Ecological Society of America
Occupancy models are increasingly applied to data from wildlife camera-trap (CT) surveys to estimate distribution, habitat use, or relative abundance of unmarked animals. Fundamental to the occupancy modeling framework is the temporal pattern of detections at camera stations, which is influenced by animal population density and the speed and scale of animal movement. How these factors interact with CT sampling designs to affect the interpretation of occupancy parameter estimates is unclear. We developed a simple yet ecologically relevant animal movement simulation to create CT detections for animal populations varying in movement rate, home range area, and population density. We also varied CT sampling design by the duration of sampling and the density of CTs in our simulated domain. A single-species occupancy model was fitted to simulated detection histories, and model-estimated probabilities of occupancy were compared to the asymptotic proportion of area occupied (PAO), calculated as the union of all simulated home ranges. Occupancy model parameter estimates were sensitive to simulated movement and sampling scenarios. Occupancy models overestimated asymptotic PAO when a low population density of simulated animals moved quickly over large home ranges and this positive bias was insensitive to sampling duration. Conversely, asymptotic PAO was underestimated when simulated animals moved slowly in large- or intermediately sized home ranges. This negative bias decreased with increasing sampling duration and a lower density of CTs. Our results emphasize that the interpretation of occupancy models depends on the underlying processes driving CT detections, specifically animal movement and population density, and that model estimates may not reliably reflect variation in these processes. We recommend carefully defining occupancy if it is applied to CT data in order to better match sampling and analytical frameworks to the ecology of sampled wildlife species. (PDF) Animal movement affects interpretation of occupancy models from camera-trap surveys of unmarked animals. Available from: https://www.researchgate.net/publication/322780234_Animal_movement_affects_interpretation_of_occupancy_models_from_camera-trap_surveys_of_unmarked_animals [accessed Oct 22 2018].
Neilson, E., T. Avgar, C. Burton, K. Broadley, and S. Boutin (2018) Animal Movement Affects Interpretation of Occupancy Models From Camera Trap Surveys of Unmarked Animals. Ecosphere, 9: e02092.