Print PageGeneralist species (e.g., in terms of diet or habitat use) are able to thrive in numerous ecological niches because of their plastic responses to biotic and abiotic environmental variation. In order to understand the mechanisms through which generalists are able to maintain use of diverse resources, it is important to understand underlying trade-offs that may be manifest a landscape-scale. We examined diet, prey quality and growth rate for a generalist fish predator, gray snapper (Lutjanus griseus) at five sites across a linear landscape gradient in the Loxahatchee River, Florida. Sites ranged from riverine habitats upstream to marine-dominated mangroves downstream.
Results/Conclusions
Snapper diets shifted from dominance by intertidal crabs upstream to an increased reliance on benthic crabs, shrimp and fishes downstream. Concurrently, the frequency of empty stomachs increased and the mean food volume decreased moving from upstream to downstream. Growth rates were fastest for downstream snapper. Prey quality, based on C:N ratios and lipid content, was highest for fishes, followed by shrimp then crabs. These results suggest that even though snapper ate less food downstream, higher prey quality may have compensated for this and resulted in higher fitness. Trade-offs between food quality and quantity may allow generalists to exist across varying environmental conditions, although these trade-offs do not necessitate equal habitat quality. Such differences in trophic niche and growth indicate that a generalist’s impact on ecosystem function (i.e., transfer efficiency of secondary production to higher trophic levels) may vary across its landscape.
