Ecosystems, adaptations and interdependence · GCSE Biology

Communities and competition

An ecosystem is the interaction of a community of living organisms (biotic parts) with the non-living (abiotic) parts of their environment.
Plants compete with each other for light, space, water and mineral ions from the soil.
Animals compete with each other for food, mates and territory.
Species depend on each other for food, shelter, pollination and seed dispersal. This is interdependence: removing one species can affect the whole community.
In a stable community, all the species and environmental factors are in balance, so population sizes stay fairly constant.

Abiotic (non-living) factors: light intensity, temperature, moisture levels, soil pH and mineral content, wind intensity and direction, carbon dioxide levels for plants, and oxygen levels for aquatic animals.
Biotic (living) factors: availability of food, new predators arriving, new pathogens, and one species outcompeting another.

Structural adaptations are features of the body, such as thick fur or a large surface area.
Behavioural adaptations are ways of behaving, such as migrating or hibernating.
Functional adaptations are processes inside the body, such as making concentrated urine or antifreeze proteins.
Extremophiles live in extreme environments with high temperature, pressure or salt concentration, such as bacteria living in deep-sea vents.

Food chains start with a producer, a photosynthetic organism such as a green plant or alga, which makes glucose and so biomass.
Producers are eaten by primary consumers, which are eaten by secondary consumers, then tertiary consumers. Consumers that kill and eat other animals are predators; those eaten are prey.
In a stable community, predator and prey numbers rise and fall in cycles: when prey increase, predators increase; then prey fall, and predators fall after them.

Trophic levels are the feeding levels in a food chain; level 1 is producers. Decomposers break down dead material.
Pyramids of biomass show the relative amount of biomass at each level. Only about 10% of biomass is transferred to the next level.
Biomass is lost because not all food is eaten or absorbed (some is egested as faeces), and much is lost as waste such as carbon dioxide, water and urea, and used in respiration.
Efficiency of transfer = (biomass transferred to next level ÷ biomass at previous level) × 100.

Ecosystem: A community of organisms interacting with the non-living parts of their environment.
Community: All the populations of different species living in a habitat.
Population: All the organisms of one species living in a habitat.
Interdependence: The way species in a community depend on each other.
Abiotic factor: A non-living factor, such as temperature or light, that affects organisms.
Biotic factor: A living factor, such as predators or disease, that affects organisms.
Adaptation: A feature that helps an organism survive in its environment.
Extremophile: An organism that lives in extreme conditions, such as high temperature or salt.
Producer: An organism, usually a plant or alga, that makes its own food by photosynthesis.
Predator: An animal that kills and eats other animals.
Trophic level: A feeding level in a food chain.
Biomass: The mass of living material.