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Applied Quiz: Systems Thinking in Ecology

A second set of questions on this chapter, weighted toward using the ideas rather than recalling them. Each one puts you in a situation and asks what the chapter's framework says to do.

1. A colleague describes an erosion spiral as "a positive feedback loop, so at least something good is happening." What has she misunderstood?

  1. Nothing — positive feedback loops produce beneficial outcomes
  2. "Positive" describes the loop's behavior, not its value: it amplifies a trend. An erosion spiral is positive feedback and destructive, while negative feedback is stabilizing and usually desirable
  3. Erosion is actually a negative feedback loop
  4. The terms are interchangeable in ecology
Show Answer

The correct answer is B. Bree flags this vocabulary trap directly in the chapter. Positive means self-reinforcing; negative means self-correcting. Fewer plants → more erosion → fewer plants is amplification, and it accelerates until the hillside is bare.

Concept Tested: Positive vs. Negative Feedback Loops

See: Chapter 15

2. Garlic mustard is described as an invasion that "feeds itself." Trace the loop.

  1. It grows faster each year because the climate is warming
  2. It releases chemicals that kill beneficial soil fungi; without those fungi native plants struggle; as natives decline garlic mustard spreads further and releases more chemicals
  3. Deer avoid it, so it outcompetes browsed natives
  4. Its seeds germinate at a higher rate each generation
Show Answer

The correct answer is B. This is the chapter's own example of a positive feedback loop, and it explains why garlic mustard removal takes years — the loop has already degraded the soil biology that native recovery depends on.

Concept Tested: Invasive Species as Positive Feedback

See: Chapter 15

3. In the Yellowstone story, what does this chapter emphasize that the wolves did beyond reducing elk numbers?

  1. Nothing more — the whole effect came from fewer elk
  2. They changed how elk used the landscape — herds moved more and avoided open valleys — which let streamside willows and aspens recover, bringing back beavers, songbirds and stable stream channels
  3. They directly restored the stream channels by damming
  4. They ate the beavers, which allowed vegetation to return
Show Answer

The correct answer is B. The behavioral change is the part the chapter singles out, and it is what makes this a systems story rather than a population one. The physical shape of the rivers changed as a downstream consequence of where elk chose to stand.

Concept Tested: Trophic Cascades

See: Chapter 15

4. A Minnesota woodland has almost no trillium, few tree seedlings, and a browse line at deer height. Using this chapter, what systems story explains it?

  1. Soil depletion from acid rain
  2. A trophic cascade — wolf decline across much of the state contributed to deer overpopulation, and overbrowsing prevents understory regeneration, which then affects ground-nesting birds, dependent insects and the forest's long-term composition
  3. Climate change acting alone
  4. Invasive earthworms only
Show Answer

The correct answer is B. The chapter presents this as Minnesota's own cascade. The visible symptom is missing wildflowers; the mechanism sits two trophic levels up. Earthworms are a real compounding factor from Chapter 8, but they are not the cascade being described here.

Concept Tested: Trophic Cascades in Minnesota

See: Chapter 15

5. A restored prairie has been in for eight years and still does not match a nearby remnant for diversity. What does this chapter offer as an explanation?

  1. The seed mix was inadequate
  2. Mycorrhizal networks take years to rebuild, and tilling, paving or fungicide destroys them; restoring that underground network is among the hardest parts of restoration, which is why restorations lag remnants for a long time
  3. Restored prairies never reach remnant quality
  4. The site needs more fertilizer
Show Answer

The correct answer is B. The chapter names this explicitly as one reason restored prairies take many years to approach remnant function. The visible planting can be complete while the system it depends on is still assembling.

Concept Tested: Mycorrhizal Networks in Restoration

See: Chapter 15

6. A developer proposes replacing one 40-acre woodland with four 10-acre woodlands connected by roads, arguing that total habitat area is unchanged. What does this chapter's edge-effect discussion say?

  1. The proposal is equivalent — area is what matters
  2. Fragmenting habitat raises the ratio of edge to interior; forest-interior species that need large unbroken habitat decline, and edges act as invasion corridors for aggressive non-natives
  3. Smaller patches are better because edges increase diversity
  4. Edge effects apply only to wetlands
Show Answer

The correct answer is B. Option C states a real fact — edges often do raise local species counts — but applies it wrongly, which is the trap. The species gained at edges are generalists; the ones lost are the interior specialists that had nowhere else to be.

Concept Tested: Edge Effects and Fragmentation

See: Chapter 15

7. Two prairies face the same drought. One has 8 species, the other 45. What does this chapter predict and through what mechanism?

  1. Identical outcomes — both are native prairies
  2. The diverse prairie is more resilient, through functional redundancy and genetic diversity: if one species fails, others fill the same role, and within-species variation allows adaptation
  3. The 8-species prairie does better because there is less competition for water
  4. Diversity affects appearance but not resilience
Show Answer

The correct answer is B. The chapter lists five sources of resilience — biodiversity, functional redundancy, genetic diversity, intact food webs and healthy soils — and the first three all favor the diverse planting. It also warns that even resilient systems have thresholds beyond which recovery needs intervention.

Concept Tested: Resilience and Functional Redundancy

See: Chapter 15

8. Why does this chapter call beavers a keystone species rather than just a common mammal?

  1. Because they are large and numerous
  2. Because their impact is disproportionately large relative to their abundance — their dams convert a narrow stream into a mosaic of ponds, wetlands and meadows supporting many other species
  3. Because they are endangered in Minnesota
  4. Because they eat invasive plants
Show Answer

The correct answer is B. Disproportionate influence relative to abundance is the definition, and the architectural metaphor carries it — remove the keystone and the arch collapses, though it was only one stone. Beavers earn it by physically engineering habitat.

Concept Tested: Keystone Species

See: Chapter 15

9. Draining wetlands for farmland is given as a case of unintended consequences. What is the chapter's actual lesson from it?

  1. That we should never intervene in ecosystems
  2. That we should think through the full web of consequences before acting, then monitor results and be willing to adapt — the intervention removed flood control, habitat and water filtration alongside the intended gain
  3. That agriculture is inherently destructive
  4. That wetland drainage was beneficial overall
Show Answer

The correct answer is B. The chapter states the lesson in nearly these words, and the distinction matters: systems thinking is a discipline for acting well, not an argument for paralysis. Monitoring and adaptation are the parts that make intervention responsible.

Concept Tested: Unintended Consequences

See: Chapter 15

10. What does the "Wood Wide Web" idea claim that studying individual trees would never reveal?

  1. That trees compete for light
  2. That a forest is partly cooperative — established trees transfer carbon and nutrients to shaded seedlings through fungal connections, stressed plants receive support from neighbors, and insect-attack warnings travel the network
  3. That trees grow faster in groups
  4. That fungi are parasites on tree roots
Show Answer

The correct answer is B. This is the chapter's clearest illustration of an emergent property: the behavior of the whole cannot be predicted from the parts. Option D inverts the relationship, which is symbiotic — the fungus supplies water and phosphorus, the plant supplies sugars.

Concept Tested: Mycorrhizal Networks and Emergent Properties

See: Chapter 15