AP Environmental Science Quiz: Island Biogeography

What this quiz covers

This quiz focuses on Island Biogeography, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Environmental Science.

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. Reserve 1, because greater distance lowers extinction by reducing arrivals of competitors.
2. Reserve 2, because closer distance increases immigration, raising equilibrium richness. (correct answer)
3. Reserve 1, because immigration increases with distance due to stronger winds offshore.
4. Reserve 2, because closer distance increases extinction by increasing predation pressure.

Explanation: Island biogeography theory predicts that immigration rate increases as distance to the mainland decreases. Reserve 2, being only 5 km offshore compared to Reserve 1's 40 km distance, will receive more colonizing species because dispersing organisms have a much higher probability of successfully reaching the closer island. Since both reserves have identical area (120 km²), they will have similar extinction rates, but Reserve 2's dramatically higher immigration rate will result in a higher equilibrium species richness. The closer distance facilitates more frequent colonization events, maintaining higher species diversity over time.

Question 2

1. lower immigration and higher extinction.
2. higher immigration and likely higher equilibrium richness. (correct answer)
3. no change in immigration because distance is unchanged.
4. lower equilibrium richness because immigration increases extinction.

Explanation: Island biogeography theory predicts that connecting an island to the mainland via land bridge dramatically increases immigration rates by eliminating water barriers to dispersal. During the land-bridge period, the small island would function more like a peninsula than an isolated island, allowing easy movement of species to and from the mainland. This connection would result in much higher immigration rates and likely higher equilibrium species richness compared to the isolated period. The island would essentially have access to the full mainland species pool rather than being limited by over-water dispersal capabilities.

Question 3

1. fewer species because larger area increases extinction.
2. the same number of species because $c$ is constant.
3. more species because species richness increases with area. (correct answer)
4. more species only if Island 2 is farther from the mainland.

Explanation: The species-area relationship S=cA^z shows that species richness increases with island area when the exponent z is positive. Since Island 2 has an area of 100 km² compared to Island 1's 25 km², and z>0, the model predicts Island 2 will support more species. This relationship exists because larger islands can support larger populations (reducing extinction risk), contain more diverse habitats and microenvironments, and provide more ecological niches for species to exploit. The constant c represents the baseline richness, but the area effect ($A^z$) means larger islands consistently support more species than smaller ones with similar environmental conditions.

Question 4

1. Island B likely has higher immigration due to distance, lowering richness.
2. Island A likely has higher immigration due to proximity, increasing richness. (correct answer)
3. Island B likely has lower extinction due to distance, lowering richness.
4. The result contradicts theory because distance should not affect immigration.

Explanation: Island biogeography theory explains that closer islands receive more immigrants due to higher colonization success rates, leading to higher species richness. Island A (near) having 75 species compared to Island B (far) having 45 species, despite identical size, demonstrates the distance effect on immigration. The proximity of Island A to the mainland increases the probability that dispersing organisms will successfully colonize it, resulting in higher immigration rates and consequently higher equilibrium species richness. This pattern supports the fundamental prediction that species richness decreases with increasing isolation from source populations.

Question 5

1. The immigration curve shifts downward (lower immigration at all species numbers), lowering equilibrium richness. (correct answer)
2. The extinction curve shifts downward (lower extinction at all species numbers), raising equilibrium richness.
3. The immigration curve shifts upward (higher immigration at all species numbers), raising equilibrium richness.
4. The extinction curve shifts upward (higher extinction at all species numbers), raising equilibrium richness.

Explanation: In island biogeography graphs, immigration and extinction rates are plotted against the number of species present. Distance from the mainland primarily affects immigration rates - far islands receive fewer colonists at any given species richness level. Moving from Island J (near) to Island K (far) causes the entire immigration curve to shift downward, meaning lower immigration rates at all species numbers. The extinction curve remains largely unchanged because it's primarily determined by island size, not distance. This downward shift in immigration results in a new equilibrium point at lower species richness, where the lowered immigration curve intersects with the unchanged extinction curve. Thus, distant islands support fewer species at equilibrium than near islands of the same size.

