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

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 ( K _t ) in a population of free-ranging spotted hyenas. K _t 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 K _t . 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.