Ökologie und Nachhaltigkeit / Ecology and sustainability
Ecology items link population data to ecosystem processes and to human impact. Typical tasks give a table of population sizes or a food web and ask for a calculation, a limiting factor, or a reasoned conservation measure - always with the mechanism, not just the label.
Populations and interactions
- Exponential growth (J-shaped) when resources are unlimited; logistic growth (S-shaped) with carrying capacity K, where density-dependent factors slow growth.
- Interactions: competition, predation (often coupled cycles), mutualism, parasitism; the niche concept explains coexistence through resource partitioning.
Energy flow and material cycles
- Energy flows one way: about 10% passes to the next trophic level; the rest is lost through respiration as heat, plus not all biomass is eaten or assimilated. Energy pyramids therefore never invert; pyramids of numbers can.
- Carbon cycles through photosynthesis, respiration, combustion and dissolution; nitrogen is fixed biologically or industrially, then nitrified and denitrified; phosphorus cycles mainly through rock and is often limiting.
Human impact and sustainability
- Eutrophication sequence: nutrient input → algal bloom → shading and death → decomposition by bacteria → oxygen depletion → fish kill.
- Habitat fragmentation reduces gene flow and increases edge effects; climate change shifts ranges; sustainable use means renewable rates are not exceeded and ecosystem services (pollination, water retention, carbon storage) are maintained.
Worked example
In a mark-recapture study, 50 animals are caught, marked and released. Later, 60 are caught and 12 carry marks. Reasoning: the marked proportion in the second sample estimates the marked proportion in the population, so N ≈ (50 × 60)/12 = 250. Assumptions: marks are not lost, marked and unmarked animals mix randomly, no major births, deaths or migration between samples. If the second sample were taken where marked animals had clustered, the estimate would be biased.
Traps that cost marks
Confusing pyramids of numbers with energy pyramids; stating energy is 'destroyed' rather than dissipated as heat; treating the 10% figure as exact; describing eutrophication as 'algae poison the water' without the oxygen-depleting decomposition step; using correlation between two species as proof of competition without a controlled test.