ecology

• An ecosystem is the interaction of a community of living organisms (biotic) with the non-living (abiotic) parts of their environment.
• To survive and reproduce, organisms require a supply of materials from their surroundings and from the other living organisms there.
• Plants compete for:

  • light
  • space
  • water
  • mineral ions
• animals compete for:

  • food
  • mates
  • territory
• Within a community each species depends on other species for food, shelter, pollination, seed dispersal etc. If one species is removed it can affect the whole community. This is called interdependence. A stable community is one where all the species and environmental factors are in balance so that population sizes remain fairly constant.
• Abiotic factors

  Abiotic (non-living) factors which can affect a community are:

  • light intensity
  • temperature
  • moisture levels
  • soil pH and mineral content
  • wind intensity and direction
  • carbon dioxide levels for plants
  • oxygen levels for aquatic animals.
• Biotic factors

  Biotic (living) factors which can affect a community are:

  • availability of food
  • new predators arriving
  • new pathogens
  • one species outcompeting another so the numbers are no longer sufficient to breed.
• Adaptations

  Some organisms live in environments that are very extreme, such as at high temperature, pressure, or salt concentration. These organisms are called extremophiles. Bacteria living in deep sea vents are extremophiles.
• Levels of organisation

  Feeding relationships within a community can be represented by food chains. All food chains begin with a producer which synthesises molecules. This is usually a green plant or alga which makes glucose by photosynthesis.

  A range of experimental methods using transects and quadrats are used by ecologists to determine the distribution and abundance of species in an ecosystem.
• Producers are eaten by primary consumers, which in turn may be eaten by secondary consumers and then tertiary consumers.
• Consumers that kill and eat other animals are predators, and those eaten are prey. In a stable community the numbers of predators and prey rise and fall in cycles.
• How materials are cycled

  All materials in the living world are recycled to provide the building blocks for future organisms.

  The carbon cycle returns carbon from organisms to the atmosphere as carbon dioxide to be used by plants in photosynthesis.
• How materials are cycled

  The water cycle provides fresh water for plants and animals on land before draining into the seas. Water is continuously evaporated and precipitated
• Decomposition (biology only)

  Gardeners and farmers try to provide optimum conditions for rapid decay of waste biological material. The compost produced is used as a natural fertiliser for growing garden plants or crops.

  Anaerobic decay produces methane gas. Biogas generators can be used to produce methane gas as a fuel.
• Impact of environmental change (biology only) (HT only)

  Environmental changes affect the distribution of species in an ecosystem. These changes include:

  • temperature
  • availability of water
  • composition of atmospheric gases.

  The changes may be seasonal, geographic or caused by human interaction.
•  Biodiversity

  Biodiversity is the variety of all the different species of organisms on earth, or within an ecosystem.

  A great biodiversity ensures the stability of ecosystems by reducing the dependence of one species on another for food, shelter and the maintenance of the physical environment.

  The future of the human species on Earth relies on us maintaining a good level of biodiversity. Many human activities are reducing biodiversity and only recently have measures been taken to try to stop this reduction.
• Waste management

  Rapid growth in the human population and an increase in the standard of living mean that increasingly more resources are used and more waste is produced. Unless waste and chemical materials are properly handled, more pollution will be caused.

  Pollution can occur:

  • in water, from sewage, fertiliser or toxic chemicals
  • in air, from smoke and acidic gases
  • on land, from landfill and from toxic chemicals.

  Pollution kills plants and animals which can reduce biodiversity.
• Land use

  Humans reduce the amount of land available for other animals and plants by building, quarrying, farming and dumping waste.
• Land use

  The destruction of peat bogs, and other areas of peat to produce garden compost, reduces the area of this habitat and thus the variety of different plant, animal and microorganism species that live there (biodiversity).

  The decay or burning of the peat releases carbon dioxide into the atmosphere
•  Deforestation

  Large-scale deforestation in tropical areas has occurred to:

  • provide land for cattle and rice fields
  • grow crops for biofuels
• Global warming

  Levels of carbon dioxide and methane in the atmosphere are increasing, and contribute to ‘global warming’.
• Maintaining biodiversity

  Scientists and concerned citizens have put in place programmes to reduce the negative effects of humans on ecosystems and biodiversity.

  These include:

  • breeding programmes for endangered species
  • protection and regeneration of rare habitats
  • reintroduction of field margins and hedgerows in agricultural areas where farmers grow only one type of crop
  • reduction of deforestation and carbon dioxide emissions by some governments
  • recycling resources rather than dumping waste in landfill.
• Trophic levels

  Trophic levels can be represented by numbers, starting at level 1 with plants and algae. Further trophic levels are numbered subsequently according to how far the organism is along the food chain.
• Trophic levels

  Level 1: Plants and algae make their own food and are called producers.

  Level 2: Herbivores eat plants/algae and are called primary consumers.

  Level 3: Carnivores that eat herbivores are called secondary consumers.

  Level 4: Carnivores that eat other carnivores are called tertiary consumers. Apex predators are carnivores with no predators.
• decomposers

  Decomposers break down dead plant and animal matter by secreting enzymes into the environment. Small soluble food molecules then diffuse into the microorganism.
• Pyramids of biomass

  
• Producers are mostly plants and algae which transfer about 1% of the incident energy from light for photosynthesis.
• Only approximately 10% of the biomass from each trophic level is transferred to the level above it.
• Losses of biomass are due to:

  • not all the ingested material is absorbed, some is egested as faeces
  • some absorbed material is lost as waste, such as carbon dioxide and water in respiration and water and urea in urine.

  Large amounts of glucose are used in respiration.
• Food security is having enough food to feed a population.
• Biological factors which are threatening food security include:

  • the increasing birth rate has threatened food security in some countries
  • changing diets in developed countries means scarce food resources are transported around the world
  • new pests and pathogens that affect farming
  • environmental changes that affect food production, such as widespread famine occurring in some countries if rains fail
  • the cost of agricultural inputs
  • conflicts that have arisen in some parts of the world which affect the availability of water or food.
• Farming techniques

  The efficiency of food production can be improved by restricting energy transfer from food animals to the environment. This can be done by limiting their movement and by controlling the temperature of their surroundings.

  Some animals are fed high protein foods to increase growth.
• Sustainable fisheries

  Fish stocks in the oceans are declining. It is important to maintain fish stocks at a level where breeding continues or certain species may disappear altogether in some areas.

  Control of net size and the introduction of fishing quotas play important roles in conservation of fish stocks at a sustainable level.
• Role of biotechnology

  Modern biotechnology techniques enable large quantities of microorganisms to be cultured for food.

  The fungus Fusarium is useful for producing mycoprotein, a protein-rich food suitable for vegetarians. The fungus is grown on glucose syrup, in aerobic conditions, and the biomass is harvested and purified.
•  Role of biotechnology

  A genetically modified bacterium produces human insulin. When harvested and purified this is used to treat people with diabetes.

  GM crops could provide more food or food with an improved nutritional value such as golden rice.