Ecology Ecological Succession 2 — Questions and Answers
Question 1: The inhibition model of succession proposes that:
- Early species facilitate the establishment of later species
- Early species resist replacement by later species until they die or are disturbed (Correct answer)
- All species colonize simultaneously and compete equally
- Climax communities form without any directional change
Correct answer: Early species resist replacement by later species until they die or are disturbed
The inhibition model suggests that early colonizers can inhibit the establishment of later species, so succession only advances when early species are removed by disturbance or die naturally.
Question 2: What is the primary source of nitrogen input during early primary succession on bare rock?
- Decomposition of animal waste
- Nitrogen fixation by cyanobacteria and lichens (Correct answer)
- Rainfall containing dissolved nitrates
- Weathering of parent rock material
Correct answer: Nitrogen fixation by cyanobacteria and lichens
Early colonizers such as cyanobacteria and certain lichens fix atmospheric nitrogen, making it available to the ecosystem and contributing to soil development during primary succession.
Question 3: Which term describes the idea that multiple stable states can exist in an ecosystem, and a disturbance can shift the system from one state to another?
- Climax theory
- Alternative stable states (Correct answer)
- Monoclimax hypothesis
- Relay floristics
Correct answer: Alternative stable states
The alternative stable states concept holds that ecosystems can exist in more than one stable configuration, and large disturbances can push a system across a threshold into a different stable state.
Question 4: How does species richness typically change during early to mid-stages of succession?
- It decreases steadily throughout succession
- It generally increases as new species colonize and habitat becomes more complex (Correct answer)
- It remains constant from the start
- It peaks immediately after disturbance then drops to zero
Correct answer: It generally increases as new species colonize and habitat becomes more complex
Species richness typically increases during early to mid-succession as habitat complexity grows, resources diversify, and more species can find suitable niches.
Question 5: Which of the following best describes the tolerance model of succession?
- Early species must establish before later species can colonize
- Later species can establish regardless of early species but are eventually out-competed by better competitors (Correct answer)
- Only the strongest competitor wins at every stage
- Disturbance resets succession to the very beginning every time
Correct answer: Later species can establish regardless of early species but are eventually out-competed by better competitors
The tolerance model proposes that later successional species can establish early but grow slowly; they eventually replace early species because they are better competitors for resources as conditions mature.
Question 6: What role do mycorrhizal fungi play in ecosystem succession?
- They prevent plant colonization by producing allelopathic chemicals
- They facilitate plant establishment by enhancing nutrient uptake, speeding succession (Correct answer)
- They only appear at the climax stage of succession
- They break down rock into sand, blocking soil formation
Correct answer: They facilitate plant establishment by enhancing nutrient uptake, speeding succession
Mycorrhizal fungi form mutualistic associations with plant roots, improving nutrient and water absorption, which helps plants establish and grow faster, thereby facilitating successional progression.
Question 7: The Intermediate Disturbance Hypothesis predicts that species diversity is highest when:
- Disturbance frequency and intensity are very high
- Disturbance frequency and intensity are very low
- Disturbance occurs at intermediate levels (Correct answer)
- There is no disturbance at all
Correct answer: Disturbance occurs at intermediate levels
The Intermediate Disturbance Hypothesis predicts peak species diversity at intermediate disturbance levels because disturbance prevents competitive exclusion while still allowing many species to persist.
Ecology Ecological Succession 2
The inhibition model of succession proposes that: