Factors That Affect Communities

Section 1 of 7Two kinds of factor

Community of organisms

Abiotic

• Abiotic Non-living factors in the environment, such as temperature, light and soil pH.

Biotic

• Biotic Factors caused by other living things, such as predators, food supply and disease.

Community

• Community All the populations of different species living in the same habitat, interacting with each other.

Section 2 of 7Abiotic factors

Factor	Effect on organisms
Light intensity	Limits the rate of photosynthesis, so plant growth
Temperature	Affects enzyme activity, growth and where species can live
Moisture level	Organisms need water; dry conditions limit species
Soil pH and mineral content	Affects which plants can grow
Wind intensity and direction	Increases water loss and disturbs organisms
Carbon dioxide (plants) and oxygen (water animals)	Needed for photosynthesis or respiration

Section 3 of 7Biotic factors

Food availability

• Food availability More food supports larger populations.
• A poor season for the food source can make the consumer population crash.

New predators

• New predators A new predator can reduce prey numbers.
• Prey that are not adapted to escape it may be wiped out locally.

New pathogens

• New pathogens Disease can lower populations, especially where individuals live close together.

Competition

• Competition Species compete for light, food, water, space or mates, and the better adapted survive.

Section 4 of 7How factors change a community

1A factor changes

• A factor changes For example a dry summer lowers soil moisture, or a new predator arrives.

2Some species suffer

• Some species suffer Organisms poorly adapted to the new conditions grow, feed or reproduce less successfully.

3Populations shift

• Populations shift Numbers of those species fall, while better adapted species may increase because competition is reduced.

4Interdependence

• Interdependence Because organisms depend on each other for food and shelter, a change in one population affects others in the food web.

Section 5 of 7Answering a data question

1

State the pattern in the data, such as 'as CO₂ concentration rises, plant height rises'.

2

Quote figures from the graph or table to support it, including units.

3

Give the scientific reason, for example CO₂ is a reactant of photosynthesis, producing more glucose for growth.

4

Say where the trend levels off and suggest a limiting factor, such as light intensity or temperature.

5

Make a conclusion that matches only what the data show.

Section 6 of 7Key terms

Term	Meaning
Abiotic factor	A non-living part of the environment.
Biotic factor	A living part of the environment, such as a predator.
Community	All the populations living together in a habitat.
Competition	Organisms trying to obtain the same limited resource.
Population	All the organisms of one species in an area.
Interdependence	The way species in a community rely on one another for food and shelter.

Section 7 of 7Exam technique

1

Giving a pattern without quoting numbers from the graph.

2

Labelling a predator or disease as abiotic. They are living, so biotic.

3

Saying more light always gives more growth; other factors can become limiting.

4

Confusing a population with a community.

5

Describing a change in one species without linking it to the others through the food web.