An ecosystem is a large system with many different interacting parts, including living and nonliving elements. Ecologists study the interactions between living things and their environment within ecosystems. The living parts of an ecosystem are called biotic factors and include organisms that interact, while the nonliving parts are called abiotic factors such as temperature, soil, sunlight and water. Ecosystems can be found in forests, grasslands, marine environments like coral reefs and estuaries, and freshwater environments like lakes and ponds.