AP Biology Quiz: Population Ecology

What this quiz covers

This quiz focuses on Population Ecology, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Biology.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. Increased mortality due to disease reduced population size despite prior growth (correct answer)
2. Carrying capacity increased, causing the population to overshoot and then stabilize lower
3. A constant immigration rate stopped, eliminating the only source of population increase
4. The population entered exponential growth, which temporarily lowers population size
5. New advantageous traits spread, reducing reproduction and shrinking the population

Explanation: This question assesses the skill of analyzing population ecology trends by identifying factors causing population declines after growth periods. The rabbit population grew from 50 to 130 over three months, likely due to favorable conditions, but the Month 4 viral disease outbreak directly increased mortality, leading to decreases to 70 and then 60 despite no changes in predators or food. This density-dependent factor, disease, reduced net population growth by elevating death rates. The timing of the decline aligns precisely with the outbreak, distinguishing it from other potential causes. A tempting distractor is choice B, suggesting carrying capacity increased causing an overshoot and stabilization lower, but this misconstrues the data as there was no overshoot followed by stability, only a direct decline. In such analyses, correlate timing of events with population changes to pinpoint causal factors accurately.

Question 2

1. Logistic growth caused by density-dependent limits reached early in the trial
2. Exponential growth with a constant doubling time over successive intervals (correct answer)
3. Linear growth because the same number of cells is added each interval
4. Growth decline because carrying capacity is exceeded by hour 4
5. Cyclic growth driven by seasonal changes in temperature and resources

Explanation: This question tests the skill of analyzing population ecology by identifying growth models from temporal data. The yeast population doubles consistently every two hours from 2 to 32 million cells/mL, reflecting exponential growth with a constant per capita rate under unlimited resources like abundant sugar and low waste. This pattern occurs because each cell divides at a steady rate without density-dependent constraints during the observed period. The closed flask and stable conditions support unchecked multiplication, typical of early exponential phases. A tempting distractor is choice C, linear growth, which assumes constant absolute additions rather than proportional increases, misconceiving the multiplicative nature of biological reproduction. When evaluating growth, plot the data on semi-log scales to check for linearity, which indicates exponential patterns transferable to other microbial studies.

Question 3

1. A shift to constant exponential growth as food becomes more abundant over time
2. Stabilization near carrying capacity due to density-dependent resource limitation (correct answer)
3. A sustained linear increase because births exceed deaths by a fixed amount
4. A decline caused primarily by increased emigration to neighboring ponds
5. A plateau caused by long‑term genetic changes reducing reproduction rate

Explanation: This question tests the skill of analyzing population ecology by explaining stabilization in population trends. The snail population rises sharply from 120 to 210 after nutrient influx boosts algae, then levels off around 205–215 as algae moderates, suggesting density-dependent resource limitation has reached carrying capacity. This plateau occurs because increased density heightens competition, reducing per capita reproduction or survival to balance births and deaths. No changes in predators or migration support that internal factors, not external, drive the stabilization. A tempting distractor is choice A, shift to exponential growth, which assumes ongoing unlimited resources, but this misconceives the density-dependent feedback from declining algae. For similar scenarios, monitor resource levels alongside population counts to identify when carrying capacity is approached, a strategy applicable to various ecosystems.

Question 4

1. Density-dependent competition increased gradually, causing a slow approach to carrying capacity by week 7.
2. A density-independent abiotic event increased mortality, producing a rapid population decrease. (correct answer)
3. Emigration increased because mosquitoes left to find mates, lowering the population temporarily.
4. Birth rates rose above death rates, causing the population to fall abruptly after week 5.
5. Individuals developed cold resistance, which immediately reduced the population size after week 5.

Explanation: This question tests population ecology analysis of sudden population changes and their causes. The mosquito population shows steady growth until a cold snap causes an abrupt 75% decline (4800→1200), characteristic of density-independent mortality where environmental factors affect populations regardless of their size. The rapid recovery to previous levels confirms this was an acute environmental event rather than a lasting change in carrying capacity. Choice A incorrectly suggests gradual density-dependent competition, but the sharp decline and quick recovery indicate an external factor rather than resource limitation. When populations crash suddenly then recover quickly, look for density-independent factors like weather events rather than competition or predation.

