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<P align= justify > The world ecology was first incorporated into scientific terminology by Ernest Haeckel in 1869. The word is derived from the Greek <I>oikos</I> meaning home . By ecology Haeckel meant the scientific study of the interactions between species and their environment. This definition has been broadened and sharpened several times. A more informative definition that gained acceptance was formulated by Krebs in 1972: Ecology is the scientific study of the interactions that determine the distribution and abundance of organisms. However, this definition does not include the word environment , which is a clear deficiency as ecology deals with the interactions between organisms and their environment. The environment of an organism consists of all those factors and phenomena outside the organism that influence it, both abiotic and biotic. Thus a more accurate definition of ecology would be the scientific study of the abiotic and biotic interactions in an environment that determine the distribution and abundance of organisms. A much used derivative of the term ecology is ecosystem, i.e. an area within which ecological processes and the above mentioned interactions take place. </P><P align= justify > Begon, Harper and Townsend in 1986 emphasized the need to expand one term of the definition: Ecology deals with three levels of concern, the individual <I>organisms</I>, the population, consisting of individuals of the same species, and the <I>community</I>, consisting of a greater or lesser number of populations. At the level of the organism, ecology studies how individuals are affected by, and how they themselves affect their abiotic or biotic environment. Examples of abiotic interactions are those between organism and substrate, while biotic ones include herbivores forage, predators prey, plant insect and plant fungi interactions. At the population level, ecology studies the existence of given species, their abundance or rarity at a defined site, as well as fluctuations in their numbers. Community ecology deals with the patterns and processes which determine the composition or structure of communities, e.g. factors affecting diversity, species composition, biomass, etc. </P><P align= justify > The distribution of organisms is usually not continuous; they occur in patches located at varying distances from each other. This has raised a relatively new approach to population level biology: metapopulation ecology. A metapopulation consist of all populations of a given organism within a specified area. The number of available or suitable habitat areas is crucial in estimating population level patterns. Individual populations are vulnerable to extinction, and their survival is thus dependent on the number of suitable habitat areas and the spreading ability of the organisms.</P><P align= justify > It is not only indigenous nature that is the concern of ecologists today; an ever increasing number of studies deal with man-made habitats like fields, urban environment, etc., and with the consequences of human activity like pollution and global warming. Modelling offers a very important tool for dealing with large-scale, complicated interactions, for it is a major aim of ecology to simplify complex subjects in order to make them easier to understand. This is crucial for predicting the causes and effects of changes in the numbers of organisms in populations and communities.</P><P align= justify > Ecology is one of the main disciplines in biology, and it overlaps with others, especially taxonomy, genetics, evolution, behaviour and physiology. Taxonomy is crucial to ecology as it provides a common nomenclature for taxa. Without precise species names it would be impossible to carry out comparative research in ecology.</P>
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