Thermoregulation in Desert Lizards - Essay Example

?Thermoregulation in Desert Lizards Introduction In the midst of changes in global temperatures due to global warming, concerns have been raised overhow the same affects thermoregulation in different species. More specifically, global warming has a far-reaching effect on thermoregulation in ectotherms. Among ectotherms, lizards inhabiting tropical regions are most likely to be affected since biodiversity in their habitats are most affected (Meek 1). Change in temperatures affects lizards in terms of thermoregulation mechanisms, energy expenditure, as well as biological activity. Investigation on how temperature changes, caused by global warming, are affecting lizards is of utmost importance especially considering that lizards are at a high risk of extinction. According to Huey et al, “Forest lizards are key components of tropical ecosystems, but appear vulnerable to the cascading physiological and ecological effects of climate warming, even though rates of tropical warming may be relatively low” (Huey et al 1939-1940). This paper explores the effect of global warming on thermoregulation mechanisms of lizards. Strategies to Thermoregulation of Desert Lizard According to theories of evolution, thermoregulatory mechanisms in many species especially reptiles has evolved with time in response to changing climatic conditions (Huey et al 1939-1942). Changes in climatic conditions cause increase in temperature variations forcing lizards to adopt both biological and behavioral temperature regulation mechanisms in order to cope with changing weather conditions. According to Meek, “The evolution of thermoregulatory behavior in reptiles almost certainly arose because environments are not usually thermally stable but fluctuate both on a daily or seasonal basis or because of uneven heat distributions within environments” (Meek 1). Meek hypothesized that any thermoregulation mechanism adopted by lizards comes at costs and benefits. For instance, lguanid lizard inhabiting high altitudes where temperatures are extremely low use ground vegetation for insulation. It was observed that the lizards could raise their body temperature to approximately 35degrees by basking on the sun for two hours. They could then return to their shelters and maintain their body temperature for the whole afternoon. However, such a thermoregulatory mechanism comes at a cost since the lizards remain inactive, minimal habitat utilization, and increased basking (Meek 1). These findings correlate with findings by Kearney et al “Warmer environments also may increase maintenance energy costs while simultaneously constraining activity time, putting pressure on mass, and energy budgets” (Kearney et al 1). One of behavioral mechanisms adopted by lizard is change of body color in relation to surrounding environment temperatures. According to Bradshaw, this type of behavior enables the desert lizard to maintain its body temperature in a normal range. As the temperature goes down the lizard turns into black. Black color is a good absorber of heat and hence it is able to absorb heat faster from the environment. Once the environmental temperature rises, light color becomes prominent. This turns the heat away and enables the lizard to cool its body. This explains why desert lizards are light in color as compared to lizards in cold regions (Bradshaw 90). Besides being a thermoregulatory mechanism, a study by Bujes and Verrastro found out that color change was also found to be a camouflage mechanism (Bujes and Verrastro 1). Activity of the Lizard in Different Seasons The most important factor in behavioral regulation of temperature in desert lizards is use of burrows. Indeed, different studies have pointed to the same fact that desert lizards spend almost 75% of their lifetime in burrows throughout annual season. These burrows offer temporary rescue or long-term survival mechanism. Lizards either dig their own burrows or use already existing ones (Bradshaw 166). Similar findings were found by “The activity of L. occipitalis throughout the year showed the following distribution: 73% of the lizards were found under sand, 14% were under vegetation, 7% were dislocating, and 6% were in basking” (Bujes and Verrastro 1). The high percentage, 73% of desert lizards living under sand is a precursor to the effects of rising temperatures due to global warming. Certainly, higher temperatures could lead to extinction of desert lizards since they will have already exhausted possible thermoregulation options. However, it is also interesting to note that some lizards have developed mechanisms for surviving under the sand. Others have scales on their ears to protect them once they burrow in the sand. Moreover, some lizards have scales on their eyes to protect them from sandy particles. Others have nose that are adapted for breathing once inside the sand (Bradshaw 102). Some use moist and humid