Ecology Terms Starting With F

Food chain is a linear sequence showing the transfer of energy and matter from producers through a series of consumers, with each organism feeding on the one before it.

A food chain begins with a primary producer, typically a photosynthetic plant or alga that converts solar energy into organic matter. Energy transfer between trophic levels averages about 10 percent efficiency, meaning 90 percent is lost as heat and metabolic work at each step; this steep loss limits most food chains to four or five levels before insufficient energy remains to support another consumer. Each link in the chain represents a trophic level: producers occupy the first, herbivores the second, and successive carnivores the third and beyond.

Food chains are abstractions of feeding relationships; in real ecosystems, most species eat and are eaten by multiple partners, forming interconnected food webs rather than isolated linear sequences. Ecologist Charles Elton described the trophic structure of food chains in his 1927 book “Animal Ecology,” establishing the conceptual framework still used today.

Food web is a diagram or model showing all the overlapping feeding relationships among organisms in an ecosystem, representing the multiple pathways through which energy and matter move from producers to consumers and decomposers.

A food web maps many simultaneous feeding pathways, such as grass to mouse to owl alongside grass to grasshopper to sparrow to hawk, revealing that most species feed at more than one trophic level and are consumed by more than one predator. These redundant connections provide stability: if one prey species declines, consumers can often shift to alternative food sources, buffering the community against collapse. Removal of a keystone species disrupts this redundancy; when sea otters (Enhydra lutris) were hunted to near-extinction along the Pacific coast in the 18th and 19th centuries, sea urchin populations exploded and grazed kelp forests down to bare rock.

Contaminants such as mercury and polychlorinated biphenyls biomagnify through food webs, reaching concentrations in top predators thousands of times higher than in surrounding water. Analysis of real food webs shows that most ecosystems contain 4 to 8 major feeding groups connected through 20 to 50 distinct pathways, though highly diverse tropical systems can exceed these figures considerably.

Forest ecosystem is a biological community in which trees form the dominant structural layer, together with the understory plants, animals, fungi, microorganisms, soil, water, and climate that interact as a functional unit.

Trees in a forest ecosystem capture solar energy, cycle water through transpiration, and build the physical structure that defines habitat for thousands of other species. A single mature oak tree (Quercus robur) can support more than 500 species of insects, which in turn supply food for birds, bats, and spiders throughout the canopy. Soil fungi form mycorrhizal networks connecting tree roots across hectares, transferring carbon and nutrients among individual trees and influencing which seedlings survive in the understory.

Temperate forests store roughly 150 to 200 tonnes of carbon per hectare in biomass and soil, making them significant regulators of atmospheric carbon dioxide concentrations. Disturbances such as fire, windstorm, and insect outbreaks reset successional trajectories and maintain structural diversity across forest habitats, preventing any single tree species from monopolizing the canopy indefinitely.

Freshwater ecosystem is a water-based ecological community occurring in low-salinity environments such as rivers, lakes, ponds, streams, and wetlands, where dissolved salt concentrations typically remain below 0.5 parts per thousand.

Freshwater habitats cover less than 1 percent of Earth’s surface yet support roughly 10 percent of all known animal species, including more than 30,000 described fish species. Organisms living in these systems face osmotic challenges that marine species do not, and many freshwater fish actively excrete dilute urine to prevent their tissues from absorbing excess water. Wetlands filter sediments and excess nutrients from runoff, with studies showing that a single hectare of wetland can remove hundreds of kilograms of nitrogen annually before water reaches downstream systems.

Rivers and standing-water bodies differ sharply in physical structure: lotic systems like rivers are shaped by current velocity, while lentic systems like lakes stratify thermally into distinct layers that control oxygen distribution and nutrient cycling.