Population differentiation in locomotor performance and the potential response of a terrestrial organism to global environmental change

Abstract

SYNOPSIS. Models of global climate change predict an increase in the mean surface temperature between 1.5° and 4.5°C by the middle of the next century. Even a moderate increase of 3°C is likely to result in a shift in the distribution of North American habitat types and vegetational associations, either in latitude or elevation or both. The challenge to Conservation Biology is to predict the responses of terrestrial organisms to the expected alteration in habitats and ecosystems. Recent biophysical models have been expanded to demonstrate the intimate associations between the thermal environment, organismal physiology and ecology. Thus, the expected turnover in habitats may have a profound influence on the distribution of organisms. I describe one possible approach that couples temporal and spatial variation in an ecologically relevant physiological trait, locomotory performance, in a widespread species of lizard, Urosaurus ornatus, to predict the expected response of species to global change.Estimates of maximum velocity and endurance capacity were obtained from 16 populations throughout the range of U. ornatus. Information on spatial variation was supplemented with data on temporal variation spanning an eight year period from a single reference population. I used thesedata to address two questions: 1) is there an association between locomotory performance and the expected habitat changes predicted from global climate models and 2) is there sufficient variation within a population to respond to habitat modification.Populations of U. ornatus varied significantly in sprint speed and stamina. Several environmental factors expected to correlate with global climatechange were evaluated using the patterns of variation in locomotor performance. Results from this study suggest that high elevation populations found in ponderosa pine forests should be most susceptible to changes in climate. Within-population variation was found to span the range of variation seen among populations and was sensitive to temporal variation in climatic conditions. Given the expected and rapid change in environments, small, ectothermic, terrestrial species may not have the ability to modify their geographic distribution. However, the results presented here suggest that only certain populations are at risk; yet the evolutionary response of the population may be long relative to the rate of environment change. ©1994 by the American Society of Zoologists.