Climate change and land-use impacts on pollinators and pollination
Climate changes may provide opportunities and threats for pollinators, and changes to the composition, extent, and configuration of habitat in the landscape are likely to pose a challenge to many pollinator species as climate change progresses. For instance, pollinator species currently at the limits of their climatic range may migrate with global warming into new geographic regions, thus increasing the abundance and diversity of recipient communities. However, if such immigrants are highly invasive there may be an attendant risk of further ecological changes, for example through alteration of pre-existing plant-pollinator relationships, interspecific competition for food or transfer of pests and diseases. Rates of migration are likely to differ among pollinator and plant species, raising the prospect of a spatial dislocation of plants and their pollinators; recent evidence of climate change impacts on bumble bees suggests there are adaptive limits to the capacity of this pollinator group to track climate change. Habitat loss and fragmentation arising from land-use changes (e.g., habitat conversion to agriculture) may also limit compensatory species migration in the face of climate change. In general, lower connectivity between habitat remnants combined with future climate shifts may reduce population sizes and increase extinction likelihoods of pollinators, especially species that are poor dispersers or habitat specialists. Land-use driven changes to landscape structure coupled with climate changes might therefore lead to increasingly species-poor plant-pollinator communities dominated by highly mobile, habitat generalist species. There is potential for climate-driven changes in the availability pollinator foods over time to be exacerbated by the reduced nutritional resources that seem to be a feature of large-scale monocultures.
There is likely to be considerable variation in how pollinator populations and communities respond to the combined effects of climate and land-use changes, due not only to variation in life-history traits among pollinator species and guilds, but also the complexity of wider ecological interactions in the ecosystem. This is illustrated by a plot-scale field experiment that mimicked the combined effects of habitat fragmentation (distance to semi-natural habitat in the landscape) and climate change (manipulation of advanced flower phenology and plant growth) on plant pollination. It showed that bee visitation was affected by isolation from other habitat patches, whereas pollinating flies were unaffected by isolation; while advancement of floral phenology did disrupt pollinator mutualisms, this was offset by the plant’s escape from herbivore enemies, meaning that net plant reproductive success was unaffected.