Trait-mediated Density Dependence
Intra-specific competition and inter-specific interactions are key drivers of ecological, evolutionary and eco-evolutionary dynamics. In most empirical and theoretical studies, competition between individuals is investigated using the number or biomass of competitors of either the same species or of an interacting one. Although this approach has provided substantial insight, it is a relatively crude way of characterizing the strength of intra-specific competition or an inter-specific interaction. This is because the approach assumes all individuals are equally competitive. In reality they are often not: when resources are limiting a larger individual may be able to exclude a smaller one from accessing them, meaning that the distribution of body sizes amongst competitors may provide a better description of the strength of competition than the total number or biomass of competitors. We refer to competition that is dependent upon both the character value of a focal individual and the distribution of competitor character values as being trait-mediated.
Body size is an important determinant of ecosystem, community and population dynamics of
both marine and freshwater fish. Understanding the dynamics of body size distributions in fish communities is consequently a key objective of many marine and freshwater biologists. Integral projection models (IPMs) provide a powerful way in which to model the dynamics of continuous quantitative characters like body size. They have been used to study both the ecological and evolutionary dynamics of single species of numerous plants and terrestrial animals. IPMs also provide an easy-to-use way of treating density-dependence in a more biologically realistic manner than previously attempted, while retaining a close link between empirical data and models. Specifically, the demographic performance of individuals of a specific size can be determined by a range of statistics that describe the distribution of competitor sizes rather than simply by the total number or biomass of competitors. Finally, IPMs offer currently untapped potential to investigate how body size distributions of interacting species interact to determine ecological and phenotypic character dynamics at both the population and community level. The modeling work goes beyond the methodological advances listed above.
These advances will allow us to address many biological questions including, but not limited to:
The approach we will take will be to initially work with single-species models of trait-mediated competition. Analyses of these models will allow us to determine how different forms of trait-mediated competition, and the part of the life cycle they most strongly impact, determine life history evolution as well as body size and population dynamics. In the second phase of work we will develop models of interacting species for our study system – the freshwater fish community of Trinidad. These models will be parameterized with data from mesocosm experiments and manipulations of natural streams, before being analyzed and used to make predictions that we will test using independent observational data from study streams. If successful, the work should provide a major step in understanding links between ecological and evolutionary dynamics at both the population and community level.
Body size is an important determinant of ecosystem, community and population dynamics of
both marine and freshwater fish. Understanding the dynamics of body size distributions in fish communities is consequently a key objective of many marine and freshwater biologists. Integral projection models (IPMs) provide a powerful way in which to model the dynamics of continuous quantitative characters like body size. They have been used to study both the ecological and evolutionary dynamics of single species of numerous plants and terrestrial animals. IPMs also provide an easy-to-use way of treating density-dependence in a more biologically realistic manner than previously attempted, while retaining a close link between empirical data and models. Specifically, the demographic performance of individuals of a specific size can be determined by a range of statistics that describe the distribution of competitor sizes rather than simply by the total number or biomass of competitors. Finally, IPMs offer currently untapped potential to investigate how body size distributions of interacting species interact to determine ecological and phenotypic character dynamics at both the population and community level. The modeling work goes beyond the methodological advances listed above.
These advances will allow us to address many biological questions including, but not limited to:
- How do different forms of trait-mediated intra-specific competition impact selection on the life history and ontogeny of body size?
- How does inter-specific competition interact with intra-specific competition to determine the body size dynamics of interacting species?
- Under what conditions does the presence of a competitor species speed up or slow down the life history of a prey species?
The approach we will take will be to initially work with single-species models of trait-mediated competition. Analyses of these models will allow us to determine how different forms of trait-mediated competition, and the part of the life cycle they most strongly impact, determine life history evolution as well as body size and population dynamics. In the second phase of work we will develop models of interacting species for our study system – the freshwater fish community of Trinidad. These models will be parameterized with data from mesocosm experiments and manipulations of natural streams, before being analyzed and used to make predictions that we will test using independent observational data from study streams. If successful, the work should provide a major step in understanding links between ecological and evolutionary dynamics at both the population and community level.