Lecture 5, 6. Synecology (ecological sociology) - Community Ecology

Biocenosis (biotic community, biocoenosis (in Greek: Bio means life and coenosis means community) is the community of populations of different species living and interacting in a given habitat (K. Mobius, 1877). Biogeocoenosis is a set of homogeneous natural phenomena (atmosphere, intrusive rocks, vegetation, wildlife and microworld, soil and water conditions) on the earth's surface which has its own specific interactions of its constituent components, and a certain type of substance and energy exchange between themselves and other natural phenomena and represents the internal contradictory unity that is in constant movement and development (Sukachev, 1940). Ecosystem (ecological system) is the community of all populations of different species living on the common territory and interacting with their environment (A. Tensli, 1935).

The state of the species (population) under various forms of relationship is indicated by conventional signs “ – “an adverse effect, the body suffers harm, "+" - positive effect, "0" - no effect. All biotic links can be divided into six groups: 1) "++"- mutually beneficial, symbiotic relationships. In this group the following is isolated: a) protocooperation when cooperation is beneficial, but not necessarily (pollination of various meadow plants by bees); b) symbiosis or inseparable links (lichens - fungi + algae, termites, and flagellate intestinal, which produce an saccharolytic enzyme); c) mutualism when a partnership is mandatory (cembretum, feeding by cedar seeds and spreading them). 2)“+0”- useful and neutral, or commensalism (shark and sucker fish).The followings should be distinguished in his group: a) sponger when the host food remnants are used (lion and hyena), b) commensal, c) tenant (orchids, lichens, mosses live in trees).3) "0" - negative-neutral, or amensalizm (grass under the trees are suffering from severe shading). 4) "00 - neutral, or neutrality. 5) "+-"- useful and harmful; in this group the following may be distingushed: a) carnivorism, and b) parasitism. 6)"--"- mutually harmful, when species that have identical ecological requirements enter into competition. This type of interaction should be referred to the Gause principle. The principle asserts that if two competing species coexist in a stable environment, this occurs due to the differentiation of niches, that is, by dividing the realized niches of these species, however, if such differentiation does not occur, or if it hampered the environmental conditions, then one competing species will be eliminated or replaced by another”.

Trophic structure of biocenosis. T wo major components: autotrophic and heterotrophic may be identified In biocoenosis or ecosystem. The autotrophic component ("self feeding") consists of green plants, which, by using solar energy synthesize organic matter of their cells (biomass) from the mineral components of environmental and is a major supplier of organic matter and related to its energy in biocenoses and ecosystems. In ecology, these organisms are called producers, while organic material they created is called primary production. Heterotrophic component ("eating others") consists of organisms that derive their energy from food resulted from destructed organic matter, originally created by producers. Heterotrophic organisms are divided into two major groups: consumers and decomposers. Consumers are organisms that consume the finished organic matter (all animals, parasitic and insectivorous plants). Decomposers are heterotrophic organisms (fungi and bacteria) that subsist on dead organic matter and during their vital activities decompose it to inorganic. Thanks to them, the most important nutrients contained in dead organisms go back into the biological cycle and are repeatedly used in the metabolism of living organisms. Joint effect of these three groups of organisms maintains a relatively endless circle of matter in ecosystems and biogeocenoses. In the "Man and Biosphere" context, functional classification of all living organisms stresses the fact that in nature, absolutely all organisms can be considered as continuous links of biogeochemical or ecological belt conveying to each other atoms of elements forming organisms, thus, indicating that there is no "extra" or "useless" species and organisms.

Food chains and trophic levels (trophic status, feeding level). Matter and energy have been transferring through a series of organisms, and each previous organism supplies the subsequent one with raw material and energy in the form of food. Such chain of organisms is called a food chain, and each of its link - a trophic level (Greek word “ trofos” means “food”). Producers, or autotrophs rank first at the trophic level. First order consuments, second order consuments, etc. rank second, third, etc. levels.

Food chains are divided into two main types: pasture chain and detrital chain:

3. Pasture chain starting with green plants transfer to organisms feeding plants, and then to the predators, feeding herbivores, or to parasites;

4.. Detrital chain starting from dead organic matter of dead organisms or their parts, then transfer to organisms feeding these dead organic matter (detritus), or their consumers (predators - hyena, condors, etc.).

Trophic chain in its totality, can be united to form food (trophic) networks

Ecological pyramids. Efficiency of ecological systems and the ratio of producers, consumers, decomposers are typically expressed graphically in the form of pyramid, first proposed by Charles Elton and it is called a pyramid of Elton. Ecological pyramids exist in several types: pyramid of biomass characterizes the total weight, pyramid of numbers of organisms represents the number of distinct populations of organisms or groups of diverse populations of the same trophic level, the pyramid of energy flow (productivity) shows the magnitude of energy flow or the amount of productivity in successive trophic levels.

