The word ecology comes from two Greek words meaning 'home' and `science'; thus ecology is the scientific study of animals and plants in their homes or natural habitats. Plants and animals live together in communities: an oak wood, a stream, an area of heathland or a rock-pool by the sea- shore are all examples of ecological communities.

Ecology deals with the relationships, or links, between the various animals and plants that live in such a community or habitat. It is also concerned with the way in which the various creatures living in any habitat are affected by such things as the soil, the climate and man's activities. Many dozens of types of plants and animals live together in a hedgerow community. If the hedge itself is of hawthorn its leaves will provide food in summer for many caterpillars, and these in turn will be eaten by small birds such as blackcaps, who use the protection provided by the hedgerow for their nests. Spiders may spin their webs between the outer twigs of the hedge. In autumn and early winter the 'haws' are eaten by birds such as thrushes, fieldfares and redwings. Mice eat the stones of the hawthorn fruit, sometimes hoarding them in old birds' nests. Sometimes hedges are planted along the crest of a low bank. Often a ditch runs along the base of a hedge. In a very small area therefore there may be a great deal of variation both in the dampness of the soil and the amount of sunlight received, so that many different types of wild flowers, such as foxgloves, primroses and fool's parsley brighten the hedgerow community in the spring or summer. 

Plants and animals have to adapt to their environment and way of life in order to survive. Cacti living in desert areas of America, where there is no rain for long periods, have fleshy stems which are able to take in large quantities of water after a sudden rainstorm and to store it for a long time. The mole, living underground, has very small eyes and strong shovel-like limbs for burrowing through the soil.

Many animals are camouflaged - coloured in such a way that they merge into their background and are difficult to see. The ground in heathland areas is frequently covered with fragments of bracken- fronds and heather twigs, and several ground-nesting, heathland birds, such as the nightjar, have grey- brown, speckled plumage so that when sitting on their nests they are almost invisible.

Similarly, the hind wings of a grayling butterfly are coloured in a way that resembles the light and dark greys of a piece of bark. When the butterfly settles on an old branch or a dried leaf, it seems to disappear!

Birds nesting amidst the sand and shingle of a seashore often have blotched or speckled light- coloured eggs that are very difficult to see. You can be within a few metres of a ringed plover's nest for an hour without finding it.

The management of land, water to maintain or enhance the plants and animals that they support requires knowledge of the ecosystem and its species. This is an aspect of applied ecology known as conservation

Thus the replanting of forests at the same rate that they are felled, and the use of the forests for wildlife protection and outdoor activities as well as for timber growing, are examples of conservation.

Ecological principles are also applied to conserve sustainable cropping of land and water.  The planting of the same crops on farmland year after year exhausts the soil and renders it infertile. Soil conservation involves crop rotation, so that land does not bear the same crop more than once in five or six years, giving it time to recover its fertility. Soil- building crops such as clover are planted to enrich the soil. In America in the 1920s and 1930s when croplands were left bare, the topsoil was blown away. Now rows oft es are planted as windbreaks, and cover crops are used so that the soil is not left exposed for long periods. Contour ploughing and strip cropping also tend to prevent the removal of te soil.

If any animals - red deer, fish, whales, grouse - are taken in great numbers at one time, few are left to breed. Wildlife conservation does not seek to prevent shooting, fishing or whaling, but tries to arrange things so that only a limited number of animals are taken each year. Fishing and shooting are not allowed in the breeding season, to give animals, birds and fish the chance to reproduce without disturbance.

The objectives of conservation are reached by making conservation management plans aimed at controlling the main factors that influence the ecosystem and its species.