Road encroachment mediates species occupancy, trait filtering and dissimilarity of passerine communities

Abstract

Assessing the road effects on biodiversity is challenging because impacts may depend on both wildlife responses to roads and on the spatial arrangement of roads. We questioned whether an increase in road encroachment leads to significant changes in species occurrence and community composition. Using a large citizen-science dataset of point-counts performed throughout Iberian Peninsula, we modelled the effect of road density on the occurrence of common birds (n = 78 species), while accounting for potential confounding effects of environment and survey effort. We then tested if species' occurrence patterns would be linked to specific traits related to the ability to cope with human presence. Finally, we assessed how road density affects the community compositional dissimilarity. We estimated 36 (46%) and 18 (23%) species to be negatively and positively affected by roads, respectively. Increased road encroachment was positively related with urban dwelling and fecundity, and negatively related with nesting on the ground. Furthermore, increasing road density translated into an increasing community compositional dissimilarity, mostly due to species turnover. Overall, we found that different species-specific responses to roads translate into changes at the community level. Landscape and road-network management should be conceived acknowledging that roads are contributing to biodiversity changes. As so, building upon the concepts of land sharing/land sparing, conservation actions should be tailored according to the different species responses e.g., road verge management targeting species having a positive relation with road density; and compensation actions targeting species showing a negative response toward roads.