Ecology is the study of interactions between living things and the environment. An ecosystem is the combination of living things, such as plants, animals and microscopic organisms, plus environmental factors such as temperature, rain and sun light and ecology studies all of these aspects of an ecosystem. As a science, ecology is a broad field and includes a number of different sciences such as biology, physics, chemistry and geology.
Organisms and the environment both effect each other. For example, a plant is affected by rain and sun light but environment beneath the plant is influenced by the plant because it reduces the amount of light, drops leaves, reduces the temperature and so on. Additionally, living things influence each other through competition, predation and other relationships. Environmental factors are often referred to as abiotic factors and relationships between living things are often called biotic factors.
Abiotic factors are environmental variables such as temperature, wind exposure, rainfall, sunlight and soil nutrients. The combination of these factors determine the overall environment of a location.
A population is a group of inter-breeding organisms found in the same place at the same time. Population ecology studies how populations interact with the environment.