Abstract
BackgroundFlower visiting insects provide a vitally important pollination service for many crops and wild plants. Recent decline of pollinating insects due to anthropogenic modification of habitats and climate, in particular from 1950's onwards, is a major and widespread concern. However, few studies document the extent of declines in species diversity, and no studies have previously quantified local abundance declines. We here make a quantitative assessment of recent historical changes in bumblebee assemblages by comparing contemporary and historical survey data.Methodology/Principal FindingsWe take advantage of detailed, quantitative historical survey data from the 1930's on bumblebee (Bombus spp.) abundances and species composition in red clover (Trifolium pratense) fields, an important floral resource and an attractant of all bumblebee species. We used the historical survey data as a pre-industrialization baseline, and repeated the same sampling protocol at nearly the same localities at present, hence setting up a historical experiment. We detected historical changes in abundances (bees/m2) of both workers (the “pollinatory units”) and queens (effective population size), in addition to species composition. In particular, long-tongued bumblebee species showed consistent and dramatic declines in species richness and abundances throughout the flowering season of red clover, while short-tongued species were largely unaffected. Of 12 Bombus species observed in the 1930's, five species were not observed at present. The latter were all long-tongued, late-emerging species.Conclusions/SignificanceBecause bumblebees are important pollinators, historical changes in local bumblebee assemblages are expected to severely affect plant reproduction, in particular long-tubed species, which are pollinated by long-tongued bumblebees.
Highlights
Pollinators play a key role in natural and agricultural ecosystems, providing an important pollination service of wild plants and crops [1]
Five species had disappeared from past to present (B. distinguendus, B. sylvarum, B. veteranus, B. ruderarius, B. subterraneus)
It is widely perceived that the regional bumblebee species richness and range extent of some species have declined historically across Europe [9,10,16,18]
Summary
Pollinators play a key role in natural and agricultural ecosystems, providing an important pollination service of wild plants and crops [1]. For bumblebees (Bombus Latreille spp.), which are among the most important and best known group of wild pollinators [14,15], a long-term decline has been documented locally and regionally, in Europe, America and Asia [9,13,16,17,18]. Change in species composition of bumblebee assemblages was recently assessed from historical survey data [21]. Flower visiting insects provide a vitally important pollination service for many crops and wild plants. We here make a quantitative assessment of recent historical changes in bumblebee assemblages by comparing contemporary and historical survey data
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