POLLINATORS POLLINATION AND FOOD PRODUCTION

THE ASSESSMENT REPORT ON POLLINATORS, POLLINATION AND FOOD PRODUCTION
change may be due to natural internal processes or external
forcings such as modulations of the solar cycles, volcanic
eruptions and persistent anthropogenic changes in the
composition of the atmosphere or in land use” (IPCC,
2013). Species respond to climate change by adaptation,
by moving out of unfavorable into favorable climates, or by
going first locally and later globally extinct (Dawson et al.,
2011, Bellard et al., 2012). Climate change is regarded as
one important factor contributing to the decline of pollinators
(Potts et al., 2010) and changes and disruptions of plant–
pollinator interactions (Memmott et al., 2007; Hegland et
al., 2009). Vulnerability of biodiversity and ecosystems
to climate change is defined as the combination of three
things: a) the degree to which their climatic environment
has or will change relative to conditions under which they
evolved; b) the sensitivity of the ecosystem processes to the
elements of climate which are changing; and c) the degree
to which the system can maintain its structure, composition
and function in the presence of such change, either by
tolerating the change or adapting to it (Settele et al.,
2014; see Oppenheimer et al., 2014 for a comprehensive
discussion on vulnerability concepts).
2.6.2 Evidence of changes in
ecosystems, pollinators and
pollination
2.6.2.1 Phenology change and interaction
mismatch
Monitoring of the phenology of biological events across a
large number of sites worldwide has allowed the detection
of an advance in spring events (breeding, bud burst,
breaking hibernation, flowering, flight time, migration) for
many plant and animal taxa in many regions, especially
in the northern hemisphere (e.g., Europe, North America,
Arctic) but also some in the southern hemisphere and
in tropical areas (e.g., Africa, Australia, South America,
Antarctica). Studies on plants include Cleland et al. (2007),
Amano et. al. (2010) and Gordo and Sanz (2010), while
plants and animal taxa in combination have been dealt with
by Høye et al. (2007), Primack et al. (2009), and McKinney
et al. (2012). Meta-analyses based on observation studies
were conducted by Parmesan (2006, 2007), Cook et al.
(2012b), Ma and Zhou (2012), and Wolkovich et al. (2012),
while those of Cleland et al. (2012) and Wolkovich et al.
(2012) were based on warming experiments.
Generally, there is great intra- and interspecific variability in
phenological responses to changing climatic factors. Insect
species with phenotypic plasticity in their life-cycle may
increase in number of generations per year due to increase
in temperatures and length of growing seasons (e.g. due
to the contraction of the onset and cessation of winter
frosts; Menzel et al., 2006; Robinet and Roques, 2010).
Uncertainties and biases are introduced in research that (1)
compares different taxonomic groups or geographic regions
with incomplete or non-overlapping temporal and/or spatial
time series and scales, or (2) fails to consider the effects of
local climatic variability (e.g., wind speed, climatic conditions
at stop-over places during migrations) or the mostly
unknown pressures on winter ranges for migratory species
(Hudson and Keatley, 2010). Further, if time series are too
short, long-term trends in phenological changes cannot be
detected, although responses to annual climate variability
can often be characterized. Cross-taxa observations show
high variation in species- and location-specific responses
to increasing temperatures in both direction and magnitude
(e.g. Parmesan, 2007; Primack et al., 2009).
Changes in interspecific interactions stemming from
changes in phenological characteristics and breakdown
in synchrony between species have been reported (Gordo
and Sanz, 2005). Species unable to adjust their behavior,
such as advancement of spring flowering in response
to temperature, are likely to be negatively affected, if
for example, their pollinators do not respond to the
same signals. The degree, direction and strength of the
asynchrony due to changing climatic variables depends
on differences in the phenology of the interacting species
(van Asch and Visser, 2007). Increasing temperatures may
either increase or decrease synchrony between species,
depending on their respective starting positions (Singer and
Parmesan, 2010). Climate changes (e.g. warming, elevated
CO 2
) and its consequences (e.g. increased drought) may
affect the synchrony between plants and pollinators by
altering the chemical signals emitted by plants (floral
volatiles) to attract pollinators (Farre-Armengol et al., 2013).
For example, increased temperatures may elevate the
overall rate of volatile emissions, and hence the strength of
the signal to pollinators, but alter the chemical composition
potentially affecting the ability of specialist pollinators that
rely on species-specific floral bouquets to locate food-plants
(Farre-Armengol et al., 2014). However, the consequences
of individual and multiple climate-stressors on pollination are
likely to be complex due to different impacts on various plant
biochemical pathways and biotic interactions and much
remains to be understood (Farre-Armengol et al., 2013).
Generally, changes in synchrony of interacting species are
assumed to affect ecological community dynamics, such
as trophic cascades, competitive hierarchies and species
coexistence (Nakazawa and Doi, 2012). For example,
fig plants are keystone species in tropical rain forests at
the centre of an intricate web of specialist and generalist
animals. Jevanandam et al. (2013) report that fig plants have
a reciprocally obligate mutualism with tiny, short-lived (1-2
days) fig wasps (Agaonidae). Their results of experiments
from equatorial Singapore suggest that the small size and
short life of these pollinators make them more vulnerable
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2. DRIVERS OF CHANGE OF POLLINATORS,
POLLINATION NETWORKS AND POLLINATION