Question 5

1. Increased immigration into the park raised population size after outside nesting habitat was reduced. (correct answer)
2. Decreased mortality from predators in the park caused the population to double immediately.
3. A sudden rise in carrying capacity occurred because park area increased substantially after year 4.
4. Density-independent drought reduced resources, leading to higher birth rates after year 4.
5. Individuals evolved higher fecundity in response to construction, increasing births within one year.

Explanation: This question requires population ecology analysis of immigration effects on local populations. The bird population remains stable (90-95 birds) until nearby habitat destruction drives immigration into the park, causing a 50% increase (92→140→155). This demonstrates how habitat loss in surrounding areas can concentrate populations in remaining suitable habitats through immigration rather than reproduction. Choice B incorrectly attributes the increase to decreased predation, but such a sudden doubling requires immigration rather than just reduced mortality. When analyzing urban wildlife populations, consider how changes in surrounding habitats affect movement patterns and local densities.

Question 6

1. The population showed exponential growth throughout because it never stopped increasing after the wildfire.
2. The population approached a carrying capacity after initial growth, then fluctuated around an equilibrium size. (correct answer)
3. The population declined due to density-independent disturbance during years 5–12, causing repeated crashes.
4. The population stabilized because individuals evolved to match resource availability, preventing overshoot.
5. The population fluctuated because immigration and emigration dominated, even though the meadow was closed.

Explanation: This question requires population ecology analysis of post-disturbance succession dynamics. The plant population shows rapid growth after wildfire (50→120→210), then stabilizes and fluctuates around 190-230 as vegetation cover increases and resources become limiting. This pattern represents initial colonization followed by equilibrium around carrying capacity as the meadow matures. Choice A incorrectly identifies this as continuous exponential growth, missing the clear stabilization phase where population fluctuates within a narrow range. Following disturbances, expect rapid initial growth in open habitats followed by stabilization as competition intensifies and resources become limiting.

Question 7

1. Density-dependent competition intensified gradually as the population approached carrying capacity
2. A density-independent disturbance abruptly increased mortality regardless of population density (correct answer)
3. Improved resource availability reduced births, lowering the population size suddenly
4. Genetic changes reduced fitness, causing an immediate population decline in one year
5. Long-term emigration steadily reduced the population, producing a single-year crash

Explanation: This question tests understanding of population ecology by distinguishing density-dependent from density-independent factors. The hurricane represents a density-independent disturbance that reduced the population from 1,200 to 700 birds regardless of population density - hurricanes affect mortality through physical destruction, not through population-mediated mechanisms. After the disturbance, the population recovered following a logistic pattern back toward the original carrying capacity as habitat recovered. Choice A incorrectly suggests gradual density-dependent competition, but the data shows an abrupt one-year decline rather than gradual change, which is characteristic of catastrophic events. When analyzing population crashes, examine whether the decline is sudden (suggesting density-independent factors) or gradual (suggesting density-dependent factors).

Question 8

1. Exponential growth because resources increased as the population became larger
2. Logistic growth because growth rate slowed as density-dependent limits intensified (correct answer)
3. Boom-and-bust cycles because the population repeatedly crashed below initial size
4. Linear growth because the population added the same number of fish each year
5. Declining growth because the population experienced continuous net emigration

Explanation: This question requires analyzing population ecology data to identify growth patterns over time. The fish population exhibits classic logistic growth: rapid initial increase (500→900), then slower growth (900→1,050), and finally stabilization (1,060-1,090). The density-dependent factors (reduced oxygen and prey availability) intensified as fish density increased, causing the growth rate to slow and eventually reach equilibrium at carrying capacity. Choice A incorrectly suggests exponential growth, which would show constant percentage increases rather than the observed slowing; exponential growth ignores resource limitations. To identify growth patterns, examine whether the rate of increase changes over time and look for environmental factors that correlate with population density.

