Trophic control of duck abundance in a prairie pothole food web
The trophic control of ducks in a prairie food web was investigated with the use of a large scale manipulation of their mammalian nest predators. The three alternative hypothesized mechanisms of trophic control were (1) predominantly by predators, (2) predominantly by prey, or (3) some contribution of both. Mammalian predator reduction was predicted to (1) initiate a trophic cascade, (2) have no effect, and (3) initiate a trophic cascade in upper trophic levels but not affect lower levels, for each mechanism, respectively. Ducks, aquatic invertebrates, primary producers and nutrients were sampled on 20 wetlands on both predator-managed and control areas in North Dakota. Stable isotope analysis of invertebrates did not reveal multiple, discrete trophic levels within the aquatic food web, but rather high incidences of omnivory. Predator reduction affected abundances of specific duck species, but neither overall duck abundance nor other compartments of the aquatic food web, suggesting that ducks are limited more by food than predators.