environment for shelter such as Gila monsters in South America. Although many desert lizard species remain relatively active throughout the year, peak activity was recorded in early morning and late evening. According to Bujes and Verrastro “lizards kept themselves active from 7:30-8:00a.m. to 6:00- 6:30p.m., during the spring and summer. Two peaks of activities were observed during spring: the first, between 8:00 and 10:00a.m., and the second, between 12:00 and 3:00p.m” (Bujes and Verrastro 1). The daily variation is attributed to a shift in favorable conditions with seasons. Consequently, a rise in global temperatures could shorten these favorable conditions making it even more difficult for desert lizards to survive unless new thermoregulation mechanisms are adopted. Within the same study, Verrastro was quoted claiming, “Substrate temperatures limit the activities of the lizards during the warmest hours of the day, when they are confined to shadows under the grassy vegetation” (Bujes and Verrastro 1). We can posit further that longer hours caused by elevated global temperatures would correspondingly limit the amount of favorable conditions for desert lizards especially during the day. The effect of the Climate Change on the Behavioral of the Lizards Climate change has affected both animal and plant life. Some changes may be beneficial while others are detrimental to organism’s survival. Climate change affects lizard life significantly. Actually, lizards can be used in assessing effects of global warming, as their response to changes in body temperature is easily understood. Some tropical lizard species are active at low body temperatures and are unable to sustain their live in warm temperatures. These species experience stressful condition during summer. Increased temperature further affects their physiological performance in summer. Moreover, improved temperature in these forests will result into warm adapted predators occupying forest threatening their existence. This eventually will result to extinction of some lizard species (Huey et al 1944). Additionally, the goals of many ectotherms are to lower body temperature more than to raise it. This is mostly observed in desert areas where there is high reptiles are rich in diversity. Climate warming mostly affect vegetative cover thereby affecting availability of shades in Elevated temperatures reduce the activity of lizard as it embark on regulating body temperature. An increase in temperatures above the normal range has made it difficult for some lizards to modify their body temperature. This leads to a higher rate of evaporation from their body, which leads to excessive loss of water and an eventual death (Adolph and Porter Web). Moreover, the reproduction period of lizards has been affected by climate change as well. Lizard requires a specific amount of heat to be able to hatch eggs. Any extreme rise in temperature leads to eggs failing to hatch (Adolph and Porter Web). Conclusion It is clear that behavioral strategy adopted by lizards enables lizards to survive in extremes conditions in the desert. However, this strategy appears to be costly as desert lizards spends most of their time in burrows maintaining a normal range of their body temperatures. The rate at which global warming is taking place will affects this form of equilibrium and adaptation. Global warming leads to climate change which in turn will affect the quality of life and habitat of lizards and this could certainly lead to extinction. Additionally, the effect of climate change in the desert and other habitat can be assessed using lizard as a model organism due to its sensitivity to changes in its external surrounding. Although extensive research has been done on thermoregulatory mechanisms in lizards, more research needs to be done to investigate the exact rate of adaptation trends of lizards in response to temperature changes. This way, it would be possible to understand how long it will take for some lizard species to become extinct. Works Cited  Adolph, Stephen and Porter, Warren. “Temperature, Activity, and Lizard Life Histories.” The American Naturalist. Web. 14 May 2012. Bradshaw, Sidney Donald. “Vertebrate Ecophysiology: An Introduction to Its Principles and Applications.” London: Cambridge University Press, 2003. Print. Huey, Raymond et al. “Why Tropical Forest Lizards are Vulnerable to Climate Warming.” Proc. R. Soc. B. vol. 276 no. 1664. 1939-1948. 2009. Print.   Meek, Roger. “Reptiles, Thermoregulation and the Environment.” British Chelonia Group. Web 15 May 2012. . Bujes, Clovis and Verrastro, Laura. “Annual activity of the lizard Liolaemus occipitalis(Squamata, Liolaemidae) in the coastal sand dunes of southern Brazil” Iheringia, Ser. Zool. vol.98 no.1. 2008. Pdf. Kearney et al. “The potential for behavioral thermoregulation to buffer “cold-blooded” animals against climate warming.” PNAS, vol. 106. no. 10 pp. 3835-3840. 2009. Pdf.   Read More