POLLINATORS POLLINATION AND FOOD PRODUCTION

THE ASSESSMENT REPORT ON POLLINATORS, POLLINATION AND FOOD PRODUCTION
The standard objective assessment of the status of a
species, e.g. a pollinator, is the IUCN Red List assessment.
Global assessments are available for many vertebrate
pollinators, e.g. birds and bats. Most insect pollinators
have not been assessed at a global level. In total 16.5% of
vertebrate pollinators are threatened with global extinction
(increasing to 30% for island species; Aslan et al. 2013).
The trend is generally towards more extinctions. Regional
and national assessments of insect pollinators indicate
high levels of threat particularly for bees and butterflies
(often >40% of species threatened) (IUCN Red List for
Europe; www.iucn.org; van Swaay et al. 2010). The recent
European-scale red lists revealed that 9% of bees and 9% of
butterflies are threatened and populations are declining for
37% of bees and 31% of butterflies (excluding data-deficient
species). Note, however, that for the majority of European
bees data are insufficient to make IUCN assessments.
Many if not most of the data-deficient species are likely to
have a very limited (endemic) distribution or are very rare,
traits often found in threatened species. At national levels
numbers of threatened species tend to be much higher than
at regional levels, e.g., more than 50% for bees in some
European countries. In contrast, crop-pollinating bees are
generally common species and rarely threatened species.
Of 130 common crop-pollinating bees (Kleijn et al., 2015)
only 58 species have been assessed either in Europe or
North America. Only two species are threatened (Bombus
affinis, Bombus terricola), two are near threatened (Andrena
ovatula, Lasioglossum xanthopus), 42 are doing well (all
assessed as Least Concern), whereas for 12 of these
species data are insufficient for assessment. Of 57 species
mentioned as crop pollinators in Klein et al. (2007) only 10
species have been formally assessed, of which one bumble
bee species, Bombus affinis, is critically endangered.
However, at least 10 other species, including three honey
bee species, are known to be very common.
Human-altered landscapes can reduce gene flow in
pollinator populations (Jha, 2015), and the interaction
between land use and fragmentation (Hadley and Betts,
2012) can also have negative impacts (Kenefic et al.,
2014). Land use intensity has also been shown to correlate
with pollinator populations (Clough et al., 2014). A recent
paper has reviewed the effects of local and landscape
effects on pollinators in agroecosystems (Kennedy et
al., 2013); bee abundance and richness were higher in
diversified and organic fields (e.g., Holzschuh et al., 2007)
and in landscapes comprising more high-quality habitats,
while bee richness on conventional fields with low diversity
benefited most from high-quality surrounding land cover
(e.g., Klein et al., 2012). Stresses from pesticides and
parasites (Chapter 2) can also alter pollinator distributions
and abundance. Increases in nitrogen inputs can also
affect flower production, pollinator visitation, and fruit set
(Muñoz et al., 2005).
3.2.2 Evidence for spatial shifts
and temporal changes in species
occurrence
Information about wild pollinator populations is primarily
available from two sources, either historical information
from museum collections and records collected by amateur
naturalists and scientists, or very recent surveys initiated
in response to concerns about current declines that can
now provide baseline information for future comparison. For
example, Biesmeijer et al. (2006) compiled almost 1 million
records for bee and hoverfly observations for Britain and
the Netherlands from national entomological databases to
compare areas with extensive sets of observations before
and after 1980. They found significant declines in the bee
species richness in many areas, and also that outcrossing
plant species that are reliant on insect pollinators (United
Kingdom) or bee pollinators (Netherlands) also declined
relative to species with wind- or water-mediated pollination.
These results strongly suggest, but do not prove, a causal
connection between local extinctions of functionally-linked
plant and pollinator species. Another example of how
museum records can be used to gain insights is a resurvey
of bee fauna and associated flora from a grassland
site in Brazil, originally surveyed 40 years ago and again
20 years ago, which found that bee species richness has
declined by 22% (Martins et al., 2013). Some previously
abundant species had disappeared, a trend that was more
accentuated for large rather than small bees. However, one
study found that the abundance of common bee species
was more closely linked to pollination than bee diversity
(Winfree et al., 2015).
A recent long-term study of relative rates of change for
an entire regional bee fauna in the northeastern United
States, based on >30,000 museum records representing
438 species (Bartomeus et al., 2013), found that over a
140-year period native species richness decreased slightly,
but declines in richness were significant (p = 0.01) only
for the genus Bombus. “Of 187 native species analyzed
individually, only three declined steeply [in abundance], all
of these in the genus Bombus. However, there were large
shifts in community composition, as indicated by 56% of
species showing significant changes in relative abundance
over time.” At the community level some of the decline was
masked by the increase in exotic species (increased by a
factor of 9, to a total of 20, including species of Anthidium,
Hylaeus, Lasioglossum, Megachile, Osmia, etc.), with an
accompanying trend toward homogenization. The study
also provided insights into the traits associated with a
declining relative abundance: small dietary and phenological
breadth and large body size, which may provide clues to
identify which species are likely to be susceptible to declines
in other areas as well. It is somewhat reassuring that,
despite marked increases in human population density in
the northeastern USA and large changes in anthropogenic
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3. THE STATUS AND TRENDS IN POLLINATORS
AND POLLINATION