specialist genera. However, niche conservatism does not tell us everytng about species differences/similarities because closely related species clearly coexist and exhibit substantial trait differences. Species coexist within niches by key divergences.

Kenneth Kozak. He presented a way that phylogeny illuminates the origin of climate-richness relationships. Only speciation, extinction or dispersal can change richness, and many models do not ask how these processes change. He examined salamader diversity and evolutionary history using 16000 occurrence records in North America, and examined climate variables for occurrences. Diversity was highly associated with cool, moist places. Richness is strongly correlated with evolutionary time of colonization of climatic conditions. For example, evolution of warm species is recent, hence fewer species. Diversity does seem to be saturating, and so time is limiting factor, and more species can probably still emerge.

David Vietes. He gave an interesting talk on the amphibians of Madagascar, which is a diversity hotspot for amphibians. There were 132 described species n 1999 and now 263 with about 200 still needing to be described. Many are endemic to small regions of Madagascar (the whole family is endemic to Madagascar). He discussed many aspects of the distribution of these species, and looked at phylogenetic patterns. Some interesting observations include: older species pairs are further separated in space and smaller species have smaller ranges. Also, there appears to be a predictable pattern of richness hotspots, but endemism hotspots are more idiosyncratic.

Joaquin Hortal. He discussed the effect of glaciation on richness, functional diversity and phylogenetic diversity for European mammals. The hypothesis he explored was that current distributional patterns driven more by past changes since glaciation than current climate. He compare several different types of measures and it turns out that current climate is more important for explaining patterns of co-occurrence and relatedness, with more closely related species occurring together at northern locales.

Catherine Graham. She also explored patterns of richness, functional and phylogenetic diversity, but was looking at hummingbirds diversity patterns across elevation gradients in South America. She compiled an impressive dataset with several morphological traits and co-occurrence patterns. Broadly, close relatives co-occur at high elevations and more distantly at lower where competition is stronger. In local communities a mix of environmental filtering and competitive dispersion seem to be operating. At high elevations, both functional and phylogenetic diversity are high.

Rob Dunn. He gave a fantastic talk on the species on the human body and in our lives and homes. He told us about projects that involve citizen scientists from across the USA and had them sample their homes and bellybuttons. Amazingly, Dunn’s group has so far identified 1400 species in belly buttons, and many of them are unknown species –which could not be classified into known species groups. He looked at many factors like ethnicity, geography, cleanliness, but none of these explained this diversity well. A subset of these species are bellybutton specialists and dominate bellybutton floras within and among people, and are phylogenetically clustered, evidence that the bellybutton habitat is a conserved trait.

Cecil Albert. I ran to another session to see this talk on intraspecific variation in species traits. She eloquently showed that for plant assemblages, there was substantial intraspecific variation in traits. Some species showed high variation and some showed almost no variation. Importantly, she showed that this variation could substantially change our ability to explain how functional traits link to abundance and coexistence. She simulated different levels of variation and looked at the strength of the correlation between expectations from mean trait versus the actual trait that varies. The strength quickly declines for some traits as variation increases, meaning that with variable traits, the explanatory ability of using a mean trait is weak.

Sally Keith (Flash talk*). She examined the Mid-domain effect (where, because of range sizes, maximal diversity is found in the centre of a geographic landmass by random chance), and process based models to test mechanism for middomain prediction. She showed that these models seem to have limited success. Perhaps environmental gradients and species interactions could be important. But when she added interactions to the model, it then predicts humped shaped pattern predicted by the mid-domain effect.

Tamara Munkemuller (Flash talk). She examined phylogenetic relationships as a way to examine niche patterns and coexistence. She hypothesized that there should be strong filtering under stressful conditions. She examined thousands of plots across elevational gradients, and plots that were in stressful locations tended to be phylogenetically clustered, meaning certain groups of species exist there.

Susanne Fritz (Flash talk). She was looking at diversification patterns in birds. Using lineage through time plots one should expect that the rate of diversification should decline trough time, which perhaps equates to niche filling. For species in tropical Asia, she found that there is not much leveling off of diversification rate. Though interestingly, groups that have not dispersed (for example, birds of paradise) do show a plateau in diversification. Globally, diversification slows down more in more speciose regions.

Jake Alexander (Flash talk). He had a very interesting talk on elevation gradients in richness in non-native plants invading mountain habitats. Most species have narrow elevational ranges in lower and mid elevations and high ranges for those species found at high elevations. The explanation is that these non-natives are generalist and that they originate form lower elevations –where human activity dominates, and must spread up the mountain to get to the high elevations.

