A spatially explicit model for density that accounts for availability: a case study with <scp>Mojave</scp> desert tortoises

Abstract Estimating population density and identifying those areas where is changing through time are central to prioritizing conservation management strategies. Obtaining reliable estimates of trends can be challenging, however, especially for long‐lived species that rare, have broad geographic distributions, difficult detect reliably during field surveys. We developed a hierarchical model distance‐sampling data characterizes spatial variation in at two scales simultaneously regional while accounting detection probability availability across applied the collected over 20‐year period (2001–2020) an area encompassed most range Mojave desert tortoise ( Gopherus agassizii ). Density adult tortoises varied with multiple biotic abiotic features, including topography, aspect, geology, seasonal precipitation temperature regimes. Across entire study area, decreased by average 1.8% per year (95% CI = −3.5% −0.2%). Trends geographically, steepest declines western part (−4.1%, −6.9% −1.3%). Accounting habitat loss our abundance this threatened declined estimated 129,000 adults (36%) between 2001 2020. Our modeling approach extends traditional frameworks ecological observational processes could mask spatiotemporal and, same time, provides spatially explicit guide strategies other rare species.