Ecosystems & Food Webs

Energy flow, matter cycling, and ecosystem balance

An ecosystem is a community of organisms interacting with each other and their physical environment. Food webs describe who eats whom, showing the flow of energy and matter. Energy flows one-way through a food web (sun → plants → herbivores → carnivores), with 90% lost as heat at each level. Matter cycles continuously: carbon (photosynthesis, respiration, decomposition), nitrogen (fixation, nitrification, denitrification), water (evaporation, precipitation). Populations in ecosystems are interdependent: removing predators causes herbivore populations to explode (trophic cascade). The Lotka-Volterra equations describe predator-prey cycles: when prey are plentiful, predators increase; then prey decline; then predators decline, letting prey recover. Biodiversity increases ecosystem stability — more species means more alternative pathways if one disappears.