Environmental sorting of vertebrate faunas: Is guild-level locomotor and dietary ecomorphology an indicator of paleoenvironment? P. David Polly How do communities and species respond to environmental change? This question is important to conservation ecologists, biologists and paleontologists because the answers help understand what principles influence which species are found together in a community, how those species and their community will respond to changing climates and environments, and how we can better determine past climates and environments from assemblages of fossils in the geological record. This project will focus on how climatic and environmental parameters in North America are associated with the average locomotion and diet in terrestrial carnivores from two major biological groups, the mammalian Carnivora and snakes, each of which have their individual physiological and locomotor specializations, but both of which function ecologically as high-trophic level carnivores in the same communities. The project will study how two properties of the species coexisting in communities ? locomotion and diet ? are associated with climate and environment on a continental scale. We expect that species within a community will each be specialized for their own niches, but at the same time we expect that the large-scale climate and environment in a local area will restrict the range of differentiation that is possible within a community (all species living in an arctic tundra community, for example, must share specializations that allow them to live in that environment). Our goal is to determine the extent to which climate and environment are associated with the geographic distribution of locomotor and dietary specializations to assess the possibility of inferring past local terrestrial climates and environment from fossil communities using these systems. Our approach is quantitative and geographically comprehensive. From museum collections, we will take measurements of limbs, bodies, and dentitions of carnivorans and snakes from across North America, with the goal of obtaining a sample of 20 or more individuals for every North American species in these two groups and of obtaining samples of 10 or more across the entire geographic range of selected widespread species. We will also measure limbs and dentitions from Pleistocene carnivorans in order to apply our results to late Quaternary paleoenvironment reconstruction. These measurements will be assembled using Geographic Information System (GIS) methods to map the community-level patterns in locomotion and diet across the whole of North America to study how they are associated with climatic parameters and we will reconstruct Pleistocene climate and environment from this association and test that reconstruction against climate models based on other lines of evidence.
This project developed new methods for evaluating data from the fossil and geological records in order to assess the impact that past climatic and environmental changes had on living organisms, especially on biological communities. The aim of this research was to provide new ways for determining how the pace and magnitude of current globcal climatic change compare to events in the geological past where we know more about the outcomes in terms of reorganization of communities, extinction of species, and other important impacts. One of the difficulties in making such comparisons is that much of global change research focuses on the impact of climate change on particular species, but the species that lived during Earth's past were different than those living today. This project circumvented this problem by focusing on functional traits with which organisms interact with their environment, such as the strcutures of their legs and feet that are related to their abilities to live in deeply forested environments (climbing specializations), open plains environments (running or digging specializations), or mixed environments. These traits are directly related to the kind of vegetative environment in which animals live, which in turn are directly related to the climatic environment. Figure 1 shows an example of the modern distribution of average ankle structure in North American mammal carnivores, demonstrating that such traits are sorted geographically by environment. As climate changes, so too will the vegetative environment, and so too will the traits possessed by species in the local community. This project looked at functional traits in two major vertebrate groups, mammal carnivores and snakes, (1) to determine to what extent species are sorted by relevant functional traits; (2) to determine which environmental factors are most responsible for the geographic sorting of species; (3) to measure the rate of reorganization of biological communities in the past by measuring the amount of change in functional traits in the fossil record; and (4) to compare the rates of past change to rates related to modern climatic change. We found that changes that have occurred over the past 50 to 100 years in North America have been as large or larger than changes that occurred over the past 350,000 years, during which time the northern hemisphere went through three glacial-interglacial cycles that buried much of North America under ice sheets and then warmed to temperatures equal to or even a little warmer than the present day. Figure 2 shows the rate of change in the geographic location of rattlesnake species during the last three glacial-interglacial cycles. Organisms can respond to climate change by migrating or adapting. The open dots show the rate of migration, the grey dots show the rate of adaptation -- the rate of migration was two orders of magnitude greater than the rate of adaptation, demonstrating that the primary response of vertebrates to climate change is by migration. When these past rates of change were compared to the pace of modern climate change, we found that the modern rate is two to three orders of magnitude faster than the fastest changes over the last 350 thousand years -- even though the Earth has been both warmer and colder than today, the pace of change that will unfold over the coming century is unparalleled in at least the last 50 million years of geological history. Our research shows that vertebrate animals are extremely unlikely to respond by adapting, the viable response being to move location in order to track the climates and environments to which they are already adapted.
