CIE A Level Biology复习笔记18.2.1 Ecosystems & Niches

Ecosystems

• Species do not exist by themselves in their own isolated environment, they interact with other species forming communities
• These communities interact with each other and the environment they live in, forming ecosystems
• An ecosystem is a relatively self-contained community of interacting organisms and the environment they live in, and interact with
• There is a flow of energy within an ecosystem and nutrients within it are recycled
• There are both living (biotic) components and non-living (abiotic)components within an ecosystem
• Ecosystems vary greatly in size and scale
  • Both a small pond in a back garden and the open ocean could be described as ecosystems
  • A human being could also be described as an ecosystem; there are thousands of species of bacteria living on and in every person
• Ecosystems vary in complexity:
  • A desert is a relatively simple ecosystem
  • A tropical rainforest is a very complex ecosystem
• No ecosystem is completely self-contained as organisms from one ecosystem are often linked to organisms from another
  • For example, birds are able to fly long distances to feed from multiple ecosystem

Example of an ecosystem

A forest is a perfect example of a complex ecosystem. There is a large community of organisms including trees, birds, small and large mammals, insects and fungi. The non-living components of the ecosystem include: the soil, dead leaves, water from the rain and streams, the rocks and any other physical or chemical factors. The non-living components of the ecosystem influence the community of organisms.

Niche

• The place where a species lives within an ecosystem is its habitat
• The role that species plays within an ecosystem is its niche
  • It encompasses where in the environment the organism is, how it gets its energy and how it interacts with other species and its physical environment
  • This is how an organism fits into the ecosystem

Example of a nicheA dung beetle occupies a very specific niche within its ecosystem. Dung beetles have learned to exploit the dung of animals as a resource and they have a characteristic behaviour of rolling the dung into balls before transporting it to their underground burrow for storage as food. Their behaviour within their ecosystem has many knock-on effects on the environment and other organisms living in it. The burrows and tunnels that they create turns over and aerates the soil and the buried dung releases nutrients into the soil both of which can benefit other organisms like plants. The transportation of the dung underground by the beetles also helps to keep fly populations under control.