The core of ecology is made of the general mechanisms which govern patterns in space and time, of assemblages of organisms as revealed by the properties of individual species.

The term ‘ecology’ was coined by Ernst Haeckel in 1869, though eco­logical problems were being studied even before the term was coined. From 1870 onwards, ecology has experienced a rather complex and divided course as it has involved a wide and highly complex range of objects.The quintessence of ecology is to explain what we observe in nature; however, this does not mean that ecology can be understood only by observation, description and inference.

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The inherent complexities among the interacting organisms and environment also require some use of mathematics with a view to make some order out of the bewildering complexity and diversity. Fenchel (1987) defines ecology, in a rather restricted sense, as “the study of the principles which govern temporal and spatial patterns for assemblages of organisms”. Others who have defined it in a broader sense include, e.g., Odum (1971): ‘the study of the structure and function of nature’: and Krebs (1978): ‘the scientific study of the interactions that determine the distribu­tion and abundance of organisms’. Ecology is a pluralistic science in the sense that it depends on a wide variety of methods and approaches rather than on a limited range of tech­niques and concepts. A true understanding of ecological systems can only be gained by understanding the properties of lower organizational levels such as communities, populations, individuals, organs, tissues, cells, or­ganelles, and molecules.

One important way in which ecology differs from most other branches of biology is that it can be properly appreciated or studied only through a multidisciplinary approach involving close cooperation from experts in sev­eral disciplines, e.g., physics, geography, engineering, mathematics and sta­tistics, zoology, botany, microbiology, limnology and chemistry. In fact most of our present day environmental problems have been caused through a lack of appreciation (or implementation) of the multidisciplinary perspec­tive and through a narrow perception of the world. Such a limited percep­tion has been misleading in the sense that it has often led to a consideration of an ecological problem from the standpoint of a single discipline. No wonder, therefore, that adequate solutions too many of the environmental problems have eluded us. In 1975, Jordan posed the interesting question: “What is ecology?” He pointed out the inadequacy of the traditional definition of ecology (viz.

, the study of interactions between organisms and environment), because most biological and agricultural research as well as some parts of medical and engineering studies can be interpreted to be studies of the interaction be­tween organism and environment irrespective of whether or not the studies are really ecological. According to Jordan (1975), an adequate definition of ecology must specify the unit of study that is unique or basic to ecology, and such a basic unit obviously is the “ecosystem”. This term was first proposed by the British ecologist A.G. Tansley in 1935 but, of course, the concept is by no means so recent. Thus, ecology may be defined as “the study of ecosystems.

” A broader, more inclusive, term than ecosystem is “ecosphere” The ecosphere is composed of a variety of ecosystems. In terms of system theory, the ecosphere represents a super system. Ecosystems may be visualized as 3-dimensional cutouts from the ecosphere: all primary and secondary producers composing the ecosystem are its essential ele­ments. The unique property of ecosystems is the maintenance of their chem­ical state and of the chemical state of their environment. An ecosystem in turn is an integrated unit, consisting of interacting plants and animals whose survival depends upon the maintenance of abiotic (physicochemical envi­ronment and gradients such as moisture, wind and solar radiation with its concomitants of light and heat) as well as biotic structures and functions. The integrated unit may or may not be isolated but it must have definable limits within which there are integrated functions.

Unlike physiologists who study various functions in individual plants or animals, the ecologists study them at the ecosystem level. A real ecologist always tries to maintain a holistic or ecosystem perspective of the process being studied by him. The basic and most important concept of an ecosystem is that everything is somehow or other related to everything else, and such rela­tionships include interlocking functioning’s of organisms among themselves as well as with their environment. Biocoenosis and bioecocoenosis are roughly equivalent to community and ecosystem respectively. Biotopes are the physical environments in which such communities exist. Complex inter­actions occur between the occupants of a biotope and the object of ecology is to sort out principal characteristics and relations between these and the abiotic factors. According to Lamotte (1969), it is this network of multiple interactions that permits us to define the ecosystem completely. Many ecol­ogists regard Interdependence as the first basic theme of ecology (see Bowen, 1970).

