Ecosystem

An ecosystem, or ecological system, is a complex network formed by living organisms interacting with their physical environment. This system is composed of two main parts: biotic and abiotic components. Biotic factors are the living parts, such as plants, animals, and microbes. Abiotic factors are the non-living parts, like soil, water, and sunlight.

These components are linked through energy flows and nutrient cycles. These cycles allow matter and energy to move from one pool to another. This movement is known as an ecosystem process. These processes can occur at many different scales. The correct scale for study depends on the specific question being asked.

Energy and matter move through a specific sequence of steps. First, energy enters the system through photosynthesis. During this process, plants capture light energy to combine carbon dioxide and water. This creates carbohydrates and oxygen. The total amount of photosynthesis in an ecosystem is called gross primary production (GPP). Plants use about half of this GPP for their own respiration to support growth. The remaining energy is called net primary production (NPP).

This NPP is either eaten by animals while the plant is alive or becomes detritus when the plant dies.

Organisms occupy different levels within a trophic system. Primary producers are the photosynthetic organisms that start the energy flow. Primary consumers, also called herbivores, eat the plant tissues. Secondary consumers, known as carnivores, eat the primary consumers. There are also microbivores that feed on microbes like bacteria and fungi. A single sequence of consumption, such as plant to herbivore to carnivore, is a food chain. However, most real systems are much more complex. They form food webs where organisms feed on multiple types of food at different levels.

Decomposition is a vital process for maintaining these systems. Decomposers break down dead organic matter and detritus. This process releases carbon dioxide back into the atmosphere. It also facilitates nutrient cycling by converting nutrients from dead biomass back into forms plants can use.

In terrestrial ecosystems, the vast majority of net primary production ends up being broken down by these decomposers. In contrast, aquatic systems see a much higher proportion of plant biomass being consumed by herbivores.

Ecosystems are controlled by both external and internal factors. External factors, or state factors, determine the overall structure. Climate is the strongest external factor, determining the biome an ecosystem belongs to. Rainfall and temperature influence photosynthesis and energy availability. Topography also plays a role by affecting microclimates and water movement.

Internal factors also control and are controlled by ecosystem processes. These include root competition, shading, and decomposition. While external factors provide resource inputs, internal factors control how available those resources are within the system.

The concept of the ecosystem has a specific history. The term was first used in 1935 by British ecologist Arthur Tansley. The word was actually coined by Arthur Roy Clapham at Tansley's request. Tansley wanted to emphasize the transfer of materials between organisms and their environment. Later, G. Evelyn Hutchinson suggested that mineral nutrients in lakes limit algal production. This, in turn, limits the animals that eat the algae. Raymond Lindeman further suggested that energy flow is the primary driver of ecosystems. Finally, Howard and Eugene Odum developed a systems approach to study these energy and material flows.

Ecosystems are dynamic and can be measured by their resistance and resilience. Resistance is the tendency of a system to remain close to its equilibrium state. Ecological resilience is the capacity to absorb disturbance and reorganize while keeping the same function and identity.

Many ecosystems provide essential goods and services. Ecosystem goods are tangible products like food, water, fuel, and medicinal plants. Ecosystem services are improvements to the environment, such as cleaning air and water or pollinating crops. However, human impacts like pollution and habitat fragmentation can cause degradation. If an ecosystem loses its defining features, it is considered collapsed.

Understanding these systems is vital for global stability. Ecosystems help maintain the hydrological cycle and atmospheric oxygen. They also play a role in the carbon cycle, which influences the global climate through the greenhouse effect. Protecting these systems through restoration can help achieve Sustainable Development Goals. By studying ecosystems through monitoring or experimentation, scientists learn how to protect these complex, living webs.