Pollinators are a key component of global biodiversity, providing vital ecosystem services to crops and wild plants. There is clear evidence of recent declines in both wild and domesticated pollinators, and parallel declines in the plants that rely upon them. Here we describe the nature and extent of reported declines, and review the potential drivers of pollinator loss, including habitat loss and fragmentation, agrochemicals, pathogens, alien species, climate change and the interactions between them. Pollinator declines can result in loss of pollination services which have important negative ecological and economic impacts that could significantly affect the maintenance of wild plant diversity, wider ecosystem stability, crop production, food security and human welfare.

/pdf/global-pollinator-declines-trends-impacts-and-drivers-5gfi4zur4k.pdf

Global pollinator declines: trends, impacts and drivers.

Human activities, especially conversion and degradation of habitats, are causing global biodiversity declines. How local ecological assemblages are responding is less clear--a concern given their importance for many ecosystem functions and services. We analysed a terrestrial assemblage database of unprecedented geographic and taxonomic coverage to quantify local biodiversity responses to land use and related changes. Here we show that in the worst-affected habitats, these pressures reduce within-sample species richness by an average of 76.5%, total abundance by 39.5% and rarefaction-based richness by 40.3%. We estimate that, globally, these pressures have already slightly reduced average within-sample richness (by 13.6%), total abundance (10.7%) and rarefaction-based richness (8.1%), with changes showing marked spatial variation. Rapid further losses are predicted under a business-as-usual land-use scenario; within-sample richness is projected to fall by a further 3.4% globally by 2100, with losses concentrated in biodiverse but economically poor countries. Strong mitigation can deliver much more positive biodiversity changes (up to a 1.9% average increase) that are less strongly related to countries' socioeconomic status.

/pdf/global-effects-of-land-use-on-local-terrestrial-biodiversity-31yzxze5ly.pdf

Global effects of land use on local terrestrial biodiversity

Bees are subject to numerous pressures in the modern world. The abundance and diversity of flowers has declined, bees are chronically exposed to cocktails of agrochemicals, and they are simultaneously exposed to novel parasites accidentally spread by humans. Climate change is likely to exacerbate these problems in the future. Stressors do not act in isolation; for example pesticide exposure can impair both detoxification mechanisms and immune responses, rendering bees more susceptible to parasites. It seems certain that chronic exposure to multiple, interacting stressors is driving honey bee colony losses and declines of wild pollinators, but such interactions are not addressed by current regulatory procedures and studying these interactions experimentally poses a major challenge. In the meantime, taking steps to reduce stress on bees would seem prudent; incorporating flower-rich habitat into farmland, reducing pesticide use through adopting more sustainable farming methods, and enforcing effective quarantine measures on bee movements are all practical measures that should be adopted. Effective monitoring of wild pollinator populations is urgently needed to inform management strategies into the future.

https://science.sciencemag.org/content/sci/early/2015/02/25/science.1255957.full.pdf

Bee declines driven by combined stress from parasites, pesticides, and lack of flowers

Global declines in insects have sparked wide interest among scientists, politicians, and the general public. Loss of insect diversity and abundance is expected to provoke cascading effects on food webs and to jeopardize ecosystem services. Our understanding of the extent and underlying causes of this decline is based on the abundance of single species or taxonomic groups only, rather than changes in insect biomass which is more relevant for ecological functioning. Here, we used a standardized protocol to measure total insect biomass using Malaise traps, deployed over 27 years in 63 nature protection areas in Germany (96 unique location-year combinations) to infer on the status and trend of local entomofauna. Our analysis estimates a seasonal decline of 76%, and mid-summer decline of 82% in flying insect biomass over the 27 years of study. We show that this decline is apparent regardless of habitat type, while changes in weather, land use, and habitat characteristics cannot explain this overall decline. This yet unrecognized loss of insect biomass must be taken into account in evaluating declines in abundance of species depending on insects as a food source, and ecosystem functioning in the European landscape.

/pdf/more-than-75-percent-decline-over-27-years-in-total-flying-4qvon60l3b.pdf

More than 75 percent decline over 27 years in total flying insect biomass in protected areas.

