How life history determines time scale sensitivity and extinction risk of age‐structured populations

Abstract

The long‐standing ecological interest in how environmental variability interacts with population dynamics to determine population variability and extinction risk has led to significant recent progress, but still lacks a direct connection to the role of a species' life history. Not only is environmental variability expected to increase with climate change, but the spectrum of environmental variability may shift, and there is a question about which life histories will be sensitive to such changes. To address this question for age structured populations, we compared environmental responses of 16 Atlantic cod populations with different life histories (longevities 7–17 years). We analyzed the sensitivities of these populations to high and low frequencies of environmental variability using simulations and analytical metrics of stability and transient dynamics to show that: 1) population's total sensitivity to all frequencies of environmental variability is greater at lower population density, and 2) the fraction of the population's total sensitivity to environmental noise at high frequencies is greater for populations with narrower spawning age distributions. Moreover, we show that population extinction risk depends on the frequency content of population variability; probability of extinction is greater when populations are less sensitive to high frequencies in the environment. These analyses indicate how changes in species' age structure, because of climate change or other anthropomorphic effects, could affect extinction risk, biodiversity and ecosystem services of age‐structured populations, especially if there are spectral shifts in the fraction of sensitivity to higher frequencies.