3.2.7 Biodiversity

3.2.7 Biodiversity: Describe how biotic and abiotic factors affect the biodiversity and distribution of organisms in an ecosystem.

Biodiversity

Biodiversity is the variety of different species living in an area together with the number of individuals of each.

Biotic factors

These are living influences such as competition, predation, disease and food availability, which change population sizes.

Abiotic factors

These are non-living influences such as light intensity, temperature, pH and moisture, which decide where species can live.

Balanced systems

High biodiversity occurs when conditions and the interactions between species stay balanced and stable over time.

Biotic Factors in Action

Grazing

Many red deer in the Highlands eat young Scots pine shoots, so trees stay short and few habitats and food sources exist.

Reducing grazers

Fencing or fewer deer lets saplings survive, undergrowth thickens, and more insects, birds and mammals can live there.

Introduced predator

American mink released in Britain hunt water voles, which has reduced the voles to a few safe areas.

Recovery

Where mink are controlled, water voles can spread out again from their refuges along connected stretches of river.

Abiotic Factors in Action

Stream oxygen

Cool, fast-flowing water holds more dissolved oxygen, so oxygen-sensitive stonefly larvae and salmon thrive there.

Warm slow water

Less oxygen dissolves in warm, slow water, so a few tolerant species dominate and biodiversity falls.

Upper rocky shore

This zone is exposed longest, so it dries and heats up, favouring barnacles and limpets that cling to rock.

Lower rocky shore

This zone stays under water longest, so kelp and anemones that need constant water live there.

Zone	Time exposed to air	Typical organisms
Upper shore	Longest	Barnacles, limpets
Lower shore	Shortest	Kelp, anemones

Pollution, deforestation or climate change alters the abiotic conditions in a habitat.

Sensitive species can no longer survive, so their populations fall or disappear from the area.

Tolerant species face less competition and may increase, so one or two species begin to dominate.

The number of species falls, so biodiversity decreases and the distribution of organisms changes.

Controlling the cause, such as culling a predator or reducing pollution, can allow biodiversity to recover.

Biodiversity: The variety of species in an area and the number of individuals of each.
Biotic factor: A living factor, such as predation or competition, that affects organisms.
Abiotic factor: A non-living factor, such as temperature or pH, that affects organisms.
Distribution: Where in an area or habitat a species is found.
Niche: The role and position of a species within its habitat, including what it eats and where it lives.

Calling temperature or pH a biotic factor; they are abiotic because they are non-living.
Saying biodiversity is only the number of species; it also covers how many individuals of each there are.
Giving an example without linking it to its effect, such as naming deer but not saying overgrazing reduces habitats.
Describing the rocky shore zones the wrong way round; the upper shore is the most exposed to air.