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The study of biosphere is called biogeography, which includes the consideration of physical environment, soil, animals and plants. ‘Biogeography as the term indicates, is both a biological and a geographical science. Its field of study is the biologically inhabited part of the lithosphere, atmosphere and hydrosphere or, as it has become known the biosphere’.
Since the living organisms of the biosphere are studied in botany, zoology, biochemistry and geography with different viewpoints and focus and hence there are variations in the meaning and scope (subject matter of study) of biogeography in the aforesaid disciplines.
If a geographer studies the distribution patterns of plants and animals of the biosphere in spatial and temporal contexts and attempts to analyse the processes and factors which are responsible for such spatial and temporal variations, the biologists limit themselves to the study of physiological, morphological, behavioural and functional aspect of an individual organism.
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A geographer besides studying the distributional patterns of community of plants and animals also emphasises two more aspects viz.:
(1) Intimate interrelationships between the abiotic and biotic components, and
(2) Reciprocal relationship between man and biosphere.
It may be pointed out that the discipline of biogeography cannot be exclusive domain of either biology or geography as its boundary is overlapping not only with these two subjects but also with other subjects. J. Tivy (1982) has aptly remarked, ‘the geologist, climatologist, pedologist, geomorphologist as well as the botanist, zoologist, geneticist and geographers all ‘cultivate’ or ‘crop’, as the case may be, particular parts of this very large and varied filed (biosphere); and in doing so they are, to a greater or lesser extent, essential to as well as being dependent on, an understanding of biogeography’. Thus, the meaning, subject matter and approach to study vary according to the interest and objective of the investigator.
The primary goal of a geographer is to present a vivid picture of spatial patterns of distribution of plants and animals, their temporal variations and processes and causes thereof. Margaret Anderson defined biogeography as the essence of ‘biological relations between man (considered as animal) and the whole of his animate and inanimate environment.’
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Since plants and animals are major components of biogeography and hence the subject is divided into two branches viz.:
(1) Plant geography, and
(2) Animal geography.
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But in geographical studies plant geography is given more attention while animal geography or zoogeography occupies back seat.
This is because of the fact that the study of distributional pattern of animals becomes difficult due to mobility of animals, very micro-forms of animal species and very high variability in their behaviour while the study of distribution patterns of plants becomes easy due to their static nature and their aggregation in static community. Simultaneously, plants represent most of total biomass of the world (say biosphere).
In comparison to animals plants depend more on physical environment of their habitats, they are more affected by their environment and in turn they also affect their environment. Plants provide food to all animals including man because they are primary producers and become most valuable resource to human society.
It may be pointed out that though biotic components of the biosphere are most significant aspect of the study of biogeography but abiotic components involving land, air and water are also studied into this discipline.