How do organisms interact in an ecosystem, and what is meant by biodiversity, niche and competition?
Ecosystems as communities of organisms with their abiotic environment, the meaning of biodiversity and niche, the biotic and abiotic factors that affect organisms, and competition within and between species.
An SQA National 5 Biology answer on ecosystems, covering ecosystems as communities of organisms with their abiotic environment, the meaning of biodiversity and niche, the biotic and abiotic factors that affect organisms, and competition within and between species.
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What this dot point is asking
The SQA wants you to define an ecosystem, explain what biodiversity and a niche mean, describe the biotic (living) and abiotic (non-living) factors that affect organisms, and explain competition both within a species and between species.
What an ecosystem is
So an ecosystem combines the living and the non-living: the plants and animals of a pond plus the water, the light and the temperature around them.
Biodiversity and niche
Two species cannot occupy exactly the same niche in the same place for long, because they would compete too strongly.
Abiotic and biotic factors
The organisms in an ecosystem are affected by two kinds of factor:
- Abiotic factors are non-living: temperature, light intensity, pH and moisture (soil water). These are measured with instruments such as a thermometer, light meter, pH meter and moisture meter.
- Biotic factors are living: competition, predation, grazing, disease and the availability of food.
Both kinds of factor influence how many organisms live somewhere and which species can survive there.
Competition
Plants compete for light, water, space and minerals; animals compete for food, water, space and mates.
Examples in context
Example 1. A rock pool ecosystem. A rock pool contains a community of seaweeds, limpets, crabs and small fish, plus abiotic factors such as the water temperature, salt concentration and light. A change in an abiotic factor, like a hot day raising the temperature, can affect which organisms survive, showing how the living and non-living parts interact.
Example 2. Red and grey squirrels. Grey squirrels compete with native red squirrels for the same food and space, an example of interspecific competition. Because their niches overlap so much, the greys have largely replaced the reds across much of Britain, showing how strong competition between species can drive one out.
Try this
Q1. State what biodiversity means. [1 mark]
- Cue. The variety and relative abundance of species in an ecosystem.
Q2. Name two abiotic factors that affect organisms in an ecosystem. [1 mark]
- Cue. Any two of: temperature, light intensity, pH, moisture.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA N5 style3 marksDefine the terms ecosystem, biodiversity and niche.Show worked answer →
Three definitions are needed, one mark each.
An ecosystem is all the organisms (the community) living in a particular habitat together with the non-living (abiotic) parts of the environment.
Biodiversity is the variety and relative abundance of the different species present in an ecosystem.
A niche is the role of a species in the ecosystem, including the resources it uses, its interactions with other organisms and the conditions it can tolerate.
Markers reward a correct definition of each term. A high biodiversity makes an ecosystem more stable.
SQA N5 style2 marksExplain the difference between interspecific and intraspecific competition, and state which is usually more intense.Show worked answer →
Two contrasting points are needed, plus the comparison.
Interspecific competition is competition between members of different species for a shared resource.
Intraspecific competition is competition between members of the same species. It is usually more intense, because members of the same species need exactly the same resources.
Markers reward (1) the two types correctly defined and (2) the point that intraspecific competition is usually more intense.
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Sources & how we know this
- SQA National 5 Biology Course Specification — SQA (2019)