The first response is unlikely, sincethe expected climate change will occur too rapidly for populations to adapt bygenetic change (evolution). As temperatures increase and exceed species’thermal tolerance levels, the species’ distributions are expected to shifttowards the poles and higher altitudes (Deutsch et al. 2008; Hegland et al.2009). Many studies have already found poleward expansions of plants (Lenoir etal. 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 ofclimate change. Crop species and managed pollinators may easily be transportedand grown in more suitable areas. However, moving food production to new areasmay have serious socio-economic consequences. In addition, wild pollinatorsmight not be able to follow the movement of crops. 1. Temperature effect on pollinatorsCurrent climate change entailsincreasing global average temperatures as a result of human emissions of thegreenhouse gases carbon dioxide, methane, and nitrous oxide.
Carbon dioxideemissions come primarily from fossil fuel use and land use change, whilemethane and nitrous oxide emissions result from agriculture. Because of thelong half-life of the gases, past 10 and current greenhouse gas emissions willcontinue to warm the planet for over a millennium (IPCC, 2014). One of theuncertainties 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 theenvironmental cues upon which flowering plants rely for the initiation ofgrowing.
Phenology refers to the annual timing of seasonal activities of plantsand animals, usually influenced by weather and climate. For flowering plants,primarily temperature affects the phenology (timing) of flowering (Walther etal., 2002), and not elevated carbon dioxide levels or nitrogen deposition fromclimate change (Cleland et al.
, 2006). In montane meadows that experience wintersnowpack, the timing of flowering depends predominantly on when the snowpackmelts in the spring. Because warming temperatures from climate change causemore precipitation to fall as rain than as snow, the snowpack will disappearsooner in the spring. Snowmelt allows the ground to warm up and thus the plantsto begin growing (Inouye, 2008; Dunne et al., 2003). Snowmelt could either be acue for plant phenology or a threshold for when plants can begin growth, afterwhich temperatures determine the rate of growth (Forrest & Thomson, 2011). Numerous studies have found that thephenology of flowering has shifted earlier in response to warming and/orearlier 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 Cwarming in Concord, Massachusetts correlated with an average shift in timing offlowering by seven days (Miller-Rushing et al., 2008). Another dataset offlowering plants in the southeastern USA from 1951 to 2009 indicates thatearly-flowering species advance about 4 days for each degree C increase in meanMarch temperatures (Park & Schwartz, 2015). To isolate the various climateeffects, Dunne et al. (2003) tested flowering responses to snowpackmanipulation and 11 experimental warming on 12 meadows in the Colorado RockyMountains. The experiment showed that the timing of flowering advances about 11days for every two weeks of earlier snowmelt or for every two degrees warmingof growing season soil temperatures.
Furthermore, the majority of thesephenological studies may even under-predict plant responses to climate change.The plants that flower earlier in the growing season typically advance more inresponse to warming than do later-flowering species, so the averaging ofphenological changes will not accurately reflect the full range of responses(Fitter & Fitter, 2002; Wolkovich et al., 2012; Hegland et al., 2009).