*Flash talks are 3 minutes long, and a great way for people to communicate new and exciting results.

The European Ecology Federation Congress, day 1

I’m in the beautiful walled city of Avila, Spain for the European Ecology Congress. It is at a lovely venue and with about 800-1000 attendees, seems like just the right size. It is a young meeting, with relatively few old-timers like me, but there is an excitement, and the talks have been excellent. Each session starts with a keynote, where the person gets 25 minutes, followed by a bunch of 15 minute talks. The most interesting aspects of the sessions I went to was that they usually include several 3-minute ‘flash’ talks, which surprisingly works. I spent the day going to talks in two sessions, plus a plenary talk by Jordi Bascompte, and here are the talks I saw*:

*sorry about the abrupt, choppy nature of some of the entries, there were a lot of talks, and they go until after 7pm.

I spent the morning in a session on biodiversity and ecosystem function under environmental change. Most of these talks we by people associated with the BACCARA project on forest biodiversity.

1) Xavier Morin, Montpellier, talked about climate change and tree diversity and productivity. Looked at SR (see glossary at end for acronyms) and FD on biomass produced. Do grassland BEF studies predict frost ones, with no opportunity for random assembly? Use forest dynamics model where species are defined by rigorous parameterization –one can examine long-term dynamics and many species combinations. Simulated 30 species monocultures and many combinations from 2-30. Strong relationship between realized richness and productivity, but a lot of variation. 93% of 30 species plots show transgressive over-yielding after 2000 years. FD predicts increase in productivity. Assess future climates from three climate change scenarios, always steeper slope with future climate, meaning diversity is more important in the future. This was a great talk.

Sibylle Stoeckli. Affects of diversity on individual tree performance. She wanted to assess the influences of tree traits (e.g., size) on the performance of neighbours. Plots planted with four species combinations, with a pool of 16 species, and treatment is different FD levels (based on 9 traits). No effect of plot diversity on tree performance. Tree height has effects on neighbours depending on whether focal tree is shade tolerant or intolerant. Diversity not important as traits of species such as growth rate. Interspecific competition lower than intraspecific.

Aitor Ameztegui. Montane-apine ecotone is diverse and are traits important for coexistence. Are interspecific differences key for coexistence, and can these tell us about biome changes. One species has advantage at low light but quickly saturated with increasing light. Silver fir had constant survivorship, while other species increased survivorship with increasing light. Fir has low plasticity, whereas Scots pine is more plasticity and should adapt to climate change.

Alfredo saldena. FD on decomposition in South American rainforest (Chile). He looked at two forest types within the Andes. In both forests strong positive relationship between FD and litter decomposition. FD is based on leaf traits.

Julia Koricheva. Forest diversity and insect communities. Boreal species (5) in southern Finland in monocultures and 2, 3 and 5 species mixtures. Looked at different types of leaf damage. For birch, increasing skelontonizing damage with diversity. During aphid outbreak, decline in density with increasing SR. They prefer birch. Leaf miner richness on birch increased with SR. In another, german, experiment (the experiment in Stoeckli's talk) where FD was manipulated. Again several types of herbivores had positive relationships with FD, again counter to expectations of more specialized herbivores declining with tree diversity.

Laura Concostrina-Zubiri. Biological soil crusts (BSC) are important for soil fertility and stability in dry ecosystems. creates soil heterogeneity. Examined the role of BSC across a grazing gradient. Measured 17 soil variables for a bunch of species. Species differ in their different soil fertilities. Less heterogeneity with higher grazing. Grazing also reduces individual species contributions to soil fertility.

Plenary talk: Jordi Bascompte. Plant-animal mutualistic networks. He talked about Global datasets to answer three questions: 1) are there regularities in network architecture; 2) Do these provide robustness to extinction; and 3) what are the contribution of species to network architecture and robustness? Networks seem to be nested such that specialist animals use most utilized plants. This means there should be a link between structure and robustness (losing an aminal should not result in plant extinction). Half of communities have interactions dictated by evolutionary history. Thus when there is extinction, it tends to be related species, nonrandom. Therefore clades are more likely to be lost. How much of the interactions that are shared can be used as a competition term in coexistence model. The higher the nestedness the lower the competition and the higher maximum diversity. Some species contribute to nestedness much more than others and therefore are much more responsible for stability and have greater probability to go extinct.

