Primary productivity, trophic levels, food webs, biogeochemical cycles (C/N/P/S/H2O).
Ecosystem Ecology
Primary productivity (GPP, NPP)
GPP: gross photosynthetic C fixation. NPP = GPP − autotrophic respiration. NPP ~55 PgC/yr terrestrial + ~50 PgC/yr ocean. Basis of all…
Food web
Network of trophic (feeding) links among species in a community. Nodes = species, edges = consumption. Properties: connectance, length of…
Carbon cycle
Global flows of C between atmosphere, biosphere, ocean, pedosphere, lithosphere. Photosynthesis: 120 PgC/yr; respiration + decomposition:…
Nitrogen cycle
Microbially-mediated transformations: N2 fixation (→NH3), nitrification (NH3 → NO2- → NO3-), assimilation, ammonification, denitrification…
Phosphorus cycle
Sedimentary cycle (no significant gas phase). Weathering from rock → soil → plants → animals → decomposition. Often limits primary…
Decomposition
Breakdown of dead organic matter by detritivores + saprotrophs (fungi, bacteria). Returns elements to biogeochemical pools. Rates vary 100×…
Ecosystem services
Benefits humans derive from functioning ecosystems. Provisioning (food, water), regulating (climate, flood), supporting (nutrient cycling),…
Trophic pyramid & 10% rule
Only ~10% of energy at each trophic level transfers upward (Lindeman 1942). Sets limit on food-chain length and biomass of top predators.
Water cycle (biological component)
Evapotranspiration from plants returns ~60% of land precipitation to atmosphere. Forests modulate regional precipitation. Deforestation…
Biomagnification
Lipid-soluble persistent pollutants (DDT, PCBs, mercury) concentrate up food chains. Silent Spring (Carson 1962); motivated environmental…