Question 6

1. Island Far will have higher equilibrium species richness because isolation reduces competition.
2. Both islands will have the same equilibrium species richness because area is the same.
3. Island Near will have higher equilibrium species richness because immigration is higher. (correct answer)
4. Island Near will have lower equilibrium species richness because immigration causes more extinctions.

Explanation: According to island biogeography theory, when two islands have identical areas, their extinction rates are similar because area determines resource availability and population sizes. However, distance from the mainland dramatically affects immigration rates - closer islands receive more colonizers. Island Near (5 km away) will have much higher immigration rates than Island Far (200 km away) because dispersing organisms are more likely to successfully reach nearby islands. Since equilibrium species richness occurs where immigration equals extinction, and Island Near has higher immigration with similar extinction, its equilibrium point will be at a higher species richness. The greater influx of new species compensates for extinctions, maintaining higher diversity.

Question 7

1. Species richness will increase because extinction exceeds immigration.
2. Species richness will decrease because extinction exceeds immigration. (correct answer)
3. Species richness will remain constant because immigration and extinction are both occurring.
4. Species richness will fluctuate randomly with no expected direction because equilibrium cannot be predicted from rates.

Explanation: Island biogeography equilibrium occurs when immigration and extinction rates are equal, maintaining constant species richness. Currently, this island experiences 3 new colonizations per year but loses 5 species to extinction annually, resulting in a net loss of 2 species per year. Since extinction (5 species/year) exceeds immigration (3 species/year), the island is above its equilibrium species richness. The species richness will decrease over time until it reaches a new equilibrium where immigration and extinction rates balance. This demonstrates the dynamic nature of island communities - species composition may change even at equilibrium, but the total number stabilizes when colonization and extinction rates are equal.

Question 8

1. Lower extinction rates because fewer species can colonize disturbed habitats.
2. Higher equilibrium species richness because disturbance increases immigration.
3. Higher extinction rates leading to lower species richness due to reduced habitat and smaller effective area. (correct answer)
4. No change in richness because island size and distance are unchanged.

Explanation: Habitat destruction effectively reduces the functional area of an island by eliminating suitable living space and resources for many species. When 70% of vegetation is destroyed on Island 1, it experiences higher extinction rates because remaining populations are compressed into smaller areas with fewer resources, leading to stronger competition, reduced population sizes, and loss of specialist species requiring specific destroyed habitats. The effective area reduction means Island 1 now functions like a much smaller island in the biogeography model, shifting its extinction curve upward. Immigration rates may remain similar or even decrease slightly if arriving species cannot find suitable habitat. The new equilibrium will stabilize at lower species richness compared to undisturbed Island 2. This demonstrates how habitat quality and availability, not just total area, determine an island's capacity to support species.

Question 9

1. Extinction rate increases; equilibrium species richness decreases.
2. Extinction rate decreases; equilibrium species richness increases. (correct answer)
3. Immigration rate decreases; equilibrium species richness increases.
4. Immigration rate increases; equilibrium species richness decreases.

Explanation: When an island's area increases through land reclamation, the primary effect is on extinction rates. Larger islands support bigger populations that are more resistant to random extinction events, provide more diverse habitats and resources, and reduce competition intensity among species. This causes extinction rates to decrease at any given species richness level. Immigration rates may increase slightly (larger target area), but the dominant effect is reduced extinction. With lower extinction rates, the island can support more species at equilibrium - the balance point between immigration and extinction shifts to higher species richness. This demonstrates why habitat area is crucial for conservation: larger areas naturally maintain higher biodiversity through reduced extinction pressure.

Question 10

1. increase because distance increases immigration.
2. decrease because immigration would decline with increased isolation. (correct answer)
3. stay the same because only area affects equilibrium.
4. become zero because extinction would immediately exceed immigration.