I spoke in a session on evolutionary history, ecosystem function and conservation, and (probably ignoring my talk) these were excellent.

Marten Winter. He asked whether phylogenetic studies purporting to do conservation actually did conservation and whether using PD was feasible. Assumptions, some not proven. Unsderstandability of terms like evolutionary potential, what that means for species and communities can cause confusion. Different measures can produce different patterns and he asked Don't we already conserve what we want? Or is there an added advantage to accounting for PD. There were a surprising number of papers that do make conservation recommendations.

Nicolas Mouquet. Phylogenetic constraints on BEF. Biodiversity crisis is a change for synthesis for diffect fields to come together. Positive relationships went from how much to what kind diversity. Evolution is necessary for understanding how biodiversity shapes ecosystem function. He tested these relationships with bacteria from Mediterranean and evolved in lab. There are ancestral and derived groups. Strong positive BEF relationships for both ancestral and derived taxa. For ancestors, a strong PD influence was observed. But not for derived taxa, a reshuffling of traits in the lab. Need to understand the history.

Ana Rodrigues. Species are not all the same such as mouse versus echidna. Need to be cognizant of tree structure and species distributions. Does it matter if we use PD for complimentary reserve design and compare maximizing PD vs SR vs random. SR conserved then look at PD. Little difference for mammals at global level, meaning that current reserve selection routines seem sufficient. Important for species level, but perhaps species level activities may have done a good job at conserving PD.

Sandrine Pavoine. Rockfish declines and phylogeny. Phylogenetic diversity based on period between speciation events. Sum abundances for lineages for each period. Sum period lengths times relative abundance. Calculate lineage contribution to total diversity. Which period is reponsible for abundance change. One period explained declines in rockfish and is actually quite an old period (6 million years).

Wilfried Thuiller. Preserving the tree of life and climate change. Are there winners and losers? Estimate phylogenetic consequences of climate change, if there are sensitive clusters, would one expect more loss than expected by chance. There is a phylogenetic signal in climate, kind of weak, but extremely close relatives respond similarly. Loss of PD is not much different than random. Sensitive species tend to be young. But there is a predicted loss of phylobetadiversity for all birds, mammals and plants with climate change.

Vincent Devictor. Comparing several components of biodiversity. Can SR, FD, PD serve as surrogates. Compared metrics using birds surveys in France with 22 traits. Abundance weighted measures. FD declining while SR increasing. Differential responses important for making conservation decisions.

Laure Turcoti (Flash talk 1). Comparison of SR FD PD on plant communities. SR increases with urbanization and FD and PD decrease with urbanization.

Laure Zupan (Flash talk 2). Current distribution of phylogenetic diversity. Covariation across different clades. Birds, amphibians and mammals. Mismatch between tax am amphibians high PD relative to SR, while mammals low.

Jonathan Davies. Plant extinction risk in the Cape using IUCN rankings. Genera level phylogeny for the over 700 genera in the Cape. Clustering of extinction risk on phylogeny, but plant extinction is correlated with clade size, meaning that large clades have more risk –opposite of what has been observed for mammals. The reason is that many small peripheral species with small range.

Sebastian lavergne. Dechronization of niches, i.e., travel back in time. Is there signal of niche conservatism, and for different niches for the birds for Europe. Climatic, habitat and trophic niches. Trophic niche evolves at slower rate but niches evolve in punctual way, not gradual. High clade disparity in niches since niches evolving faster.

Glossary

BEF: Biodiversity and ecosystem function

FD: Functional diversity

PD: Phylogenetic diversity

SR: Species richness

Ecological interactions and evolutionary relatedness: contrary effects of conserved niches

Over the past several years a multitude of papers linking patterns of evolutionary relatedness to community structure and species coexistence. Much of this work has looked at co-occurrence patterns and looked for non-random patterns of relatedness. The key explanations of patterns has been that communities comprised of more distantly-related species is thought to be structured by competitive interactions, excluding close relatives. Alternatively, communities comprised of species that are closely related, are thought to share some key feature that allows them to persist in a particular set of environmental conditions or stress. This whole area of research is completely predicated on close relatives having more similar niche requirements then two distant relatives. This predication is seldom tested.In a recent paper in the Proceedings of the National Academy of Science, Jean Burns and Sharon Strauss examine the ecological similarity among 32 plant species and tested if evolutionary relationships offered insight into these similarities. The ecological aspects they examined were germination and early survival rates as well as interaction strengths among species. To assess how these were influenced by evolutionary relatedness, they planted each species in the presence of one of four other species varying in time since divergence from a common ancestor, creating a gradient of relatedness for each species. They found that germination and early survival decreased with increasing evolutionary distance. This surprising result means that species germinating near close relatives do better early on then if they are near distant relatives. The explanation could be that they share many of their biotic and abiotic requirements, and these conserved traits influence early success.

