Individuals within a population are not identical. Instead, they differ from one another physically and in their behavior, due to differences in their genetic make-up and in the environments in which they grow up, including how they are treated by their parents. This causes individuals in a population to have different chances of birth and death, a phenomenon known as demographic heterogeneity. Although widespread, this phenomenon has rarely been considered in studies of populations of animals or plants. Previous theoretical work by the researchers heading this project has suggested that demographic heterogeneity can increase the rate of growth of a population and the maximum number of individuals that the environment can support, reducing the risk that the population will go extinct. The new work for the project will expand this theory to include interactions between species and use it to predict the future of a wild population of conservation concern, the Florida scrub jay. First, the theoretical model will be extended to account for the fact that biological populations are not isolated, but interact with other species through competition and through eating and being eaten. Research will help understand whether heterogeneity makes it easier or harder for species to coexist, and how individual variation in competitive or predatory ability affects the dynamics and long-term persistence of a community of different species. Second, spatial models will be used to examine how demographic heterogeneity affects population dynamics when individuals mainly interact with their immediate neighbors, as in plants. To start to apply the models to real populations, the project will use data collected on a population of scrub jays in central Florida, which other researchers have studied since 1969. Florida scrub jays have an unusual social structure that promotes demographic heterogeneity: young adults often help their parents raise younger siblings, improving both the breeding success of their parents and their own subsequent breeding. Using recent statistical advances, the project will measure the amount of demographic heterogeneity in the population and project the impact of that heterogeneity on the population's future growth and survival. The project will train a post-doctoral researcher and a graduate student, improve scientific understanding of the link between individuals and populations, and help develop tools for the conservation of biodiversity.
