B7 - 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 in a community or habitat often compete with each other for light and space, and for water and mineral ions from the soil. Animals often compete with each other for food, mates and 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 (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 (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.
• Organisms have features (adaptations) that enable them to survive in the conditions in which they normally live. These adaptations may be structural, behavioural or functional.
• 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.
• Structural Adaptations are physical features, such as a Giraffe's long neck to help reach higher leaves.
• Behavioural Adaptations are how animals react to their environment, such as seeking shade or migrating.
• Functional Adaptations are how the animal's body works, such as the ability to hold breath for a long time in marine mammals, or being able to digest cellulose in cow stomachs.
• 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.
• 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.
• The water cycle provides fresh water for plants and animals on land before draining into the seas. Water is continuously evaporated and precipitated.
• 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.
• 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
• 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.
• Humans reduce the amount of land available for other animals and plants by building, quarrying, farming and dumping waste.
• 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.
• Large-scale deforestation in tropical areas has occurred to:

  • provide land for cattle and rice fields

  • grow crops for biofuels
• Levels of carbon dioxide and methane in the atmosphere are increasing, and contribute to ‘global warming’.
• 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.
• The consequences of global warming are:

  • melting of the polar ice caps
  • the rise in sea level may one day threaten many cities such as London, New York and Amsterdam
  • weather patterns will change with more unusual weather
  • animals will migrate towards the poles to find habitats with suitable temperatures
  • tropical diseases may become more common in other regions, such as the Europe
  • many species will become extinct
• Decomposing bacteria and fungi help dead organisms break down and rot. They help recycle minerals and nutrients to the environment.
• As they decompose dead matter, the decomposers also respire and so release carbon dioxide to the environment, contributing to the carbon cycle.
• Water turns from a liquid to a gas when it evaporates. Energy from the Sun can evaporate water from all places on the Earth’s surface such as puddles, ponds, lakes and oceans.
• Condensation is when water can cool and convert from gas to liquid, often forming clouds.
• Water within clouds can be blown many miles by strong winds and so transported to other areas through transportation
• Precipitation occurs when rain, snow, hail and sleet fall from the sky.
• Much water will be absorbed into the ground after precipitation but if a large volume falls or the ground is already wet some water can run along the surface of the ground. Known as surface runoff
• Infiltration occurs when water that has fallen as precipitation is absorbed into the ground. This can then be stored within underground rocks called aquifers.
• Plants need to maintain a constant stream of water to their leaves for transport and support. So they allow some water to evaporate as water vapour from their leaves to mean that more is continually ‘pulled’ to their leaves from the soil. This is known as transpiration.