Question 9

1. Exponential growth because the population size increased by a constant percentage
2. Logistic growth because the population rapidly approached a stable carrying capacity
3. Linear growth because the population increased by a similar number each year (correct answer)
4. Irregular growth because density-independent factors changed unpredictably each year
5. Negative growth because deaths exceeded births after the wildfire

Explanation: This question tests your ability to analyze population ecology patterns and distinguish between different growth models. The plant population shows a consistent increase of 20 plants per year (200→220→240→260), which represents linear growth where a constant number is added each time period. With similar environmental conditions and reproductive parameters each year, the population maintains steady additive growth rather than multiplicative growth. Choice A incorrectly identifies this as exponential growth, which would require constant percentage increases (like doubling) rather than constant numerical additions; this reflects confusion between additive and multiplicative patterns. When analyzing population data, calculate both absolute change and percentage change between time points to distinguish linear from exponential growth.

Question 10

1. A boom-and-bust cycle driven by alternating years of drought and heavy rain
2. Logistic growth approaching a carrying capacity near 300 individuals (correct answer)
3. Exponential growth with a constant per capita growth rate through Year 6
4. A linear increase caused by a constant number of births added each year
5. A decline caused by increased genetic variation lowering population growth

Explanation: This question assesses the skill of analyzing population ecology trends by identifying growth models from sequential population estimates. The deer population increased from 120 to nearly 300 over six years, with the rate of increase slowing as it approached 300, indicating density-dependent limitations from vegetation browse damage after Year 3. This slowdown reflects logistic growth, where factors like food scarcity reduce net growth as the population nears the carrying capacity of about 300 individuals. The stable counts in Years 5 and 6 further support that the population equilibrated at this level. A tempting distractor is choice C, which claims exponential growth with a constant per capita rate, but this overlooks the decelerating growth rate, a common misconception ignoring density dependence. For future problems, plot the data on a graph to visualize if the curve is J-shaped (exponential) or S-shaped (logistic).

Question 11

1. Per capita seed production decreased at higher density, consistent with intraspecific competition (correct answer)
2. Per capita seed production increased at higher density, indicating unlimited resources
3. Total seed production must be equal in both plots because area is the same
4. Seed production differences are best explained by trait changes in Plot 2 plants
5. Density-independent factors must be responsible because density does not affect reproduction

Explanation: This question assesses the skill of analyzing population ecology trends by interpreting density effects on reproductive output. In Plot 1 with 20 plants producing 100 seeds (5 per plant), per capita reproduction was higher than in Plot 2 with 80 plants producing 160 seeds (2 per plant), suggesting density-dependent intraspecific competition reduced individual seed production at higher densities. This pattern implies resources like space or nutrients became limiting as density increased, lowering net reproductive rates. Similar germination and no migration support that density alone drove the difference. A tempting distractor is choice B, stating per capita production increased at higher density indicating unlimited resources, but this reverses the actual trend, misconstruing competition's suppressive effect. To evaluate density dependence, always calculate per capita metrics and compare across densities for regulatory patterns.

Question 12

1. 5,000 adults, because births and deaths balance exactly
2. 5,500 adults, because immigration exceeds emigration by 500
3. 5,200 adults, because net change is $-1,200+900-700+1,500=+500$ (correct answer)
4. 4,300 adults, because deaths exceed recruitment by 300
5. 6,500 adults, because juveniles automatically double the population

Explanation: This question tests population ecology calculations by requiring you to track all demographic processes affecting population size. Starting with 5,000 adults, we must account for deaths (-1,200), immigration (+900), emigration (-700), and juvenile recruitment (+1,500), giving a net change of -1,200+900-700+1,500 = +500, resulting in 5,200 adults. The calculation follows the fundamental population equation: N(t+1) = N(t) + births - deaths + immigration - emigration, where juvenile recruitment represents successful births from the previous year. Choice B incorrectly considers only migration (900-700=200, not 500), ignoring mortality and recruitment which are essential components of population dynamics. When solving population problems, systematically list all additions and subtractions, ensuring you account for every demographic process mentioned in the problem.

