Waterfowl Communities and Seasonal Environments: Temporal Variability in Interspecific Competition

Controversy over the role that interspecific competition plays in structuring avian communities has polarized the debate into two alternative points of view. One school of thought, exemplified by Wiens (1977), de—emphasizes the role that competition plays in structuring communities, while the opposing school, exemplified by Schoener (1982), invokes competition as a driving force in resource partitioning and community structure. To test these alternative arguments, I examined a guild of dabbling ducks (Anas spp.) that co—occur throughout the year. Species—pairs exhibited significantly lower overlap values for foraging, habitat utilization, and food items during winter than summer. In addition, food resources (both relative and absolute abundances) were lower during winter than summer. From these data I infer that the intensity of interspecific competition and its effect on waterfowl community structure is seasonal, with greater resource limitation and, therefore, resource partitioning during "lean" winter months than during "fat" summer months. Consequently, on a yearly cycle, avian communities may exhibit periods of intense interspecific competition, alternating with times of resources abundance where competition may be insignificant or absent.