Environment if often described as the sum total of the living and non-living components. Environment is constituted by the interacting systems of physical, biological and cultural elements inter-related in various ways, individually as well as collectively. These elements may be explained as under:
Hence, an environment is the complex of physical, chemical, and biotic factors that act upon an organism or an ecological community and ultimately determine its form and survival.
Also, we should realise that the environment is not static. The biotic and abiotic factors are in a flux and keep changing continuously. The organisms can tolerate changes in environment within a certain range called ‘range of tolerance’.
Environments are not just natural; they can be artificial also. In several instances man has greatly altered the natural conditions and created new situations known as artificial or manmade environments. For example, cultivated fields or cities.
Ecology
Ecology is the scientific study of the reciprocal relationship between organisms, including microbes, plants, animals as well as man, with their environment. It deals with how the environment affects the organisms, how organisms utilise natural resources provided by the environment and how organisms interact with each other and in turn impact the environment. Everything that surrounds or affects an organism during its life time is collectively known as its environment.
Evolution of the concept
The term ecology was coined only as late as 1868. It has been derived from two Greek words namely, ‘Oikos’ meaning home or estate and ‘logos’ meaning study. Literally it means the study of the home or household of nature.
In India, ecological studies began as elsewhere with the descriptive phase at the end of the nineteenth century. Descriptive accounts of the forests were prepared by the forest officers (1875-1929). However, the first comprehensive ecological contribution was made in 1921 by Prof P. Dudgeon of Allahabad University who described the role of environment in the succession of communities.
Roots of Ecology
In primitive societies, people were required to know about their surroundings. The environment determined the human actions hence humans needed to understand their environment in order to survive. Take for instance, the advent of fire, activities like hunting and food gathering, migration to cope up with change in seasons, selective the sites for temporary or permanent settlement and start of agriculture, all this required deep understanding of the environment.
For that matter, all the major civilizations like the Indus valley civilisation, Mesopotamian civilisation, the Greeks, the Romans and the Maya could flourish only because they studies and understood the environment surrounding the.
Similarly, our ancient Indian classical texts like the Vedas, the Samhitas, the Brahmanas and the Aranyakas-Upanishads are full of references to ecological principles.
The Indian treaties on medicine like Charak Samhita and Sushruta Samhita show that people during this period had a good understanding of plant and animal ecology.
Subdivisions of ecology
Levels of ecological organisation
- Organisms: It is an individual basic unit.
- Population: It is defined as a group of freely inter breeding individuals of same species present in a specific area at a given time.
A population exhibits certain characteristics which can only be expressed at the population level and not shared by the individuals of the population. For example, individual organisms are born, grow and die but characteristics such as birth rate, death rate, density are only meaningful at the population level.
In analysing population, the main attributes studied is the density of the population which depends on four parameters: i) natality, ii) mortality, ii) immigration and, iv) emigration.
| Deme – Demes are geographically separated populations of the same species. Consequently, in a deme each individual has an equal opportunity of mating with another individual of the opposite sex, but not with individuals in another deme. Because of frequent . mating and similar environmental conditions members of a deme resemble each other more closely. |
3. Communities: In nature ‘an aggregation of populations of different species (plant and/or animals) in an area, living together with mutual tolerance and beneficial interactions amongst themselves and with their environment, form a biotic community.
We understand, that in a real ecosystem, individuals of one species is dependent on the individuals of the other species. Even plants cannot exist by themselves; for example, they require animals for , seed dispersal, pollination and soil microorganism to facilitate nutrient supply to them through decomposition.
Types of community:
a. Major Community: These are large-sized, well organised and relatively independent. They depend only on the sun’s energy from outside and are independent of the inputs and outputs from adjacent communities. A tropical ever green forest in the North-East of India is a good example of a major community.
b. Minor Communities: These are dependent on neighbouring communities and are often called societies. They are secondary aggregations within a major community and are not therefore completely independent units as far as energy and nutrient dynamics are concerned. A cow dung pad would be a good example of such a community.
In each community, a few over topping species are present in greater bulk. They have greater number or biomass (living weight) and are called as Dominant species. They modify the habitat characteristic and influence the growth of other species in the community. . In some communities, however, there may be more than one dominant species, as in oak-fir forest in the west Himalayas.
Species diversity is another important attribute of the community. The diversity is calculated both by the number of species (richness) and the relative abundance of each species (evenness).
| Relation between diversity and dominance: Species diversity is inversely related to the dominance aspect. Communities with one or a few dominant species are characterised by low species diversity whereas communities where no single species is truly dominant and individuals are equally distributed among all species. are characterised by high species diversity. |
Mutual relationship includes all the direct and indirect effects that organisms have upon each other in terms of competition, dependence and stratification.
Competition results because of the demand for a common resource by different organisms. Competition between individuals of different species is called interspecific; when it occurs between individuals of the same species it is called intraspecific.
Stratification refers to the layered arrangement of different species. Different organisms in a community develop a characteristic pattern of stratification to minimise competition and conflict among the members of the community. Plants and animals of each layer differ in size, behaviour and adaptation. In the tropical evergreen forest, this stratification can go upto five different layers.
Dependence refers to the fact that some species which are wholly dependent on the dominant member for survival. These dependent organisms require special conditions such as shade and moisture provided by the dominant species. The dependent species will die if the dominant species are eliminated. Animals in a community are usually dependent on plants. The feeding relationships among different members of the community are told by the Trophic structure.
4. An ecosystem is a community of living organisms along with their nonliving components that work and live together as a system. An ecosystem is defined as a network of interactions between organisms and the interactions between organisms and their environment.
5. A biome is a series of ecosystems that have relatively the same abiotic and biotic factors spread over a large area. The defining feature of biomes is their plant life. A desert’s plant life consists of cacti and other plants that have adapted to surviving with little to no water, whereas a tropical rainforest contains plants that require a large amount of water for survival.
6. The biosphere is a global ecosystem composed of living organisms (biota) and the abiotic (nonliving) factors from which they derive energy and nutrients.
