Trade-Offs of Ecological Specialization: An Intraspecific Comparison of Pumpkinseed Sunfish Phenotypes

Most empirical studies of specialists and generalists have focused on com- parisons among different species. Interspecific comparisons have recently been criticized because phenotypic trade-offs can evolve after ecological specialization. As a result, it has been suggested that intraspecific variation is the appropriate level to demonstrate functional trade-offs. We demonstrate functional trade-offs for two components of fitness in pump- kinseed sunfish (Lepomis gibbosus) from a single trophically polymorphic population: con- dition factor and growth rate. Condition factor was estimated using somatic lipid content, while growth rate was determined from scale measurements. Fish with extreme benthic and limnetic morphologies are on average superior to fish with intermediate morphologies, especially in the pelagic habitat. Our study is a particularly stringent test of functional trade-offs at the intraspecific level because the morphological variation is very subtle in this population.