Are they ready against climate change??
All species have an ecological niche within which its conditions for survival are met. From among the many different niche parameters that determine the fate of an organism, temperature assumes special significance, particularly in the present times when effects of climate change and the resulting increases in ambient temperatures have been reported. We can see relationship between amphibians and climate change. In this backdrop, understanding the stability of a species’ environmental niche is crucial for predicting a species’ response to climate change (Pearman, Guisan, Broennimann, & Randin, 2008).
It has been suggested that the fundamental niches of some species might evolve and change rapidly which may allow for an attenuation of the current effects of global change on ecosystems (Hoffmann & Sgrò, 2011; Hoffmann & Willi, 2011). Assessing the differences between species and between populations of the same species that occupy geographically disjunct regions, would provide an insight into the ability of species to adapt to climate change (Pearman et al., 2008; Wiens & Graham, 2005).
Ectotherms encompass most of the terrestrial and aquatic biodiversity and so would predictably, show greater sensitivity to temperature fluctuations, since their basic physiological functions, development and behaviour, are closely associated with the ambient temperature (Novo, 2009). For amphibians, it is important to have moist skin or/and to be aquatic to regulate their body temperature (Brattstrom, 1979). Because amphibians have varying body temperatures, which are highly dependent upon the ambient climate temperature, they are ideal models for characterizing effects of temperature on behaviour and physiology (Du, Lu, Shu, & Bao, 2007). In general, the rate of biochemical processes doubles with a 10 °C rise in ambient temperature.
Thus, as anurans are exposed to daily or seasonal changes in temperature, their rate of muscle contraction and the rate of nerve impulse conduction may change, in turn influencing important survival traits such as anti-predatory behaviour and foraging efficiency. Any deviations from the typical patterns induced by unexpected changes in ambient temperature would, particularly in the long term, have serious negative implications on the fitness of the species (Putnam & Bennett, 1981).
Effect of Environmental Temperature
Temperature is an important environmental parameter that influences all metabolic functions in organisms, which in turn govern changes in physiology, behaviour and biochemical processes (Gaitán-Espitia, Arias, Lardies, & Nespolo, 2013). It affects animals at all levels of organization from cellular and enzymatic processes to whole animal performance (Young & Gifford, 2013).
Amphibians achieve a thermal balance, to be safeguarded from high ambient temperatures which cause additive discomfort enhancing the stress levels, which in turn can cause depression in physiology and metabolic activities of the animal. Hence, amphibians have evolved different physiological adaptations to protect from extreme temperature fluctuations. As they cannot produce their heat by themselves, they depend upon behavioural mechanisms to capitalize on environmental processes of the environment. For instance, anurans increase their metabolic rate and heart rate with rising temperature (Barcroft & Izquierdo, 1931). Some species demonstrate physiological acclimation, a strategy for surviving long term or seasonal temperature fluctuations (Young & Gifford, 2013).
Anurans perform various forms of locomotion such as jumping and swimming, foraging, sitting, waiting and hiding, during their daily course of activities (Putnam & Bennett, 1981). Locomotor performance is a crucial ecologically relevant parameter since it affects the success of reproduction, foraging and predator evasion abilities of an individual (Cortes, Puschel, Acuña, Bartheld, & Bozinovic, 2016; Garland & Losos, 1994). The majority of Sri Lankan toad species are nocturnal and are active at night, but some frog species (e.g. Euphlyctis cyanophlyctis)show both diurnal and nocturnal activity. Depending on the species and their behaviour patterns and the ambient temperatures to which they are exposed, an anuran may undergo daily fluctuations in their metabolic responses thus resulting in interspecific variability in circadian rhythms (Dunlap, 1969).
Relationship with Geographical Locality
According to the findings of Bennett and Licht (1974) bufonids (terrestrial toads) have limited ability to escape from predators in comparison to the ranids (aquatic frogs) due to the more powerful jumps of the latter group. Locomotor performance has been shown to generally improve as one moves from low to moderate temperatures but decreases at higher temperatures (Navas, Úbeda, Logares, & Jara, 2010). Some extreme temperatures impede enzymatic reactions that reduce muscle contraction, which ultimately affect locomotion (Bennett & Huey, 1990).
The extent to which species are affected by climate change and the associated elevations in temperature depends upon the physiological sensitivity of organisms (Deutsch et al., 2008). Accordingly, for ectotherms, their thermal sensitivity as it is linked to performance would be impacted by an elevation in the temperature beyond their limits of tolerance. It has been reported that populations living in higher altitudes would have better thermal tolerance since; generally, the ambient temperature lies below the physiological optima so that any increase in the ambient temperature would result in increased fitness. On the contrary, for those in warmer climates, whose physiological optima is generally below the ambient temperature, a rise in ambient temperature would result in reduced performance and fitness leading to detrimental consequences.
According to the predicted climate change data, global environment temperature is estimated to increase by about 6.4 °C on average in the present times (Challinor, Wheeler, Garforth, Craufurd, & Kassam, 2007). Deutsch et al. (2008) report that tropical amphibian species are more susceptible to climate warming. They explain that warming will cause tropical ectotherms to reach their critical maximum temperature proportionately faster compared to similar species at a higher latitude. For species that can acclimatize (over the short term) or specialize (over the long term) such impacts will be less detrimental (Stillman, 2003). However, also of importance is the rate of increase in the global temperature since a species or a population would require adequate time to change through adaptive evolution, acclimatization or at the extreme migration.
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