AP Biology: Unit 8, Community Ecology & Disruptions (Drill 37)

Question 1. Based on the table, which species most clearly exhibits pioneer characteristics following the disturbance?

• A) Red oak, because it had the highest pre-storm cover and recovered most rapidly.
• B) Blackberry, because its cover increased dramatically immediately after the storm and declined as canopy species recovered. ✓
• C) Spicebush, because it maintained relatively stable cover across all three time points.
• D) Trout lily, because it declined after the storm and then recovered fully by Year 5 as a pioneer.

Explanation: Pioneer species colonize disturbed areas rapidly, exploit newly available resources, and are later replaced as succession proceeds. Blackberry increased from 4% to 31% cover in Year 1 -- a nearly eightfold increase -- then declined to 6% by Year 5 as canopy trees recovered and shading increased. This is the classic early-successional pattern. A is incorrect -- red oak declined after the storm; high pre-storm cover reflects climax dominance, not pioneer behavior. C is incorrect -- spicebush stability reflects shade tolerance, not pioneer characteristics. D is incorrect -- trout lily declined due to canopy loss and recovered as shade returned, the opposite of pioneer behavior.

Question 2. Garlic mustard increased from 2% to 18% cover in Year 1, then declined to 4% by Year 5. A researcher argues this pattern demonstrates that invasive species can exploit disturbance windows but are suppressed by recovering native communities. Which additional data would most strengthen this argument?

• A) Evidence that garlic mustard produces allelopathic chemicals that inhibit native seedling germination.
• B) Documentation that garlic mustard produces more seeds per plant in high-light conditions than in shaded conditions.
• C) Evidence that garlic mustard cover increased as canopy closure increased across multiple disturbed forest plots over time under the circumstances described.
• D) Measurements showing garlic mustard cover is negatively correlated with canopy closure across multiple disturbed forest plots. ✓

Explanation: The argument requires showing that canopy recovery suppresses garlic mustard, not some other factor. A negative correlation between garlic mustard cover and canopy closure across multiple plots would provide correlational evidence consistent with a causal mechanism linking native recovery to invasive suppression. A describes allelopathy -- a mechanism by which garlic mustard harms natives, not the reverse, which would weaken the argument. C would undermine the argument by providing an alternative explanation for the decline. B explains the Year 1 increase but does not address suppression.

Question 3. The recovery of red oak and sugar maple cover between Year 1 and Year 5 represents which ecological process?

• A) Primary succession, because the ice storm created entirely bare substrate with no surviving organisms, from which new biological communities then developed.
• B) Competitive exclusion, because dominant canopy species eliminated all pioneer species from the community.
• C) Secondary succession, because the disturbance reduced but did not eliminate the existing community, and recovery proceeds from remnant soil, seed banks, and surviving organisms. ✓
• D) Mutualistic facilitation, because red oak and sugar maple aided each other's recovery through shared mycorrhizal networks.

Explanation: Secondary succession occurs when a disturbance disrupts an existing community without destroying the soil seed bank or all resident organisms. The ice storm reduced canopy cover but left soil, root systems, seed banks, and understory plants largely intact. A is incorrect -- primary succession begins on bare substrate with no prior biological legacy, such as a lava flow or glacial retreat. B is incorrect -- pioneer species declined but were not eliminated; competitive exclusion implies complete removal of one species by another. D introduces mycorrhizal facilitation, which is not demonstrated by the table and is not the process the recovery pattern represents.

Question 4. A conservation biologist argues that the five-year post-storm community is not yet fully recovered because species composition still differs from pre-storm values. A second biologist argues the community is functionally recovered because canopy dominants have reestablished. Which reasoning best evaluates this disagreement?

• A) The first biologist is correct because ecological recovery requires exact restoration of pre-disturbance species percentages.
• B) The disagreement cannot be resolved without additional data because species cover percentages are not a valid measure of community structure.
• C) The second biologist is correct because canopy cover is the only ecologically meaningful measure of community recovery, and species composition is irrelevant.
• D) Both positions reflect legitimate but different definitions of recovery -- compositional recovery requires return to pre-disturbance species proportions, while functional recovery requires restoration of dominant guild structure; the data support functional recovery but not full compositional recovery, as canopy dominants have only partially recovered toward pre-storm levels. ✓

Explanation: Ecological recovery is not a single binary state -- it depends on the metric used. By Year 5, red oak and sugar maple have partially recovered toward pre-storm levels, and pioneer and invasive species have declined sharply, suggesting functional recovery of canopy structure. However, exact pre-storm proportions have not been restored, supporting the first biologist on compositional grounds. D correctly identifies both positions as valid within their own frameworks and accurately reads the data. A is incorrect -- exact restoration is rarely the standard for ecological recovery. C is incorrect -- canopy cover is important but not the only valid measure. B is incorrect -- species cover is a standard and widely accepted community metric.

Question 5. Which hypothesis about the role of disturbance in maintaining community diversity is most supported by the data in the table?

• A) The competitive exclusion principle, which predicts that disturbance allows the single best competitor to dominate and permanently exclude all other species.
• B) The neutral theory of biodiversity, which predicts that all species are competitively equivalent and community composition is determined by random dispersal.
• C) The resource partitioning hypothesis, which predicts that species avoid competition by using different resources regardless of disturbance level.
• D) The intermediate disturbance hypothesis, which predicts that moderate disturbance increases diversity by creating openings that allow multiple species with different strategies to coexist temporarily. ✓

Explanation: The intermediate disturbance hypothesis predicts that moderate disturbances prevent competitive dominance, temporarily increasing diversity by creating openings for pioneers and opportunists alongside surviving residents. The data show exactly this pattern -- blackberry and garlic mustard increased sharply in Year 1 alongside reduced but surviving canopy species, suggesting increased coexistence of multiple species before canopy dominants reasserted control by Year 5. A is incorrect -- no single species dominated permanently; the pattern reversed as canopy species recovered. C describes niche differentiation in stable communities, not a response to disturbance. B predicts random directionless community change, inconsistent with the structured successional pattern in the data.