**2.1.1 Physiological performance**

There are basic physiological aspects of amphibians that are highly sensitive to temperature increase; first water balance due to their permeable skin and high evaporation rates (Shoemaker et al., 1992), second since amphibians are poiquiloterms1, the thermoregulatory performance are related to the water balance, digestion, oxygen supply, vision, hearing, emergence from hibernation, development, metamorphosis, growth, and immune response. Amphibians do not perform physiological process when they are near of their critical body temperatures, instead they are able for perform many functions in suboptimal temperatures and do not exhibit a unique thermal optimum. Therefore, temperature may strongly influence on species' geographic distribution, so on the amphibian's distribution limits are determined by the extreme temperatures, in consequence the species that with broad tolerance to thermal regimens should be able to expand their ranges and then colonize new habitats. Finally, the two processes that are more sensitive to changes in temperature in amphibians are reproduction and development (Berven et al, 1979; Rome et al., 1992). The hormonal regulation of reproduction are affected by temperature, then an increase in temperature could affected the reproductive cycles of amphibians due to changes in the concentration of the hypothalamic hormone (GnRH) which acts directly on the gonads (Herman, 1992; Jorgensen, 1992).

Considering the information presented above, there are four aspects of climate change that could strongly affect the physiological performance in amphibians: 1) temperature increase,

 1For which the temperature determines the appropriate functioning of many processes that have different thermal sensitivities.

Amphibians are very susceptible to environmental variation since they have permeable skin, eggs without shell (not amniotic eggs), and a complex life cycle that expose them to changes in both the aquatic and terrestrial environment (Blaustein, 1994; Blaustein & Wake, 1990, 1995; Vitt et al., 1990), also they are particularly sensitive to changes in temperature and humidity, as well as to exposure to large doses of UV radiation (Blaustein & Bancroft, 2007). During the last twenty years a decline o of more 500 populations of frogs and salamanders has been documented (Stuart, 2004; Vial & Saylor, 1989). The reasons for this decline stills unclear because of the factor complexity and their interactions (Alford & Richards, 1999; Blaustein & Kiesecker, 2002; Kiesecker et al., 2001). However many cases of species decline share ecological traits, life histories or demographic traits such as: 1) high habitat specialization, 2) reduced population size, 3) long generation time, 4) fluctuating abundance, 5) low reproductive rate, and 6) complex life cycles. These characteristics suit species more vulnerable to threats (Reed & Shine, 2002; Williams & Hero, 1998). The traits alone may not cause the decline, but cause that organisms become more vulnerable after an initial perturbation like the rise of environmental temperature (Lips et al., 2003). Climate change may have adverse effects by itself on the survival, distribution, reproductive biology, ecology, physiological performance, and immune system of organisms when they are exposed to higher environmental temperatures or dryness (beyond their threshold of tolerance). Also, the effects of climate change could act in synergy with various biotic and abiotic agents like diseases and infections, intense UV radiation, habitat loss, exotic species (competitors and depredators), and chemical pollution (Young, 2001, as cited in Lips et al.,

There are basic physiological aspects of amphibians that are highly sensitive to temperature increase; first water balance due to their permeable skin and high evaporation rates (Shoemaker et al., 1992), second since amphibians are poiquiloterms1, the thermoregulatory performance are related to the water balance, digestion, oxygen supply, vision, hearing, emergence from hibernation, development, metamorphosis, growth, and immune response. Amphibians do not perform physiological process when they are near of their critical body temperatures, instead they are able for perform many functions in suboptimal temperatures and do not exhibit a unique thermal optimum. Therefore, temperature may strongly influence on species' geographic distribution, so on the amphibian's distribution limits are determined by the extreme temperatures, in consequence the species that with broad tolerance to thermal regimens should be able to expand their ranges and then colonize new habitats. Finally, the two processes that are more sensitive to changes in temperature in amphibians are reproduction and development (Berven et al, 1979; Rome et al., 1992). The hormonal regulation of reproduction are affected by temperature, then an increase in temperature could affected the reproductive cycles of amphibians due to changes in the concentration of the hypothalamic hormone (GnRH) which acts directly on the gonads

Considering the information presented above, there are four aspects of climate change that could strongly affect the physiological performance in amphibians: 1) temperature increase,

1For which the temperature determines the appropriate functioning of many processes that have

**2.1 Amphibians** 

2003).

**2.1.1 Physiological performance** 

(Herman, 1992; Jorgensen, 1992).

different thermal sensitivities.

2) the increase of the dry season length, 3) decrease of soil moisture (due changes of precipitation and temperature rise), and 4) increase in rainfall variation. This would affect organisms at population and community levels. As an example Carey & Bryant (1995) found that the individual growth rate, reproductive effort, and life span could change, with a parallel change in the activity patterns, microhabitat use, and thermoregulation.