Conversely, when they examined interaction strengths over a longer period (measured as relative individual biomass with and without a competitor), they found that negative interactions were stronger among close relatives.

These two results reveal how evolutionary history can offer insight into ecological interactions, and that the mutually exclusive models of competitive exclusion versus environmental filtering do not capture the full and subtle influence of conserved ecologies. Evolutionarily conserved traits can explain both correlated environmental responses and competitive interactions.

Burns, J., & Strauss, S. (2011). More closely related species are more ecologically similar in an experimental test Proceedings of the National Academy of Sciences, 108 (13), 5302-5307 DOI: 10.1073/pnas.1013003108

Reinterpreting phylogenetic patterns in communities

Examining the phylogenetic structure of a community in order to understand patterns of community assembly has become an increasingly popular approach. A quick web search of “community”, “phylogenetics”, and “ecology” finds several hundred papers, most written in the last ten years.

Eco-phylogeneticists examine how patterns of evolutionary relatedness within communities may reflect the processes structuring those communities. In particular, a commonly tested hypothesis is the competition-relatedness hypothesis, which suggests that more closely-related species having more similar niches and therefore stronger competitive interactions, making coexistence between them less likely. As a result, if competition is important, communities may exhibit phylogenetic overdispersion, with species being less related on average than if drawn randomly from the regional species pool. The contrasting pattern, phylogenetic clustering, where species tend to be more closely related than expected, is often interpreted as being the result of strong environmental filtering, such that only a closely related group of species, best adapted to that environment, surviving in the community.

Evidence for the competition-relatedness hypothesis has been mixed, and since most tests of this hypothesis focus on patterns in observed data, conclusions about the underlying mechanism driving community phylogenetic patterns are rarely testable, and yet widely made.

In Mayfield and Levine (2010, Ecology Letters), the authors critique the current ecological justification for the competition-relatedness hypothesis, noting that it does not agree with a more current view of the processes driving species coexistence. As established by Chesson (2000, Annual Review of Ecology and Systematics), coexistence can involve both stabilizing forces (niche differences between species), and equalizing forces (fitness differences between species). In a simplistic example, plants using different soil types (niche differences) may coexist, while plants with similar high growth rates may exclude those species with lower growth rates (fitness differences). The final community should reflect the interplay of both these processes.

The implication of this view of species coexistence is that there is no preconceived phylogenetic pattern which should reflect competition: if species with the highest heights are competitively superior and exclude other species (coexistence driven by fitness differences), and height is a phylogenetically conserved trait, the community will appear to be phylogenetically clustered. Traditionally, a clustered pattern would not be considered to indicate the effects of competition. In fact, Mayfield and Levine show that the expected phylogenetic pattern depends entirely on whether niche and/or fitness differences are important and/or related to phylogenetic distance.

This suggest that conclusions in past studies may need to be reinterpreted. It also adds to the list of assumptions about evolutionary relatedness and ecological function which need to be tested: for example, how do niche and fitness differences tend to change through time? Do they tend to be conserved among closely related species? Does one or the other tend to dominate as a driver of coexistence in different systems? If nothing else, we need to be careful about making generalizations which don’t account for the differing evolutionary history, geographical location, and ecological setting that communities experience, when interpreting observed patterns in those communities.

Picante's coming out party

This past decade has seen a rapid expansion of the use of evolutionary phylogenies in ecological studies. This expansion is largely due to the increased availability of phylogenies, but has resulted in new types of hypotheses and statistics aimed to test the phylogenetic patterns underpinning ecological communities. The main computational tool used has been phylocom, created by Cam Webb, David Ackerly and Steve Kembel, which has its own binaries to be installed on one’s computer. However, a new R package, picante has been created by Steve Kembel and colleagues which runs many of the same routines as in phylocom, but in the R framework, allowing one to tie these analyses in better with other, non-phylogenetic tests. Picante also has a number of features and tests not found in phylocom, including tests of phylobetadiversity and phylogenetic signal using Blomberg’s K.

