Ecosystem Change Arguments Practice Test

A stream near farms had increased fertilizer runoff in spring, raising nitrate levels. Data were collected before the runoff increase and after.

Evidence (before → after): nitrate: 2 mg/L → 9 mg/L; algae: 200 → 900 cells/mL; dissolved oxygen: 8.5 → 4.0 mg/L; trout: 35 → 10 per 100 m.

Which argument best explains the trout population shift using the evidence and reasoning that links the change to the population response?

A forest area was logged, reducing tree canopy cover. Surveys were done before logging and one year after.

Evidence (before → after): canopy cover: 80% → 30%; shade-tolerant ferns: 60 → 15 per plot; sun-loving grasses: 10 → 55 per plot; deer: 18 → 26 per km$^2$.

Which claim about ecosystem change is incorrect based on the evidence? (Select the claim that is NOT supported by the evidence.)