CFE agenda 091117 - Laserfiche WebLink

Browse Search

2, I o l tlIf' /rrgor'Xcts ("'�( Tr'rrqoeran we SI-11(ts sl'oeclesarl / iahIMts The impacts of rising temperatures on terrestrial species and habitats will depend on a number of other climate change factors. However, there are a few key trends in extreme temperatures as well as shifts in growing season that may have a direct physiological impact on species and habitats or an indirect impact on community relationships through competition. The temperature range under which plants grow normally is 0 to 40 °C (Went 1953), but many plants have more specific temperature requirements beyond which significant damage can occur. Moderate tempera- ture increases can speed up plant growth as well as processes such as decomposition and nutrient cycling (Karl et al. 2009) Some of the largest shifts in terrestrial systems are observed in the timing of the seasons. Many species are flowering an average of four to five days earlier than they did in previous decades (Wolfe et al. 2005, Fitter and Fitter 2002), and experiencing longer growing seasons (Myneni et al. 1997). Increased temperatures may also cause shifts in the geographic distribution of species in places where temperature increases exceed physiological toleranc- es. In the northern hemisphere, shifts are expected to track temperatures, primarily along northward or elevational gradients (Parmesan 2006). Such range shifts are likely to result from population extinc- tions at southern latitudes or lower elevations and expansions at the northern range limits. This pattern has been observed in populations of Edith's check - erspot butterfly (Euphycdryas ecditha), which occurs in the western U.S. (Parmesan 1996). Iverson and Prasad (2001) looked at projected climate warming on tree distributions for 80 species occurring in the U.S., and showed that almost half would shift their ecological optima at least 100 km to the north. Most of the species included in their study either expand- ed or contracted their range in response to climate warming. In other cases, temperature may have significant effects on developmental pathways or behaviors influencing reproduction and survival. For exam- ple, sex determination in hard -shell turtles is largely temperature dependent (Bull 1980). A recent study on viviparous lizards occurring in Mexico linked local population extinction to loss of thermal niches (Sinervo et al. 2010). Their research suggests that high temperatures during the reproductive cycle affect foraging behavior and limit reproduction. Rising temperatures can also affect metabolic and growth rates in insects and other ectotherms (e.g., Dukes et al. 2009, Bickford et al. 2010), resulting in faster development and shorter lifecycles in some cases. Increased winter temperatures and frost -free days may also affect overwinter survival of some insects and pathogens (Dukes et al. 2009), result- ing in increased population sizes that contribute to outbreaks. Rapid changes in water temperature will have direct impacts on the physiology and metabolic rates of freshwater biota (Allan et al. 2005), which are domi- nated by cold - blooded organisms with no physi- ological ability to regulate their body temperature. Furthermore, the ability of freshwater organisms to move to new locations is constrained by the connec- tivity of streams and rivers within drainage basins. Eaton et al. (1995) reported maximum temperature tolerance estimates for 30 species of freshwater fish- es occurring in the U.S. (Table 2 -2). Temperature tolerance ranges are species specific, and the avail- ability of cooler waters may become limiting to some species in their current range in a warmer climate.