Ecology

An ecosystem is the interaction between a community of living organisms and the non-living parts of their environment. A habitat is the place where an organism lives. Organisms within ecosystems depend on each other and on environmental conditions for food, shelter, reproduction and survival.

A community consists of populations of different species living and interacting in the same habitat. Plants compete for light, space, water and mineral ions, while animals may compete for food, mates and territory. Interdependence means that changes to one species can affect many other organisms in the ecosystem.

Abiotic factors are non-living environmental factors that affect organisms and their distribution. Important examples include light intensity, temperature, moisture, soil pH and mineral content, wind intensity and direction, carbon dioxide concentration for plants, and oxygen concentration for aquatic organisms.

Biotic factors are living factors that affect communities. These include availability of food, new predators, new pathogens and competition. A change in a biotic factor can cause population sizes to rise or fall and may alter the balance of an ecosystem.

Adaptations are features that help organisms survive and reproduce in their environment. Adaptations can be structural, behavioural or functional. Organisms living under extreme conditions are called extremophiles; for example, some microorganisms can survive very high temperatures, pressures or salt concentrations.

Producers such as green plants and algae form the first trophic level because they make glucose by photosynthesis. Photosynthesis occurs mainly in chloroplasts and transfers light energy into chemical energy. Producers provide biomass and therefore energy for the rest of a food chain.

Food chains show feeding relationships and the transfer of biomass through an ecosystem. Herbivores are primary consumers that eat plants, carnivores obtain food by eating other animals, and omnivores eat both plant and animal material. Predators and prey can show linked population cycles as the abundance of one affects the other.

Ecologists estimate the distribution and abundance of organisms using sampling methods such as quadrats and transects. Samples should be representative and, where appropriate, randomly placed to reduce bias. Students should be able to calculate mean abundance and interpret ecological data from tables, charts and graphs.

Materials are continually recycled between the living and non-living parts of ecosystems. In the carbon cycle, photosynthesis removes carbon dioxide from the atmosphere, while respiration, decomposition and combustion return carbon dioxide. The water cycle involves evaporation, condensation and precipitation, continuously recycling water through the environment.

Decomposers, including microorganisms such as bacteria and fungi, break down dead organisms and waste material. Decomposition is faster when conditions provide suitable temperature, water and oxygen. Decomposers return mineral ions to the environment and carbon dioxide to the atmosphere through respiration.

Biodiversity is the variety of different species living in an ecosystem or across the Earth. High biological diversity can make ecosystems more stable because organisms are less dependent on a small number of species. Biodiversity also provides resources, ecosystem services and potential future food and medicines.

Human activities can reduce biodiversity through pollution, waste production, destruction of habitats, intensive land use, destruction of peat bogs and deforestation. Deforestation, including removal of tropical rainforest such as areas of the Amazon rainforest, destroys habitats and can reduce species populations while increasing atmospheric carbon dioxide.

Global warming is linked to increasing concentrations of greenhouse gases such as carbon dioxide and methane. Environmental change, including changes in temperature, water availability and atmospheric composition, can alter the distribution of species. These changes may be seasonal, geographical or caused by human activity.

Biodiversity can be maintained through conservation programmes, breeding programmes for endangered species, protection and regeneration of habitats, reintroduction of field margins and hedgerows, reduced deforestation, reduced carbon dioxide emissions and increased recycling. International cooperation, including agreements such as the Convention on Biological Diversity, also supports biodiversity conservation.

Biomass decreases between trophic levels because not all material is eaten or absorbed and energy is lost through respiration, movement, waste and excretion. Food security is affected by population growth, changing diets, pests, pathogens, environmental change, farming costs and conflict. Sustainable food production can include efficient farming, fishing quotas and net-size controls, while biotechnology can produce mycoprotein, human insulin and genetically modified crops with useful characteristics.