Ecosystems
5.1 Understand the terms ecosystem, community, population and habitat.
5.2 Understand that the numbers and distribution of organisms in a habitat are controlled by biotic and
abiotic factors.
5.3 Understand how the concept of niche accounts for distribution and abundance of organisms in a
habitat.
Key Terms
Ecosystem: All of the communities, organisms (biotic) and non-living (abiotic factors) living in a
particular area.
These factors are interacting and interdependent – they make up a self-contained
system, which is self-supporting in terms of energy flow.
Community: All of the organisms of different species that live in the same habitat and interact with
each other.
Population: All the interbreeding individuals of one species in a habitat.
Population Size: The number of individuals of one species in a particular area.
Habitat: The place with a distinct set of conditions where an organism lives.
Abiotic Factors: The non-living features of an ecosystem.
E.g. Light intensity, climate, pollution, catastrophes.
Biotic Factors: The living features of an ecosystem.
E.g. Competition, disease, predation, mutualism.
Abundance: The number of individuals of one species in a particular area.
Distribution: Where a species is in a particular area.
Niche
• Niche: The role of a species within its habitat, including its biotic and abiotic interactions.
• Every species has its own unique niche – a niche can only be occupied by one species.
• The abundance of different species can be explained by the niche concept:
• Two species occupying similar niches will compete, so fewer individuals of both species will be able
to survive in the area.
• The distribution of different species can be explained by the niche concept:
• Organisms can only exist in habitats where all of the conditions that make up their role exist.
Distribution
• Distribution varies due to abiotic factors – organisms can only exist where the abiotic factors they
can survive in exist.
• Distribution also varies due to biotic factors – if two species are competing, but one is better adapted
to its surroundings, the less well-adapted species is likely to be out-competed.
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