Combined demographic and resource models quantify the effects of potential land-use change on the endangered Carnaby's cockatoo (Calyptorhynchus latirostris)

Abstract

Measuring how land-use changes affect the availability of resources for threatened species is critical for conservation policy and management. Combining demographic population models with models of food supply provides a means of quantifying the relative effects of land-use change and life-history characteristics on population viability. However, few phenomenological population models explicitly link demography to food supply, probably because of the lack of sufficient quantitative data necessary to estimate them. We synthesized detailed demographic and food resource data to model future population size and extinction risk of the endangered Carnaby's cockatoo Calyptorhynchus latirostris under potential land-use scenarios in a rapidly expanding urban region. Carnaby's cockatoo relies primarily on the annual seed crops of native Banksia spp. woodlands and introduced Pinus pinaster plantations. Population viability analysis was combined with estimates of food resources and a daily ration model to estimate carrying capacity, predict the number of birds that could be supported in the region, and the extinction risk. Assuming no changes in the extent or quality of breeding habitat, and current breeding or survival rates, the most important factor currently limiting population growth for Carnaby's cockatoo is adult survival rate, whereas population size is limited by recurring bottlenecks in food availability resulting from a trend of resource depletion combined with large variability in annual seed production.