The Ecosystem. An Introduction

Transcription

1 The Ecosystem An Introduction

2 Ecosystem A community of interdependent organisms and the interactions with the physical environment in which they live. It can also be defined as the abiotic and biotic factors and the interactions between them. The interaction between organisms and the environment is the key!

3 Kind of ecosystems: [1] Natural Ecosystem: this operates by themselves Ex: Terrestrial Ecosystem: forest, grassland, desert Aquatic Ecosystem: Fresh water, Marine water [2] Artificial Ecosystem: These are man-made or man-engineered. Ex: Croplands, rice fields, gardens, aquarium etc.

4 Niche vs habitat A habitat is a place in which an organism lives. The habitat must provide a source of food, water and shelter for the organism. Niche: The role of the organism. This is largely to do with the trophic level of the organism. For example: plants produce food for the rest of the food chain. Tigers keep herbivore populations under control.

5 Abiotic and Biotic factors Abiotic factor: A non-living, physical factor that may influence an organism or a system [1] Climatic conditions: Ex: water, soil, light, temperature, ph etc. [2] Inorganic substances: Ex: H 2 O, C, N, S, P [3] Organic substances: Ex: proteins, carbohydrates, lipids etc.

6 Biotic Factor: A living, biological factor that may influence an organism or a system. [1] Autotrophic component (Producers): (i) Photoautotrophs: convert solar energy into chemical energy. Ex: Trees, grass (ii) Chemoautotrophs: energy generated by redox reaction. Ex: Sulphur bacteria [2] Heterotrophic component (consumers): they consumes matter built by producers.

7 (i) Macroconsumers/ Phagotrophs: Herbivores, Carnivores (ii) Microconsumers/decomposers/saprophytes: Decompose organic compounds of dead or living protoplasm & release inorganic nutrients in the environment. Ex: micro-organisms such as bacteria, fungi etc.

8 Function: 1. Means how much sunlight is trapped by plants in a year. 2. How much plant material is eaten by herbivores. 3. How many herbivores are eaten by carnivores. 4. Energy flow in a ecosystem is non-cyclic (unidirectional) whereas minerals keep in moving in a cyclic manner.

9 Limiting factors An abiotic factor can limit the population size if there is too much or too little of it. Even if there is the right amount of other factors Examples to consider: Sunlight Precipitation Salinity Nutrients in the soil

10 Trophic levels Ecosystems are often broken up and described according to feeding relationships. Trophic level: Number of links by which it is separated from the producer, or as nth position of the organisms. The position of an organism in a food chain. The pattern of eating and being eaten forms a linear chain called food chain. A group of organisms that occupy the same place in a food chain

11 Trophic levels in food chains Primary producers (autotrophs) Primary consumers (herbivores) Secondary consumers(carnivores) Tertiary consumers (top carnivores) Decomposers Detrivores

12 Energy flow and material cycling

13 Food Chains

14 Types of food chain: [1] Grazing Food Chain: Autotrophic energy capture & movement of energy to herbivores. Solar radiation Herbivores Primary carnivore secondary carnivore

15 [2] Detritus food chain: Organic wastes & dead matter derived from the grazing food chain are termed as detritus. Energy of detritus is serve as energy for a group of organisms (detritivores) that are separate from grazing food chain. Organism: Algae, Bacteria, Molluscs, Rotifer, Mites etc. Grazing food chain Dead & Excretory material Decomposer organisms soil organisms consumed by carnivores in the grazing food chain soil animals which consume other living organisms Organic material permanently incorporated into sediments, soil &

16 Significance: 1. It helps us to understand the feeding relationship and interactions between organisms in any ecosystem. 2. Energy flow mechanisms & matter circulations. 3. Movement of toxic substances & process of biomagnification.

17 Food webs In a given ecosystem various food chains are linked together & intersect each other to form a complex network called food web Show energy flow through an ecosystem

18 Food webs

19 Ecological Pyramids: It represent the trophic structure & also trophic function of the ecosystem. It may be of three types: (1) Pyramid of number (2) Pyramid of biomass (3) Pyramid of energy

20 Pyramid of Number, Energy

21 Pyramid of biomass

22 Primary productivity Primary productivity is the rate of energy capture by producers. = the amount of new biomass of producers, per unit time and space

23 Gross primary production (GPP) = total amount of energy captured Net primary production (NPP)= GPP - respiration Net primary production is thus the amount of energy stored by the producers and potentially available to consumers and decomposers.