Question 13

1. 260 mice, because emigration exceeds immigration by 30
2. 300 mice, because births and deaths cancel and movement is negligible
3. 330 mice, because net change is $+90-60+20-50=0$
4. 300 mice, because net change is $+90-60+20-50=0$ (correct answer)
5. 360 mice, because births are added without subtracting deaths

Explanation: This question tests population ecology calculations requiring careful accounting of all demographic changes to predict future population size. Starting with 300 mice, we add births (+90), subtract deaths (-60), add immigration (+20), and subtract emigration (-50), yielding a net change of +90-60+20-50 = 0, maintaining the population at 300 mice. The calculation demonstrates that populations remain stable when gains (births + immigration) exactly balance losses (deaths + emigration), a condition that defines zero population growth. Choice A incorrectly focuses only on migration balance while ignoring the larger contributions of births and deaths to overall population change. When solving population arithmetic, use the complete demographic equation systematically, ensuring each process is included with its correct sign to avoid overlooking major population drivers.

Question 14

1. Logistic growth approaching a carrying capacity near 320 rabbits
2. Exponential growth with a roughly constant per capita growth rate (correct answer)
3. Linear growth with a constant number added each month
4. Declining growth caused by increasing emigration from the grassland
5. Cyclic growth driven by seasonal changes in predator abundance

Explanation: This question tests your ability to analyze population ecology patterns by identifying growth trends from numerical data. The rabbit population shows a doubling pattern (20→40→80→160→320), where each month's count is twice the previous month's, indicating exponential growth with a constant per capita growth rate. In exponential growth, the population multiplies by the same factor each time period, unlike linear growth where a constant number is added. Choice C incorrectly assumes linear growth, missing that the absolute increase gets larger each month (20→40→60→80→160) while the multiplicative factor stays constant. When analyzing population data, calculate both absolute changes and ratios between consecutive time points to distinguish exponential from linear patterns.

Question 15

1. Oxygen became limiting, increasing mortality and reducing net population growth (correct answer)
2. The population entered continued exponential growth because doubling persisted
3. Immigration into the flask stopped, so population size could no longer increase
4. A new beneficial trait spread rapidly, causing the growth rate to level off
5. Predators were introduced at hour 4, causing an immediate population crash

Explanation: This question assesses the skill of analyzing population ecology trends by explaining shifts in growth phases due to limiting factors. The bacterial population doubled consistently from 1,000 to 8,000 cells in the first three hours, showing exponential growth under unlimited conditions, but after hour 3, growth nearly halted and then declined as dissolved oxygen dropped sharply. This change indicates oxygen became a density-dependent limiting resource, increasing mortality and reducing net population growth. By hour 5, the population decreased to 7,900, consistent with resource depletion overriding reproduction. A tempting distractor is choice B, suggesting continued exponential growth because doubling persisted, but this ignores the post-hour 3 slowdown and decline, misconstruing temporary patterns as indefinite. When evaluating growth curves, identify points where rates change and link them to environmental data for causal explanations.

Question 16

1. Exponential growth indicated by an increasing rate of increase over time (correct answer)
2. Logistic growth because the population leveled off near a stable carrying capacity
3. Linear growth because the population increased by a constant number each week
4. A population crash caused by density-independent disturbance during Week 3
5. Growth driven by changes in traits, producing higher survival in later weeks

Explanation: This question assesses the skill of analyzing population ecology trends by recognizing growth patterns in newly introduced populations. The fish population increased from 100 to 510 over five weeks with a consistent multiplication factor of about 1.5 each week, indicating a constant per capita growth rate typical of exponential growth under abundant resources like plankton. This accelerating increase, without signs of slowdown, reflects unlimited conditions allowing unchecked reproduction and survival. No evidence of density dependence or disturbances appeared during this period. A tempting distractor is choice C, claiming linear growth with constant additions, but this ignores the increasing increments (e.g., +50 then +75), a misconception confusing arithmetic with geometric progression. For pattern identification, compute ratios of successive population sizes to confirm if growth is exponential.

