POLLINATORS POLLINATION AND FOOD PRODUCTION

THE ASSESSMENT REPORT ON POLLINATORS, POLLINATION AND FOOD PRODUCTION
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2. DRIVERS OF CHANGE OF POLLINATORS,
POLLINATION NETWORKS AND POLLINATION
The impact of invasive alien species on pollinators and
pollination is highly contingent on the identity of the
invader and the ecological and evolutionary context
(well established). Alien plants or alien pollinators change
native pollinator networks, but the effects on native species,
diversity, or networks can be positive, negative or neutral
depending on the species and ecosystem involved (2.5.1,
2.5.2, 2.5.5). Invasive alien predators affect pollination
and plant fitness by consuming pollinators (established
but incomplete). Invasive alien herbivores can affect
pollinators and pollination, but this varies with the species
and ecosystem concerned (established but incomplete).
Alien plant pathogens are a potential but unquantified risk
(inconclusive) (2.5.4). The impacts of invasive aliens are
exacerbated or altered when they exist in combination with
other threats such as disease, climate change and land-use
change (established but incomplete) (2.5.6).
Several pollinator species have moved their ranges,
altered their abundances and shifted their seasonal
activities in response to observed climate change
over recent decades (well established). These effects
are expected to continue in response to forecasted
climate change. The broad patterns of species and biome
shifts toward the poles and higher altitudes in response
to a warming climate have been observed over the last
few decades in some well-studied species groups such
as butterflies and bumble bees. A recent analysis has
shown that bumble bees appear to be undergoing range
contractions as climate changes across Europe and North
America (established but incomplete). Climate change
impacts on pollinators, pollination and agriculture may
be manifested in the short-term (years) to longer-term
(decades) depending on the pollinator species, but it is
possible that the full impacts on nature and agriculture will
not be apparent for many decades, due to long response
times in and complexity of ecological systems (well
established) (2.6.2.2).
Under all climate change scenarios for the second
half of the 21 st century, (i) pollinator community
composition is expected to change as a result of
decreases in the abundance of some species and
increases in others (well established); and (ii) the
seasonal activity of many species is predicted to
change differentially, potentially disrupting life
cycles and species interactions between plants and
pollinators (established but incomplete). Changes in
composition and seasonality are both projected to
alter ecosystem function (established but incomplete).
In high-altitude and high-latitude ecosystems, climate
changes exceeding low-end scenarios (e.g. RCP 2.6) 1 are
very likely to lead to major changes in species distributions
1. Low end scenarios are e.g., the Representative Concentration
Pathway 2.6; http://sedac.ipcc-data.org/ddc/ar5_scenario_process/
RCPs.html
and ecosystem function, especially in the second half of the
21 st century (well established) (2.6.2.3).
The change in climatic conditions, especially under
mid- and high-end scenarios, exceeds the maximum
speed at which several groups of pollinators (e.g.
many bumble bees or butterflies) can disperse or
migrate (well established). Such species are predicted
to find themselves in unfavorable climates and unable to
reach areas of potentially suitable habitat (established but
incomplete). To keep pace with shifting climates, species
occupying extensive flat landscapes are particularly
vulnerable because they must disperse over longer
distances than species in mountainous regions (well
established). Even if a species has the biological capacity
to move fast enough to track suitable climates, those
species with spatially restricted populations, such as
those confined to small and isolated habitats or mountain
tops, are expected to be particularly vulnerable to major
climatic changes (established but incomplete). There is
potential for differences in migration rate or ability to lead
to a geographical or phenological dislocation of pollinator
populations from populations of their historic food plants,
which may present problems for pollination delivery
(established but incomplete) (2.6.2.3).
Multiple pressures that individually impact the
health, diversity and abundance of many pollinators
across levels of biological organisation (from gene
to biome scales), can combine in their effects and
thereby increase the overall pressure on pollinators
(established but incomplete). This variety of threats
(often anthropogenic) to pollinators and pollination
poses a potential risk to food security, human health and
ecosystem function (inconclusive). The actual magnitude
of interactions between these different pressures varies
with location and among pollinator species, according
to their biological attributes (established but incomplete).
Nonetheless it is likely that changes in pollinator biodiversity
and pollination are being exacerbated by both the individual
and combined effects of multiple pressures (established but
incomplete) (2.7).
2.1 INTRODUCTION
There are a number of potential drivers of changes in
pollinators, pollination networks and pollination. In the present
chapter, these drivers and their impacts are assessed,
especially as they relate to the link of pollinators and
pollination to food production, but also to semi-natural parts
of the ecosystem. The pollinators under consideration here
are mainly bees (honey bees, bumble bees, stingless bees
and solitary bees), and to some extent other groups including
syrphid flies, butterflies, moths, birds, mammals and reptiles.