A natural ecosystem is an assemblage of plants, animals, and microorganisms that functions as an integrated unit and maintains its identity over time. Examples of natural ecosystems include forests, grasslands, estuaries, and tundra. These ecosystems operate without significant human intervention and depend entirely on solar energy. Broadly, natural ecosystems are divided into two categories:

• Terrestrial ecosystems: Found on land, such as forests, grasslands, deserts, and tundra.
• Aquatic ecosystems: Found in water bodies, further classified into:

• Freshwater ecosystems: rivers, lakes, ponds.
• Marine ecosystems: oceans, estuaries.