Explanation: Island biogeography theory predicts that equilibrium species richness increases with immigration rate and decreases with distance from the mainland. If the near island currently has higher equilibrium richness than the far island due to its proximity advantage, increasing the near island's distance to match the far island would reduce its immigration rate. With lower immigration but unchanged extinction (same area), the near island's equilibrium would decline because fewer colonization events could sustain fewer species before immigration and extinction balance. The reduced connectivity would shift the equilibrium toward the lower richness level characteristic of more isolated islands.

Question 11

1. Immigration rate decreases because the island is larger.
2. Extinction rate decreases because populations can be larger and habitats more diverse. (correct answer)
3. Immigration rate increases because larger islands are farther away.
4. Extinction rate increases because larger islands attract more predators.

Explanation: Island biogeography theory predicts that expanding island area will primarily affect extinction rates rather than immigration rates. Increasing the reserve from 20 km² to 60 km² provides more habitat space, allowing for larger population sizes and greater habitat diversity. Larger populations are less vulnerable to demographic stochasticity, environmental fluctuations, and local extinctions. Additionally, more area typically means more habitat types and microenvironments, providing more ecological niches and refugia. These factors combine to lower extinction rates across all species richness levels, while immigration rates remain largely unchanged since distance to the mainland stays constant.

Question 12

1. The ratio is less than 1, so the larger island has fewer species.
2. The ratio equals 1, so both islands have the same richness.
3. The ratio is greater than 1, so the larger island has more species. (correct answer)
4. The ratio is negative, so the model cannot be used.

Explanation: Using the species-area relationship S=cA^z with z=0.25, the ratio calculation gives (40/10)^0.25 = 4^0.25 = √2 ≈ 1.41. Since this ratio is greater than 1, the larger island (40 km²) is predicted to have more species than the smaller island (10 km²). The positive exponent z indicates that species richness increases with area, which is consistent with island biogeography theory. Larger islands support more species due to lower extinction rates from larger population sizes and greater habitat diversity, following the well-established species-area relationship pattern observed across many island systems.

Question 13

1. A > C > B > D (correct answer)
2. D > B > C > A
3. B > A > D > C
4. C > D > A > B

Explanation: Island biogeography theory ranks islands by combining area and distance effects: larger islands and closer islands have higher equilibrium richness. Island A (large & near) has both advantages - high immigration due to proximity and low extinction due to large area. Island C (small & near) has high immigration but high extinction. Island B (large & far) has low extinction but low immigration. Island D (small & far) has both disadvantages - low immigration due to distance and high extinction due to small area. This creates the ranking A > C > B > D, with the large near island having highest richness and the small far island having lowest richness.

Question 14

1. Both islands reach equilibrium at the same time and have the same equilibrium richness.
2. The 100 km² island is expected to have higher equilibrium richness due to lower extinction; it may also take longer to fully accumulate species. (correct answer)
3. The 1 km² island is expected to have higher equilibrium richness due to higher immigration.
4. The 100 km² island is expected to have lower equilibrium richness because larger islands have lower immigration.

Explanation: Island biogeography theory predicts that larger islands will have higher equilibrium species richness due to lower extinction rates, and may take longer to reach equilibrium because they can potentially support more species. The 100 km² island can support larger populations and more habitat types than the 1 km² island, resulting in lower extinction rates and higher equilibrium richness. Additionally, reaching equilibrium on the larger island may take more time because more colonization events are needed to fill the greater number of ecological niches available. The larger island's greater carrying capacity means it takes longer for immigration and extinction rates to balance at the higher equilibrium point.

Question 15

1. immigration rate is zero.
2. extinction rate is zero.
3. immigration rate equals extinction rate. (correct answer)
4. immigration rate is greater than extinction rate for all richness values.

