| To determine if the presence of fish influenced the structure of food webs in ponds used as foraging habitats by Whooping Cranes, I sampled aquatic biota and measured environmental characteristics in 36 nesting-area ponds in Wood Buffalo National Park. Principal component analysis indicated that invertebrate communities in ponds with fish were relatively discrete, while fishless ponds were separated into two groups, with beetles and odonates, respectively, occurring as top predators. Isolation from colonization sources and pond morphometry influenced which ponds fish could colonize and persist in, respectively, and which were fishless. Interactions between the biotic and abiotic environment thus contributed to the occurrence of the three community types. Stable isotope analysis revealed differences in the isotopic signatures of food webs containing and lacking fish, with the former being more negative in δ13C and δ15N, potentially the result of altered carbon sources and different predatory regimes, respectively. |
