Patterns of the Distribution and Abundance of Competing Species when Resources are Heterogeneous

Detecting interspecific competition from census data may be difficult and often impossible when resources are spatially and temporally heterogeneous. This difficulty comes about because the effects of interspecific competition vary with the levels of resources. This phenomenon is clearly shown in the assemblage of arthropods found living in Heliconia wagneriana bracts, microaquatic habitats that are readily manipulated and censused. I manipulated the number of flowers that naturally fall into the bracts and serve as food for many of the arthropods. By the addition or the removal of flowers, the effects of interspecific competition for these resources became evident in changes of the distribution and abundance of the arthropod species. Analyses of these changes revealed that competition was readily detected for two species when resources were diminished, but not detectable when resources were augmented. Thus, census studies of communities that use heterogeneous resources are likely to include assemblages in patches where competition is not occurring, along with other patches where competition is occurring, but knowledge of the resource heterogeneity can itself be used to discern the effects of competition.