Ecology
Ecology tests how organisms interact with each other and with their environment, how energy and matter move through ecosystems, and how populations and communities change.
Levels and populations
- Organisation runs from organism to population, community, ecosystem, biome and biosphere.
- Population size depends on births, deaths, immigration and emigration. Exponential growth is J-shaped; logistic growth is S-shaped and levels off at carrying capacity K.
- r-strategists produce many small offspring; K-strategists produce few, well-cared-for offspring.
- Interactions include mutualism, commensalism, parasitism, predation, competition and amensalism.
Ecosystems
- Producers, consumers and decomposers form food chains and webs; decomposers are not a trophic level in the grazing chain.
- Lindeman's 10% law: only about 10% of energy passes to the next trophic level. Energy pyramids are always upright; pyramids of numbers or biomass may be inverted.
- GPP is total production; NPP = GPP − respiration.
- Nutrient cycles include carbon, nitrogen (fixation, nitrification, denitrification) and phosphorus (sedimentary).
- Ecological succession may be primary or secondary; pioneer species give way to a climax community.
Worked example
If GPP is 10,000 kcal m⁻² yr⁻¹ and respiration is 4,000, NPP = 6,000. With 10% transfer, herbivores receive 600 and secondary consumers 60 kcal m⁻² yr⁻¹. The reasoning applies the 10% law successively and subtracts respiration only at the producer step.
Traps
Energy pyramids are never inverted; the 10% law applies between trophic levels, not within a population; GPP and NPP are not the same; nitrogen fixation differs from nitrification; decomposers recycle nutrients but do not form a trophic level in the food chain.