Evolutionary responses to limiting factors in heterogeneous environments

University Of California-Davis, Davis CA

Investigators

Abstract

All organisms have the potential to produce descendants whose numbers grow exponentially, but are eventually prevented from doing so by the action of various factors that limit reproductive success. The field of ecology is largely devoted to the study of these limiting factors. Debates concerning the relative importance of different potentially limiting factors for particular microbe, plant, and animal taxa pervade the evolutionary ecology literature; prominent examples include extrinsic versus intrinsic sources of mortality, different macro- and micronutrients required for organismal growth, physical wear or breakage of different key structural features of an organism, resources versus predators in population regulation, pollen versus resource limitation in plants, and egg versus host limitation in insects. While important progress has been made developing theory to resolve these debates in particular contexts, these theoretical treatments have been developed in isolation from one another. Many of these debates, however, share a common logical structure: the focal organism lives in a heterogeneous environment, has a finite pool of metabolic resources to ameliorate multiple limiting factors, and can not instantaneously adjust metabolic allocations to perfectly match the environment. This project will develop a general mathematical framework for analyzing evolutionary problems with this logical structure, apply this framework to several major limiting factor debates in evolutionary ecology, and confront the modeling predictions with empirical data. The mathematical framework will provide broadly applicable methods at the interface of stochastic processes and dynamical systems. These methods will be used to understand (i) whether insects are limited by a finite supply of eggs or a short lifespan to locate hosts and (ii) whether plants are limited by their ability to attract pollinators or by other aspects of reproduction. To establish a dialogue between the theory and the natural world, data on egg limitation and pollen limitation will be collected and analyzed to evaluate the theory. Conservation and restoration ecologists are interested in anticipating the responses of animals and plants to changing environments and in being able to manipulate those responses to beneficial ends. This project will contribute to these goals by providing a deeper understanding of how organisms evolve in response to different factors that may limit reproductive success. A population of organisms whose fitness is consistently limited by one particular factor will respond predictably to perturbations of that factor. On the other hand, a population of organisms whose fitness is limited by different factors at different times or places will respond to perturbations less predictably. A key topic of this project, pollen limitation, has direct bearing on documented global declines in the populations of pollinating insects such as bees. These population declines threaten plant communities and crop productivity world wide. Results from this project will be incorporated into a new course on pollination ecology, into two textbooks dealing with calculus and modeling as applied to the life sciences, and into entry-level courses for biology students. Moreover, undergraduates, graduate students, and post-doctoral associates will be trained in a vertically integrated manner.