GCSE level School biology notes: Ecosystems biotic and abiotic factors, interactions, interdependence

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Ecology, ecosystems, biotic and abiotic factors, organism interactions, interdependence, parasitic & mutual relationships, interdependence, environmental changes, effects on populations

Doc Brown's biology exam revision study notes

 This page will help you answer questions such as ...  

What is an ecosystem?  What are biotic factors?  

What are abiotic factors?

 Why do populations of species rise and fall?  

How do environmental changes affect communities?


Sub-index for this page on ecosystems

(1) Introduction: Ecology and ecosystems: technical terms and definitions explained

(2) Competition for resources

(3) Effects of environmental changes on communities - introduction and abiotic factors

(4) Methods of surveying-monitoring pollution - measuring abiotic factors

(5) Changes in communities - biotic factors and populations

(6) Examples of how a population might change in size when a biotic/abiotic factor changes

(7) More examples of interactions - interdependence - mutualism and parasitism

See also Ecological surveying - using quadrats and transects 

and Food chains and webs, trophic levels, pyramids of biomass & numbers, transfer efficiency

and Biodiversity, land management, waste management, maintaining ecosystems - conservation


Learning objectives for this section on ecology and related sections to links above

  • Know that interdependence is the dynamic relationship between all living things.
    • It is important to understand that all living things are interdependent on each other, especially through the pathways of food chains, which are effectively energy chains too.

    • Apart from the obvious need for food and energy to survive and reproduce, there are many other factors too for particular organisms e.g. most flowering plants rely on insect pollination,

  • Be able to demonstrate an understanding of how some energy is transferred to less useful forms at each trophic level and this limits the length of a food chain.
  • Be able to show an understanding that the shape of a pyramid of biomass is determined by energy transferred at each trophic level.
    • Know and understand that the mass of living material (the biomass) at each stage in a food chain is less than it was at the previous stage.

      • Appreciate that the biomass at each stage can be drawn to scale and shown as a pyramid of biomass.

      • Up the food chain: producer ==> primary consumer ==> secondary consumer ==> tertiary consumer etc.

        • The producer is usually a photosynthesising plant or algae.

      • In a biomass pyramid, each horizontal bar (drawn to scale) is proportional to the mass of the living material at that producing level and feeding levels (trophic levels).

      • How to construct a biomass pyramid: To draw to scale, you can keep the vertical height the same for each level and make the horizontal length of the bar proportional to the biomass of that level in the pyramid.

        • Obviously, the bigger the bar, the greater the biomass at the producer/feeding-trophic level.

      • Up the food chain and 'up the pyramid' the biomass gets less because of loss of organic material, waste energy and even the energy from respiration, required to sustain life, eventually becomes waste energy too eg heat energy to the surroundings. More in section (c).

      • Know and understand that the amounts of material and energy contained in the biomass of organisms is reduced at each successive stage in a food chain because:

      • (i) some materials and energy are always lost in the organismsí waste materials by eg excretion (urine, droppings), fallen leaves from trees etc.

      • (ii) respiration supplies all the energy needs for living processes, including movement and much of this energy is eventually transferred to the surroundings, particularly with warm blooded mammals where much energy is spent in maintaining their raised body temperature.

        • the overall simplistic equation for respiration is the opposite of photosynthesis

        • glucose + oxygen ==> water + carbon dioxide (+ energy)

        • This energy is needed for all life processes, energy to do things like movement of any organism, heat to keep mammals warm,

        • The fact of the matter is, that up a food chain/biomass pyramid, only a small percentage of the mass is passed on eg

          • plants producers (100%) ==> primary consumers (caterpillars, 40%) ==> secondary consumers (small birds 5%) ==> bird of prey (owl, 0.5%)

          • This means in this particular food chain, that of all the mass /energy you start with, only 0.5% (1/200th) eventually ends up as the owl.

          • In the food chain: plants ==> rabbits ==> foxes, all these fields of plants of large areas of grass support a relatively smaller population of rabbits, which in turn support a very small number of foxes - you only get a relatively small numbers of a top predator!

          • This is the reason why you rarely get food chains of more than five stages (feeding/trophic levels) because there is so little mass/energy left in the end.

          • Once the energy is lost, it can't be used by the animal in the next stage of the food chain i.e. the next trophic level.

