Forest-edge associated bees benefit from the proportion of tropical forest regardless of its edge length

Abstract

Natural areas are important for wild bees in human-dominated landscapes as they provide permanent feeding and nesting resources. Understanding how bee communities vary with the amount of natural areas is thus key to guide conservation measures. This information, however, is largely lacking in montane tropical ecosystems. Here we explore to what extent the amount of forest area or forest edge (as landscape variables) influence the species richness and abundance of forest-edge associated bees in the Colombian Andes. In addition, we assess the effects of flower species richness and abundance (as local variables) to better understand the individual and interactive effects of forest conservation. Bees were surveyed along 20 forest edges differing in forest proportion and forest edge length within four spatial scales (250, 500, 1000 and 1500 m radii). We conducted trait-specific analyses as bees with different traits associated to body size, sociality and nesting behavior might differ in their response to local and landscape variables. We found that overall bee species richness and abundance increased with an increasing proportion of forest within 1000 m radius, but also with flower abundance. Similarly, the species richness and abundance of social, large and above-ground nesting bees increased with an increasing proportion of forest area, mainly within 500 and 1000 m radii. However, only the abundance (not the species richness) of solitary and small bees were positively related to the proportion of forest within 1000 m. Below-ground nesters did not respond to the individual effect of forest area at any spatial scale. Interactive effects between local and landscape variables were mainly found between flower richness and the proportion of forest. Forest edge length influenced only the abundance of solitary bees. These findings highlight the importance of conserving and/or restoring forest areas – at meaningful spatial scales – to promote diverse bee communities in montane tropical regions.