Ch.23 INTER-RELATIONSHIPS OF ORGANISMS WITH EACH OTHER AND WITH THEIR ENVIRONMENT Part II Study after Field Study has been completed

Transcription

1 Ch.23 INTER-RELATIONSHIPS OF ORGANISMS WITH EACH OTHER AND WITH THEIR ENVIRONMENT Part II Study after Field Study has been completed

2 h. 27 Inter-relationship of organisms with ach other and with their environment

3 23.1 The syllabus An understanding of the terms biosphere', 'biome' and 'ecosystem'. The concept of habitat and niche of an organism. A general understanding of the interaction of organisms with the abiotic and biotic factors of the environment with reference to ONE local habitat such as grassland, a stream, a rocky shore, a mangrove and an urban ecosystem.

4 Producers, consumers and decomposers. Energy flow, food chains, food webs and trophic Levels. The pyramid of numbers, pyramid of biomass and pyramid of energy. Water, nitrogen and carbon cycles. (Names of individual bacteria are NOT required.) Predation, competition, commensalism, mutualism and parasitism. A simple account of ecological succession.

5 23.2 DEFINITIONS

6 What is an ecosystem? An ecosystem is a functioning, interacting system which consists of two main parts: Biotic (living) components - these refer to all the living organisms, e.g., plants and animals. Abiotic (non-living) components - these refer to the physical environment, e.g., soil, climate, etc.

7 According to the size, ecosystems can be classified as (starting from the biggest): largest smallest biosphere biomes habitats microhabitats e.g. the Earth, a tropical rain forest, a rocky shore, a rock pool Within each ecosystem, there are

8

9

10 23.4 Within a stable system, there are always 1 Energy flow Energy flows from organism to organism in the form of food and is eventually lost as heat. Nevertheless, there is constant input of energy from the sun into the ecosystem. This balances the lost energy so that a stable system is maintained.

11 2 Cycling of materials Useful elements such as carbon and nitrogen inside organisms are mostly not lost from the ecosystem when the organisms respire, excrete or die. They are recycled so that they can become available again.

12 3 Interdependence of organisms Organisms within an ecosystem develop special relationships with each other. Several major types of relationships have been identified, for example,

13 4 Interactions between physical factors and organisms The physical conditions affect the organisms in the ecosystem in many ways. On the other hand, organisms may affect the physical

14 23.5 Ecological categories of biotic components in a typical ecosystem, e.g. rocky shore Producers (autotrophs) Producers are mainly green plants which are able to produce their own food through the process of photosynthesis.

15 Consumers (heterotrophs) Consumers are mainly animals which obtain their food by eating plants or other animals. They can be further divided into several groups according to their feeding habits: (a) Herbivores - animals which only feed on plants, e.g., chiton, (b) Carnivores - animals which only feed on herbivores, e.g., tiger, fox. (c) Omnivores - animals which feed on both plants and herbivores and carnivores, e.g., man.

16 Decomposers Decomposers are certain bacteria and fungi their function is to break down the dead bodies of both plants and animals.

17 23.6 The trophic structure of a food chain

18 23.7 Energy loss within food chains and food webs Energy within organisms in a trophic level can be lost by respiration excretion (not much in plants) death and predation by predators in the next trophic feeders from the members in that trophic level.

19 Energy losses from all trophic levels

20 elow is an energy flow diagram showing the losses

21 Members in a higher trophic level always receive less energy as some of the energy always leaves any trophic level: (R for respiration; E for excretion & egestion and D for death) e.g. ox man energy input in ox = 3060 kj (p.a.) energy input in man = 130 kj (p.a.)

22 Energy loss from all trophic levels

23 Ecological pyramids graphical representation of a food chain expressed in terms of each trophic level s number, biomass or total energy content

24 Ecological pyramid

25 Pyramid of number (they can have any shape)

26 Pyramid of biomass

27 Pyramid of energy Figures: energy flow in kj m -2 yr -1 (energy input)

28 A comparison of Ecological pyramids pyramid of numbers pyramid of biomass pyramid of energy NB. In nature, most carnivorous consumers occupy a few trophic levels in a food web so that it is difficult to assign them to trophic levels.

29 Food web Grasshoppers lizards hawks grass earthworms birds A B C D A: first trophic level 進食層 B: second trophic level C: third trophic level D: fourth trophic level

30 pyramid of numbers It is a bar diagram of numbers of individuals in each trophic level observed at any one time Provided that each upper member feeds on many lower ones, the upper level must contain fewer members than the lower one.

