Environment: Meaning and Scope

The environment of any organism is the sum total of everything that surrounds it and can affect its growth, survival, reproduction, and behaviour. Ecologists conventionally split the environment into two broad, interacting components.

The abiotic component consists of the non-living, physical and chemical factors of the surroundings. The most important of these are temperature, water (availability, quality, and salinity), light (its intensity, quality, and duration), and soil (its texture, mineral composition, pH, and topography). These factors vary enormously across the earth -- from the near-boiling hot springs of the Himalayan foothills to the permanently sub-zero polar ice caps, from the humid rainforest to a bone-dry desert -- and it is this variation that ultimately explains why different regions of the world support such strikingly different communities of plants and animals. An organism cannot survive outside the range of abiotic conditions to which its physiology is adapted.

The biotic component consists of all the living organisms present in an area -- plants, animals, fungi, and microbes -- along with the network of relationships they form with one another: who eats whom, who pollinates whom, who competes with whom for the same resource, and who lives on or inside whom. A single organism, therefore, does not experience the abiotic world in isolation; it experiences an environment that is simultaneously shaped by physical conditions and by the presence and activity of other living things around it.

Ecology is the branch of biology that studies these relationships -- between organisms and their abiotic surroundings, and between organisms and other organisms. It is conventionally organised as a hierarchy of increasing scale: the individual organism, the population (a group of individuals of one species sharing an area), the community (all the populations of different species living together and interacting in an area), the ecosystem (a community together with its physical environment, linked by energy flow and nutrient cycling), and finally the biosphere, the global sum of every ecosystem on Earth. This chapter of the WBCHSE syllabus is concerned mainly with the organism and population levels of this hierarchy: how a single organism copes with its environment, and how a population of such organisms behaves, grows, and interacts with other populations sharing its habitat.