1 Definition and scope

An ecosystem is a functional unit formed by living organisms and the physical environment they inhabit. Its defining feature is interaction: organisms affect one another and also influence air, water, soil, light, and nutrients around them. Ecologists use the term to describe both the parts of a natural setting and the relationships that make it operate as a system.

1.1 Core concept

The central idea of an ecosystem is that life does not exist in isolation. Plants, animals, fungi, and microbes exchange energy and matter with their surroundings in continuous cycles. These exchanges shape growth, reproduction, survival, and the overall condition of the environment.

1.2 Living and nonliving components

Ecosystems include biotic components, such as organisms, and abiotic components, such as sunlight, temperature, water, and minerals. The balance between these elements influences the kinds of species that can live there and how abundant they may become.

1.3 Boundaries and scale

Ecosystem boundaries are often practical rather than absolute. A pond, a meadow, or a coral reef can each be studied as an ecosystem, yet all are connected to neighboring areas through wind, water, migration, and nutrient movement. The scale may be small, as in a fallen tree trunk, or broad, as in an entire biome.

1.4 Types of ecosystems

Ecosystems are commonly grouped by habitat and dominant conditions. They may be terrestrial, aquatic, or artificial. Each type has characteristic species, physical settings, and patterns of energy use.

2 Structural components

The structure of an ecosystem refers to the organisms present and the physical conditions that support them. These components determine how energy enters the system, how resources are used, and how species occupy space.

2.1 Biotic components

Biotic components are the living parts of an ecosystem. They include organisms with different roles in obtaining energy and recycling matter.

2.1.1 Producers

Producers, also called autotrophs, create organic material from inorganic substances. Most use sunlight through photosynthesis, while some rely on chemical energy. They form the base of most ecological food systems.

2.1.2 Consumers

Consumers obtain energy by feeding on other organisms. They may eat plants, animals, or both, and are often classified as herbivores, carnivores, omnivores, or detritivores. Their feeding links species together through energy transfer.

2.1.3 Decomposers

Decomposers break down dead organisms and waste products into simpler substances. Fungi and bacteria are major decomposers, and their activity returns nutrients to soil or water for reuse by other organisms.

2.2 Abiotic components

Abiotic components are the nonliving physical and chemical factors that shape ecosystem conditions. They limit or support biological activity and often vary by season, altitude, depth, or location.

2.2.1 Climate

Climate includes long-term patterns of temperature, rainfall, humidity, sunlight, and wind. These factors strongly influence what kinds of vegetation and animals can survive in an area.

2.2.2 Water

Water is essential for life and often a key limiting factor. Its availability, movement, salinity, and depth affect metabolism, reproduction, and the distribution of species.

2.2.3 Soil and minerals

Soil provides support, moisture, and nutrients for many land organisms. Its texture, organic content, pH, and mineral composition help determine plant growth and, indirectly, the animals that depend on plants.

2.3 Habitat and niche

A habitat is the physical place where an organism lives. A niche describes its role in the ecosystem, including how it obtains food, uses space, and interacts with other species. Different species may share a habitat while occupying distinct niches.

3 Ecosystem processes

Ecosystem processes are the movements and transformations that keep the system functioning. They include energy transfer, nutrient recycling, and the breakdown of organic matter.

3.1 Energy flow

Energy enters most ecosystems as sunlight and moves through organisms in one direction. At each step, some energy is used for life processes and much is lost as heat.

3.1.1 Primary production

Primary production is the creation of organic matter by producers. It determines how much energy is available to other organisms and is a major measure of ecosystem productivity.

3.1.2 Food chains

A food chain is a simplified path of energy transfer from one organism to another. It begins with producers and continues through successive consumers, though in nature such pathways are usually only part of a larger network.

3.1.3 Food webs

Food webs show the many interconnected feeding relationships in an ecosystem. They provide a more realistic picture than a single chain because most organisms have multiple food sources and predators.

3.2 Nutrient cycling

Nutrients move through organisms, soil, water, and air in repeated cycles. Unlike energy, which flows through and is lost, nutrients are reused many times.

3.2.1 Carbon cycle

The carbon cycle involves the exchange of carbon among the atmosphere, living organisms, oceans, and soil. Photosynthesis, respiration, decomposition, and combustion are important processes in this cycle.

3.2.2 Nitrogen cycle

The nitrogen cycle describes how nitrogen moves through the atmosphere, soil, water, and living things. Microorganisms play a major role in converting nitrogen into forms that plants can absorb and later returning it to the environment.

3.2.3 Water cycle

The water cycle circulates water through evaporation, condensation, precipitation, runoff, infiltration, and transpiration. It connects terrestrial and aquatic ecosystems and affects temperature and productivity.

3.3 Decomposition

Decomposition is the breakdown of dead organic matter into simpler compounds. It is essential for nutrient recycling and varies with temperature, moisture, oxygen levels, and the nature of the material being decomposed.

4 Ecosystem dynamics

Ecosystem dynamics describe change over time within populations, communities, and habitats. These changes arise from biological interactions, growth, disturbance, and recovery.

4.1 Population interactions

Species interact in ways that influence survival and reproduction. Such interactions help shape community structure and can shift as resources or conditions change.

4.1.1 Competition

Competition occurs when organisms use the same limited resource, such as light, food, water, or space. It may occur within a species or between different species.

