Decline of parasitic and habitat-specialist species drives taxonomic, phylogenetic and functional homogenization of sub-alpine bumblebee communities.

Yoan Fourcade,Sandra Åström,Erik Öckinger

doi:10.1007/s00442-021-04970-3

Abstract

The ongoing biodiversity crisis is characterised not only by an elevated extinction rate but also can lead to an increasing similarity of species assemblages. This is an issue of major concern, as it can reduce ecosystem resilience and functionality. Changes in the composition of pollinator communities have mainly been described in intensive agricultural lowland areas. In this context, using a replicated survey of historical and recent bumblebee diversity, we aimed here to test how documented changes in climate and land use influenced the potential homogenization of sub-alpine bumblebee communities in southern Norway. We assessed the change in community composition in terms of taxonomic, phylogenetic and functional (β-)diversity, and estimated the impact of various species traits in probabilities of species gains and losses. Overall, we found a strong reduction in functional diversity, but no change in phylogenetic diversity over time. The β-diversity decreased, especially at high elevations, and this pattern was consistent for taxonomic, phylogenetic and functional β-diversity. The spatial distribution, measured as the average site occupancy, decreased in habitat-specialist species. This was explained by both a higher risk of species loss and a lower probability of species gain for habitat-specialist and parasitic species than for generalist and social species. These findings demonstrate that a narrow niche breadth may contribute to a higher extinction risk in bumblebee species. This non-random impact of disturbance on species may lead to large-scale biotic homogenisation of communities, a pattern that can be detected by investigating biodiversity changes at different scales and across its multiple facets.

Highlights

Land-use and climate change are two of the main contemporary drivers of biodiversity change (Oliver and Morecroft 2014)
There was no net change in local species richness (Fourcade et al 2019), we detected a considerable loss of functional diversity in bumblebee assemblages, along with a taxonomic, phylogenetic and functional homogenization of these assemblages
Patterns in phylogenetic diversity largely mimicked those observed in terms of species richness, i.e. no change in average diversity between the historical and contemporary surveys, even if we used an index of phylogenetic diversity that is corrected by the number of species observed

Summary

Introduction

Land-use and climate change are two of the main contemporary drivers of biodiversity change (Oliver and Morecroft 2014) Such changes are typically not random, but instead depend on species traits (Öckinger et al 2010, Vandewalle et al 2010). Phylogenetic and functional diversity do not necessarily coincide (Devictor et al 2010, Monnet et al 2014, De Palma et al 2017). For this reason, drawing a comprehensive picture of biodiversity trends requires monitoring at the same time all these aspects of the diversity of assemblages, over large environmental gradients and long periods of time

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