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Temperature is one of the many limiting factors that can determine the presence of life on earth. Other limiting factors include; sunlight, water, nutrients, oxygen, a balanced pH. Australian animals often have to cope with extreme environmental temperatures and have developed many different adaptations.

Chemical reactions that occur in cells take place only within a relatively narrow range of temperatures due to the sensitivity of enzymes. We have learnt that enzymes have an optimal range of temperatures at which they can function. For example, tissue temperatures greater than 42 are lethal to most organisms, as important enzymes begin to denature at this temperature, resulting in reduced ability to function.

As a result, organisms live within a specific temperature range to survive. Endotherms’ Temperature Tolerance. Organisms which regulate their internal body temperature are restricted to: Living in places where the temperature of the environment is within the range of temperature over which their enzymes work. Only being active at times when the environmental temperature is close to the optimum temperature of their enzymes.

Outside this range of temperatures, the enzymes would either be denatured, due to the temperature being too hot, or would be prevented from working by it being too cold. These species, which do not regulate their body temperature constantly, are called ectotherms. Many ectothermic animals have a limited ability to cope with different environmental temperatures. This is because they alter their body temperature using energy from the sun. For example, ectothermic species can bask in the sun to absorb the heat energy it provides. In many species a dark colour facilitates absorption of heat.

These animals move into the shade during hot periods to prevent overheating. Because of an ectotherms ability to change its metabolism with the environmental temperature, they can live in a wider temperature range, however they remain inactive when it’s outside their optimal temperature. This temperature range in which a species can survive is termed its tolerance range for temperature and is usually only a few degrees outside the range at which the organism is comfortable.

The great majority of living organisms are found in the 10°C to 35°C range and for each individual species the range is even narrower. Active plant growth in most plants occurs between 5-40°C. Below 0°C, cells risk ice crystals forming in them and above 45°C, proteins within cells may denature. Broad Temperature Range. The broad range of temperatures over which life is found. Life, in some form, can be found at extremes ranging from: -89°C, to 60°C in deserts. Up to 350°C (in hot vents in the sea) and in most aquatic environments (-2°C -30°C).

Some living organisms have a high tolerance for extreme temperatures. Species that occupy habitats with extreme conditions (such as very hot water, ice or extreme salt conditions) are sometimes referred to as extremophiles. For example the microorganism pyrolobus fumarii (hyperthermophilic microbe), grows optimally at 106°C in hydrothermal vents, and can withstand temperatures from 95°C - 113°C.

Thermophilic bacteria called spirochete live in sulphurs volcanic hot springs such as Champagne pool (NZ). This bacteria can move by twisting like a corkscrew. However, individual species cannot survive in an environment with a large temperature range; they need much narrower ranges. Why Organisms Live in a Narrow Temperature Range? Most species have a limited range of temperatures over which they can survive and reproduce.

Examples of Tolerance Ranges for Individual Species. Tolerance ranges for individual species. Water-holding frog 3 - 39°C, Platypus –8 - 34°C, Sydney blue gum Eucalyptus –1 - 34°C, Silky oak found in alpine regions 0 to 38°C.

The most heat-tolerant animal known is the Pompeii worm, discovered in the 1980s. They live in tubes on the sea floor near hydrothermal vents and they show extraordinary tolerance to an extremely wide range of temperatures—they have been recorded living in water with the tail end at 80°C and the head end at 22°C.

Research has shown Pompeii worms can withstand such extreme temperatures because of a fleece-like covering of bacteria on their backs. They have a symbiotic relationship with the bacteria—the worms secrete mucus from tiny glands on their backs to feed the bacteria, the bacteria protect worms from excess heat.

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