Reptiles in cold climates have to deal with extremely low environmental temperatures. They can only withstand these without damage by exposing their bodies to an appropriate thermal gradient (Fig. 5).
In Part A you simulated a number of different reptile behaviors to determine their effects on body temperatures. Now it is time to look at the results and analyse your findings.
In habitats where temperatures are high, but sunshine hours low, burrowing forms can help regulate reptile thermoregulation. Burrowing involves a considerable energy cost because the organism must produce more metabolic 크레스티드게코 heat and dissipate a significant amount of carbon dioxide. In some cases, burrowing animals may use their own body heat to generate the energy needed.
Thermoregulation can also be facilitated by the presence of environmental gradients in the soil. In intertropical humid forests, for example, reptiles can use the temperature gradients to control their body temperature. This is called thigmothermism.
For desert-dwelling reptiles, such as the flat-tailed horned lizard of Arizona and California and the Baja California legless lizard, thermal energy is obtained by lurching across sandy surfaces. These lizards have lost the ear openings that collect sand to reduce friction and are equipped with an unusual form of locomotion in which the body contacts the surface at only two points as it lurches across.
In some instances, a desert reptile will enter its burrow when the climate becomes extremely harsh, such as during a winter or a sultry summer. Such periods of inactivity, known as estivation or hibernation, have a profound impact on metabolism and body processes, but they can still ingest water and other nutrients from their environment. For instance 크레스티드게코 , tortoises can store more than 40 percent of their body weight in their urinary bladders. Some pythons can even shiver to generate their own body heat, which is an anomaly for ectotherms.
Reptiles that inhabit the semi-aquatic environment can use a number of different methods to regulate their body temperature. For example, they can evaporatively cool themselves by panting to lower their body temperature. Alternatively, they can bask on rocks or river banks to warm themselves up. They can also absorb heat through their scales. Some species of semi-aquatic terrapins spend long periods in the sun to elevate their body temperatures.
In some cases, the thermal gradients available to semi-aquatic reptiles are not as large as in polar regions but they do exist. For example, ponds and lakes may contain warm water from sources such as volcanic activity or solar heating. As a result, these environments can provide ideal conditions for reptiles to experience the optimum hypothetical climate.
On the other hand, the habitats of terrestrial chelonians offer a series of critical constraints on their thermoregulatory options. These conditions restrict their ability to escape from the conditions that would eventually cause them to die through heat stress. This is because the heavy armour of their shells prevent them from exchanging body heat rapidly with the environment.
These problems are also likely to reduce the precision with which a reptile’s internal thermal set point can be maintained. In environments where heat flow patterns are intermittent and difficult to access (high cost habitats) a reptile can be expected to have to make significant adjustments in its thermal regime on a daily or seasonal basis.
Intertropical humid forests
While reptiles possess a very large number of means to maintain their internal body temperatures at their preferred level, these methods must be adjusted according to the climate and habitat where they live. For example, a habitat with abundant sunshine and low ambient air temperatures requires an entirely different strategy to that of a tropical forest with a high number of sun hours but much lower ambient air temperature.
Similarly, sand-living reptiles such as the Saharan viper Cerastes are able to regulate their body temperatures to a remarkable degree by burrowing in the sand with only the head poking out. This allows them to achieve a body temperature of around 30 degrees Centigrade despite very large fluctuations in both ambient air and ground surface temperatures.
In laboratory experiments, where reptiles are kept in thermal gradient chambers with high temperatures at one end and cooler conditions at the other, they often exhibit a behaviour known as “bathing”. This is an attempt to maintain their core body temperature at its preferred level. However, this approach can be counterproductive, and in the long run it leads to a metabolic cost as the animal spends more time basking than necessary. In order to avoid this, it is necessary to develop behavioural strategies that allow reptiles to control their core body temperature without resorting to artificial means of achieving the desired state.
Thermoregulation is a key feature of the biology of reptiles. It helps to buffer effects of climatic change on these ectotherms, which make up a substantial portion of global biodiversity. This is important because climatic changes may impact the energy budget of these animals and reduce their activity, potentially leading to local extinctions. This is especially the case for reptiles that inhabit middle latitudes.
The ability to thermoregulate is a major adaptive advantage in these species, which typically experience large annual variations in temperature. Consequently, these animals must be able to cope with both cold in spring and autumn and heat in summer. This can be accomplished by adjusting their metabolic rate and by using natural thermal gradients to regulate their body temperatures.
In addition, a few nocturnal species such as the New Zealand gecko genus Hoplodactylus can also achieve their preferred body temperature by basking during the day. However, they are unable to use this strategy in a very cold region, where the temperature of the environment may be below freezing.
Nevertheless, a small number of reptiles living in the middle latitudes have been shown to be able to reach their preferred body temperature over extended periods of time, as demonstrated by continuous body-temperature records obtained using implanted dataloggers. This is particularly true for the New Zealand tuatara (Sphenodon punctatus). The data indicate that the voluntary hypothermia of this species can be modulated by light intensity, photoperiod, and climatic conditions.