Effects of environmental change on population growth: monitoring time-varying carrying capacity in free-ranging spotted hyenas

Abstract

In conservation, a growing population is often taken as a sign of success. But trends in population size can be misleading. When individuals are long-lived, populations may keep growing--for a time--even as the environment begins to stabilize or deteriorate. Trends in carrying capacity (K) would better reflect the situation that a population finds itself in, yet K is commonly assumed to be static. We developed an individual-based modelling approach to estimate time-varying carrying capacity (Kt) in a population of free-ranging spotted hyenas. Kt noticeably varied due to events such as disease outbreaks, but not in response to recent conservation interventions. Although the population tripled in size during the 26-year study period, we found no corresponding trend in Kt. Rather, population recovery resulted from earlier environmental improvements. Our approach, which can be applied to populations of other species, allows for a faster and more accurate assessment of conservation needs.