Question

(wet) to –10 (very dry) with zero representing the long-term average.

charts: first chart (1995–2010) with “wolves/1,000 km²” (blue) and “elk per km²” (green); second chart with “drought index (deviation from long - term average)” (red) and “elk per km²” (green).

considering all the data provided, what conclusion can be made regarding the effect of the wolf introduction on the abundance of elk?

○ there is not enough evidence to suggest that either predation by wolves or drought affected the elk population.
○ wolves are the sole factor affecting the elk population size
○ the elk population exhibits boom - and - bust cycles independent of the wolf population.
○ wolves apply predation pressure on elk, but they are not the only cause of the decrease in the elk population.

Explanation:

1. Analyze the first graph: As wolf population (Wolves/1,000 km²) increases, elk population (Elk per km²) generally decreases, showing predation pressure from wolves.
2. Analyze the second graph: Drought severity (Drought Index) also correlates with elk population changes (e.g., when drought is more severe, elk population tends to decrease further).
3. Evaluate options:

• Option 1: Incorrect, as there is evidence (from both graphs) of wolf predation and drought impact.
• Option 2: Incorrect, since the second graph shows drought also affects elk, so wolves are not the sole factor.
• Option 3: Incorrect, the first graph shows elk population is related to wolf population (not independent).
• Option 4: Correct, as wolves do apply predation pressure (seen in first graph), but drought (from second graph) also contributes to elk population decrease, so wolves are not the only cause.

Answer:

D. Wolves apply predation pressure on elk, but they are not the only cause of the decrease in the elk population.