What is an ecosystem?
An ecosystem is a system in which living communities and their interactions with nonliving surroundings such as water, soil, air and light are studied together. A pond, forest or coastline can be considered an ecosystem at a chosen scale; boundaries often depend on the research question.
Energy flow and food webs
Plants and other primary producers make organic matter using light or chemical energy. Herbivores and carnivores obtain energy by feeding; decomposers break down organic compounds in dead material. A food chain shows one pathway, while a food web better represents many connections. A substantial share of energy is dissipated through metabolism and heat at each transfer, so energy reaching higher levels is limited. Species also influence one another through competition, symbiosis and changes to their environment.
Matter cycles and resilience
Energy flows through ecosystems, while substances such as carbon, nitrogen and phosphorus cycle between organisms and the physical environment. Decomposers are crucial to nutrient reuse. Climate, fire, invasive species, pollution and land use can shift species distributions. Biodiversity can support different functions, but high diversity does not guarantee stability under every condition. Resilience depends on the kind of interaction, the scale of disturbance and recovery speed. Conservation needs to monitor habitats and processes, not just one species.