Lotka-Volterra community organization increases with added trophic complexity
USGS Center for Earth Resources Observation and Science
Last modified: April 24, 2006
The Lotka-Volterra (L-V) equations are a venerable model in community ecology, and have been used to examine a number of theoretical issues, including the diversity-stability question, community assembly, invasion resistance, etc. Michael Gilpin (Proc. Natl. Acad. Sci. USA 91 (1994) 3252) made a unique application of the L-V equations to what he termed ‘community-level competition’, in which separate L-V systems were mixed, analogous to removal of a physical barrier between two isolated ecological communities. Gilpin found a significant increase in asymmetric outcomes, i.e. outcomes where one L-V system comes to dominate the mixed community, if separate L-V systems were first subjected to a process of community assembly prior to mixing (during assembly, one-half of an original pool of species were forced to extinction by competitive interactions). In short, assembled communities exhibited a cohesiveness that allowed them do battle as a group against other L-V systems. However, all species occupied the same trophic level, interacting solely by competition. In this study, I extended Gilpin’s finding by adding a trophic level, simulating what could be considered, nominally, ‘autotroph-heterotroph’ or ‘predator-prey’ communities. When these L-V systems were self-organized by community assembly and then mixed, the frequency of asymmetric outcomes increased by 36% relative to competition-only communities. By this test, more ecologically realistic communities are also more organized.