Camera trapping and GPS telemetry for detecting and quantifying animal interactions: Not anything goes

Abstract GPS telemetry and camera trapping are two widely used approaches to detect animal interactions involving wildlife. However, while the former follows an individual-based approach, the latter follows a population-based approach, which may lead to different outcomes when describing interaction networks. This study compares GPS telemetry, regular grid camera trapping (CT-RG), and resource monitoring through camera trapping (e.g., in water or food; CT-RM) for detecting and quantifying animal interactions. We used simulated trajectories of 150 individuals of 3 imaginary species. We simulated 9 different scenarios of resource visitation frequency and spatial resource aggregation to assess the potential influence of animal behavior and landscape structure. The simulated trajectories were sampled using the three approaches with six different sampling efforts each, and the direct and indirect interactions between the three species were quantified. Additionally, CT-RG and CT-RM were applied in Doñana National Park to evaluate their differences and limitations in field application. In terms of simulation, CT-RM offered the best performance in detecting direct interactions, and GPS achieved good performance at high efforts. Both also achieved good performance in detecting indirect interactions. CT-RG, on the other hand, missed most direct and indirect interactions, but correctly identified all pairs of species interacting indirectly. In the field trial, CT-RM and CT-RG detected almost the same number of pairs interacting indirectly. However, CT-RG missed at least half of the pairs of species interacting directly. GPS performs better than CT-RM when the resource is spatially aggregated, but the opposite is true when the resource is frequently visited. To summarize, CT-MR is the most reliable method for detecting interactions when resource monitoring is feasible (e.g., small ponds in arid areas). Otherwise, GPS may show better performance, although it may miss direct interactions. CT-RG should only be used to detect potential indirect interactions between species, not to quantify them.