Caring for Pollinators - Bundesamt für Naturschutz

Potts, Roberts, Kunin & Biesmeijer The status of European pollinators
Several causes of the declines in European honeybees have been recorded and include the
increased incidence of diseases (e.g. Varroa and tracheal mites, chalk brood), unusually
cold winters and summer droughts, overuse of pesticides and loss of good bee forage
habitats. Combinations of different drivers in each country and region are likely to be the
causes of the observed patterns but further research is needed to quantify this. Though
CCD has been suggested to be in Europe, actual evidence has not been provided to date.
However, given that CCD, small hive beetle and other diseases are potential threats to
European honeybees, future risks for further losses are high. As honeybees and wild bees
have such a high economic value in Europe and many of our food crops and wild plants rely
on their services, it is essential that we invest in research to fully understand the nature of
the problem and in activities which will help safeguard pollinators and pollination services for
the future.
Are European wild bees and hoverflies in decline?
While there has been substantial discussion about loss of wild pollinator and some striking
case studies, until recently there was little solid evidence of geographically widespread
declines. This is largely due to the lack of any coordinated monitoring programmes for bees
or other pollinators – or indeed for any but the most charismatic (butterflies) or destructive
(agricultural pest) invertebrates. In the absence of such monitoring data, scientists have had
to rely on less direct methods to test for changes in the pollinator community.
Biesmeijer and colleagues (2006) devised a novel approach based on the accumulation of
records in national entomological databases. Many countries have societies of largely
amateur naturalists, who record sightings of insect species in shared databases. While
these databases are not systematic sampling programmes, they nonetheless include
hundreds of thousands of carefully collected records. Biesmeijer and his colleagues used a
technique called rarefaction, in which random samples of records of different sizes are
repeatedly sub-sampled from the pool of all records, providing a fairly robust measure of
species diversity despite uneven sampling effort. They examined bees and hoverflies, the
two biggest groups of insect pollinators, in two countries with excellent entomological data:
the UK and the Netherlands.
The results were striking (see Figure 2). In both countries, the diversity of bees has fallen
significantly in the majority of landscapes (80% in the Netherlands, 70% in the UK), while
very few landscapes showed significant diversity increases. The results for hoverflies were
quite different, with increased diversity in the Netherlands, and a mixed response in the UK.
Reduced biodiversity in itself might have only a limited impact on pollination services, if the
species remaining had traits similar to those being lost. However, further analyses of the
traits of the pollinators involved suggested that this was not the case. In both bees and
hoverflies, there tended to be declines in specialist and sedentary species, while mobile
generalists tended to thrive.
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