CHAPTER TEE VILLAGE PMAYAKDRICHI AS AH ECOSYSTEM. recent years ecology has become an ubiquitous

Transcription

1 16 CHAPTER II TEE VILLAGE PMAYAKDRICHI AS AH ECOSYSTEM In recent years ecology has become an ubiquitous word. It has begun to enter into discussions on economic development,industrial growth, standards of living and more especially regarding the threats to the quality of human life ( Vyas and Golley >,1975)* The word ecology was first coined by Haeckel (1869) who defined it as the total relationship of an organism to its organic and inorganic environment. Odum (1963) defined ecology as the study of the structure and function of nature. According to Mitchell (1976) ecology is the study of the processes responsible for the conversion of light energy from the sun into the biomass of plants (producers) and the processes that determine the numbers and abundances of the animals (consumers) that eat the plants and other animals. The focal theme of ecological studies is the concept of an ecosystem. The term ecosystem was coined by Tansley (1935) and according to him the term includes not only the living organisms but also the whole complex of physical factors forming what we call the environment. According to Lindeman (19^2 ) an ecosystem is a system composed of physical -chemicalbiological processes active within a space-time unit of any

2 17 dim ension. Odum ('1959).defined an ecosystem as any a re a of n a tu re th a t in clu d es liv in g organism s and n o n -liv in g substances in te r a c tin g to produce an exchange of m a te ria ls between th e liv in g and n o n -liv in g p a r ts. components j An ecosystem i s composed of th e follow ing fo u r a. b. c. d. A biotic (n o n -liv in g ) substances P roducer organism s namely green p la n ts Consumer organism s namely th e anim als which consume th e food prepared by th e green p la n ts B a c te ria and fu n g i which break down th e organic m atter a t the death of th e p la n ts and anim als and re le a s e th e m inerals f o r re c y c lin g. The re la tio n s h ip s between th e various components of an ecosystem a re based on th e trophic-dynam ic asp ect (Lindeman, 19^2; C olinvaux, 1973 and G a llu e c i, 1973). The green p la n ts a re cap able of sy n th e sisin g complex organic m olecules from sim ple in o rg an ic m olecules w ith th e h elp of sun«s energy by the. procese of p h o to sy n th e sis. T his is the process of primary p ro d u ctio n. The green p la n ts are a u to tro p h ic ( s e lf fe e d in g ) and form th e f i r s t tro p h ic le v e l. Animals a re h e te ro tro p h ic because they cannot prepare t h e i r own food and depend on food alread y prepared by o th er organism s. H erbivorous anim als consume p la n t p a rts and

3 18 utilise the energy rich organic molecules of the plant body f o r their growth and metabolism. These animals comprise the s e cond trophic level of the ecosystem. Carnivorous animals consume the herbivores and utilise the energy rich organic molecules of the animal tissue f o r their growth and metabolism. This is the third trophic level. Both the herbivores and carnivores are collectively called phagotrophs. The decomposers are c a lled saprotrophs b e cause they subsist on dead plant and animal organic matter. They break d o w n dead plant and animal matter and release the c o n s t i t u ents which can b e reused by other organisms. The herbivores, carnivores and the decomposers together constitute the c o n s u m e r component of the ecosystem, and they all derive their energy ultimately from the sun. Ecosystems are solar po w e r e d machines (Mitchell, 1980). The l i v i n g part of the environment is the biotic community. A community is a n aturally occuring assemblage of plants and animals that live together in the same environment, are mutually sustaining and interdependent and are constantly fixing, utilising and storing energy (Smith, 197*+)«A commu n i t y is made up of populations of plants a n d animals. A population is a group of interacting organisms of the same kind occupying a particular space. A h a b i t a t is the n a t u r a l abode of a population. It includes all the features

4 19 o f the environment i n a given locality including the physical a n d b iological features. S o l a r energy enters the e c osystem through green plants (producers), flows to the carnivores through the herbivores and finally to the decomposers which release it o u t of the ecosystem as heat energy. The transfer of energy from one component to another is governed by two laws of thermodynamics. The first law states that energy can neither be created nor destroyed, b u t can be transformed f r o m one f o r m to another. Solar energy is transformed into potential (chemical) energy of plant matter by green plants: herbivorous animals t r a n s f o r m this p otential energy of plant body into potential energy of animal tissues. According to the II law of thermodynamics, processes involving energy transformations w i l l not occur spontaneously unless there is a degradation o f energy into heat. In the flow of energy through the d ifferent compartments of an ecosystem, there is a progressive d i m i n u t i o n of the total energy b e cause at every step there is loss of energy as heat. In his w o r k on silver springs, O d u m (1957) observed that the solar energy available for the ecosystem was ,700,000 kcal m y r. The gross primary productivity (the total p h o t osynthesis) was.20,810 kcal m 2 y r ~ 1. The

5 20 net primary productivity (photosynthesis after respiration of plants) -was 8,833 keal m yr. The secondary productivity _2 of herbivores (second trophic level) was 383 keal m yr and the secondary productivity of carnivores (third trophic -2-1 level) was 21 kcal m yr These trophic levels can be represented in the form of a diagram which is palled the ecological pyramid or the energy pyramid (Fig. 3), The most striking feature of the energy pyramid is the progressive loss of energy as it moves through various trophic levels of the ecosystem. The flow of energy in the ecosystem can also be represented in the form of compartments linked together by arrows denoting the direction of the flow of energy. Fig. b is the energy flow diagram for the Cedar Bog Lake (Lindeman, 19^2). The most important character of the energy flow in ecosystems is that it is unidirectional. The energy trapped by the green plants cannot be reconverted to solar energy; that which passes to the herbivore cannot pass back to the green plants and so on. Fig. 5 is the energy flow diagram of a generalised ecosystem (Odum, 1959 )* This model can be adopted with suitable modifications for working out the energy flows of actual ecosystems. While energy is flowing unidirectionally through the ecosystem and is finally released out of it, there is a distinct cycling of nutrients within the ecosystem.

