4.1Ecology and the Environment
The Organism in the Environment — Edexcel Linear - OL Revision Notes & Topical Questions
15 min read 17 parts Lesson 7 of 10 Unit quiz
Ecology Key Terms, Quadrats, Population Size and Biodiversity — EDEXCEL LINEAR - OL notes: Define population, community, habitat and ecosystem, use quadrats to estimate abundance and biodiversity, and explain why biodiversity matters.A population is a group of organisms of the sa…
- Worked example 1
- Worked example 2
- Worked example 3
- Worked example 4
- Percentage cover
- Species richness
Part 1 of 5Key terms in ecology
A population is a group of organisms of the same species living in the same place at the same time.
- so removing one can affect the whole community.
- such as light, mineral ions and water) interacting in an area at one time.
Part 2 of 5Investigating population size with quadrats
Ecology is the study of species distribution, abundance and their interactions with each other and the abiotic environment. Quadrats are square frames of wood or wire, such as 0.25 m2 or 1 m2, placed on the ground to record organisms inside. They measure:
Method (comparing two areas)
- lay two tape measures to mark a survey area, use a random number generator to give coordinates and place the quadrat there, count the species, repeat for at least 10 quadrats, then repeat in the second area and compare the averages.
- Abundance is influenced by biotic factors (competition, predation, food web interactions) and abiotic factors (light, minerals, water, pH, temperature, salinity).
Limitations
- organisms can be missed, especially if hidden under another species, so move leaves aside with a pencil or stick;
- identifying species may be difficult, so use a species key.
- Spell it "quadrat", not "quadrant".
Part 3 of 5Biodiversity and why it matters
Biodiversity is the range and variety of species on Earth or in an ecosystem. It considers species richness and also variation within species, their distribution and population size. High biodiversity means many different species that show variation and are evenly spread. Human activities such as waste production, deforestation and global warming are reducing biodiversity locally and globally.
Species depend on each other for food, for shelter (birds nesting in trees) and for maintaining the physical environment (tree roots stabilise soil so it is not washed away, giving a stable habitat for other plants).
- and diverse populations are more resilient to sudden environmental change or disease.
Part 4 of 5Measuring biodiversity and evaluating the method
Use the same quadrat method, but count the number of different species in each quadrat.
Part 5 of 5Worked examples
Distinguish between a community and an ecosystem. [2]2 marks
A community is all the populations of different species in an area. An ecosystem is the community together with the abiotic factors, interacting.
Explain why quadrats should be placed using random numbers. [2]2 marks
This avoids bias, so the sample is representative of the whole area.
A student counts 5, 8, 6, 9 and 7 daisies in 0.25 m2 quadrats. Calculate the mean number per quadrat and per m2. [3]3 marks
Mean = (5+8+6+9+7)/5 = 7 per quadrat. Per m2 = 7 / 0.25 = 28.
Explain why high biodiversity makes an ecosystem more stable. [3]3 marks
Organisms depend on many species rather than one for food and shelter, so loss of one species has a smaller effect, and the community can cope better with disease or change.
Key terms
| Term | Meaning |
|---|---|
| Population | Group of the same species in one place at one time. |
| Community | All populations in an area. |
| Habitat | Place where an organism lives. |
| Ecosystem | Community plus its abiotic environment interacting. |
| Quadrat | Square frame used to sample organisms. |
| Percentage cover | Estimated percentage of a quadrat covered by a species. |
| Biodiversity | Range and variety of species in an area. |
| Species richness | Number of different species present. |
Avoid these mistakes
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