The ecology of ecosystems (5.1, 5.2, 5.3, 5.4)
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A habitat is the environment in which an organism lives characterised by biotic (living) and abiotic (non-living) components that influence its survival and reproduction.
A population is all of the organisms of one species, living in the same place at the same time.
A community consists of all the populations of different species living and interacting in the same habitat or ecosystem.
An ecosystem is a self-contained dynamic system influenced by the biotic (living) and abiotic (non-living) factors in an area.
Ecosystems range in size and constantly change over time due to shifts in environmental conditions, species interactions, and disturbances.
Biotic factors are all the living organisms within an ecosystem.
Biotic factors include plants (producers), animals (consumers), bacteria, fungi, and microorganisms (including decomposers).
Biotic components interact with each other through predation, competition, and symbioses/mutualism (mutually beneficial relationships).
Anthropogenic factors are environmental changes caused by human activities. They can be considered biotic or abiotic and affect both living and non-living components of an ecosystem.
Human activities have altered many ecosystems through processes such as deforestation, pollution, urbanisation, and climate change, meaning that many ecosystems are no longer completely natural.
Abiotic factors are the non-living components of an ecosystem that influence living organisms.
Abiotic factors include light, temperature, water, oxygen, , and nutrient levels.
Abiotic components affect the availability of resources and the conditions for survival, influencing the distribution and abundance of organisms.
Primary succession occurs on newly exposed or bare land with no existing soil and no previous community.
Primary succession involves:
- Colonisation by pioneer species – the first organisms to colonise the barren environment are typically lichen and algae.
- Soil formation – pioneer species die and decompose, forming basic soil (humus). The weathering of rock adds minerals – plants like ferns and moss begin to populate the area, replacing the lichen and algae.
- Climax community – eventually, a stable, self-sustaining community develops, often including trees (depending on the climate). The species composition remains relatively constant until disturbed.
Secondary succession occurs when a disturbance affects land that previously supported a community, but the soil remains intact. The area is then recolonised by organisms.
As soil, nutrients and microbes are already present in the area, secondary succession will occur much faster than primary succession.
An example of secondary succession is the recovery of a woodland after a forest fire.
Deflected succession occurs when human activity prevents an ecosystem from reaching its natural climax community.
This is when a regular disturbance (e.g., grazing, mowing, burning, ploughing) interrupts succession and maintains the ecosystem at an earlier stage. This results in a stable but artificial community, maintained only by continued human management. If human intervention stops, succession will continue toward the natural climax community.
Examples include grassland maintained by grazing and heathland maintained by burning or grazing.
An organism’s niche is its role within an ecosystem, including how it interacts with both the biotic and abiotic factors in its environment and the conditions to which it is adapted for survival.
Although different species may share some habits, behaviours, or resources, no two species can occupy exactly the same niche in the same habitat at the same time. This is known as the competitive exclusion principle.