Ecosystems include interacting and interdependent compo­nents that are open and linked to each other. Barrett (1978) proposed the new term noosystem to define a basic unit of study encompassing biological, physical, social, economic, and cultural influences on the total system. He advocates restriction of the term ecology to define that discipline which attempts to understand the structure and function of ecosystems, whereas “environmental science” be defined as an interdisciplinary science which attempts to study the impact of man on the structure and function of social and ecological systems (i.

e., noosystem), as well as management of these systems for human survival and benefit. A second basic theme is Limitation which means that limits are ubiqui­tous and that no individual or species goes on growing indefinitely. Various species control and limit their own growth in response to overcrowding or other environmental signals and the total numbers keep pace with the re­sources available.

Not only are the resources limited but there are limits both to the rates at which the environment can receive and recycle wastes and to its capacity for storing them in a suitable form. Complexity is a third characteristic of any ecosystem. The three-dimen­sional interactions of the various constituent elements of an ecosystem are highly complex and often beyond the comprehension of the human brain. It is because of such complexity that human intervention in or the meddling with a balanced ecosystem with the objective of producing some desirable effect, also often brings forth some additional, unexpected and undesirable side effect. Man’s activities very often result in a simplification of the communities or ecosystem.

The definition of ecology stated above is, however, not accepted uni­versally. In certain countries, e.g., the USA, Canada and England, ‘ecology’ includes within its scope both description of communities and the more experimental ecological investigations, e.g.

, energetic. On the European Continent, on the other hand, the term ‘ecology’ (also sometimes called eco-physiology) is restricted to the experimental part only whereas the de­scriptive part is styled as sociology, e.g., plant sociology or animal sociolo­gy. The chief objective of an experimental ecologist or eco-physiologist is to understand the mass and energy turnover within different ecosystems and to estimate quantitatively the primary and secondary production. Ecology may also be defined as a system-theory oriented synthesis of both earth and life sciences, and can be studied by developing suitable and comprehensive flux-analytical and hierarchical medelling approaches. As in most other branches of biology, the descriptive aspects of ecology were the main focus of attention during the early 1900s but during the past few decades the trend of research has shifted to the experimental aspects. A fundamental aspect of ecology’ is to study the distribution and abun­dance of various organisms, but no reliable method is available to obtain accurate information on the spatial patterns of most organisms, including the sessile ones (see Rohlf and Archie, 1978).

A few commonly employed methods include quadrats, transects, and plotless, nearest-neighbour dis­tance techniques. Greig-Smith (1964) has pointed out the limitations and inadequacies of these methods for estimating spatial patterns. The data obtained by laying quadrats depend on the quadrat size used. Transect methods are rather inefficient and give reliable information only for the small area actually sampled. Plotless techniques give useful information only for the nearest-neighbours, and measurements of distances to second, third, or more remote neighbours consume much time in the field. In view of the above limitations of the extant methods, Rohlf and Archie (1978) proposed a new method for the mapping of the relative locations of sessile objects (e.g., plants and nests) as points in a two-dimensional space.

This method is based on a least-squares estimate of the coordi­nates using observed distances between the objects being mapped. Only a small subset of the possible inter point distances needs to be measured to obtain an accurate map. This method differs from conventional mapping in that the latter use a compass or transit to locate each individual by triangulation. The chief limitation of the new method is that one must physically reach each plant so as to measure the inter point distances. Ecology is characterized by the rapidly growing complexity and in­creasing diversity of facts, data, aspects, examples and findings.

What is badly needed is the development of common patterns or rules that can explain the increasing complexity and variability observed in more general terms. Such rules have already become available for physics and some other branches of science. One currently popular view is that the competition for energy may be the most important factor in ecological interactions. However, this view is not shared by White (1993) who gives several examples from the animal kingdom that suggest a different pattern, viz., the universal hunger for nitrogen as the significant driving force in the ecology of all organisms.

According to White, nitrogen limitation plays a fundamental role in the ecology of all organisms. According to him, it is nitrogen and not energy that is the most limited currency in the animal kingdom for the production and growth of the young animals.