24 Secondary Productivity Secondary productivity is the rate of production of new biomass by consumers, i.e., the rate at which consumers convert organic material into new biomass of consumers. Secondary production simply involves the repackaging of energy previously captured by producers--no additional energy is introduced into the food chain.

25 Energy flow in ecosystems: Energy flow is the movement of energy through an ecosystem : from the external environment through organisms and back to the external environment. Energy flow can be explained by various energy flow models.

26 [1] Single Channel Energy Flow Model: Unidirectional flow of energy. In each trophic level, there occurs progressive decrease in energy

27 [2] Y-Shaped or double channel energy flow model: Given by H.T. Odum in Shows a common boundary, light and heat flows as well as the import, export & storage of organic matter. Decomposers are placed in separate box. Explain stratified structure of ecosystems. Separates the food chain.

28 [3] Universal Energy Flow model: Given by E.P. Odum. Energy was lose at each energy level, thereby resulting in less energy available at next trophic level as indicated by narrow pipes (energy flow) & smaller boxes (stores energy in biomass).

29 Energy transfer in a food chain: First law of thermodynamics

30 Ecological Succession The development of the community by the action of vegetation on the environment leading to the establishment of new species is termed succession. Final & stable community is termed as climax community. Traditional community is called sere or seral stage. Its directional change in vegetation.

31 Causes 1. Initiating Causes: climatic (erosion, deposits, wind, wire etc.), Biotic 2. Ecesis or continuing causes: migration, competition, reaction etc. 3. Stabilizing causes: climate of area which stabilize the community.

32 Changes during succession 1. Continuous change occurs in the kinds of plants & animals. 2. Increase in diversity of species takes place. 3. Progressive increase in the amount of living biomass & dead. 4. Green pigment go on increasing during primary succession. 5. Food chain become more complex. 6. Role of detritus becomes progressively more & more important. 7. Quality of the habitat gets modified. 8. Life cycle of mature community species are longer & complex.

33 Types of succession 1. Primary: its an area in any of the basic environments is colonized by organisms for the first time. 2. Secondary: if the area under colonization has been cleared by an agency as burning, grazing, clearing, sudden change in climatic factor etc. of the previous plants 3. Autogenic: community itself modifies its own environment and, thus, causing its own replacement by new community.

34 4. Allogenic: replacement of one community by another is largely due to force other than the effects of communities on the environment. 5. Autotrophic: its characterized by early & continued dominance of autotrophic organisms such as green plants. 6. Heterotrophic: it is characterized by early dominance of heterotrophic organisms as bacteria, fungi & animals.

35 7. Induced: activities such as overgrazing, frequent scrapping, shifting cultivation or industrial pollution may cause deterioration of an ecosystem. 8. Retrogressive: return to simpler & less dense or even improvised form of community from an advanced or climax community causes are allogenic. 9. Cyclic: repeated occurrence of certain stages of succession whenever there is an open condition created within a large community.

36 Process of succession 1. Nudation: development of a bare area without any form of life. It may occur due to landslides, erosion, deposition. Three types are there: (a) Topographic: soil erosion by gravity, water or wind causes disappearance of existing community. (b) Climatic: Glaciers, dry period etc. may destroy community. (c) Biotic: man-made destruction of forest, grasslands for housing, industry, agriculture etc. disease epidemics caused by fungi, bacteria, virus etc.

37 2. Invasion: Successful establishment of a species in a bare area. (a) Migration (Disposal): seeds, spores etc. may reach to bare area by air, water etc. (b) Ecesis (Establishment): After reaching new areas, the process of successful establishment of the species means adjustment with condition there. For ex: seeds germinate grow adult start to reproduce (c) Aggregation: colonization by successive offsprings & new migrants help increase the population. Number of individuals of the species increases in number.

38 3. Competition and coaction: Due to aggregation of a large number of individuals of the species at the limited place, there develops competition (i.e. interspecific & intraspecific) for space & nutrition. Individuals of a species affect each other s life in various ways this is called coaction. The species which fail to compete with other species are discarded.

39 4. Reaction: It includes mechanisms of the modification of the environment through the influence of living organisms on it. As a result of reaction, the environment is modified & become unusable for existing community which sooner or later replaced by another community. Whole sequence of communities that replaces one another in the given area called sere and different communities constituting the sere are called seral stages or development stages.

40 5. Stabilization (Climax): Finally, there occur a stage in the process, when the final community become more & less established for a longer period of time & it can maintain itself with climate. The final community is not replace & known as climax community & stage is climax stage.

41 Primary succession-

42 Secondary succession- Ex: A fire levels portions of a forest

43 Secondary succession- Ex: A farmer plows his field

44 Secondary succession-