POLLINATORS POLLINATION AND FOOD PRODUCTION

THE ASSESSMENT REPORT ON POLLINATORS, POLLINATION AND FOOD PRODUCTION
100
2. DRIVERS OF CHANGE OF POLLINATORS,
POLLINATION NETWORKS AND POLLINATION
shift in the areas suitable for passion fruit pollinators by
2050. Polce et al. (2014) modelled the present and future
distributions of orchard crops in the UK, and 30 species of
bees and hoverflies known to visit fruit tree flowers under a
medium emissions scenario. They showed that the present
distribution of orchards in the UK largely overlaps with areas
of high pollinator richness, but there could be a substantial
geographical mismatch in the future (2050), as the area
with climate most suitable for orchards moves substantially
north and west. Future ranges also have been projected for
some bee species using the approach in Europe (Roberts
et al. 2011) and South Africa (Kuhlmann et al. 2012), and
in particular for bumble bees and butterflies on a European
continental scale (see Box 2.6.1). Giannini et al. (2012)
modelled a decrease in bee habitats due to climate change
in Brazil. However, the possibility that pollinators gradually
change their target plant species is not taken into account
in such approaches. There are indications for such shifts
(Schweiger et al., 2008) which would mean that there is no
necessity to move with the current plant species. Instead,
this is a component of novel ecosystems evolving under
climate change.
Due to considerable differences in larval resources among
the different pollinator groups, it is uncertain whether
the impacts of climate change on bees and syrphid flies
will show similar patterns as those for butterflies and
bumble bees (Settele et al., 2008, Rasmont et al., 2015a).
Carvalheiro et al. (2013) show that bumble bees and
butterflies are far more prone to local and regional extinction
than other bees or hoverflies, and Kerr et al. (2015) show the
drastic effects of climate change on bumble bees. However,
in all groups, landscape connectivity, the mobility of species
and effects on plants and on floral resources are important
and widely unknown factors, which might drastically change
the expected future impacts.
to regulate the temperature inside the colony (hive) by
thermogenesis or cooling, this species seems not directly
threatened by global warming.
While for the majority of species climate space itself is
already limiting (e.g., on the pollinators’ physiology), all
pollinators that more or less depend on certain plants,
potentially suffer indirectly because of climate change
impacts on these plants (Schweiger et al., 2008; Schweiger
et al., 2010; Schweiger et al., 2012). In butterflies the
nectar plants are more independent from the insect in
their development (as there is mostly no specific link for
the plants’ pollination), while one might expect impacts in
“tighter” pollination systems. The absence of a pollinator
could mean absence of a pollination-dependent plant and
vice versa (Biesmeijer et al. 2006). These effects can be
expected only for the rare cases of high specialization,
and indeed Carvalheiro et al. (2013) reanalyzed the data
from Biesmeijer et al., (2006) and found that declines
are not parallel in time. Hoover et al. (2012) have shown,
in a pumpkin model system, that climate warming, CO 2
enrichment and nitrogen deposition non-additively affect
nectar chemistry (among other traits), thereby altering the
plant’s attractiveness to bumble bees and reducing the
longevity of the bumble bee workers. This could not be
predicted from isolated studies on individual drivers.
Generally, it can be assumed that climate change results
in novel communities, i.e. creation of species assemblages
that have not previously co-existed (Schweiger et al.,
2010). As these will have experienced a much shorter (or
even no) period of coevolution, substantial changes in
pollination networks are to be expected (Tylianakis et al.,
2008; Schweiger et al., 2012). This might generally result in
severe changes in the provision of services (like pollination),
especially in more natural or wild conditions (Montoya and
Raffaelli, 2010).
2.6.2.4 Further climate change impacts
on pollinators
Climate change might modify the balance between honey
bees and their environment (including diseases). Le Conte
and Navajas (2008) state that the generally observed
decline of honey bees is a clear indication for an increasing
susceptibility against global change phenomena, with
pesticide application, new diseases and other stress (and a
combination of these) as the most relevant causes. Honey
bees also have shown a large capacity to adjust to a large
variety of environments (not at least as they are often
managed and hence may be buffered accordingly) and
their genetic variability should allow them to also cope with
climatic change, which is why the preservation of genetic
variability within honey bees is regarded as a central aim to
mitigate climate change impacts (Le Conte and Navajas,
2008). Also, due to the great capacity of the honey bee
Climate change-induced changes in habitat encompass
i) shifts in habitat distributions that cannot be followed by
species, ii) shifts in distribution of species that drive them
outside their preferred habitats and iii) changes in habitat
quality (Urban et al., 2012). However, these phenomena
are not yet widespread, while models of future shifts in
biome and vegetation type (and species distributions, see
previous sections) suggest that within the next few decades
many species could have been driven out of their preferred
habitats due to climate change (Urban et al., 2012). Wiens
et al. (2011) also find that climate change may open up new
opportunities for protecting species in areas where climate is
currently unsuitable. Indeed, in some cases climate change
may allow some species to move into areas of lower current
or future land use pressure (Bomhard et al., 2005). These
and other studies strongly argue for a rethinking of protected
areas networks and of the importance of the habitat
matrix outside protected areas to enhance the ecosystem