Explanation: Island biogeography theory describes equilibrium as a dynamic balance between immigration and extinction processes. As species richness increases on an island, the immigration rate decreases because fewer new species remain in the mainland pool that aren't already present on the island. Simultaneously, extinction rate increases with more species due to increased competition, smaller average population sizes, and resource limitation. Equilibrium occurs when these two opposing forces balance each other - when the rate at which new species arrive equals the rate at which existing species go locally extinct.

Question 16

1. Larger islands generally support larger populations and more habitat diversity, reducing extinction risk. (correct answer)
2. Larger islands receive fewer immigrants, reducing competitive exclusion.
3. Extinction is higher on larger islands because predators are more common.
4. Extinction rate depends only on distance, not on area.

Explanation: Island biogeography theory states that larger islands have lower extinction rates than smaller islands of equal distance from the mainland. Island Large (150 km²) can support larger, more stable populations of each species compared to Island Small (5 km²). Larger islands also typically contain more habitat types and microenvironments, providing more ecological niches and refugia during environmental fluctuations. Additionally, larger islands offer more spatial separation between competing species and greater resource availability, all of which reduce the probability of local extinctions and contribute to higher equilibrium species richness.

Question 17

1. The remote island accumulates species faster due to reduced competition.
2. The near island accumulates species faster due to higher immigration. (correct answer)
3. Both accumulate species at identical rates because area is the same.
4. Neither accumulates species because extinction prevents establishment.

Explanation: Island biogeography theory predicts that islands closer to the mainland receive more immigrants due to higher colonization success rates. The near island (5 km offshore) will accumulate species faster than the remote island (70 km offshore) because dispersing organisms have a much higher probability of successfully reaching closer destinations. During the initial colonization phase, when both islands start with zero species, the difference in immigration rates will be most apparent since extinction rates are minimal with few species present. This higher immigration rate allows the near island to build up species richness more rapidly.

Question 18

1. Island X
2. Island Z
3. Island Y (correct answer)
4. Island W

Explanation: Island biogeography theory predicts that species richness increases with island area (lower extinction rates due to larger populations and more habitats) and decreases with distance from the mainland (lower immigration rates). Island Y has the largest area (200 km²) and is closest to the mainland (5 km), giving it both the highest immigration rate and lowest extinction rate. This combination of high immigration and low extinction results in the highest equilibrium species richness. Islands with smaller areas or greater distances will have lower equilibrium richness due to higher extinction rates or lower immigration rates respectively.

Question 19

1. Island A should have more species because smaller islands have lower extinction rates.
2. Island B should have more species because larger islands support larger populations and lower extinction rates. (correct answer)
3. Both islands should have the same richness because distance is the only factor affecting immigration.
4. Island A should have more species because species density increases as area decreases.

Explanation: The species-area relationship ($S=cA^z$) predicts that larger islands support more species. Island B (80 km²) is 8 times larger than Island A (10 km²), and since the exponent z is positive, Island B will have more species than Island A. Larger islands have lower extinction rates because they can support larger, more stable populations and typically contain more diverse habitats and microenvironments. The greater habitat diversity provides more ecological niches, allowing more species to coexist. Additionally, larger populations are less vulnerable to random demographic fluctuations and local extinctions, contributing to higher species richness at equilibrium.

Question 20

1. Island 1 will always have more species because distance is the only factor.
2. Island 2 will always have more species because area is the only factor.
3. Either could have higher richness depending on how immigration (distance) and extinction (area) trade off. (correct answer)
4. Both will have zero species because islands cannot be colonized.

Explanation: Island biogeography theory involves trade-offs between immigration (affected by distance) and extinction (affected by area), making either island potentially superior depending on the relative strength of these effects. Island 1 (15 km², 2 km from mainland) has high immigration due to proximity but potentially high extinction due to small area. Island 2 (150 km², 70 km from mainland) has low extinction due to large area but low immigration due to distance. The outcome depends on whether the immigration advantage of proximity outweighs the extinction disadvantage of small area, or whether the extinction advantage of large area compensates for the immigration disadvantage of distance.