AP Biology: AP Biology: Ecology Practice Questions
Test yourself on AP Biology: Ecology with 13 original AP Exams practice questions. Pick an answer to see instant feedback and a full explanation.
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1. A population of rabbits has a per capita birth rate of 0.5 and a per capita death rate of 0.2 per year. If immigration and emigration are equal, what is the per capita growth rate (r)?
Explanation. Per capita growth rate r = birth rate − death rate = 0.5 − 0.2 = 0.3. Since immigration equals emigration, those terms cancel. A positive r means the population is growing exponentially in this scenario.
2. Which of the following best describes the logistic growth model compared to the exponential model?
Explanation. The logistic model dN/dt = rN(K−N)/K incorporates carrying capacity. As N approaches K, the term (K−N)/K approaches zero, slowing growth. Exponential growth (dN/dt = rN) assumes unlimited resources and no slowing.
3. In a food chain, approximately what percentage of energy is typically transferred from one trophic level to the next?
Explanation. On average about 10% of energy is transferred between trophic levels (the 10% rule). The remaining ~90% is lost mainly as heat through cellular respiration and used in metabolic processes, which limits food chain length.
4. Two species of paramecium grown together cannot coexist when using identical resources; one outcompetes the other. This illustrates:
Explanation. The competitive exclusion principle (Gause) states that two species competing for the exact same limiting resource cannot stably coexist; one will eliminate the other. Resource partitioning and character displacement are mechanisms that allow coexistence when niches differ.
5. A relationship in which one organism benefits while the other is neither harmed nor helped is called:
Explanation. Commensalism is +/0: one species benefits and the other is unaffected. Mutualism is +/+, parasitism is +/−, and competition is −/−. An example is barnacles attaching to a whale for transport.
6. Which process in the nitrogen cycle converts atmospheric N2 into a form usable by plants (ammonia)?
Explanation. Nitrogen fixation, performed by bacteria (e.g., Rhizobium and cyanobacteria), converts N2 gas into ammonia (NH3). Nitrification converts ammonia to nitrate, ammonification converts organic N to ammonium, and denitrification returns nitrogen to the atmosphere as N2.
7. A keystone species is best defined as one that:
Explanation. A keystone species exerts a strong influence on community structure despite being relatively low in abundance. The classic example is the sea star Pisaster; its removal allowed mussels to dominate, drastically reducing diversity.
8. Which type of survivorship curve (Type I) is characterized by high survival through early and middle life with mortality concentrated in old age?
Explanation. Type I survivorship (e.g., humans, large mammals) shows high survival during early/mid life and steep decline in old age. Type II has constant mortality, and Type III (e.g., many fish, plants) shows high early mortality with few surviving young.
9. During ecological succession, which group typically colonizes a bare rock surface first (primary succession)?
Explanation. In primary succession (e.g., new volcanic rock), pioneer species such as lichens and mosses arrive first. They help break down rock and build soil, enabling later successional species like grasses, shrubs, and eventually trees to establish.
10. Increased atmospheric CO2 from burning fossil fuels contributes to global warming primarily because CO2:
Explanation. CO2 is a greenhouse gas that absorbs and re-emits infrared (heat) radiation emitted from Earth's surface, trapping heat in the atmosphere. It does not primarily reflect incoming sunlight, and it is distinct from ozone-depleting chemicals.
11. A species with traits such as small body size, rapid maturation, many offspring, and little parental care is best described as:
Explanation. r-selected species maximize reproductive output (high r) with many small offspring, fast maturation, and minimal parental care—favored in unstable environments. K-selected species have fewer offspring, slow maturation, and high parental investment, thriving near carrying capacity.
12. A density-dependent factor that limits population growth would most likely be:
Explanation. Density-dependent factors have stronger effects as population density increases—disease spreads more readily in crowded populations. Volcanic eruptions, freezes, and droughts are typically density-independent, affecting individuals regardless of population size.
13. Net primary productivity (NPP) is calculated as:
Explanation. NPP = GPP − R, where GPP is the total energy captured by producers through photosynthesis and R is the energy producers use for their own respiration. NPP represents the energy stored as biomass and available to consumers.
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FAQ
How math-heavy is the ecology section of AP Biology?
Expect to use simple equations like exponential growth (dN/dt = rN), logistic growth (dN/dt = rN(K−N)/K), and the 10% energy transfer rule. Calculations are basic algebra—the harder part is interpreting graphs and applying concepts, so practice reading population and energy-flow diagrams.
What ecology topics show up most on the AP Bio exam?
High-yield topics include population growth models (exponential vs. logistic), survivorship curves, r/K selection, energy flow and trophic levels, biogeochemical cycles (carbon, nitrogen), species interactions (mutualism, competition, predation), succession, and human impacts like climate change and eutrophication.
How should I study ecology for free-response questions?
Practice explaining mechanisms and making predictions, not just memorizing terms. Be able to describe how a perturbation (e.g., removing a keystone species, adding nutrients) ripples through a community, justify answers with data from graphs, and connect ecology to evolution and energy concepts.