Statistical method for testing the neutral mutation hypothesis by DNA polymorphism.

Worldwide decline of the entomofauna: A review of its drivers

Many ecosystem services are delivered by organisms that depend on habitats that are segregated spatially or temporally from the location where services are provided. Management of mobile organisms contributing to ecosystem services requires consideration not only of the local scale where services are delivered, but also the distribution of resources at the landscape scale, and the foraging ranges and dispersal movements of the mobile agents. We develop a conceptual model for exploring how one such mobile-agent-based ecosystem service (MABES), pollination, is affected by land-use change, and then generalize the model to other MABES. The model includes interactions and feedbacks among policies affecting land use, market forces and the biology of the organisms involved. Animal-mediated pollination contributes to the production of goods of value to humans such as crops; it also bolsters reproduction of wild plants on which other services or service-providing organisms depend. About onethird of crop production depends on animal pollinators, while 60–90% of plant species require an animal pollinator. The sensitivity of mobile organisms to ecological factors that operate across spatial scales makes the services provided by a given community of mobile agents highly contextual. Services vary, depending on the spatial and temporal distribution of resources surrounding the site, and on biotic interactions occurring locally, such as competition among pollinators for resources, and among plants for pollinators. The value of the resulting goods or services may feed back via market-based forces to influence land-use policies, which in turn influence land management practices that alter local habitat conditions and landscape structure. Developing conceptual

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Pollination and other ecosystem services produced by mobile organisms: a conceptual framework for the effects of land-use change.

1. What are Allee effects? 2. Mechanisms for Allee effects 3. Population dynamics: modelling demographic Allee effects 4. Genetics and evolution 5. Conservation and management 6. Conclusions and perspectives

Allee Effects in Ecology and Conservation

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.

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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

Owing to habitat loss populations of many organisms have declined and become fragmented. Vertebrate conservation strategies routinely consider genetic factors, but their importance in invertebrate populations is poorly understood. Bumblebees are important pollinators, and many species have undergone dramatic declines. As monoandrous social hymenopterans they may be particularly susceptible to inbreeding due to low effective population sizes. We study fragmented populations of a bumblebee species, on a model island system, and on mainland Great Britain where it is rare and declining. We use microsatellites to study: population genetic structuring and gene flow; the relationships between genetic diversity, population size and isolation; and frequencies of (sterile) diploid males — an indicator of inbreeding. We find significant genetic structuring (θ = 0.12) and isolation by distance. Populations > 10 km apart are all significantly differentiated, both on oceanic islands and on the mainland. Genetic diversity is reduced relative to closely related common species, and isolated populations exhibit further reductions. Of 16 populations, 10 show recent bottlenecking, and 3 show diploid male production. These results suggest that surviving populations of this rare insect suffer from inbreeding as a result of geographical isolation. Implications for the conservation of social hymenopterans are discussed.

Population structure and inbreeding in a rare and declining bumblebee, Bombus muscorum (Hymenoptera: Apidae)

Habitat fragmentation may severely affect survival of social insect populations as the number of nests per population, not the number of individuals, represents population size, hence they may be particularly prone to loss of genetic diversity. Erosion of genetic diversity may be particularly significant among social Hymenoptera such as bumblebees (Bombus spp.), as this group may be susceptible to diploid male production, a suggested direct cost of inbreeding. Here, for the first time, we assess genetic diversity and population structuring of a threatened bumblebee species (Bombus sylvarum) which exists in highly fragmented habitat (rather than oceanic) islands. Effective population sizes, estimated from identified sisterhoods, were very low (range 21-72) suggesting that isolated populations will be vulnerable to loss of genetic variation through drift. Evidence of significant genetic structuring between populations (theta = 0.084) was found, but evidence of a bottleneck was detected in only one population. Comparison across highly fragmented UK populations and a continental population (where this species is more widespread) revealed significant differences in allelic richness attributable to a high degree of genetic diversity in the continental population. While not directly related to population size, this is perhaps explained by the high degree of isolation between UK populations relative to continental populations. We suggest that populations now existing on isolated habitat islands were probably linked by stepping-stone populations prior to recent habitat loss.

