POLLINATORS POLLINATION AND FOOD PRODUCTION

THE ASSESSMENT REPORT ON POLLINATORS, POLLINATION AND FOOD PRODUCTION
Under all climate change scenarios for the second half of
the 21 st century, (i) community composition will change
as a result of decreases in the abundances of some
species and increases in others, leading to the formation
of novel communities; and (ii) the seasonal activity of many
species will change differentially, disrupting life cycles and
interactions among species. Both composition and seasonal
change will alter ecosystem structure and function in many
instances, while in other cases the phenology of pollinators
(e.g., generalist bee species) will keep pace with shifts in
forage-plant flowering.
Climate change impacts may not be fully apparent for
several decades (Settele et al., 2008; Rasmont et al.,
2015a), owing to long response times in ecological systems.
In high-altitude and high-latitude ecosystems, climate
changes exceeding low end scenarios (e.g., SEDG –see
box 2.6.1; or Representative Concentration Pathway 2.6;
http://sedac.ipcc-data.org/ddc/ar5_scenario_process/
RCPs.html) will lead to major changes in species
distributions and ecosystem function, especially in the
second half of the 21 st century. Honey bees do not appear
directly threatened by climate change because of their large
capacities of thermoregulation.
For many pollinator species the speed of migration is
unknown (including bees, for which foraging ranges are
known once the nest is stablished, but not their dispersal
ability). For those where more knowledge exists, the rate of
movement of the climate across the landscape will exceed
the maximum speed at which pollinators can disperse or
migrate, especially in order to reach new areas of suitable
habitats where climate and other requirements are fulfilled
in synchrony. Populations of species that cannot keep up
with their climate niche will find themselves in unfavorable
climates. Species occupying extensive flat landscapes are
particularly vulnerable because they must disperse over
longer distances than species in mountainous regions to
keep pace with shifting conditions in climates and habitats.
Large magnitudes of climate change will particularly affect
species with spatially restricted populations, such as
boreo-alpine relicts and those confined to small and isolated
habitats (e.g., bogs), as they may no longer find suitable
habitats, or mountain tops (no upwards move possible),
even if the species has the biological capacity to move fast
enough to track suitable climates.
A large fraction of pollinator species may face increased
extinction risk under projected climate change during
the 21 st century, especially as climate change interacts
with other pressures, such as habitat modification,
overexploitation, pollution, and invasive species.
2.7 MULTIPLE, ADDITIVE
OR INTERACTING THREATS
Changes in land use or climate, intensive agricultural
management and pesticide use, invasive alien species and
pathogens affect pollinator health, abundance, diversity
and pollination directly (Sections 2.2-2.6). Moreover, these
multiple direct drivers also have the potential to combine,
synergistically or additively, in their effects leading to
an overall increase in the pressure on pollinators and
pollination (González-Varo et al., 2013; Goulson et al.,
2015; Vanbergen and the Insect Pollinators Initiative,
2013). These drivers differ in being a physical, chemical
or biological threat, in the spatial or temporal scale at
which they impact, and in whether they interact simply
(additive interactions), or in complex or non-linear ways
(e.g., synergistic or antagonistic). For instance, drivers
may constitute a chain of events such as when indirect
drivers (e.g., increases in economic wealth, changes in
consumption) lead to a direct driver (e.g., agricultural
intensification) that changes pollinator biodiversity and
pollination (Figure 2.7.1). Another possibility is that a direct
driver’s impact on pollinators and pollination (e.g. climate
changes decouple plant and pollinator distributions) might
also be manifested through interaction with a second
driver (e.g., climate change exacerbates invasive alien
species or disease spread) thereby compounding the
impact (González-Varo et al., 2013; Ollerton et al., 2014;
Potts et al., 2010; Vanbergen and the Insect Pollinators
Initiative, 2013). Moreover, certain drivers of change (e.g.,
conventional agricultural intensification) are themselves a
complex combination of multiple, factors (e.g., pesticide
exposure, loss of habitat, altered pollen and nectar food
resources), which affect pollinators and pollination (Ollerton
et al., 2014; Potts et al., 2010; Vanbergen and the Insect
Pollinators Initiative, 2013).
This inherent complexity (Figure 2.7.1) means that,
to date, this phenomenon of a multifactorial impact on
pollinators and pollination has only been demonstrated in
comparatively few studies, limited in the scope of species
(i.e. honey bees and bumble bees) or combinations of
pressures considered (Table 2.7.1). Consequently, the
current empirical evidence base is relatively poor due to
a relative scarcity of data. It is rarely possible to rule out
a single, proximate cause for changes in pollinators and
pollination in a particular locality, for a given species or
under a certain set of circumstances. However, it seems
likely that in the real world a complex interplay of factors
is affecting pollinator biodiversity and pollination, although
the exact combination of factors will vary in space, time
and across pollinator species (Cariveau and Winfree, 2015;
Goulson et al., 2015; Vanbergen and the Insect Pollinators
Initiative, 2013). Therefore, science and policy need to
consider equally the separate and combined impacts of
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2. DRIVERS OF CHANGE OF POLLINATORS,
POLLINATION NETWORKS AND POLLINATION