Thanks Steve for all your hard work and for making these tests available to everyone.

Kembel, S., Cowan, P., Helmus, M., Cornwell, W., Morlon, H., Ackerly, D., Blomberg, S., & Webb, C. (2010). Picante: R tools for integrating phylogenies and ecology Bioinformatics DOI: 10.1093/bioinformatics/btq166

Predicting endangered carnivores: the role of environment, space and phylogeny

For conservation biology, there are several research thrusts that are of critical importance, and one of these is to find predictors of species' extinction risk. Oft-cited is the particular susceptibility of large-bodied organisms, with their large ranges and slow reproductive rates. But there should be other predictors too, especially within larger mammals. In a forthcoming paper in Global Ecology and Biogeography, Safi and Pettorelli use just a few variables to predict extinction risk in carnivores.
They quantified species extinction risk according to the IUCN risk assessments and asked how well three attributes explained variation in extinction risk. They quantified the environmental characteristics of the species' ranges (temperature, precipitation, etc.), spatial distances between species' ranges and the phylogenetic distances among species. Overall, spatial and phylogenetic distances were good predictors of threat status -generally predicting between 21-70% of variation in extinction risk, whereas the environmental variables were weaker predictors. Full models incorporating all three variables (and accounting for their covariance), were able to explain upwards of 96% of the variation in extinction risk!

Although these variables do not represent causal mechanisms of extinction risk -rather they are correlative, they do provide conservation biologists with a rapid assessment tool to evaluate extinction risk. These tools should be particularly important in cases were population data are lacking and immediate pragmatic decisions are required.

Safi, K., & Pettorelli, N. (2010). Phylogenetic, spatial and environmental components of extinction risk in carnivores Global Ecology and Biogeography DOI: 10.1111/j.1466-8238.2010.00523.x

March of the polyploids!

Speciation by polyploidy (see here for a general description of polyploidy) is one of the mechanisms of speciation and evolutionary diversification. We all learn about it in Bio 101, right after allopatry and sympatry. It is thought to be an especially important driver of speciation in plants, and anecdotal evidence, such as the origination of the invasive polyploid, Spartina anglica in the UK in the 1800's, reinforced that view. But how important has been unanswered until now.

In a new publication in PNAS by Wood et al. -from the Loren Rieseberg lab (one of the best lab homepages BTW) this questions has been answered. The authors go through all available chromosome counts on the Missouri Botanical Garden's Index to Plant Chromosome Numbers, and assess the proportion of polyploid species. They find that about 15% of all angiosperm speciation events coincided with an increase in chromosome number (and about 30% of fern species). Further, about 35% of all genera contain polyploids. Looking across the phylogeny of major plant groups, they find that all major lineages, except Gymnosperms, have significant proportions of polyploids (again with ferns have the greatest proportion). Polyploidy is a ubiquitous feature of plant diversity and a major driver of plant speciation. And now we can quantify just how important.

Wood, T., Takebayashi, N., Barker, M., Mayrose, I., Greenspoon, P., & Rieseberg, L. (2009). The frequency of polyploid speciation in vascular plants Proceedings of the National Academy of Sciences, 106 (33), 13875-13879 DOI: 10.1073/pnas.0811575106

Whence diversity?

It is a truism to say that ecological communities are diverse. They often contain dozens or hundreds or thousands of species that represent many of the deep origins in the tree of life. A recent paper by Prinzing and colleagues published in Ecology Letters tested the hypothesis that communities of plants that include more of the ancient divergences from the evolutionary tree of plants should also contain a greater diversity of physical traits. They examined over 9000 plant communities and found that those that contain fewer evolutionary lineages actually had greater trait diversity than those randomly assembled from more lineages. This result reveals that when communities are assembled from a few lineages (likely due to strong environmental selection -e.g., drought tolerance) those members tended to have evolved large differences. That is, while species may be constrained to certain habitat types due to their evolutionary heritage, successful coexistence depends on maximizing differences.
Andreas Prinzing, Reineke Reiffers, Wim G. Braakhekke, Stephan M. Hennekens, Oliver Tackenberg, Wim A. Ozinga, Joop H. J. Schamine, Jan M. van Groenendael (2008). Less lineages more trait variation: phylogenetically clustered plant communities are functionally more diverse Ecology Letters, 11 (8), 809-819 DOI: 10.1111/j.1461-0248.2008.01189.x