Extremely low effective population sizes, genetic structuring and reduced genetic diversity in a threatened bumblebee species, Bombus sylvarum (Hymenoptera: Apidae)

Much of the ecology of rare bumblebee species remains poorly understood and in need of further study. It has recently been suggested that differences in the range and rate of decline among bumblebee species may relate to differences in their degree of habitat specialization. We examine biotope use by 17 bumblebee species in the Hebrides, southern UK and South Island, New Zealand. We identify a cluster of widespread and abundant species that occur in almost all biotopes and exploit man-made environments such as gardens and arable margins, this group corresponding to the “mainland ubiquitous” species of previous studies. A second grouping of species includes those associated to varying degrees with heathland. It is notable that some species occupy markedly different biotopes in different parts of their range; for example B. soroeensis is found largely on upland heaths in the Hebrides, but on calcareous grassland in the south. Some species, such as B. subterraneus and B. distinguendus, now survive only in specific rare biotopes and could be mistaken for habitat specialists, but it is clear from their historic distributions that they formerly occupied a broader range of biotopes. Surviving populations of several of the species that have declined most (B. distinguendus, B. sylvarum, B. muscorum sladeni, B. humilis) exhibit a markedly coastal distribution, when once they were widespread inland. We suggest that this is probably simply because some coastal biotopes are less amenable to agricultural improvement, and so more have escaped the detrimental effects of intensive farming. Our results concur with previous suggestions that bumblebees are generally not habitat specialists, so that the conservation of most bumblebee species could be achieved by restoration of flower-rich unimproved meadows.

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Biotope associations and the decline of bumblebees (Bombus spp.)

1. In contrast to other social bees, bumble-bees exhibit considerable size variation within the worker caste. This size variation has not been adequately explained, although it is known that larger workers tend to be foragers and smaller bees spend more time in the nest. We quantify size variation and mean size for foragers of 22 bumble-bee species inhabiting climates ranging from arctic and montane to the lowland tropics. 2. Mean size was larger in bee species from cold climates compared with temperate bumble-bees. Within species, individuals from Scotland tended to be larger than those from southern England. However, tropical bumble-bees (mostly belonging to the subgenus Fervidobombus) were largest of all. We suggest that although a lower limit to size may be imposed by inhabiting cold climates, overheating does not constrain large size in bumble-bees from hot climates, perhaps because they have efficient mechanisms for heat loss through shunting heat to their extremities. 3. Tropical bees had shorter thoracic setae than species from cooler climates, while B. terrestris from Greece had shorter setae than those from southern UK. Presumably shorter setae enhance heat loss in warm climates. 4. Larger workers of B. terrestris were found to have smaller extremities, in proportion to their size, than small workers. We suggest that heat retention is more important in large bees that spend more of their time foraging, than in small bees which spend much of their time in the nest where incubation of the brood requires them to lose heat. 5. In the temperate climate of southern UK, we found no evidence for ambient temperature having a differential effect on activity of workers of B. terrestris according to their size. We suggest that, at least in temperate climates, size variation in bumble-bee foragers is probably not an adaptation to temperature variation. Instead it may improve colony foraging efficiency since foragers of different sizes are suited to, and tend to visit, different flower species.

http://www.sussex.ac.uk/lifesci/goulsonlab/documents/peat-et-al-funct-ecol-2005.pdf

Jonathan Ellis

Papers

Causes of rarity in bumblebees

Population structure and inbreeding in a rare and declining bumblebee, Bombus muscorum (Hymenoptera: Apidae)

Extremely low effective population sizes, genetic structuring and reduced genetic diversity in a threatened bumblebee species, Bombus sylvarum (Hymenoptera: Apidae)

Biotope associations and the decline of bumblebees (Bombus spp.)

Effects of climate on intra- and interspecific size variation in bumble-bees