Ecosystems, distribution and the niche

Key terms

• Population: all the organisms of one species living in a habitat at the same time.
• Community: all the populations of different species living and interacting in a habitat.
• Habitat: the place where an organism lives.
• Ecosystem: a community together with the non-living (abiotic) parts of its environment, interacting as a system.

Biotic and abiotic factors

The numbers and distribution of organisms are controlled by:

• Abiotic (non-living) factors: temperature, light intensity, water availability, humidity, pH, mineral ions, oxygen, soil type, wind and exposure.
• Biotic (living) factors: competition (within a species, intraspecific, and between species, interspecific), predation, grazing, parasitism, disease and food supply.

A population grows until a factor (food, space, predators, disease) limits it.

The niche

A niche is the way an organism exploits its environment: its role in the habitat, including what it feeds on, where and when it is active, and its interactions with biotic and abiotic factors.

Two species cannot occupy exactly the same niche in a habitat for long: one outcompetes the other. So the niche each species occupies determines where it is found (distribution) and how many there are (abundance).

Worked example

Classify each factor affecting a population of limpets on a rocky shore as biotic or abiotic: (a) wave action, (b) predation by crabs, (c) competition with barnacles for space, (d) temperature of rock pools.

1. (a) non-living: abiotic
2. (b) living: biotic
3. (c) living: biotic
4. (d) non-living: abiotic

Answer: (a) abiotic, (b) biotic, (c) biotic, (d) abiotic.

Check yourself

1. What is a population?
   • All the species living in a habitat
   • A community and its abiotic environment
   • All the organisms of one species in a habitat at the same time
   • The place where an organism lives
   Show answer

   All the organisms of one species in a habitat at the same time. Population = one species.

2. What is an ecosystem?
   • A community and the abiotic factors it interacts with
   • All the members of one species
   • A single habitat with no living things
   • The role of a species
   Show answer

   A community and the abiotic factors it interacts with. Ecosystem includes living and non-living parts.

3. Which term describes all the populations of different species living in a pond?
   • Population
   • Niche
   • Community
   • Habitat
   Show answer

   Community. Many species together form a community.

4. Which is an abiotic factor?
   • Predation
   • Soil pH
   • Disease
   • Competition for mates
   Show answer

   Soil pH. pH is non-living; the others involve organisms.

5. Competition between individuals of different species is called
   • intraspecific competition
   • predation
   • mutualism
   • interspecific competition
   Show answer

   interspecific competition. Inter- means between (different species).

6. Two species of bird feed on the same insects but at different heights in the same trees. What does this show?
   • They occupy exactly the same niche
   • They occupy different niches, reducing competition
   • They are one species
   • They are not competing for any resource
   Show answer

   They occupy different niches, reducing competition. Different feeding positions mean different niches.

Practise with instant feedback Print this lesson

Sources

• Pearson Edexcel International Advanced Level in Biology specification (XBI11/YBI11, first teaching 2018)

Last updated 7 November 2026. Spotted a mistake? Tell us.