A food web is a diagrammatic representation of who eats whom in an ecosystem, showing the multiple, overlapping connections that link organisms into a network of energy and nutrient flow. Unlike a single food chain, which traces a straight line of consumption, a food web combines many chains into a more realistic picture. Diagrams and models (diagram) use arrows to indicate direction of energy transfer: an arrow typically points from the organism being eaten toward the organism that eats it.
Basic components and trophic structure
At a broad level the web separates two major functional groups: the producers and the consumers. Primary producers, or autotrophs, capture energy from sunlight or chemical sources and synthesize organic matter. Consumers, or heterotrophs, obtain energy by eating other organisms or organic material. Common feeding relations include herbivory, in which animals eat plants, and carnivory, where animals eat other animals; other interactions such as scavenging and parasitism also appear in webs.
- Primary producers: green plants, algae and photosynthetic microbes (for example, cyanobacteria).
- Primary consumers: herbivores and some detritivores that eat producers.
- Secondary and tertiary consumers: predators that feed on other animals or omnivores that feed at multiple levels.
- Decomposers and detritivores: organisms that break down dead matter and recycle nutrients.
Energy flow and ecological consequences
Energy captured by producers enters the web and moves upward when one organism eats another. Much of that energy is consumed by metabolism and lost as heat, which is why fewer resources are available at higher trophic levels; ecologists often cite a substantial drop in available energy between levels (a rule-of-thumb is sometimes given as about ten percent transferred, though actual transfer efficiencies vary). Organic molecules such as simple sugars are important energy carriers, while large biomass contributors range from microscopic producers to massive plants (giant redwoods) and animals (blue whales).
Complexity, stability and real-world examples
Food webs are typically highly interconnected: many species occupy multiple roles (omnivores), and a single prey species may feed many predators. This complexity can buffer ecosystems against change but can also propagate disturbances. For example, aquatic webs often start with phytoplankton and microbes and extend through zooplankton to small fish and larger predators, while terrestrial webs may connect grasses and shrubs to herbivores and carnivores. Parasites and viruses (viruses) alter dynamics by changing hosts' mortality or behavior. Simple educational diagrams often omit such subtleties, but realistic webs include detrital pathways and microbial loops.
History, modelling and human impacts
The concept of interconnected feeding relationships has a long history in ecology and natural history. Modern approaches use network theory and quantitative models to measure properties like connectance, strength of links and resilience. Humans act as consumers within many webs and exert strong effects through hunting, agriculture, pollution and species introductions; these pressures can reconfigure local webs, remove apex consumers, or increase invasive species that change energy pathways. Conservation efforts often use food-web perspectives to identify keystone species and prioritize actions.
For further reading on definitions and related concepts see plants and animals, or consult overview resources that treat both theoretical and applied aspects of trophic interactions. Additional background material and illustrative resources can be found via linked summaries and diagrams (diagram, food chain). For applied examples and case studies, researchers often reference databases and review articles (heterotrophs, autotrophs).