Worldwide decline of the entomofauna: A review of its drivers

Declines in bumble bee species in the past 60 years are well documented in Europe, where they are driven primarily by habitat loss and declines in floral abundance and diversity resulting from agricultural intensification. Impacts of habitat degradation and fragmentation are likely to be compounded by the social nature of bumble bees and their largely monogamous breeding system, which renders their effective population size low. Hence, populations are susceptible to stochastic extinction events and inbreeding. In North America, catastrophic declines of some bumble bee species since the 1990s are probably attributable to the accidental introduction of a nonnative parasite from Europe, a result of global trade in domesticated bumble bee colonies used for pollination of greenhouse crops. Given the importance of bumble bees as pollinators of crops and wildflowers, steps must be taken to prevent further declines. Suggested measures include tight regulation of commercial bumble bee use and targeted use of environmentally comparable schemes to enhance floristic diversity in agricultural landscapes.

/pdf/decline-and-conservation-of-bumble-bees-1thgzzqlml.pdf

Decline and conservation of bumble bees

http://www.sussex.ac.uk/lifesci/goulsonlab/documents/goulson-et-al-biological-conservation-2005.pdf

Causes of rarity in bumblebees

http://www.sussex.ac.uk/lifesci/goulsonlab/documents/goulson-et-al-animal-behaviour-2002.pdf

Can alloethism in workers of the bumblebee, Bombus terrestris, be explained in terms of foraging efficiency?

The ecology of all bumblebees (Bombus spp.) is similar, yet some species have declined greatly while others remain abundant. We examine whether abundance is related to diet breadth. The floral visits of bumblebees were examined on Salisbury Plain, UK. All of the species examined gathered pollen mostly from Fabaceae. All species gathered nectar from a broader range of flowers than they did pollen, and longer-tongued bees had a narrower diet breadth when collecting nectar. B. hortorum (the species with the longest tongue) specialized on Trifolium pratense. As predicted, abundant species had a broader diet than rare species. Species with similar-length tongues visiting similar flowers. However, interspecific competition did not appear to be important since species with similar tongue lengths and high niche overlap co-occurred at high abundance. We suggest that the rare species may be those with short colony cycles, in which dependence on high quality food to rear larvae quickly forces specialization.

/pdf/niche-overlap-and-diet-breadth-in-bumblebees-are-rare-2tpv02qovr.pdf

Niche overlap and diet breadth in bumblebees; are rare species more specialized in their choice of flowers?

Bumblebees (Hymenoptera: Apidae) are important pollinators of crops and wildflowers, but many species have suffered dramatic declines in recent decades. Strategies for their conservation require knowledge of their foraging range and nesting density, both of which are poorly understood. Previous studies have mainly focussed on the cosmopolitan bumblebee species Bombus terrestris, and implicitly assume this to be representative of other species. Here we use a landscape-scale microsatellite study to estimate the foraging range and nesting density of two ecologically dissimilar species, B. terrestris and B. pascuorum. Workers were sampled along a 10 km linear transect and 8-9 polymorphic microsatellite markers used to identify putative sisters. We provide the first published estimates of the number of colonies using a circle of radius 50 m in an agricultural landscape: 20.4 for B. terrestris and 54.7 for B. pascuorum. Estimates of nest density differed significantly between the two species: 13 km-2 for B. terrestris and 193 km-2 for B. pascuorum. Foraging ranges also differed substantially, with B. pascuorum foraging over distances less than 312 m and B. terrestris less than 625 m. Clearly bumblebee species differ greatly in fundamental aspects of their ecology. This has significant implications for the development of conservation strategies for rare bumblebees and isolated plant populations, for the management of bumblebees as pollinators, and for predicting patterns of gene flow from genetically modified plants.

/pdf/use-of-genetic-markers-to-quantify-bumblebee-foraging-range-30udgh9c7e.pdf

Ben Darvill

Papers

Decline and conservation of bumble bees

Causes of rarity in bumblebees

Can alloethism in workers of the bumblebee, Bombus terrestris, be explained in terms of foraging efficiency?

Niche overlap and diet breadth in bumblebees; are rare species more specialized in their choice of flowers?

Use of genetic markers to quantify bumblebee foraging range and nest density