Ecology Cheat Sheet 2026

The 30 highest-yield Ecology facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. In the logistic growth equation dN/dt = rN(1 − N/K), population growth rate is greatest when N equals: → K/2
2. Which interaction type is most likely to increase both species' population sizes simultaneously? → Mutualism
3. During old-field succession in the eastern United States, which sequence correctly represents the typical order of community change? → Annual weeds → perennial grasses → shrubs → forest
4. Which type of succession begins on a substrate that has never previously supported life, such as bare rock after a volcanic eruption? → Primary succession
5. Which gas produced during the anaerobic decomposition of organic matter in wetlands is a potent greenhouse gas? → Methane (CH₄)
6. Scramble competition occurs when limited resources are divided among all competitors such that: → Everyone gets an insufficient share and many die
7. A population grows from 500 to 550 individuals in one year. What is the per capita growth rate (r) approximately? → 0.095
8. Genetic erosion in a species most directly refers to the loss of: → Allelic diversity within the gene pool
9. Which factor is most likely to influence the carrying capacity of a population? → The availability of resources like food and space
10. What is the primary distinction between proximate and ultimate explanations for behavior? → Proximate explains immediate mechanisms; ultimate explains adaptive significance
11. What is the role of detritivores in biogeochemical cycles? → Break down dead organic matter, releasing nutrients for recycling
12. Which concept describes the idea that restored or conserved ecosystems provide benefits to people? → Ecosystem services
13. What does the term 'genetic rescue' refer to in conservation biology? → Introducing new individuals to increase genetic diversity in inbred populations
14. The Intermediate Disturbance Hypothesis predicts that species diversity is highest when: → Disturbance occurs at intermediate levels
15. Source-sink dynamics in a landscape occur when: → High-quality patches export individuals that subsidize populations in low-quality patches
16. What is 'litterfall' and why is it important to ecosystem processes? → Dead plant material deposited on the soil surface, fueling decomposition
17. What is the primary focus of organismal ecology? → The study of how organisms adapt to their environment
18. What role do mycorrhizal fungi play in ecosystem succession? → They facilitate plant establishment by enhancing nutrient uptake, speeding succession
19. What does the term 'phenotypic plasticity' mean in the context of animal behavior? → The ability of one genotype to produce different behaviors in different environments
20. What is the biological significance of the parameter 'b' in the Beverton-Holt stock-recruitment model used in fisheries ecology? → The density-dependence parameter that limits recruitment
21. What is the fate of most energy that passes through a trophic level? → It is lost as heat
22. Which metric is used to estimate the number of species expected to go extinct relative to habitat loss, based on species-area relationships? → Extinction debt calculation using the species-area curve
23. Which metric is commonly used to assess the integrity of a restored wetland? → Index of Biotic Integrity (IBI)
24. What is the primary focus of population ecology? → The study of population size, density, and changes over time
25. An organism that is an osmoconformer in a marine environment means it: → Allows its internal osmolarity to match that of the surrounding seawater
26. How might an organism's reproductive strategy be considered an adaptation? → It ensures offspring survive in a given environment
27. The concept of 'honest signaling' in animal communication requires that signals: → Carry a cost that prevents low-quality individuals from faking them
28. What does the term 'defaunation' describe in conservation ecology? → The loss of animal species and populations from ecosystems due to human activity
29. Trophic cascades demonstrate that removing a top predator from an ecosystem typically leads to: → Herbivore population increase, overgrazing, and reduced plant diversity
30. An animal living in a stable, long-term pair bond that defends a territory together is most likely exhibiting which mating system? → Monogamy