Evidence of density-dependent cohort splitting in age-0 yellow perch, (Perca flavescens): potential behavioural mechanisms and population-level consequences

Abstract

Two sequential cohorts of age-0 yellow perch (Perca flavescens), differing approximately threefold in density, were observed for their ontogeny of spatial distribution, growth, and diet in Lake St. George, Ontario. The lower density cohort exhibited typical ontogenetic spatial behaviour patterns consisting of an early pelagic phase followed by a complete migration to the littoral zone by midsummer. The high-density cohort appeared to split into a faster growing littoral component and a slower growing pelagic component which persisted throughout the growing season and into the next spring. The differences in spatial behaviour between these two cohorts could not be explained by spatial patterns in prey availability. The overwinter mortality rate for the high-density cohort was approximately double that observed for the low-density cohort. No direct observations of behaviour were made of the two cohorts, but distribution and growth data, along with arguments from competition theory, support the hypothesis that interference competition is the density-dependent mechanism responsible for the aberrant ontogeny of spatial distribution of the high-density cohort. The occurrence of interference competition in which competitively superior individuals can monopolize optimal habitats, relegating other individuals to suboptimal habitats, infers an asymptotic stock and recruitment relationship.