Effects of Trophic Polymorphism on Population Dynamics and Resiliency

Differences in phenotypes within a population that occur as a consequence of specialization are called trophic polymorphism and can arise as a result of genetic differentiation or differential expression (i.e. phenotypic plasticity) of a common genotype.  To date, most research on trophic polymorphism has focused on identifying conditions that lead to polymorphism, with little attention paid to their ecological consequences.  Here, we evaluate if populations that exhibit trophic polymorphism are resilient to fluctuating or changing environments because the relative abundances of morphs can shift in response to changing resource and habitat distributions.  Preserved age-0 yellow perch samples collected from Oneida Lake, NY were analyzed from four years before and after zebra mussel introduction (8 years total) that differ in yellow perch density (i.e. low and high).  Within each year, analyses were conducted during two time periods (mid and late-summer) from 20 fish collected from littoral and pelagic habitats.   Individual fish were analyzed for individual diet specialization, morphological indices and stable isotopes ratios of δ¹³C and δ¹⁵N to quantified level of specialization and presence of trophic polymorphism.  Data were integrated with time series of habitat-specific catch statistics to evaluate morph-specific contributions to system-wide population dynamics under different ecological conditions.  Preliminary results indicate that age-0 yellow perch demonstrate density-dependent habitat and resource specialization.  At high densities, yellow perch separate into pelagic and littoral specialists, and little mixing occurs between habitats.  At low densities, yellow perch show directional movement from pelagic to littoral habitats and the establishment of pelagic and littoral specialization is less pronounced.  Catch statistics from pelagic and littoral habitats suggest age-0 yellow perch population dynamics are increasingly driven by littoral habitats due to consistently low pelagic densities and habitat changes associated with zebra mussel introductions.  Increased recruitment from littoral habitats may provide an additional mechanism to explain stable age-1 yellow perch densities despite reduced densities across all pelagic age-0 life stages.  Results highlight the ability of fish to integrate both littoral and pelagic energy pathways, and identify environmental conditions governing the importance of these pathways in supporting age-0 yellow perch.  This research provides empirical evidence of the effects of trophic polymorphism on population dynamics and represents a step-forward towards further incorporation of habitat-specific processes into the functioning of lake ecosystems and modeling of fish populations.