Will intra-specific variation buffer species and help reduce extinction risks due to climate change?

Many studies have touted the role of biodiversity in buffering ecosystems against disturbances such as climate change.  A new study indicates that intra-specific diversity may also buffer species against the negative effects of climate change.

One of the most commonly employed tools for predicting the effects of climate change is species distribution modeling. Species distribution models, or SDMs, use different techniques to relate the known occurrences of a species to underlying environmental variables and estimate the realized niche of the species. Based on the duality of the niche, suitable conditions can then be identified across a wider map of environmental variables to predict the potential geographic distributions of the species. By changing the map of environmental variables, SDMs can also predict the geographic distribution of species under altered conditions.  For example, the distribution of a species can be predicted under current climate and then again under the future climatic conditions forecast by GCMs as a means of predicting the effects of climate change on that species.  Many studies have done just this for large number of different species and have generally predicted rapid decreases in the range areas of the species which leads to the concern that many of these species will be at increased risk of extinction.

There are many different forms of SDMs each with their own assumptions and hence limitations. One common assumption in almost all SDMs is a lack of local adaptation or intra-specific variation in environmental tolerances/preferences. Oney et al. argue that this is a very significant oversight and that the inclusion of intra-specific variation will change the SDM predictions for the future.

To test this contention, Oney et al., in their study “Intraspecific variation buffers projected climate change impacts on Pinus contorta published in the journal Ecology and Evolution, model the current and future (2070-2100) distributions of the conifer tree species, Pinus contorta. The researchers generate their SDMs while ignoring intra-specific variation and also while accounting for potential differences between three subspecies: contortamurrayana and latifolia. The change in the habitat area of the entire species and each subspecies due to climate change are then calculated assuming no or perfect migration.

Ignoring sub-species, Oney et al. predict 60% habitat loss for Pinus contorta with no migration and 51% habitat loss with perfect migration. Conversely, if intra-specific variation is accounted for, and the species range is assumed to be the sum of the individual subspecies ranges, the authors predict a 26% habitat loss with no migration and 8% habitat gain with perfect migration. Importantly, the different sub-species have very different results with latifolia predicted to do relatively well and murrayana predicted to suffer from large losses in habitat .

To be honest, these results surprise me. A general belief is that smaller-ranged ‘species’ are assumed to be more sensitive to climate change (especially under no migration scenarios). As such, I would expect a greater overall risk of extinction if you break one species into three smaller sub-species. What I think is happening in the present study is that in the species model (i.e., ignoring sub-species), differential sampling of the different sub-species could decrease the predicted probability of occurrence in some parts of the range that are assumed to be suitable in the sub-species model. In other words, the sub-species model weights each sub-species equally while the species model functionally weights the subspecies by abundance (real or sampled abundance). In addition, since in the sub-species model the probability of the species occurring in a given area was calculated as the sum of the sub-species probabilities, the overall probability in any given cell will generally be higher than under the species model, especially since the probabilities are relativized (on a scale of 0 to 1) across the species’ or subspecies’ entire range (this is related again the weighting issue mentioned above).

So in the end, I am convinced that the inclusion of intra-specific variation is a necessary improvement or next step in the development of SDMs. I am unconvinced that intra-specific variation will generally buffer species against climate change. Instead, I think that in many cases, local adaptation of populations, especially when coupled with limited dispersal/migration abilities, will actually result in even greater extinction risks for species in a changing world.

–Ken Feeley

Species can’t keep upwithclimate

When I teach or give seminars about climate change, I often start by reminding the audience that there are only four possible responses of any species to climate change: species can adapt, individuals of a species can acclimate, species can shift their geographic distributions, or failing in these species can become committed to extinction. I then usually go on to dismiss adaptation as a non-viable option due to the fact that climate is changing so fast and adaptation happens so slow. Now I have some support for my dismissal of adaptation.

Ignacio Quintero and John J. Wiens (of Yale and U. Arizona, respectively) have just published a new paper entitled, “Rates of projected climate change dramatically exceed past rates of climatic niche evolution among vertebrate species” the journal Ecology Letters. This article describes a study looking at past rates of evolution in the climatic niches of species. More specifically, the authors used time-calibrated phylogenies and estimates of species’ current climatic distributions/niches to calculate the time since divergence and most likely ancestral climatic niche for many different pairs of sister species (540 species in 17 clades of terrestrial vertebrates). For each species, the rate of climatic adaptation was then calculated as the difference between its current and ancestral climatic niche divided by time since divergence.

Based on this simple analysis, Quintero and Wiens find that rates of past climatic evolution were ‘slow’ across all the taxa examined. For example, in the case of mean annual temperature, the mean rate of evolution was generally less than 1°C change per million years. Given that global mean temperatures thave increased by approx. 0.6°C over the past 30 years and expected to increase by more than 4°C over the next century, 1°C of evolution per million years is about 10000 to 100000 times too slow.

As indicated above, the reported analyses are very simplified. This is fully acknowledged by the authors and indeed nearly the entirety of their discussion is spent addressing potential sources of error. In addition to several potential minor sources of error, the authors identify three potential major sources of error:

1) The assume a constant rate of evolutionary change through time. It is possible that species are capable of much faster bursts of evolution than indicated by the analyses which looked at the average rate across long periods of time including any periods of stasis.

2) Subspecies or populations may be capable of faster evolutionary change than entire species.

3) The species may not have been evolving at their maximum possible rates in the past. This is my biggest complaint with the study. Rate of evolution will depend on many factors including eh strength of selection. If climate change was slower in the past, selection pressure would have been less resulting in slower evolution. Now that climate change is fast, selection pressure is greater and species may be able to evolve faster. But even with the greater selection pressure, I think it is inconceivable that species can evolve the 100000 times faster that will be required to keep pace with future climate change.

Despite these and other concerns, the results of this study very strongly support the contention that climate change will simply be too fast for species to respond to through adaptation. If species can’t keep upwithclimate through evolution, then it becomes more and more likely that their only real option to escape extinction will be to move upwithclimate to higher elevations or latitudes.

–Ken Feeley

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why the denial?

Over this summer, Justin Catanoso, a journalism professor at Wake Forest University, was embedded with myself and other researchers of the Andes Biodiversity and Ecosystem Research Group (ABERG) as we conducted our field studies in the Kosnipata Valley of the Peruvian Andes.  He has just published the first in a series of reports based on his experiences and time with us.  In this first report, Miles Silman and I discuss some of the confusion over climate change and why climate change denialism persists in the USA.  You can find the article HERE.

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A related article was also just published in the New York Times, discussing the ongoing and growing public denial of science.  You can find the article HERE.

Why is it that most people would never think to question doctors of medicine, but don’t hesitate to challenge doctors of philosophy?

–Ken Feeley

the start of a new blog

5799409117_2d9273858b_zThe Tropical Ecology and Conservation (TREC) research group at Florida International University (FIU, Miami USA) has decided to try our hands at blogging.  The blog will focus on sharing ideas and information related to our research on the effects of climate change on tropical and subtropical systems.  Posts will primarily be regurgitations of new papers that we find to be particularly interesting or noteworthy, musing about our lives as undergrads, grad students, postdocs and faculty members, and general commentary. More information about who we are and what we do can be found at: http://www2.fiu.edu/~kfeeley/

–Ken Feeley