People change communities

Ecosystems and the stability of populations

• To give a broad view of the levels of ecological organisation, the following definitions are important:

Habitat

• Part of the environment occupied by an organism.
• If particular region an individual organism is normally confined to is extremely small, it is known as a microhabitat.

Niche

• Position organism occupies in it's habitat.
• Determined by sum of characters required for survival,eg:
  • Physical,
  • Chemical,
  • Spatial factors.
• No two species occupy the same niche, in the same environment in each other's presence.

Population

• Total number of particular species in a habitat.

Community

• The total of all populations of different species of organisms, that live and interact in the same habitat.
• based on Dynamic Feeding Relationships within a food chain.

Ecosystem

• An settled, stable unit of nature that includes all the organisms (biotic component) and the non-living (abiotic) components of the environment.
• Ecosystems are very variable in size.
• Ecosystems can support a limited population size of any single species.
• Influencing factors:
  • Abiotic Factors
  • inter-organism interactions
  • inter-organism competition
  • predation

Example

• A tropical rainforest is an ecosystem, in which one of the habitats within it as a teak tree. On the tree is a community of insects, which consists of an ant population, a bee population and a beetle population. The niche of the ant is to be the primary consumer by consuming food it locates on the tree, eg. leaves and seeds.

People change communities.

• The introduction of new plant/animal species to different countries changes the stability of native species.
• Changes may influence whole:
  • populations
  • communities
  • ecosystems.
• We must be able to evaluate evidence and make balanced judgements between meeting human demands and the need to conserve the environment.

Winners and Losers

• An alien species is a type of organism that has been introduced to an area it does not occur naturally by humans.
• May be very invasive and cause considerable ecological damage.
• Domesticated species may also give rise to problemsto native species.
• Introduced species may affect ecosystems by competing with native species.
  • Examples:
    • domestic cats,
    • grey squirrels,
    • Floating fern (Salvinia molesta),
• These may eventually replace the native species by interspecific competition.
• The floating fern was introduced around the world as a pond or aquarium plant but has damaged many lakes in the tropics due it its rapid growth.
• It has been controlled by the introduction of another alien species - salvinia weevil (Cyrtobagus salviniae).
• An example of biological control.
• Humans may influence ecosystems in other ways.
• Growth of the urban environment has increased the habitats and niches for:
  • foxes
  • rats
  • pigeons
  • cockroaches and others.

GM Organisms

• The creation of genetically modified organisms and their release may have unexpected and undesirable consequences on native populations.
• Environmental Impact Assessment report must be undertaken to minimise impact of large-scale introduction of GM organisms.
• An EIA is an assessment of the possible impact (positive or negative) that a proposed project may have on the environment.
• Some examples of genetic modification are controversial.
• Maize crops are often damaged by corn borer insects.
• A gene from a bacterium (Bacillus thuringiensis) has been transferred to maize.
• The gene codes for a bacterial protein called Bt toxin that kills corn borers feeding on maize.