Ecological pyramids represent the relationship between organisms at different trophic levels in terms of numbers, biomass, or energy. Three types: Pyramid of numbers: number of organisms at each trophic level. Pyramid of biomass: total dry weight of organisms at each trophic level. Pyramid of energy: total energy at each trophic level. Each pyramid has a base (producers) and successive levels (consumers). The shape (upright, inverted, spindle) depends on the type of pyramid and the ecosystem.

Shows number of organisms at each trophic level. Usually upright: grassland (millions of grass plants support fewer herbivores support even fewer carnivores). Inverted: tree ecosystem (1 tree supports thousands of insects which support fewer birds). Spindle-shaped: in parasitic food chains where each host supports many parasites which support even more hyperparasites. Limitation: does not account for size differences (one elephant vs million grass blades — both count as 1).

Shows total dry weight (biomass) of all organisms at each trophic level at a given time. Usually upright in terrestrial ecosystems: grassland, forest — producer biomass > herbivore > carnivore. Inverted in aquatic/marine ecosystems: sea — phytoplankton are tiny, have rapid reproduction and turnover. At any snapshot, their total standing biomass is LESS than the total biomass of zooplankton and fish that feed on them. Important: this does NOT violate the energy pyramid because phytoplankton productivity (energy production rate) is still higher than zooplankton. The inverted biomass pyramid reflects standing crop (snapshot) not productivity (rate).

Shows energy content at each trophic level. ALWAYS upright — never inverted in any ecosystem. Based on Lindemann's 10% law (1942): only ~10% of energy at one trophic level transferred to next. Rest lost as heat through respiration. Example: if producers have 10,000 kcal: herbivores have ~1000 kcal, carnivores ~100 kcal, top predator ~10 kcal. This 10% rule explains: why food chains are short (usually 3-5 levels), why there are fewer large predators than herbivores, why vegetarian diet is more energy-efficient than meat diet. Unlike biomass pyramid, energy pyramid can NEVER be inverted because energy flow is strictly unidirectional and always decreasing.

Trophic level = position of organism in food chain. T1 = Producers (plants, algae, phytoplankton). T2 = Primary consumers (herbivores). T3 = Secondary consumers (primary carnivores). T4 = Tertiary consumers. Decomposers (bacteria, fungi) — not assigned a trophic level, they break down all levels. Grazing food chain: starts with living plants. Most energy in terrestrial ecosystems flows through this chain. Detritus food chain: starts with dead organic matter. Dominant in forests and aquatic ecosystems. Energy flow: NOT cyclical (unlike matter). Enters as solar energy, exits as heat. NPP (Net Primary Productivity) = what is available for consumers. About 10% transferred upward at each level.

Phytoplankton: microscopic photosynthetic organisms (diatoms, green algae, cyanobacteria). Despite small size, they contribute ~50% of global primary production (25 billion tonnes carbon/year). Rapid reproduction (cell doubling time: hours to days). Short lifespan — rapidly consumed by zooplankton. This is why standing biomass at any moment is low relative to zooplankton. NPP of open ocean: 2-400 g C/m2/yr (one of lowest). But due to enormous area: total ocean NPP comparable to terrestrial. Coastal waters, estuaries, coral reefs: 500-4000 g C/m2/yr (highest productivity). Eutrophication: nutrient enrichment of water bodies → excessive algal growth → algal bloom → oxygen depletion → dead zones.

Food web: interconnected food chains showing all feeding relationships in a community. More interconnected food webs are more stable (if one species lost, energy flows through alternative pathways). Keystone species: species with disproportionately large ecological effect relative to their biomass. Remove keystone species → entire ecosystem changes. Examples: sea otters eat sea urchins → without otters, urchins overgraze kelp → kelp forest disappears → ecosystem collapses. Wolves in Yellowstone: reintroduced 1995 → preyed on elk → elk avoided streams → streamside vegetation recovered → beavers returned → more ponds → more fish → trophic cascade. Top-down control: predators regulate lower trophic levels. Bottom-up control: primary production regulates entire food web.

GPP (Gross Primary Productivity): total rate of photosynthesis including what is used in plant respiration. NPP (Net Primary Productivity) = GPP minus plant respiration. This is available for herbivores. Secondary productivity: energy stored at consumer level. Always less than primary productivity. Most productive ecosystems: tropical rainforests (2000-3000 g/m2/yr), estuaries and wetlands (up to 4000 g/m2/yr), coral reefs. Least productive: open ocean, deserts, tundra. Global NPP: terrestrial ~120 Pg C/yr, ocean ~50 Pg C/yr. Deforestation and climate change are reducing terrestrial NPP globally.