Communities, adaptations and interdependence – GCSE Combined Science Biology

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Living things never live alone. A fox needs rabbits to eat. A rabbit needs grass. The grass needs light, water and soil. Ecology is the study of how living things fit together with their surroundings.

This matters because when one part of a community changes, many others can change too. That is why losing bees or a predator can affect a whole area.

By the end you will be able to name the levels from habitat to ecosystem. You will sort factors into living and non-living. You will read a predator and prey graph and describe three kinds of adaptation.

Levels of organisation

A habitat is the place where an organism lives, such as a pond. A population is all the organisms of one species in that habitat, such as all the frogs.

A community is all the populations of different species living there. The frogs, fish, snails and weeds together make a community. An ecosystem is the community plus the non-living parts of the environment, such as water and temperature.

Think of a school. All the Year 9 students are like one population. Everyone in the building, students and staff, is more like a community.

Abiotic factors

Abiotic factors are the non-living parts of the environment. Abiotic is just a word for non-living. These factors can change how many organisms live in a place.

Examples are light intensity, temperature, moisture, soil pH, mineral content and wind. Plants also depend on the carbon dioxide level, and water animals depend on the oxygen level.

A change in one factor can change the size of a population. For example, too little light limits photosynthesis in a plant, so the plant grows less.

Biotic factors

Biotic factors are the living parts of the environment. Biotic means living. They include the food supply, new predators arriving and new pathogens. A pathogen is a microorganism that causes disease.

Competition is another biotic factor. It happens when organisms try to get the same limited thing. Animals compete for food, mates and territory. Plants compete for light, space, water and mineral ions.

Think of a long queue at the school canteen. There is only so much food, so not everyone gets their first choice. A species that cannot compete well will fall in number.

Interdependence and stable communities

Interdependence means that species depend on each other. They rely on each other for food, shelter, pollination and seed dispersal. Pollination is moving pollen between flowers. Seed dispersal is spreading seeds to new places.

If one species is removed, many others can be affected. For example, losing bees would mean fewer flowers are pollinated.

In a stable community, species and environmental factors are in balance, so population sizes stay fairly constant. The carbon cycle and water cycle help the community to be self-sustaining.

Predators and prey

A predator is an animal that hunts and eats other animals. Prey is the animal that gets eaten. In a stable community their numbers rise and fall in a cycle.

When prey numbers rise, there is more food, so predator numbers rise. More predators eat more prey, so prey numbers fall. Then predators have less food and their numbers fall. The prey recover and the cycle starts again.

Look at the graph. The predator peak comes after the prey peak, because predators need time to respond.

Adaptations

An adaptation is a feature that helps an organism survive in its environment. There are three kinds. Structural adaptations are body features, such as the thick fur and blubber of a polar bear.

Behavioural adaptations are how an organism acts, such as migration or hibernation. Migration is moving to another place for the winter. Hibernation is a deep sleep through the cold months. Functional adaptations are processes in the body, such as a camel making concentrated urine.

Extremophiles are organisms adapted to extreme conditions, such as high heat, salt or pressure. Some bacteria live in hot springs and deep sea vents.

Recap

A population is one species. A community is all the species. An ecosystem adds the non-living environment.

Abiotic factors are non-living. Biotic factors are living, including predators, pathogens and competition.

Predator and prey numbers rise and fall in linked cycles, with the predators peaking later.

Adaptations can be structural, behavioural or functional.