 |
| Edaphic Factors |
|
| These include |
| |
 Soil and substrate |
| |
 Topography |
| |
 Minerals |
| |
 pH |
| |
| Soil |
| |
| The word soil is derived from the Latin word solum meaning earthy material in which plants grow. The science which deals with the study of soil is called Soil Science, Pedology (pedos = earth) or edaphology (edaphos = soil). The process of formation of soil is called pedogenesis. A soil complex is formed of 5 categories of components namely mineral matter, organic matter or humus, soil water, soil air and living organisms. The quality of soil is due to its fertility, texture, structure, organic contents and air - water relationship. |
| |
| Soil profile |
| |
| The vertical layered structure of soil is called the soil profile. There are 4 main horizons in a soil profile. |
| |
| O - horizon is the organic layer composed of dead organic residues. |
| |
| A - horizon is the top soil, the upper most layer which contains roots. |
| |
| B - horizon is the sub soil. |
| |
| C - horizon is the less weathered parent material. |
| |
  |
| Comparison of soil profile |
| (a) temperate deciduous forests (b) tropical rain-forests |
| |
| The organic matter in the soil is of 2 types. |
| |
| 1. Freshly dead and partially decomposed plant and animal material called litter or detritus |
| |
| 2. Colloidal, amorphous and dark coloured humus. |
| |
| Soil helps in |
| |
 providing water and minerals to the land plants |
| |
 It acts as a substratum for a variety of organisms like bacteria, fungi, many kinds of animals and plants. |
| |
 It is the site for decomposition of plants and animals. |
| |
 It provides water, minerals and fossil fuels to man. |
| |
| The type of soil (clayey, sand and loamy) and its water retention aeration and mineral contents determine the nature of plants and animals. On the basis of these characters of soil, the plants are divided into 5 ecological categories. |
| |
| Halophytes - plants found on saline soil |
| |
| Psammophytes - plants found on sandy soil |
| |
| Lithophytes - plants found on rocky surface |
| |
| Chasmophtyes - plants found in rock - crevices |
| |
| Oxylophytes - Plants found on acid soils |
| |
| The ground dwelling animals which may be cursorial (running) such as ostrich, rhea, ungulates, wolves, cats, bears, hyaenas etc, saltatory (jumping) such as rodents, rabbits, wallabies, kangaroos or graviportal (heavy) such as turtles armadillos, elephants etc exhibit different kinds of adaptations for different kinds of soil. For E.g., if the soil is firm and hard, the large animals inhabiting the ecosystem tend to have small hooves or paws. If the soil is wet and spongy, they tend to have broad hooves or paws. |
| |
| Topography |
| |
| Topography includes the physical features of the earth like altitude, slope, exposure, mountain chains, valleys, plains, etc. |
| |
 |
| |
| Marked variations in temperature at different altitudes result in the division of earths vegetation into different zones such as equatorial, tropical rain forests, desert or grasslands, deciduous forests, coniferous forests, tundra, ice and snow of poles. |
| |
| Height above sea level forms the altitude. At high altitudes, the velocity of wind remains high, temperature and air pressure decrease, humidity as well as intensity of light increases. Due to these factors, vegetation at different altitudes is different showing distinct zonation. |
| |
| The directions of mountain chains or ranges and high mountains act as wind barriers and affect the climate and rainfall and other factors which have a significant effect on the growth of vegetation and the distribution of animals. |
| |
| Slope is the characteristic feature of mountains. The steepness of a slope has a distinct effect on the climate of the area, namely the incidence of solar radiations, rainfall, wind velocity and the temperature of the region. Steepness of the slope decides the rapidity with which water flows away from the surface and determines the characteristic of the soil. A slope remains exposed to the sun and wind and this affects greatly the kind of plants growing there. |
| |
|
| |
| Minerals are also called as biogenic materials and are essential for the proper growth of organisms. So the type and distribution of plants and animals are determined by specific distribution of minerals. Deficiency or absence or excess of minerals results in abnormal growth or even death of organisms. To derive the required nutrients, organisms are adapted differently. |
| |
| Examples: |
| |
| a) Plants found in nitrogen - deficient bog soil have either nitrogen fixing bacteria or become insectivorous. |
| |
| b) Snails occur in soils rich in calcium content to form their shell. |
| |
| c) Halophytes and many marine animals have salt secreting glands. |
| |
| d) Leguminous plants like pea, gram methi show symbiosis with nitrogen fixing bacteria in their root nodules. |
| |
| High concentration of minerals generally limits the distribution of animals. |
| |
| Example: Dead sea is devoid of vegetation because of high salt content. |
| |
 pH is the relative acidity or alkalinity of medium. Every organism needs a specific pH called optimum pH for its optimum growth. Some organisms prefer alkaline medium (more than pH 7). For example prtozoans and molluscs, where as some organisms prefer acidic (less than pH 7) |
| |
| For example euglena and other pyhtoflagellates flourish in water having pH 2.8. Still other forms can survive in a wide range of pH. |
| |
| For example tapeworm (pH range from 4 to 11). |
| |
| Fire |
| |
| Fire has important effects on the environment. Fire removes plant cover, burns litter on the soil surface and causes loss of nutrients. Due to forest fires a variety of animals groups die. |
| |
| Range of tolerance |
| |
| Plants and animals show a range of tolerance to environmental factors. The factor, which is present in least amount may become limiting. For example water availability limits plant growth in deserts. |
| |
| But, not only “too little” of something is a limiting factor, even “too much” may be the limiting factor. |
| |
 |
| The response of an organism to a range or gradient of an environmental factor |
| |
| The organisms are abundant in the central optimum range. In the zone of stress, only a few organisms survive and in the zone of intolerance, organisms are absent. |
| |
| If the organism has wide range of tolerance, it is usually distributed and if its tolerance range is narrow it is restricted. |
| |
| The gradual adjustment of an organism to slowly changing new environmental condition is called as Acclimatisation. |
| |
