Rotation of earth around the sun and its tilt along its axis causes annual variation in the intensity and duration of temperature, which results in distinct seasons. When Compounded with latitudinal and longitudinal variation in precipitation and temperature , this gives rise to formation of major biomes such as deserts , rainforest and tundra.
There are a wide variety of habitats which are the result of regional and local variations within each biome. So the natural question that arises is what are the key elements that lead to so much variation in the physical and chemical conditions of different habitats?
The most important ones are temperature, water, light and soil (abiotic). We must remember that the abiotic components alone do not characterise the habitat of an organism completely; the habitat includes biotic components also – pathogens, parasites, predators and competitors – of the organism with which they interact constantly.
Major Abiotic factors and their significance in species distribution
- Temperature is the most important environmental factor that is responsible for variations in the habitat as well as the species that reside in such habitats. Temperature affects the basal metabolism of organisms. With reference to capacity of tolerance to temperature range there can be two categories of organisms. A few organisms can tolerate and thrive in a wide range of temperatures (eurythermal) for ex. Humans , Monkeys etc, but a vast majority of them are restricted to a narrow range of temperatures (stenothermal) for ex Penguin, Polar beers . The levels of thermal tolerance of different species determine to a large extent their geographical distribution.
- Water is another important factor in deciding the species distribution. Availability of water decides the adaptations needed by an organism to survive in a particular habitat for ex. Adaptation in Desert biome. Similarly productivity and distribution of plants heavily depends upon availability of water. Quality of water in terms of salinity and chemical composition also act as a deciding factor in distribution of species. Some organisms are tolerant of a wide range of salinities (euryhaline) but others are restricted to a narrow range (stenohaline). Many freshwater animals cannot live for long in sea water and vice versa because of the osmotic problems they would face.
- Light and its availability is particularly vital for the autotrophs which depend on it for their source of energy and for producing food through photosynthesis. Many plants are also dependent on sunlight to meet their photoperiodic requirement for flowering. For many animals too, light is important in that they use the diurnal and seasonal variations in light intensity and duration (photoperiod) as cues for timing their foraging, reproductive and migratory activities.
- Soil and their properties exhibit spatial variation in terms of their composition, grain size and water holding capacity which in turn determine the vegetation in any area. This in turn dictates the type of animals that can be supported.
See also: Definitions : Ecology, Environment, Ecological hierarchy
