Maintaining a Balance Topic 5: Temperature Regulation in Animals. Biology in Focus, HSC Course Glenda Childrawi , Margaret Robson and Stephanie Hollis. DOT POINT. Identify the broad range of temperatures over which life is found compared with the narrow limits for individual species
Biology in Focus, HSC Course
Glenda Childrawi, Margaret Robson and Stephanie Hollis
Temperature is one of the many limiting factors that can determine the presence of life on Earth. For example, tissue temperatures greater than 42C are lethal to most organisms as important enzymes begin to denature.
Extreme temperatures (above 100C ) denature not only proteins, but also nucleic acids. This destruction of DNA results in cell death. Its therefore not surprising that habitats that offer temperature conditions that are fairly stable are highly sought after and result in much competition.
Most living things live at temperatures between 10 and 35C. Active growth in most plants occurs between 5 and 40C. Some species of plants and animals have moved and adapted to occupy niches where temperatures fall outside the optimal range of temperatures over which life can be found.
The diverse array of living organisms on Earth are found across a broad range of temperatures. There are living creatures that can survive as low as -70Cor as high as 56C. Some bacteria can even survive at temperatures of 350C near deep ocean vents.
There is an enormous variation in temperatures over the Earth. The average variation in environmental temperature is more prominent on land (-89 to 60C). This vast range of temperatures found on Earth has been beneficial in allowing diversity of niches for species.
Much like enzymes, individual species have an optimal range of temperatures at which they can function. For each living species, this is a fairly narrow range. The temperature range in which a species can survive is called its tolerance range. It’s usually only a few degrees outside of the range at which it is comfortable.
The terms ectotherms and endotherms relate to the ability of an animal to regulate its body temperature. ‘Therm’ relates to temperature, ‘ecto’ means outside and ‘endo’ means inside.
Ectothermsdepend on an external source (the environment) for heat energy. Fish, amphibians, reptiles and most invertebrates fall into this category.
Endotherms rely on internal sources for energy such as metabolic activity. Birds and mammals are all endothermic.
The body temperature of ectotherms fluctuates over a smallrange of temperatures. It is influenced by the ambient temperature (temperature of the environment) and the organism has only a limited ability to control its body temperature.
In nature, these organisms adapt their behaviour to regulate their body temperature and so if it is measured in the wild , their body does not show as wide a range of fluctuation. Scientists can do this using a radio telemetry device.
Brown snakes are found across most of Australia, inhabiting a range of habitats from open grasslands to desert scrub, but not in rainforest areas.
Brown snakes are usually diurnal (awake during the day). If the ambient temperature rises beyond the brown snake’s tolerance level, it will seek shelter in the shade during the day and become active in the later part of the day when it is cooler, or even at night.
If the ambient temperature drops below the optimum range, brown snakes bask in the sunlight to gain additional heat. In very cool weather, the snake becomes less active, slowing down its metabolism and uses fat reserves. If the cold period is prolonged, the snake will hibernate in a sheltered spot.
Under laboratory conditions and in nature, the body temperature of an endothermic organism tends to remain stable despite variation in the ambient temperature. An endothermic organism has the ability to control its body temperature and maintain it at a stable level within a very narrow range.
In low ambient temperatures, the main source of heat in the body of endotherms is that generated as a result of the metabolic activity of their cells, particularly the muscle and liver cells. The size of the animals body also plays a significant role.
Some endotherms have special heat-producing tissue called brown fat, which can be quickly metabolised in cold conditions. The common bentwing bat produces brown fat in late summer and through autumn when food is abundant. In the cold winter months, the brown fat is metabolised and used to increase body temperature, allowing these bats to fly after periods of hibernation.
If the ambient temperature is high, endotherms have a physiological cooling mechanism as well. The rate of heat loss from the body can be adjusted by altering the flow of blood near the surface.
Evaporative cooling such as sweating, panting or licking saliva onto the body surface is a common cooling mechanism. Evaporative cooling brings with it the risk of water loss. Animals that live in hot, dry climates have to develop mechanisms for cooling that do not allow too great a loss of water.
Endotherms also show adaptations in their behaviour to help regulate their body temperature. Body temperature in humans is approximately 37C and that of birds is 40C (these may fluctuate within about 1.5C).
The fairy penguin is found along the southern Australian coastline and in Tasmania and New Zealand. It is the smallest of all penguins and lives in burrows in coastal sand dunes, not in the ice and snow like most penguins.
Fairy penguins have feathers that provide an insulating layer. These feathers trap a layer of air close to the skin which reduces the amount of heat lost. This layer of air can be altered depending on the ambient temperature.
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