The figure above shows how expected community productivity changes as species go extinct in communities of competing species.  In each panel, the black line shows the effect of extinction when all species have the same probability of going extinct, and the red, green, and blue lines show the effect of extinction when the correlation between extinction probability and per capita productivity is strongly positive (red), weakly positive (green), or strongly negative (blue).  Alpha scales the degree of resource partitioning (alternatively, interspecific competition): alpha=0 corresponds to species that use distinct resources, and alpha=1 corresponds to species that compete for identical resources.  Each community begins with 10 species.  For more details, see Gross & Cardinale (2005).

The photograph above shows a grassland at the Hopland Research and Extension Center in Hopland, California.  Grasses such as those shown here are subject to infection by barley yellow dwarf virus (BYDV), an aphid-transmitted luteovirus that, as its name suggests, causes yellowing and stunting of grass leaves.  BYDV and related cereal yellow-dwarf viruses are important because they reduce yield of commercial grain crops, and because they provide a useful model system for investigating the ecology of infectious disease.  Working together with several close collaborators, I develop mathematical models to characterize and understand the dynamics of systems with multiple interacting pathogens, such as BYDV.  For more details about this research, see the website here.  Photo courtesy C. E. Mitchell.