Limitations and trade-offs in the use of species distribution maps for protected area planning

Range maps represent the geographic distribution of species, and they are commonly used to determine species coverage within protected areas and to find additional places needing protection. However, range maps are characterized by commission errors, where species are thought to be present in locations where they are not. When available, habitat suitability models can reduce commission errors in range maps, but these models are not always available. Adopting a coarse spatial resolution is often seen as an alternative approach for reducing the effect of commission errors, but this comes with poorly explored conservation trade-offs. Here, we characterize these trade-offs by identifying scenarios of protected area expansion for the world's threatened terrestrial mammals under different resolutions (10–200 km) and distribution data deriving from range maps and habitat suitability models. We found that planning new protected areas using range maps results in an overestimation of the species protection level when compared with habitat suitability models (which are more closely related to species presence). This overestimation increases when more area is selected for protection and is higher when higher spatial resolutions are employed. Adopting coarse resolutions reduced the overestimation of species protection and also halved the spatial incongruence between protected areas prioritized from range maps or habitat suitability models. However, this came at a very high cost, with an area of up to four times greater (12 M km 2 vs. 3 M km 2 ) needed to adequately protect all species. Synthesis and applications. Our findings demonstrate that adopting coarse resolutions in protected area planning results in unsustainable increases in costs, with limited benefits in terms of reducing the effect of commission errors in species range maps. We recommend that, if some level of uncertainty is acceptable to practitioners, using range maps at resolutions of 20–30 km is the best compromise for reducing the effect of commission errors while maintaining cost-efficiency in conservation analyses.