  • Be able to explain how the survival of some organisms may depend on the presence of another species:
    • a) parasitism - where one organism, to survive, feeds off another that acts as the host - parasites 'take with no give', live in or on the host which they may harm in the process!, including:
      • (i) fleas - insects that live in the fur of live animals and in the bedding of us humans. They feed by sucking the blood of their host provides all their feeding needs and helps them to reproduce rather too efficiently for our liking!
      • (ii) head lice - insects that live on the upper skin layer of the human scalp. Like fleas, they suck human blood for all their feeding needs and make your head feel itchy!
      • (iii) tapeworms - a parasite that can live in a person's intestines (bowel) and they tend to be flat, segmented and ribbon-like. Humans can catch them by touching contaminated faeces (stools) and then placing their hands near their mouth, swallowing food or water containing traces of contaminated faeces or eating raw contaminated pork, beef or fish. Tapeworms are common in many animals and feed by attaching themselves to the walls of an animal's intestine and absorb food through their outer body covering. In extreme cases you can suffer from malnutrition - all take and no give!
      • (iv) mistletoe - is a parasitic plant that attaches itself to trees and shrubs and grows by penetrating between the branches and absorbs nutrients and water from the host plant. Like the tapeworm producing malnutrition in animals, mistletoe can affect and reduce the host plant's growth.
    • b) mutualism - where two organisms mutually benefit from a relationship - 'give and take' in a good evolutionary Darwinian deal! - known as a mutualistic relationship!, examples include:
      • (i) oxpeckers that clean other species - these are birds that live on the backs of grazing animals (e.g. large mammals like buffalo, oxen, rhinos etc.) and eat large quantities of ticks, flies and maggots to feed themselves. In doing so they remove unwanted parasites from the animal, hence they are classed as a 'cleaner species'.
      • (ii) cleaner fish - these small fish feed off dead skin and parasites on the skin of larger fishes. In doing so they feed well, remove unwanted parasites from the big host fish and don't get eaten by the host fish!
      • (iii) nitrogen-fixing bacteria in legumes - most plants cannot absorb and chemically process the nitrogen in air to help synthesise amino acids to convert into proteins. However, leguminous plants (e.g. beans, clover, peas etc.), have in their root nodules, bacteria with the right enzymes to convert the nitrogen in air into nitrates, which the plant needs and can use to make proteins. In return the bacteria get a regular supply of water and sugar for energy, to everyone's mutual satisfaction!
      • (iv) chemosynthetic bacteria in tube worms in deep-sea vents - these extremophiles mutually depend on each other to survive. The bacteria get their necessary 'life chemicals' from the tube worms and in reproducing themselves they become food for the tube worms which act as the host.
  • Know and understand that changes in the environment affect the distribution of living organisms.

    • Exam question examples might include, but not limited to, the changing distribution of some bird species and the disappearance of pollinating insects, including bees.

  • Know and understand that animals and plants are subjected to environmental changes.

    • Realise that such changes may be caused by living or non-living factors

      living: Change in competitor (a new or rise/fall in native ones), spread of an infectious disease from parasites and pathogens, levels of prey available to hunt,

      • One species population might be affected by a 'living' factor. If it is the prey for some other animal, then in turn the predator is affected, so population changes are frequent in the animal world and can rise or fall significantly with the availability of food.

      • The decline in the bee population in many countries is attributed to them carrying pathogens/parasites and their food supply contaminated with pesticides - but nobody is quite sure, what is sure, is that bees immune system can't cope.

      • The spread of Dutch elm disease, and other diseases, are devastating tree populations.

    • non-living: Change in the average temperature or rainfall,

      • The average temperature in some northern European countries has risen, so populations of some bird species from southern areas eg the Mediterranean countries, are beginning to increase in northern Europe.

      • Acid rain, from the industrial revolution onwards, has affected forests and ecosystems in lake by decreasing the pH of water.

      • The English Channel separating England and France has become slightly warmer (only by 0.5oC in 100 years), so species of animals from warmer waters are moving north-east into warmer water ie the geographical distribution of marine life is changing.


 WHERE NEXT?

See also

Carbon cycle, nitrogen cycle, water cycle and decomposition 

Food chains, food webs and biomass  

Biodiversity, land management, waste management, maintaining ecosystems - conservation

Ecological surveying - using quadrats and transects


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