Question 17

1. It is density-dependent because higher density always increases death rate
2. It is density-independent because mortality occurred regardless of population size (correct answer)
3. It causes logistic growth by increasing carrying capacity after hour 3
4. It causes exponential growth by making per capita growth rate decrease to zero
5. It reflects emigration because cells leave the flask during the heat shock

Explanation: This question tests the skill of analyzing population ecology by classifying factors affecting growth rates. The heat shock in Flask 2 kills 90% of cells independently of density, as both flasks started at the same size, and post-shock growth resumes similarly, defining it as a density-independent event. This external factor reduces population size proportionally regardless of crowding, unlike density-dependent mechanisms that intensify with numbers. The identical flasks highlight that the shock's impact is not modulated by population state. A tempting distractor is choice A, density-dependent increase in mortality, which assumes higher density worsens effects, but this misconceives the uniform kill rate observed. To distinguish factors, compare impacts across varying densities, a strategy applicable to experimental ecology.

Question 18

1. Carrying capacity is reached as density-dependent limits reduce net growth (correct answer)
2. Exponential growth continues because resources remain effectively unlimited
3. Population stabilizes due to constant immigration balancing emigration annually
4. Population stabilizes because births stop entirely once predators are absent
5. Population stabilizes because individuals change traits to require less food

Explanation: This question tests the skill of analyzing population ecology by explaining long-term population stabilization. The fish population grows rapidly initially with abundant food, then stabilizes around 12,000 as reduced food per fish indicates density-dependent limitation at carrying capacity. This occurs because increased density heightens competition, balancing births and deaths without exceeding resources. The enclosed lake with no migration underscores internal regulation. A tempting distractor is choice B, continued exponential growth, which presumes unlimited resources persist, but this misconceives the measured food decline. For such analyses, assess per capita resource availability over time to identify carrying capacity, a method transferable to fisheries management.

Question 19

1. Density-dependent limitation, such as competition for food or space, reduced per-capita birth and survival rates. (correct answer)
2. Density-independent limitation, because temperature fluctuations increased as density increased.
3. Exponential growth, because per-capita birth rates increase as population density increases.
4. A constant carrying capacity is impossible, so the population must be declining due to random chance alone.
5. Genetic change in adults reduced egg laying when density is high, lowering growth rate immediately.

Explanation: This question tests population ecology analysis of density-dependent regulation mechanisms. The snail data shows classic density-dependent limitation: when density exceeds 200/m², both egg production and juvenile survival decrease, reducing population growth rate. This negative feedback prevents unlimited growth and maintains population stability near carrying capacity. Choice C incorrectly claims exponential growth increases birth rates with density, but the data shows the opposite—birth rates decrease at high density. To identify density-dependent regulation, look for changes in vital rates (birth, death, growth) that correlate with population density rather than external factors.

Question 20

1. The population entered logistic growth as a limiting resource declined, reducing the per-capita growth rate. (correct answer)
2. The population became exponential because resources increased, raising the per-capita growth rate.
3. The population leveled off because immigration balanced emigration in the closed flask.
4. The population slowed because density-independent predators increased in the flask over time.
5. The population slowed because cells changed genetically to stop reproducing when sugar is low.

Explanation: This question tests population ecology analysis of resource-limited growth in closed systems. The yeast population exhibits classic logistic growth: rapid initial increase followed by leveling off as sugar (the limiting resource) becomes depleted. The correlation between sugar depletion at hour 14 and population plateau confirms density-dependent resource limitation is controlling growth. Choice B incorrectly suggests resources increased to cause exponential growth, but the data shows resources decreased while growth slowed. In closed systems with fixed resources, always expect logistic rather than indefinite exponential growth patterns.