POLLINATORS POLLINATION AND FOOD PRODUCTION

THE ASSESSMENT REPORT ON POLLINATORS, POLLINATION AND FOOD PRODUCTION
report concludes that most of these are declining rapidly in
parts of their range and are in need of conservation action.
The major drivers of butterfly habitat loss and degradation
are related to agricultural intensification, although climate
change plays a role, as do changes in management of
forested and grassland areas that affect butterfly host plants
and nectar resources.
Although some moth species are also important pollinators,
there are even fewer studies of their population dynamics
outside of economically important pest species. Some
moths have closely coevolved relationships with their nectar
plants, with a close correspondence between proboscis
length and corolla size (Nilsson, 1998), although in Kenya
Martins and Johnson (2013) found that adult hawkmoths
are routinely polyphagous and opportunistic, regardless
of their proboscis length. Many families of large moths,
including sphingids, erebids, noctuids and geometrids,
are very species-rich and also contain a large number of
nectar-feeding species that are potential pollinators, but our
knowledge of these primarily nocturnal pollinators is scant.
More seems to be known about their distribution than their
significance as pollinators, or population trends, but data
on larger moths in Britain (http://butterfly-conservation.org/
files/1.state-of-britains-larger-moths-2013-report.pdf) show
a 28% decline from 1968-2007, with two-thirds of 337
species of common and widespread larger moths declining
over the 40-year study.
Forister et al. (2011) and Casner et al. (2014) analyzed data
from a decades-long study of butterfly distributions along an
altitudinal transect in California’s Central valley. They found
that declines in the area of farmland and ranchland, an
increase in summer minimum temperatures and maximum
temperatures in the fall negatively affected net species
richness, whereas increased minimum temperatures in the
spring and greater precipitation in the previous summer
positively affected species richness. Changes in land use
contributed to declines in species richness (although the
pattern was not linear), and the net effect of a changing
climate on butterfly richness was more difficult to discern,
but given the dramatic changes in the climate of that
area (probably the most severe drought in 500 years –
Belmecheri et al., 2015) it is not surprising that butterfly
populations are being affected.
Most of these studies reporting changes in species richness
or species abundance are not able to identify specific
causes for declines. For one high-altitude butterfly species,
Speyeria mormonia, Boggs and Inouye (2012) found that
snowmelt date explained a remarkable 84% of the annual
variation in population growth rate, but studies successfully
identifying environmental factors driving population size
remain rare.
Beetles (Coleoptera)
Beetles are the largest order of insects, and although they
are relatively uncommon as pollinators, they have had a long
evolutionary history with flowers (Gottsberger, 1977). They
have also been overlooked in comparison to other groups
of pollinators (Mawdsley, 2003). Beetle (weevil) pollinators
are very important for oil palms, and they have been
successfully introduced to tropical areas where these plants
have been introduced; they now replace hand-pollination
that was initially required (Greathead, 1983). They are also
pollinators of some minor crops such as Annona (Podoler
et al., 1984). There do not appear to be any studies of the
trends in beetle pollinator populations.
Vertebrate pollinators
Two recent papers address the conservation status of
vertebrate pollinators and the consequences of their loss.
Aslan et al. (2013) estimated the threat posed by vertebrate
extinctions to the global biodiversity of vertebrate-pollinated
plants. While recognizing large gaps in research, their
analysis identified Africa, Asia, the Caribbean, and global
oceanic islands as geographic regions at particular risk of
disruption of pollination (and dispersal). Plants that lose their
mutualists are likely to experience reproductive declines of
40–58%, potentially threatening their persistence. A recent
survey (Regan et al., 2015) of bird and mammal pollinators
was undertaken using IUCN Red List data that are probably
the best source for global information about extinction risk
for threatened species. Of the 901 bird species reported
as pollinators that they considered, 18 were uplisted (e.g.,
from Endangered to Critically Endangered) during the period
2008 – 2012, while 15 of the 341 mammal pollinators
qualified for uplisting or were added to the list during the
period 1996 – 2008. Thus, it appears that these two groups
of vertebrate pollinators are suffering significant declines.
This conclusion is also supported by reports of overhunting
of flying foxes (Brooke and Tschapka, 2002), which are
important pollinators and seed dispersers on some oceanic
islands (Cox et al., 1991; Elmqvist et al., 1992).
Hummingbirds are charismatic pollinators in the New World.
Some data for hummingbirds are available from the Breeding
Bird Survey in the USA and Canada. Although sample sizes
are relatively small, the time period surveyed (1962-2012)
is long, and the data appear to be the best available for
trends in population size. Three species (Table 3.1) show
increases of between 1-2%/yr, while four others seem to be
declining at 1-5%/yr. These are migratory species, which
overwinter in Mexico or further south in Central America
(e.g., Calder, 2004), and no data are available for their
overwintering populations (it is not even clear where most
of these birds are going in winter). However, based on
the extent of habitat loss, it is estimated that the Mexican
hummingbird populations may have declined by 15-49% in
the past century (Berlanga et al., 2010). For some species
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3. THE STATUS AND TRENDS IN POLLINATORS
AND POLLINATION