Table of Contents
Physiologically structured population models: from numerical techniques to ecological insight
Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam
Summary
Many problems in ecology and evolution revolve around the question how individual life history influences population and community dynamics or vice versa how the population and community setting influences selection and adaptation of individual life histories. Physiologically structured population models are well suited to address such questions as this class of models represents the reproduction, development and mortality of individuals during their life history as dependent on the state of the individual itself and the environment it lives in. These structured population models hence consistently translate the individual life history to the population level and in turn account for density dependent, population feedback on life history through changes in the environment that the individual experiences. In recent years, a general methodology has been developed to carry out demographic, equilibrium (bifurcation) and evolutionary analysis of physiologically structured population models, which in its simplest form boils down to the numerical evaluation of the Lotka-Euler integral equation for computing population growth rates. I will give an introduction to the general methodology and illustrate its application with a few examples.
Subsequently, I will discuss how physiologically structured population models have been used to develop novel and counterintuitive ecological theory about the population and community effects of ontogenetic development. Growth in body size is by far the most prominent aspect of the ontogenetic development that every individual goes through during its life history. Necessarily, development depends on the availability of food and thus indirectly on the feedback from population foraging. I will show that population models accounting for food-dependent growth in body size of individuals make predictions that are in line with the classical unstructured theory about population and community dynamics, only in case of ontogenetic symmetry in energetics, meaning that development and reproduction are limited to the same extent by food availability. In contrast, in case of ontogenetic asymmetry in energetics, when either development or reproduction is more food-limited than the other process, models that account for food-dependent development make different and counter-intuitive predictions, as it may, for example, result in positive relationships between population biomass and individual mortality. The body size effects on community structure are even more substantial when species have a complex life cycle and growth in body size hence leads to a change in resource use or habitat during ontogeny. I will provide an overview of possible consequences of ontogenetic development for community structure and show how they come about because the population size distribution changes with changes in the environmental conditions, like productivity or mortality.