The addition, wild pollinators might not be able

The first response is unlikely, since
the expected climate change will occur too rapidly for populations to adapt by
genetic change (evolution). As temperatures increase and exceed species’
thermal tolerance levels, the species’ distributions are expected to shift
towards the poles and higher altitudes (Deutsch et al. 2008; Hegland et al.
2009). Many studies have already found poleward expansions of plants (Lenoir et
al. 2008), birds (Thomas and Lennon 1999; Brommer 2004; Zuckerberg et al. 2009)
and butterflies (Parmesan et al. 1999; Konvicka et al. 2003) as a result of
climate change. Crop species and managed pollinators may easily be transported
and grown in more suitable areas. However, moving food production to new areas
may have serious socio-economic consequences. In addition, wild pollinators
might not be able to follow the movement of crops.


Temperature effect on pollinators

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Current climate change entails
increasing global average temperatures as a result of human emissions of the
greenhouse gases carbon dioxide, methane, and nitrous oxide. Carbon dioxide
emissions come primarily from fossil fuel use and land use change, while
methane and nitrous oxide emissions result from agriculture. Because of the
long half-life of the gases, past 10 and current greenhouse gas emissions will
continue to warm the planet for over a millennium (IPCC, 2014). One of the
uncertainties surrounding climate change is how various ecosystems and species,
such as plants and pollinators, will respond to changes in climate.

 Increased temperatures threaten to disrupt the
environmental cues upon which flowering plants rely for the initiation of
growing. Phenology refers to the annual timing of seasonal activities of plants
and animals, usually influenced by weather and climate. For flowering plants,
primarily temperature affects the phenology (timing) of flowering (Walther et
al., 2002), and not elevated carbon dioxide levels or nitrogen deposition from
climate change (Cleland et al., 2006). In montane meadows that experience winter
snowpack, the timing of flowering depends predominantly on when the snowpack
melts in the spring. Because warming temperatures from climate change cause
more precipitation to fall as rain than as snow, the snowpack will disappear
sooner in the spring. Snowmelt allows the ground to warm up and thus the plants
to begin growing (Inouye, 2008; Dunne et al., 2003). Snowmelt could either be a
cue for plant phenology or a threshold for when plants can begin growth, after
which temperatures determine the rate of growth (Forrest & Thomson, 2011).

Numerous studies have found that the
phenology of flowering has shifted earlier in response to warming and/or
earlier snowmelt (Fitter & Fitter, 2002; Ahas et al., 2002; Inouye et al.,
2002; Bradley et al., 1999). For example, from 1852 to 2006, 2.4 degrees C
warming in Concord, Massachusetts correlated with an average shift in timing of
flowering by seven days (Miller-Rushing et al., 2008). Another dataset of
flowering plants in the southeastern USA from 1951 to 2009 indicates that
early-flowering species advance about 4 days for each degree C increase in mean
March temperatures (Park & Schwartz, 2015). To isolate the various climate
effects, Dunne et al. (2003) tested flowering responses to snowpack
manipulation and 11 experimental warming on 12 meadows in the Colorado Rocky
Mountains. The experiment showed that the timing of flowering advances about 11
days for every two weeks of earlier snowmelt or for every two degrees warming
of growing season soil temperatures. Furthermore, the majority of these
phenological studies may even under-predict plant responses to climate change.
The plants that flower earlier in the growing season typically advance more in
response to warming than do later-flowering species, so the averaging of
phenological changes will not accurately reflect the full range of responses
(Fitter & Fitter, 2002; Wolkovich et al., 2012; Hegland et al., 2009).