Stochastic density effects on adult fish survival and implications for population fluctuations

TL;DR

This study reveals that stochastic food supply and population density significantly influence adult fish survival, affecting population fluctuations and highlighting the importance of considering adult survival variability in marine population management.

Contribution

It demonstrates that density-dependent adult survival can buffer against recruitment variability, a novel insight into population fluctuation mechanisms in marine fish.

Findings

Both population density and stochastic food supply impact adult survival.

Variable adult survival has a comparable effect to recruitment on population variability.

Density-dependent survival can reduce the impact of recruitment fluctuations.

Abstract

The degree to which population fluctuations arise from variable adult survival relative to variable recruitment has been debated widely for marine organisms. Disentangling these effects remains challenging because data generally are not sufficient to evaluate if and how adult survival rates are regulated by stochasticity and/or population density. Using unique time-series for a largely unexploited reef fish, we found both population density and stochastic food supply impacted adult survival. The estimated effect of variable survival on adult abundance (both mean and variability) rivaled that of variable recruitment. Moreover, we show density dependent adult survival can dampen impacts of stochastic recruitment. Thus, food variability may alter population fluctuations by simultaneously regulating recruitment and compensatory adult survival. These results provide an additional mechanism for why intensified density independent mortality (via harvest or other means) amplifies population fluctuations and emphasizes need for research evaluating the causes and consequences of variability in adult survival.