31 Drawbacks 1. All organisms are equated, regardless of their sizes. For example, An oak tree is counted as one individual in the same way as an aphid. 2. The numbers of some individuals are so great that it is impossible to represent them accurately on the same scale as other species in the food chain.

32 pyramid of biomass It is a bar diagram which shows the total amounts of dry masses (of standing crops) of all the organisms in each trophic level at any one time.

33 Upper members total biomass may be greater if they absorb calcium from the sea water to build calcarious shells or there is seasonal fluctuation of biomass, e.g. much fewer algae in winter while the algae feeders can remain in greater number.

34 Drawbacks 1. It is almost impossible to measure exactly the biomass of all individuals in a population. A small sample is normally taken and measured. This sample may not be representative of the habitat studies. 2. The time at which a sample is taken may affect the result.

35 Drawbacks 3. Weight for weight, two species do not necessarily have the same energy content so that comparison based on biomass may be misleading, e.g. a crab may be heavier than a fish bigger in size but the crab s weight

36 Drawbacks 4. The great importance of soil bacteria in terms of energy flow is not obvious form their small biomass.

37 pyramid of energy It is a bar diagram with each bar length (for each of the trophic levels) drawn proportional to the amount of energy per unit area or volume that flows through each of the trophic levels in a given time period

38 The pyramid s shape must be erect: the lower level must contain a greater energy content than the upper one so that there can be enough energy for flowing to the upper level both for them to build their bodies and for them to lose.

39 Drawbacks The energy data are very difficult to obtain and it requires combustion (killing) of representative sample organisms.

40 Advantages 1. It takes into account the rate of production for the members 2. The great importance of soil bacteria in terms of energy flow can be obviously shown. 3. The input of solar energy can be added as an extra

41 Cycling of materials Some elements are cycled through organisms in an ecosystem many times. The cycling elements such as carbon and nitrogen, in their elemental forms or in the form of organic or inorganic compounds flow from one stations to the next and will eventually flow back to these stations so that they are not exhausted. (However, solar energy cannot be

42 The carbon cycle tations and the input/output paths :

43 The carbon cycle

44 The carbon cycle

45 The nitrogen cycle ow nitrogen, in the form of nitrate, is added to the soil :

46 N-cycle stations

47 How nitrogen, in the form of nitrate, is removed from the soil

48 The nitrogen cycle

49

50 (Symbiosis is where two different types of organism live together in close association.) The five TYPES OF ECOLOGICAL RELATIONSHIP SYMBIOSIS commensalism mutualism parasitism predation competition

51 Ecological Succession 生態繼位 A community is all the plants and animals which occupy a particular area. The individual populations within the community interact with one another. The community is a constantly changing dynamic unit, which passes through a number of stages from its origin (pioneer community) to its climax. The transition from one stage to the next is called

52

53 Imagine an area of bare rock. The first group of organisms capable of surviving is the lichens. The mutualistic relationship between an alga and a fungus which makes up a lichen allows it to survive in considerable drying out. As the first organisms to bring about colonization of a new area, the lichens are called pioneers or the pioneer community.

54 Mutualism in lichen (a fungus + alga)

55 The weathering of rocks produces sand or soil, but in itself this is inadequate to support other plants. With the decomposing remains of any dead lichens after many years, however, sufficient fertilizers are made available to support a community of small plants.

56 Mosses are typically the next stage in the succession, followed by ferns. With the continuing erosion of the rock and the increasing amounts of organic material available from these plants, a thicker layer of soil is built up. This will then support smaller flowering plants such as grasses and, by turns, shrubs and trees. Animals also come to live here.

57 The ultimate community is a woodland. The stable state thus formed comprises a balanced equilibrium of species with few, if any, new varieties replacing those established. This is called the climax community.

58 Within the climax community there is normally a dominant plant and animal species, or sometimes two or three co-dominant species. The dominant species is normally very prominent and has the greatest biomass. The succession described above, where bare rock or some other barren terrain 荒廢苔原 is first colonized, is called primary succession.

59 A typical primary succession on bare rock lichen mosses ferns grasses and other herbaceous plants shrubs trees woodland of diversified organisms (a stable climax community)

60 secondary succession If, however, an area previously supporting life is made barren, the subsequent recolonization is called secondary succession. Secondary succession occurs after a forest fire or the clearing of agricultural land.

61 Spores, seeds and organs of vegetative propagation may remain viable in the soil, and there will be an influx of animals and plants through dispersal and migration from the surrounding area. In these circumstances the succession will not begin with pioneer species but with organisms from subsequent successive stages.

62