Identify the biotic and abiotic components of ecosystems and explain how abiotic factors shape distribution.

What this dot point is asking

Biotic and abiotic components

Every ecosystem has two kinds of components:

• Biotic components: all the living things, including producers, consumers, and decomposers, and the interactions between them such as predation and competition.
• Abiotic components: the non-living physical and chemical factors, including temperature, light, water availability, soil type, pH, oxygen, salinity, and wind.

These two sets of components are interdependent. Abiotic conditions determine which organisms can survive, and organisms in turn change their environment, for example when plants alter soil moisture or trees create shade.

Levels of ecological organisation

Ecology is studied at increasing scales, each nested inside the next:

• Organism: a single living individual.
• Population: all individuals of one species in an area.
• Community: all the populations of different species living together in an area.
• Ecosystem: the community plus its abiotic environment.
• Biosphere: all ecosystems on Earth combined.

Distinguishing these levels matters because questions are asked at different scales, for example population size versus community diversity versus ecosystem energy flow.

How abiotic factors shape distribution

Each species can only survive within a certain range of conditions for each abiotic factor. This is called its range of tolerance. Within that range there is an optimum zone where the organism thrives, flanked by zones of stress, and beyond the limits the organism cannot survive.

Key abiotic factors and their effects include:

• Temperature: controls the rate of metabolism and limits which organisms can survive; many have narrow thermal tolerances.
• Water: essential for all life; availability shapes the difference between rainforest and desert communities.
• Light: drives photosynthesis, so light availability controls plant growth and, indirectly, the whole food web.
• Soil and pH: affect which plants can take up nutrients and therefore what grows where.
• Salinity: limits which organisms survive in estuaries, salt marshes, and marine environments.

Habitat and niche

Two related ideas describe where and how an organism lives:

• A habitat is the physical place where an organism lives, defined largely by abiotic conditions.
• A niche is the organism's full role, including the resources it uses, the conditions it tolerates, and its interactions with other species.

No two species can occupy exactly the same niche indefinitely in the same place, because one would outcompete the other. This principle, competitive exclusion, helps explain how diverse communities partition resources.

Microhabitats and edge effects

Within a single ecosystem, conditions vary on a small scale, creating microhabitats such as the cool, moist underside of a log. These local differences in abiotic factors increase the variety of niches available and therefore support more species. Where two ecosystems meet, the boundary (an ecotone) often has its own mix of conditions and species, an edge effect that can raise local diversity.