Summary

Ecosystem structure: Every ecosystem has two interacting components — abiotic (physical factors like light, temperature, water, soil) and biotic (living organisms). Biotic components are grouped into producers (autotrophs), consumers (herbivores, carnivores, omnivores, decomposers), and decomposers (bacteria, fungi).

Productivity: The rate of biomass production is primary productivity. Gross primary productivity (GPP) is the total rate of photosynthesis. Net primary productivity (NPP) = GPP – respiration by producers; it is the energy available to consumers. Secondary productivity is the rate of biomass production by consumers.

Decomposition: Dead organic matter is broken down by detritivores and decomposers. Key steps: fragmentation, leaching, catabolism, humification, and mineralisation. Rate depends on temperature, moisture, and substrate quality — faster in warm, moist conditions.

Energy flow: Energy enters as sunlight, is fixed by producers, and flows unidirectionally through trophic levels. Only about 10% of energy is transferred from one trophic level to the next (10% law; Lindeman). The rest is lost as heat in respiration.

Ecological pyramids: Graphical representations of trophic structure. Pyramid of numbers (count of organisms), pyramid of biomass (dry weight), and pyramid of energy (always upright, because energy decreases at each step). In some ecosystems (e.g., tree–insect), number and biomass pyramids can be inverted. …