BIOLOGY Volume 2 - A Guide to General Biology - 2004

19. HOMEOSTASIS

19.3. Thermoregulation

19.3.4. Effect of temperature on animal growth and distribution

Temperature affects metabolic rate in animals in various ways.

1. The primary Effect of temperature lies in its influence on enzyme activity and the velocity of atomic and molecular motion. This directly affects the growth rate of animals (ch. 22).

2. Temperature can indirectly determine the Geographical Distribution of animals through its impact on plants as primary producers in food chains. The habitat ranges of most animals are determined by the availability of local food resources. Exceptions include certain insects, birds, and mammals capable of migration.

The Diversity of Animal responses to temperature depends on: 1) the degree of environmental temperature stability, and 2) the ability of a given species to regulate its body temperature.

It is believed that life originated in the marine environment, where animals faced few problems related to temperature fluctuations, as these variations in the sea are negligible. Living in relatively constant temperature conditions, aquatic organisms are much less sensitive to cooling and heating than terrestrial species. In most aquatic organisms, including invertebrates and fish, body temperature fluctuates along with Water temperature, although some highly active fish (such as tunas) are able to maintain a higher temperature through muscular activity.

Another important factor in the aquatic environment is that water reaches its maximum density at 4 °C; therefore, at 0 °C it freezes only at the surface, and the resulting ice does not sink, forming a thermal insulation layer that usually prevents water bodies from freezing to the bottom. Consequently, many aquatic animals remain active during times when terrestrial species would be unable to maintain activity due to sub-zero temperatures.

Air has a relatively low heat capacity, so its temperature can fluctuate significantly even over the course of a single day. One of the challenges associated with the colonization of land by animals was the difficulty of adapting to these temperature fluctuations. The necessity for such adaptation led to the evolution of diverse physiological, structural, and behavioral features and served as a major factor determining the geographical Distribution of Animals. The Nature of these adaptations and Examples thereof will be discussed in subsequent sections.