A phylogenetic approach to conservation prioritization for Europe's bumblebees (Hymenoptera: Apidae: Bombus)

Abstract

Bumblebees are an essential component of our agroecosystems, and their decline represents a major threat for the sexual reproduction — and hence survival — of wild flowers and several important pollinator-dependent crops alike. The EU bumblebee fauna encompasses many highly imperiled species characterized by a relatively narrow range size and often restricted to high elevation mountain habitats where the threats of both current and future global warming are expected to be particularly severe. In this context, identifying how and where limited conservation resources should be targeted is a pressing priority to meet our fundamental biodiversity conservation targets in an economically-efficient way. Because classical taxonomic approaches to conservation can potentially overlook important alternative aspects of biodiversity such as the phylogenetic diversity, a key component for the maintenance of ecosystem processes and services, I used a multi-gene molecular phylogeny encompassing more than 85% of the EU species to combine categories of the IUCN Red List with the evolutionary legacy and range size of EU bumblebees. My results from phylogenetic generalized least squares (PGLS) and phylogenetic independent contrasts (PIC) analyses first indicate that, contrary to theoretical prediction, evolutionary relatedness explains none of the range size similarity or the probability of extinction risk in EU bumblebees. Furthermore, although the extinction of extant threatened EU bumblebee species is unlikely to have a significant effect on the expected phylogenetic dispersion of the remaining Bombus species at the EU scale, my results clearly illustrate that a significantly disproportionate amount of phylogenetic diversity/evolutionary history might be lost if the extant threatened EU bumblebee species would become extinct. Collectively, this study exemplifies the fact that the incorporation of a phylogenetic approach can increase the efficacy of the existing prioritization for the conservation of EU bumblebees (i) by capturing the phylogenetic diversity and its associated functions, as well as (ii) by better targeting species that are both evolutionarily unique (or non-redundant), threatened and restricted in their range size.