Ecosystem Components (Cambridge (CIE) IGCSE Environmental Management): Revision Note

What are the components of an ecosystem?

• A biotic factor is a living thing that has an impact on other populations of living things or on the environment

• Abiotic factors do the same thing, but they are non-living

• Together, biotic and abiotic factors make up an ecosystem

• We can therefore define an ecosystem as:

• Ecosystems vary in size and scale 

  • A small ecosystem could be a garden pond

  • A large-scale ecosystem could be all tropical rainforests—this is known as a biome

• The living parts of an ecosystem are made up of communities

  • Communities are the interacting populations of different organisms in a particular area

  • For example, a woodland community of organisms such as oak trees, ferns, mosses, foxes, rabbits, butterflies, beetles, mushrooms, woodlice, spiders, etc.

• Communities are made up of populations

  • Populations are all the individuals of the same species in the same place

  • For example, a population of puffins on a clifftop or a population of sunflowers in a garden

• The place where an organism lives, which provides food, shelter and a place to reproduce, is called a habitat

  • Within its habitat, the species has a particular role in terms of its interactions with other species and its effect on the environment; this is called its niche

  • A niche describes:

    • The abiotic factors that the species can withstand

    • The resources in the ecosystem that it is able to make use of (e.g. the soil nutrients available to it)

    • Its interactions with other organisms (biotic factors)

• Each individual species has its own distinct niche because only one species can occupy a given niche

• If two species try to occupy the same niche, they will compete with each other for the same resources

  • One of the species will be more successful and out-compete the other species until only one species is left and the other is either forced to occupy a new, slightly different niche or go extinct from the habitat or ecosystem altogether

• For example, if there were three bird species occupying the same habitat (such as a forest), they would occupy slightly different niches as each species would feed at a different height along the trees

  • This avoids competition between the three species, allowing them to coexist closely with each other in the same habitat

• A predator is an organism that hunts, kills and eats prey for food

  • Populations of predators and prey are closely linked

    • Many predators have niche prey – the food that predators prefer to eat

• An apex predator doesn't have any natural predators, so its role is to keep the ecosystem healthy and control the population of prey species

Abiotic & biotic components of an ecosystem

• Within an ecosystem the different biotic components – plants (flora), animals (fauna), fungi, and microorganisms like bacteria – depend on each other and the abiotic components

• This is known as interdependence

Biotic (living) components

• Biotic components interact with each other through food chains, competition, and mutual support

• Producers

  • Plants and algae produce their own food using energy from sunlight

  • The energy that they store serves as food for the consumers and decomposers, either directly or indirectly

  • They form the first level in a food chain

• Consumers get their energy by feeding on other organisms: plants or animals or both

  • Primary consumers are herbivores/omnivores that feed mostly on producers – plants and plant-derived material

    • For example, a grasshopper consumes grass

    • The producers' chemical energy is then transferred to the primary consumers

  • Secondary consumers are predators (carnivores/omnivores) that feed on primary consumers

    • For example, a frog eats the grasshopper

  • Tertiary consumers are predators that feed on secondary consumers

    • For example, a snake eats the frog, etc.

  • The final consumer is called a top (or apex) predator and is not eaten by anything else but dies and is recycled by decomposers

• Decomposers are organisms that break down dead organisms in a process called decomposition (rotting) into simpler substances and play a vital role in the recycling of matter (nutrient cycling)

  • For example, bacteria decompose organic matter, releasing nutrients for plant uptake

  • Fungi break down dead plant material, such as fallen leaves and wood, into simpler compounds

Abiotic (non-living) components

• Temperature: Both plants and animals have evolved to thrive at ideal temperatures

• Water:

  • Most plants are killed by waterlogging, as they are unable to respire

  • Animals and plants have adapted to tolerate different levels of moisture

• Oxygen is required for animal respiration

  • Oxygen dissolves in water for aquatic animals

  • Some animals are bioindicator species, as their presence or absence indicates the condition of the habitat

• Carbon dioxide is needed for photosynthesis

• Greater concentrations increase plant growth and yields

  • However, CO₂ is an acidic gas and some plants are sensitive to changes in pH levels

• Salinity: The amount of salt in the soil/water has an impact on plant growth and animal health

  • High levels kill plants and leave bare, easily eroded soil

  • Wetlands deteriorate, placing species at risk and reducing biodiversity

• Light: Photosynthesis requires light, and plant species have adapted to grow best in the light that is available in their environment

• pH: Many plants are sensitive to pH levels