IRSCHICK, DUNCAN J.*; Tulane University: Studying performance in nature: Implications for fitness variation within populations

Many biologists believe that the ability of an organism to survive in nature is influenced by key performance traits, such as maximum speed. Studies of ecological performance (the level of performance exhibited in nature) can thus provide general insight into organismal fitness. For example, field studies are necessary for documenting that species use their maximum performance capacities in nature, and in which ecological contexts they do so. I discuss both the utility of quantifying ecological performance, as well as its implications for studies of fitness by reviewing data gathered on both desert lizards and Caribbean Anolis lizards. In addition, I discuss recent work examining the relationship between fitness and performance in a population of anoles in Louisiana. A comparison of terrestrial desert and arboreal tropical lizards shows that structural habitat can exert a substantial influence on the percentage of maximum sprint capacity that species use. Both desert lizards examined (Uma scoparia, Callisaurus draconoides) altered their locomotor behavior as a result of environmental heterogeneity, indicating that fine-grained microhabitat variation may be important for overall energy expenditure during movement, and thus fitness. Further, studies of ecological performance in Caribbean Anolis lizards suggest that selection has favored performance during certain key tasks (i.e., escape) to a greater extent than for other tasks (e.g., feeding). These data provide a testable framework for future studies that examine how fitness is related to ecological performance within species. On-going work examining fitness in anoles in Louisiana should shed light on how different kinds of performance (i.e., locomotion, bite-force) interactively affect fitness. Supported by NSF grant IBN 9983003 to D. Irschick.