Productivity of biocenoses. There are primary and secondary productivity of biocenoses. Primary productivity is called the rate at which solar energy is absorbed by the body-producers (green plants) in the process of photosynthesis through accumulation in the form of organic substances of synthesized biomass. There are two types of primary production: gross and net. One ought to bear in mind that consumers constantly eat away part of the produced biomass. Consequently, productivity is usually higher than the observed biomass growth rate.

Gross primary productivity is the overall rate of photosynthesis, including the rate of formation of the organic matter, which is spent by plants to breath in the course of measurement. Net primary productivity is the rate of substance accumulation by environment minus substance spent to breath. Productivity (or product) of consumers is called secondary productivity.

Energy flow and circulation of chemical elements in the ecosystem (Chart 7). Any ecosystem consists of biotic and abiotic components, which closely interact with each other, exchanging matter and energy: living organisms consume matter and energy from the environment and give them back into the environment during the life-sustaining activity. All living organisms appear to be consumers of food, that is of matter and energy. In the process of respiration of energy from its rich substances obtained from food releases. In process of breathing energy appears to release from energy-rich matter received from food. The first law of thermodynamics says: “Energy can be neither created nor disappeared”. It exists in various forms: light, chemical, mechanical, acoustic, thermal, electrical, etc. And all of these forms can be transformed into one another. Energy can be defined as an ability to do work. All living organisms can be considered as working "machines" that require a constant flow of energy from outside.

Living organisms can only use two forms of energy: photoenergy and chemical energy. All organisms are divided into phototrophic and chemotrophic depending on the energy source. Organisms synthesizing all necessary organic matter by means of light energy (photosynthesis) belong to a phototrophic group, it includes all plants and cyanobacteria. Chemotrophic organisms synthesize organic matter through the energy of chemical bonds of various substances. This includes all animals and bacteria. As a result of photosynthesis, all green plants capture 1% of entire solar energy registered on he Earth's surface and this energy supplies life-sustaining activity of all living organisms on the planet (the 1% energy law). When energy flows from the one to another trophic level, 90% of energy is spent to life-sustaining activity and entropy. Consequently, when flowing from one to another trophic level of the ecological pyramid on the average 10% of biomass energy or matter in the energy terms (the Lindemann law) is consumed. Hence, the energy pyramid objectively reflects the energy flow in ecosystems, and always is of a regular shape. Dynamic processes in the ecosystem. The primary property of ecosystems is stability and balance of processes of matter and energy exchange between all the components. It is typical of the ecosystem to be in the state of dynamic balance or homeostasis (Greek homeo - like, stasis - state). Homeostasis is provided by the feedback mechanisms. The feedback approach means that a certain controlling component of a certain system receives information from the controlled components using this information to make allowances to a further control process. all the time, balance is maintained in ecosystems, which exclude irreversible destruction of any given links in trophic chains (food chains). All the time any ecosystem is balanced or stable (it means that homeostasis maintains). Population of predators maintains a certain prey population level (a positive feed back). Under certain circumstances a negative feedback, that is transfer of information can be violated for some reason. Violation of a balanced system can be reversible or irreversible. Human activities may cause such violation. Violation of stability or disintegration of the entire ecosystem depends upon the extent and time of impact of the anthropogenous factor. A large body of research with the application of the mathematical analysis approach showed that the more complex ecological systems the more stable they are in time and space. Stability of the community should be determined by the number of links between species in the food chain (trophic chain).

Succession of geobiocoenosis. Homeostasis, or balance of the mobile ecosystems is not something fixed. Any ecosystem undergoes changes both in time and space, in addition, changes are seen in the biocenosis structure, ecosystem structure and its productivity. Continuity of biocenoses occurring on the same territory as a result of impact of natural factors or human activities, is called succession (Latin word: successio means succeed). Changes of biocenoses occur by virtue of the ecological law on successional substitution: "Natural biotic communities successively form a logical series of ecosystems, leading to climax which is the most stable state under such conditions (“climax” in Greek means stairs)". Climax means the final, relatively stable state of alternated ecosystems (biocenoses) arising as a result of succession and being in compliance with environmental conditions of the given area. Agriculture represents a special case of anthropogenic succession. Any farm after plowing a virgin land and seeding it, gathers the harvest, which is represented by plants with assimilated soil nutrients, atmosphere oxygen and carbon received from the ecosystem.

Ecological pyramid (by Willie K. and B. Dete, 1986). Figures on the right show the ratio of biomass at different levels of the food chain.

An example of the food chain in an oak forest, represented as Eltonian pyramid (or a pyramid of numbers).

Self Test Questions

12. What are the ecosystem and biogeocoenosis.What is the difference?

13. Please give examples of specific and space structure of biocenosis?

14. What types of relationships exist between organisms in the community?

15. How does energy flow in the ecosystem?

16. What is the trophic structure of biocenosis?

17. What types of food chains exist? Please give examples?

18. What does the ecological pyramid reflect?

19. What determines the productivity of ecosystems?

20. What determines the stability of ecosystems?

21. What is homeostasis of ecosystems and ecological succession?

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