Disentangling the effect of the spatial scale and species spatial pattern on the abundance–suitability relationship

Knowledge about species abundance across broad spatial areas is crucial for unraveling ecological processes. Yet, abundance estimation often demands extensive sampling effort associated with logistical challenges. Using suitability values obtained from species distribution models (based on species' presence data) as a proxy for abundance has garnered interest during the last decades. Previous studies suggest a triangular relationship between species abundance and suitability. Specifically, higher suitability can display both low and high abundances, while low suitability only low abundances. This triangular pattern arises because suitability models often fail to consider limiting factors that drive abundance. In this study, we investigate the effect of spatial scale and pattern shaping this relationship. We use a simulation study and a case study to explore how these factors affect the abundance–suitability relationship. The effects of spatial scale are represented by three model levels: 1) only broad-scale covariates, 2) broad and intermediate covariates, and 3) broad, intermediate and local covariates. The effects of spatial patterns are characterized by two different species distribution shapes: aggregated and uniform. Our findings reveal that models integrating local-scale covariates and species exhibiting more aggregated spatial patterns show a stronger relationship. Additionally, we observe an interaction between a species' spatial pattern and model scale. For aggregated species, the abundance–suitability relationship benefits most notably from the addition of intermediate-scale covariates. In contrast, for uniform species, the benefit remains consistent regardless of whether intermediate- or local-scale covariates are added. Our results underscore the importance of considering both methodological and ecological factors to improve proxies for abundance derived from suitability models. We highlight the need for considering information operating at a local scale to make reliable inferences about species abundance from suitability models and suggest potential strategies for doing it.