Empirical Links Between Demography, Life History, and Recovery in Fishes

Abstract

Studies on small and declining populations dominate research in conservation biology. This emphasis reflects two overarching frameworks: the small-population paradigm focuses on correlates of increased extinction probability; the declining-population paradigm directs attention to the causes and consequences of depletion. Neither, however, particularly informs research on the determinants, rate, or uncertainty of population increase. Compounding this deficiency is a long-standing assumption that Allee effects (declining per capita growth rate, ‘r’, with declining population size) either do not exist, or are generally not important, in aquatic systems. Several recent studies challenge the assumption that population-size thresholds, or ‘tipping points’, do not exist in fishes. Key conclusions emerge from this body of work. The greater the reduction in population size, the greater the likelihood that Allee effects impair recovery. Secondly, life-history traits, although poor predictors of recovery when considered singly, can reliably predict recovery potential when combined to estimate natural mortality. Coupling population-dynamical correlates of recovery with evolution – the result of natural and human-induced selection – provides additional challenges to forecasting rates and probabilities of recovery in depleted fishes.