Ecology is the science of relationships among living things and the environments they share.
Ecologists study life at many scales, from individual organisms to populations, communities, ecosystems, and the biosphere. They investigate how energy flows, how nutrients cycle, how species depend on one another, and how environmental changes can reshape living systems.
Living communities interact with air, water, soil, climate, and other nonliving parts of their surroundings.
Learn MoreEnergy moves through producers, consumers, and decomposers in interconnected feeding relationships.
Learn MoreEcologists study how groups of the same species grow, shrink, spread, and respond to limiting factors.
Learn MoreCompetition, predation, cooperation, and symbiosis can influence where organisms live and survive.
Learn MoreClimate and geography help shape broad regions such as deserts, forests, grasslands, tundra, and aquatic systems.
Learn MoreDisturbances, succession, invasive species, pollution, and climate shifts can alter ecosystems over time.
Learn MoreAn ecosystem includes a community of organisms and the nonliving environment with which those organisms interact. Plants, animals, fungi, bacteria, water, soil, sunlight, temperature, and nutrients can all be part of the same system. Ecosystems range from tiny ponds and rotting logs to forests, coral reefs, and entire river basins. Ecologists often study how a change in one part of an ecosystem affects many others, because the parts are connected rather than isolated.
Most ecosystems receive energy from sunlight, which producers such as plants and algae capture through photosynthesis. Herbivores eat producers, predators eat other animals, and decomposers break down dead material and return nutrients to the environment. These feeding relationships form food webs rather than simple chains because most organisms eat or are eaten by more than one species. A change in the abundance of one species can therefore affect several others across the web.
A population is a group of individuals of the same species living in the same area. Population size changes through births, deaths, immigration, and emigration. Food, water, shelter, disease, predation, weather, and available space can all limit population growth. Ecologists measure population trends to understand whether a species is stable, expanding, declining, or moving into new areas.
Species interact in many different ways. Predators hunt prey, organisms may compete for the same resources, and some species form close partnerships called symbioses. In mutualism, both partners can benefit; in parasitism, one benefits while the other is harmed; and in commensalism, one benefits while the other is affected little or not at all. These interactions help shape community structure and can influence evolution over many generations.
Biomes are large ecological regions defined mainly by climate and characteristic forms of life. Tropical rainforests are warm and wet, deserts receive little precipitation, grasslands are dominated by grasses, and tundra has short growing seasons and cold conditions. Freshwater and marine systems are also grouped into broad ecological zones. Biome boundaries are not perfectly sharp, and local elevation, soil, water, and geography can create important differences within the same region.
Ecosystems are always changing. Fires, floods, storms, volcanic eruptions, and other disturbances can remove organisms and create new opportunities for others. Ecological succession describes how communities develop after disturbance or on newly formed surfaces. Human activities can also drive change through habitat loss, pollution, introduced species, resource use, and climate change. Studying these changes helps scientists understand resilience and guide conservation and restoration work.