4.1.2 Predation

Predation is a relationship in which one organism kills and consumes another. It can regulate population sizes and influence behavior, body form, and habitat use.

4.1.3 Symbiosis

Symbiosis refers to close and long-term associations between different species. These relationships may be beneficial, harmful, or neutral for the partners involved.

4.2 Succession

Succession is the gradual change in ecosystem composition and structure over time. It often follows the creation of new habitat or the disruption of an existing one.

4.2.1 Primary succession

Primary succession begins on surfaces with little or no soil, such as lava flows or bare rock. Organisms that first colonize the area help create conditions for later species.

4.2.2 Secondary succession

Secondary succession occurs after a disturbance in an area where soil remains. Because nutrients and seed sources are still present, recovery is usually faster than in primary succession.

4.3 Disturbance and recovery

Disturbance includes events such as fire, storms, floods, drought, or human activity that alter ecosystem conditions. Recovery depends on the severity of the disturbance, the resilience of species, and the availability of nearby sources for recolonization.

5 Ecosystem classification

Ecosystems are often classified according to their physical setting, dominant organisms, and water conditions. Such categories help compare ecological patterns across regions.

5.1 Terrestrial ecosystems

Terrestrial ecosystems occur on land and are shaped strongly by climate, soil, and altitude. Their vegetation often forms the framework for associated animal communities.

5.1.1 Forests

Forests are dominated by trees and usually have layered structure. They may be tropical, temperate, or boreal, each with distinct climate and biodiversity patterns.

5.1.2 Grasslands

Grasslands are characterized by grasses and few trees. They often develop where rainfall is moderate or seasonal and where fire or grazing helps maintain open conditions.

5.1.3 Deserts

Deserts receive very little precipitation and are defined by water scarcity. Organisms there often show adaptations for conserving moisture, avoiding heat, or remaining inactive during harsh periods.

5.1.4 Tundra

Tundra ecosystems are cold and have short growing seasons. Limited temperatures and permafrost restrict tree growth, producing low, hardy vegetation.

5.2 Aquatic ecosystems

Aquatic ecosystems are found in water and are influenced by depth, salinity, movement, temperature, and light penetration. They include both freshwater and marine settings.

5.2.1 Freshwater ecosystems

Freshwater ecosystems include rivers, lakes, streams, and ponds. They generally have low salt content and support organisms adapted to flow, depth, or still water.

5.2.2 Marine ecosystems

Marine ecosystems occur in seas and oceans. They cover most of Earth’s surface and include highly productive coastal zones as well as deep-water environments.

5.2.3 Wetlands

Wetlands are areas where water saturates the soil for at least part of the year. They are often rich in biodiversity and play major roles in water storage and filtration.

5.3 Artificial ecosystems

Artificial ecosystems are created or strongly modified by humans, such as croplands, reservoirs, gardens, and urban parks. They depend on human management and typically have altered species composition and resource flows.

6 Ecosystem services

Ecosystem services are the benefits humans obtain from ecosystems. These benefits may be direct, such as food, or indirect, such as climate regulation and nutrient support.

6.1 Provisioning services

Provisioning services are material outputs from ecosystems. They include food, fresh water, timber, fibers, medicinal resources, and other useful biological products.

6.2 Regulating services

Regulating services are the environmental functions that help maintain stable conditions. Examples include pollination, flood control, water purification, pest regulation, and climate moderation.

6.3 Supporting services

Supporting services are the underlying processes that make other services possible. They include soil formation, photosynthesis, nutrient cycling, and habitat creation.

6.4 Cultural services

Cultural services are nonmaterial benefits such as recreation, aesthetic enjoyment, education, inspiration, and spiritual significance. They often shape how people value landscapes and wildlife.

7 Human impacts

Human activities can alter ecosystem structure and processes by changing land cover, resource use, species composition, and physical conditions. Effects may be local or widespread.

7.1 Land use change

Land use change includes conversion of forests, grasslands, wetlands, and other habitats for agriculture, settlements, roads, or industry. It often fragments habitats and reduces ecological connectivity.

7.2 Pollution

Pollution introduces harmful substances or excess energy into ecosystems. Common forms include air pollution, water contamination, nutrient runoff, plastics, and chemical residues.

7.3 Resource extraction

Resource extraction includes logging, mining, fishing, groundwater withdrawal, and fuel production. These activities can deplete populations, disturb soils and waterways, and alter long-term ecosystem function.

Changes in temperature, precipitation, and the frequency of extreme events can stress ecosystems. Species may shift ranges, alter timing of life cycles, or decline when conditions change faster than they can adapt.

8 Conservation and management

Conservation and management aim to protect ecosystem function while allowing appropriate human use. Effective approaches combine ecological knowledge with long-term planning.

8.1 Protected areas

Protected areas are designated places managed to conserve habitats, species, and natural processes. They may limit development, regulate access, or focus on preserving representative ecosystems.

8.2 Restoration ecology

Restoration ecology seeks to repair degraded ecosystems. Common methods include replanting native species, improving soil conditions, removing invasive organisms, and reestablishing natural water flow.

8.3 Sustainable use

Sustainable use involves harvesting resources in ways that do not undermine future ecosystem health. It emphasizes balance among ecological capacity, human needs, and long-term resilience.

8.4 Monitoring and assessment

Monitoring and assessment track ecosystem condition through surveys, measurements, and indicators. These tools help detect change, evaluate management efforts, and guide conservation decisions.