Unit 8 Carrying capacity (K) Tap / Space to flip
Unit 8 Maximum population size the environment can sustain given resources, predation, and disease.
Unit 8 · 10–15% of exam
Ecology
Population & community ecology, energy flow, biogeochemical cycles, and human impacts.
Must-know content
- Levels of organization: organism → population → community → ecosystem → biosphere.
- Population ecology:
Population growth
dN/dt = rN (exponential)
dN/dt = rN[(K − N)/K] (logistic)
K = carrying capacity. Exponential = J-curve, logistic = S-curve.
- r-selected (many offspring, little care, unstable env.) vs. K-selected (few offspring, high care, stable env.).
- Survivorship curves: Type I (humans, late mortality), Type II (birds, constant), Type III (fish, early mortality).
- Community ecology:
- Interactions: competition (−/−), predation (+/−), parasitism (+/−), mutualism (+/+), commensalism (+/0).
- Competitive exclusion principle: two species with identical niches cannot coexist.
- Keystone species, ecosystem engineers, trophic cascades.
- Symbioses and coevolution.
- Ecosystems & energy flow:
- Producers → primary → secondary → tertiary consumers.
- 10% rule: only ~10% of energy passes between trophic levels (rest lost as heat).
- Biogeochemical cycles: carbon, nitrogen, phosphorus, water.
- Net primary productivity (NPP) = GPP − producer respiration.
- Disturbance & succession: primary (no soil, e.g., volcanic rock) vs. secondary (soil intact, e.g., after fire).
- Biodiversity: species richness vs. evenness; Simpson's index. Higher diversity → greater resilience.
- Human impacts: climate change, eutrophication, invasive species, habitat fragmentation, ocean acidification.
- Animal behavior: innate vs. learned (imprinting, classical, operant). Altruism and inclusive fitness (kin selection).
Example questions
MCQ If a primary producer trophic level contains 10,000 kcal of energy, approximately how much energy is available to tertiary consumers? (A) 1,000 kcal (B) 100 kcal (C) 10 kcal (D) 1 kcal
Answer: C. Apply the 10% rule three times: 10,000 → 1,000 (primary consumer) → 100 (secondary) → 10 (tertiary).
FRQ A pond receives heavy fertilizer runoff. Predict and explain the sequence of changes leading to a fish kill.
Answer: Fertilizer (N and P) triggers an algal bloom — eutrophication. When the algae die en masse, decomposer bacteria proliferate and consume large amounts of dissolved O₂ during aerobic respiration, creating hypoxic conditions. Fish, which require dissolved O₂ for cellular respiration, suffocate.
MCQ A species of bird arrives on a new island and rapidly diversifies into multiple species exploiting different food sources. This is an example of: (A) Convergent evolution (B) Adaptive radiation (C) Coevolution (D) Genetic drift
Answer: B. Adaptive radiation: rapid diversification of a lineage into ecologically distinct descendants when new niches open up (e.g., Galápagos finches, Hawaiian honeycreepers).
Drill flashcards
Unit 8 Logistic growth Tap / Space to flip
Unit 8 Population growth that slows as N approaches K. S-shaped curve. dN/dt = rN[(K−N)/K].
Unit 8 Exponential growth Tap / Space to flip
Unit 8 Unconstrained growth: dN/dt = rN. J-shaped curve, only sustainable in unlimited resource environments.
Unit 8 Keystone species Tap / Space to flip
Unit 8 Species whose impact on its community is disproportionately large relative to its biomass (e.g., sea otters).
Unit 8 Niche Tap / Space to flip
Unit 8 The sum of an organism's use of biotic and abiotic resources — its role in the community.
Unit 8 Mutualism (+/+) Tap / Space to flip
Unit 8 Symbiosis where both species benefit (e.g., mycorrhizae and plant roots).
Unit 8 Commensalism (+/0) Tap / Space to flip
Unit 8 Symbiosis where one species benefits and the other is unaffected.
Unit 8 Trophic level Tap / Space to flip
Unit 8 Position in a food chain — producer, primary consumer, secondary, tertiary. Energy flows up the levels.