Optimizing camera‐trap survey designs for multi‐species density estimation using spatial capture–recapture models

Abstract Conservation efforts are increasingly required to move beyond single‐species perspectives and towards community‐level inferences. Obtaining reliable multispecies population size estimates poses practical challenges as analytical tools and design recommendations are primarily focused on single species. Density estimation using spatial capture–recapture methods requires deploying detectors (e.g. camera‐traps) with spacing proportional to the space use of the focal species. Given that the design itself is species‐specific, sampling can be inefficient for species with larger ranges than the focal species due to restricted spatial coverage and insufficient for species with smaller ranges because fewer recaptures are generated. To address this practical issue, we developed a two‐stage optimization approach to generate camera‐trap survey designs that are appropriate for estimating density of a suite of individually identifiable species that vary in home range sizes. Our approach applies an algorithm to first optimize placement of a subset of detectors for large and vagile species based on maximizing spatial coverage, followed by a second optimization for the remaining cameras based on maximizing spatial recaptures for smaller and less mobile species. We empirically tested our approach using six individually identifiable carnivore species with varying home range sizes in the Munywana Conservancy, South Africa. Our design included 60 camera locations optimized for leopards ( Panthera pardus ) and 40 cameras optimized for small‐bodied, less‐mobile carnivores. Our design optimization procedure generated designs characterized by a distribution of inter‐trap distances, based on ecological parameters, and resulted in plausible density estimates for all species. The two‐stage approach resulted in moderate precision gains for larger ranging species and, importantly, substantial gains for smaller ranging species. Simulations demonstrated improved precision of spatially explicit capture–recapture (SCR) parameter estimates for all species compared to standard grid‐based designs, driven not solely by increased sampling but also by the optimized spatial configuration. Synthesis and applications . We developed and tested a new camera‐trap survey design method for estimating population densities for multiple co‐occurring species with differing spatial ecologies. By streamlining multispecies population monitoring, our approach reduces costs associated with species‐specific programmes and broadens opportunities for community ecology and conservation research based on explicit demographic parameters.