Pollinator perils

Abstract

Concern grows about the plight of bees and other key insects that function as pollinators of wild and commercial plants in many regions. In a new study, Jane Memmott, at the University of Bristol, and Nicholas Waser and Mary Price at the University of California, Riverside, report in the Proceedings of the Royal Society, published online, modelling analysis of the possible impact of pollinator loss on two classic studies of plant–pollinator interactions. The researchers' plan was to analyse how pollination networks respond to loss of component pollinator species. Evidence is accruing that pollinator loss can lead to the extinction of plant species. Loss of floral resources is also a key threat facing pollinating insects. However, the patterns of extinction within entire pollination networks remain unknown. The authors used exhaustive data from classic studies by Clements and Lang from Pikes Peak in the Rocky Mountains of Colorado, published in 1923, and work by Robertson in the prairie-forest transition of western Illinois published in 1929. The team modelled three different scenarios: the loss of pollinators at random; the loss first of specialised pollinators then of more generalised pollinators; and vice versa, the loss of more generalised then more specialised pollinators. Under their model, they found that random removal of pollinators elicited a steadily accelerating decline in plant species, with the bulk of plant extinctions occurring only after 70–80 per cent of all pollinator species had been lost. Their model for systematic removal beginning with the most specialised pollinators led to a scenario of a very slow loss of plant species until almost all pollinators had been removed, at which point plant species numbers dropped precipitously to zero. This was especially true in the Illinois work: plants in this network were virtually unaffected until removal of the last few most generalised pollinators, representing less than one per cent of the 1,430 total animal species. Finally, systematic loss beginning with the most generalised predators led to a more rapid loss of plant species, but in a linear manner. The study highlights, in particular, the importance of generalised pollinators. In both the systems studied these core pollinators derive mainly from the insect orders Hymenoptera and Lepidoptera. Six families of bees, including bumble bees, form part of the core pollination group at both sites. The authors highlight the need for management decisions formulated in advance from the best available information. “These groups should be given high priority for research and management in an effort to conserve the pollination interaction in northern temperate ecosystems,” the authors report.