Thermal biology of bee pollinators: diversity and community-level correlates

Abstract

Community-wide assembly of plant-pollinator systems depends on an intricate combination of biotic and abiotic factors, including heterogeneity among pollinators in thermal biology and responses to abiotic factors. Studies on the thermal biology of pollinators have mostly considered only one or a few species of plants or pollinators at a time, and the possible driving role of the diversity in thermal biology of pollinator asemblages at the plant community level remains largely unexplored. More specifically, it is unknown whether diversity in the thermal biology of bees, a major pollinator group worldwide, contributes to the assembly and maintenance of diverse bee communities, broadens the spectrum of possibilities available to bee-pollinated plants, facilitate interspecific partitioning of ecological gradients across habitats, seasons and time of day, and/or enhance plant pollination success through complementarity effects. The objectives of this study were to assess the diversity in thermal biology of the bee assemblage that pollinates plants in a Mediterranean montane area, evaluate its taxonomic and phylogenetic underpinnings, and elucidate whether there existed seasonal, daily, between-habitat or floral visitation correlates of bee thermal biology which could contribute to partition ecological gradients among plant and bee species. Thermal biology parameters were obtained in the laboratory (K, intrinsic warming constant) and the field (thoracic and ambient temperature at foraging site, Tth and Tair) on individual bees of a diverse sample (N = 204 bee species) comprising most bee pollinators of the regional plant community. Species-specific thermal biology parameters were combined with quantitative field data on bee pollinators and flower visitation for the regional community of entomophilous plants (N = 292 plant species). Results revealed that the regional bee assemblage harbored considerable diversity in thermal biology features, that such diversity was mostly taxonomically, phylogenetically and body-size structured, and that the broad interspecific heterogeneity in thermal biology represented in the bee community as a whole eventually translated into daily, seasonal, among-habitat and flower visitation patterns at the plant community level. This lends support to the hypothesis that broad diversity in thermal biology of bees can act enhancing opportunities for bee coexistence, spatio-temporal partitioning of floral resources, and plant pollination success.