The Organism in the Environment

An ecosystem comprises all the organisms, the environment in which they live, and all the interactions within it.
There are two types of environment: the physical environment which includes factors such as temperature and light levels, and the biological environment which includes other living organisms.

A population refers to all the organisms of the same species living in an ecosystem.
A community consists of all populations of different species living together in an ecosystem.
Species diversity within a community can affect population size and variety - the more diverse the community, the more stable it’s likely to be.

Producers are able to make their own food through processes like photosynthesis.
Consumers rely on eating other organisms for their energy needs.
- Primary consumers eat producers.
- Secondary consumers eat primary consumers.
- Tertiary consumers eat secondary consumers.
Decomposers feed on dead organisms and help recycle nutrients back into the soil.

Abiotic factors can greatly influence a population’s size and distribution such as levels of light, temperature, water, and soil pH.
Light: Plants rely on sunlight for photosynthesis so availability of light can limit plant growth and influence the distribution of plant species.
Temperature: Species have different optimum temperatures for survival; too cold or too hot conditions can limit growth and reproduction.
Water: Water availability can affect both plant and animal distribution. Some species are adapted to survive in dry conditions while others require moisture.
Soil pH: Some plants prefer acidic soil while others prefer alkaline. Soil pH can therefore influence the distribution of plant species.

Biotic factors include competition, predation, symbiosis and disease which can influence the size and distribution of populations.
Competition: Organisms compete for resources such as light, water, food, or space. The ‘winners’ of this competition will survive and reproduce, influencing the distribution of species.
Predation: The relationship between predator and prey can cause changes in the size of both populations.
Symbiosis and Mutualism: Some species live in close relationship with each other, either benefiting from or being dependent on another species.
Disease: Diseases can reduce population size, especially if the population is densely packed.

Two main methods of studying ecosystems are observation and sampling. Sampling involves studying a small part of the habitat and assuming that it’s representative of the whole.
Quadrat and transect sampling are common methods used to investigate the abundance and distribution of species in a particular area.
Accurate identification of species is important in investigating ecosystems. Misidentification can alter findings and interpretations.