Predicting effects of future development on a territorial forest songbird: methodology matters

Context Projected increases in human population size are expected to increase forest loss and fragmentation in the next century at the expense of forest-dwelling species. Objectives We estimated landscape carrying capacity ( N k ) for Ovenbirds in urban, suburban, exurban, and rural areas for the years 2000 and 2050, and compared changes in N k with changes in occupancy probability. Methods Maximum clique analysis, a branch of mathematical graph theory, was used to estimate landscape carrying capacity, the maximum potential number of territories a given landscape is capable of supporting ( N k ). We used occupancy probability maps as inputs for calculating Ovenbird N k in the northeastern USA and a spatially explicit growth model to forecast future development patterns in 2050. We compared occupancy probability with estimates of N k for urban, suburban, exurban, and rural areas for the years 2000 and 2050. Results In response to human population growth and development, Ovenbird N k was predicted to decrease 23% in urban landscapes, 28% in suburban landscapes, 43% in exurban landscapes, and 20% in rural landscapes. These decreases far exceeded decreases in mean occupancy probabilities that ranged between 2 and 5% across the same development categories. Thus, small decreases in occupancy probability between 2000 and 2050 translated to much larger decreases in N k . Conclusions For the first time, our study compares occupancy probability with a species population metric, N k , to assess the impact of future development. Maximum clique analysis is a tool that can be used to estimate N k and inform landscape management and communication with stakeholders.