The following points highlight the top four abiotic factors that influencing habitats. The factors are: 1. Temperature 2. Pressure 3. Radiation 4. Light.
Factor # 1. Temperature:
Life can exist within a narrow range of temperature. Even within this narrow range, temperature tolerance of various species of animals varies. The temperature tolerance of a given species at different stages of its life history may vary. The narrow range of tolerable temperature for animals can be distinguished into three levels.
These levels are:
(i) Maximum temperature:
The maximum temperature at which some organisms are known to survive is about 88°C. Hot springs often bear a temperature of this kind. Living bacteria have been found in such hot springs. Cysts of protozoans and seeds can withstand this temperature.
Multicellular blue algae live successfully in waters of Yellowstone National Park in Wyoming at a temperature of 85°C. The maximum temperature that can be tolerated by most of the animals ranges between 40°C. -45°C. One species of snow algae dies when the temperature rises above 4°C.
The death of animals at a temperature above the lethal maximum is due to a number of factors. The protein of the cells in most cases becomes denatured or coagulated at high temperatures. The chemical composition and reaction of the chemicals in the protoplasm also change at high temperature.
(ii) Minimum temperature:
The minimum temperature that life can withstand is dependent upon certain physiological adaptations of the organisms concerned (Fig. 3.5). Studies in this line have been made with the animals of north-temperate regions.
The study has recognised three types of animals:
(a) Those which can survive in temperature approaching absolute zero (—273°C.),
(b) Those that die at or near the freezing point (-4°C.) and
(c) Lastly those that die at some temperature level above the freezing point. It has been observed that death is due to the freezing of body fluid.
Animals included in the first group are cysts of Protozoa, Rotifers, Nematodes. The second group includes the ectothermic animals. Ectothermic animals are those which have little or no ability to maintain a body temperature above that of surrounding environment. The third group includes mammals and birds where body temperature is independent of environmental temperature.
(iii) Optimum temperature:
Optimum temperature lies between the two lethal limits of temperature and at this temperature life processes function smoothly. It is to be remembered that optimum temperature is not midway between the maximum and minimum levels for a given animal but it lies nearer the maximum end of the range.
Factor # 2. Pressure:
Animals are found in all available habitats. They have extended their domain from high mountain tops to the deepest part of the ocean. The average pressure on a high mountain top is less than one atmosphere while that in the deepest part of the ocean is about one thousand atmosphere? Since one atmosphere is about 14.7 lbs per square inch at sea level living organisms experience pressures of less than a pound to more than 14,000 pounds per square inch.
Of course, no single species is found over this entire range. Because of this pressure factor most animals remain confined within the range of pressure that it can withstand. In an indirect way lower pressure is harmful because of lowered oxygen availability. In a direct way, it is harmful in the case of deep-sea fishes which may literally burst when exposed to surface.
Factor # 3. Radiation:
The sun emits rays ranging from short ultra-violet rays through the range of radio waves, solar flares and X-rays. Most of the X-rays and ultraviolet rays become filtered out while passing through the atmosphere round the earth.
Besides these, radiations of particulate nature composed of Alpha and Beta particles, protons, neutrons and mesons are also emitted by the sun. Several of these together with Gamma rays constitute the cosmic rays which reach us.
Moreover, disintegration of radio-active elements emits Gamma rays and X-rays. Particulate radiations, X-rays and Gamma rays have damaging effects on the protoplasm. X-rays, however, can be tolerated in small doses.
Under careful medical supervision, X-rays in small doses is used in the cure of localised tissue growths, tumours and warts. Many animals require ultra-violet rays for the activation of vitamin D. Too much ultra-violet rays cause sun-burns and too much of it is lethal to unicellular animals.
The infra-red light is important for the life, because in this particular band of light 60% of the solar energy remains concentrated. Our earth is bombarded with radio waves of different kinds. Most of the waves have no effect on the biological system. Most of them irritate us by interfering with our own radio communication.
Factor # 4. Light:
Light is essential in most animal habitats because the process of photosynthesis is directly dependent upon light and without photosynthesis food resources cannot grow. It is a popular saying that cows are assimilating grass and grass is assimilating sunlight, carbon dioxide, water and salts.
Light brings advantages as well as disadvantages in every habitat. Light undergoes diurnal and seasonal variation and influences the behaviour of animals in many ways.