6 21 A very important point about the concept of ecosystem is that it can be applied at any scale: a d r o p of water f r o m a pond is an ecosystem; so is the entire planet earth. There are some ecosystems which are incomplete e.g. caves and the floor of the d e e p seas. D u e to the absence of sunlight, no photosynthesis can take place and so there are no producers. Organic matter is imported f r o m outside, and in the case of the deep sea floor, the,,rain,, of dead organic matter f r o m the upper layers of the seas sustains a detritus food chain. U r b a n industrial areas which are sustained by huge subsidies of fossil fuel, and where there is practically no primary p roduction and which are totally ^dependent upon food imported from rural centres can be classified in the s a m e category of i n complete ecosystems. M i t c h e l l (1976) h i nted that subsistence agriculture in India operated with insignificant amounts of f o ssil fuel inputs and is almost entirely dependent upon solar energy f o r its input of la.bour and n utrient cycling. Agricultural operations are conducted with the muscle power of the humans a n d the bullocks, which depend upon food produced from the previous year's crops i.e. t h e previous year's solar energy. Therefore Indian agriculture is solar powered. Secondly, in subsistence agriculture in d r yland farming in India, very

7 22 l i ttle of fertilizers or. pesticides are used. Fertilizers a n d pesticides are manufactured with the h e l p of fossil fuels. In the case of Indian agriculture the tendency is to recycle nutrients by the use of 'farmyard manure prepared from the dung of cattle. Since dung is only the r e sidue of the previous year's crop, the organic nutrient recycling is also solar powered. Thus in an I n d i a n village there are a set of producers (crops ) which trap sunlight a n d produce energy rich organic food to s u s t a i n the consumers (human and the i cattle). The h u m a n and bullock populations in turn invest their labour, in the agroecosystem. The dung is used as f armyard manure a n d so the nutrients are recycled (Fig. 1*+). Thus the Indian village has all the components of an ecosystem- it is an agroecosystem. Hence the agroecosystem of an Indian v i llage needs to be analysed qualitatively and quantitatively f r o m an ecological point of view. M i s r a (1972 b ) has shown that the methods of ecosystem analysis can be a p p l i e d to the croplands as w e l l as to grasslands and forests. In fact it is easier to apply ecosystem analysis to an agroecosystem b e cause there are very few species and the basic physiology of these species has been worked out threadbare (Mitchell, 1980). On the contrary, a w o r k e r on a n a tural e cosystem is p l agued by many ambiguities as pointed out by Engelman (1966) and Kormondy (1976). A w o r k e r on agroecosystem

8 23 however has a more unambiguous data base. While systems theory is not new either to the physical or social sciences, its application to the study of agriculture is just beginning. According to Saint and Coward (1977) an ecological systems approach is emerging among scientific researchers, in which both physical and organisational aspects of agricultural production are included as components of the same system that includes agronomy, biology and ecology / and vice versa. Relations that link the crop, the crop producer and the crop producing community are explored. Such studies are in progress in the International Institute of Tropical Agriculture, Nigeria and the International Maize and Wheat Improvement Center, Mexico. An interdisciplinary approach is emerging, as evidenced by the work of the botanist Loomis (1976) on agricultural systems. Hence there is ample lacuna in approaching the study of agroecosystem from an ecological point of view. The energy flow of the village Panayakurichi in the Tiruchirapalli district is investigated by the method of input-output analysis of energy and an ecosystem model is construetured. The aims of the present study ares 1. Constructing the. agroecosystem model of energy flow for the village Panayakurichi in the district of Tiruchirapalli.

9 2b 2. Evaluating the extent to which the study of agroecosystem in an Indian village can contribute to the science of ecology in terms of concepts and principles. 3. Comparing the productive efficiencies of the crops and cropping systems of the village Panayakurichi with other systems. *+. ' Examining the food producing potential of the Indian agroecosystem in terms of future prospects. The study encompasses the following spheres: i. Estimating the M P of the grasslands present in the village Panayakurichi and assessing their contribution to the energy flow of the cattle of the village. ii. Working out the productivities and photosynthetic efficiencies of the various crops growing in the village. iii. Drawing up the energy budgets of the various components of the agroecosystem in the village. iv. Constructing the agroecosystem model of energy ' flow for the village. v. Comparing the ecosystem model of Panayakurichi with the standard reference model of Indian

10 25 k&)\ agroecosystem (Figs.18 and 19) constructed by Mitchell (1980) and with other ecosystems. India has a population of 628 million (1977) and agriculture is central to its economy. Nearly half of the GNP is generated in agriculture. Before 19*4-0, asian countries were all net exporters of wheat, rice etc. to industrial nations. Ey the end of the war they lost their surpluses (Ehrlich and Ehrlich, ). The study of the solar powered agriculture of India is important from the point of view of evolving new strategies of food production (Mitchell, 1980). According to Levins (1973) researchers working in basic science must be convinced that agriculturally relevant research is of fundamental significance, and at the same time agricultural scientists must also be convinced that \ theory is practical, in the context of the global energy crisis, energy analysis has become a supplement to other methods of analysing questions concerning resources and environment. Just like economic analysis, energy analysis permits different production processes to,be compared (Johnson et al., 1977). In the light of these remarks the relevance and importance of this study cannot be. overemphasized.