Ecology is the branch of biology which deals with the study of interaction between organism and environment.Ecology deals with four levels of biological organisation such as organism, population, community and biome.
Within each biome, there exists a wide range of habitats.A habitatis a specific place or locality where an organism dwells.A particular area occupied by an organism in its habitat is called niche.Major habitats of world’s aredesert, rainforest, oceanic trenches, Polar Regions, sea coast etc. The most important abiotic factors of the environment are temperature, light, water, and soil.
The maintenance of a constant internal environment called homeostasis by the organisms contributes to optimal performance. But only some organisms (regulators) are capable of homeostasis in the face of changing external environment
To manage different stressful abiotic conditions, organisms respond to them and regulate, conform, migrate and suspend. In animals, the organism who is unable to migrate might avoid stress by escaping in time such as hibernation and aestivation.
Some species have evolved adaptations to avoid unfavorable conditions.
Apart from these physiological responses some organisms show behavioral response to cope with variations in their environment. A population is a group of individuals of a given species sharing or competing for similar resources in a defined geographical area.
A population has certain attributes that an individual organism does not, for example an individual may have births and deaths, but a population has birthrates and death rates, sex ratio and age distribution. The proportion of different age groups of males and females in a population is graphically represented by age pyramid.
The effect of any ecological factors on a population is generally reflected in its population density.

The population density can be expressed in numbers, biomass etc depending upon species. When resources are unlimited, the population growth show exponential growth but when resources becomeprogressively limiting, the population growth show logistic growth.  In eithercase, growth is ultimately limited by the carrying capacity of theenvironment.

In nature, animals, plants and microbes cannot live in isolation but interact in various ways to form a biological community. Interspecific interactions arise from the interaction of populations of two different species.

Depending on the outcome, these interactions between two species are classified as competition (both species suffer), predation and parasitism (one benefits and the
other suffers), commensalism (one benefits and the other is unaffected), amensalism (one is harmed, other unaffected) and mutualism (both species benefit).

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