Using Fig. 4, suppose lawmakers are concerned about the survival of a species and pass a law that bans hunting of that species from now on. Provided the law is successfully enforced, we should:

Fig. 4 Population Model

Question

Using Fig. 4, suppose lawmakers are concerned about the survival of a species and pass a law that bans hunting of that species from now on. Provided the law is successfully enforced, we should:

Fig. 4 Population Model

BlackTom AI · Accepted Answer

On the growth versus stock-size graph, points where the red curve crosses the horizontal axis are equilibria (growth = 0). The sign of the red curve (above or below the axis) at a given stock size tells us whether the population will increase (positive growth) or decrease (negative growth) when no hunting occurs.

Relevant concepts:
- Natural growth curve: how population growth rate depends on current stock size (biomass).
- Equilibrium points: where growth = 0. If the growth curve is below the axis at a stock size, the population declines; if above, it increases.
- Depensatory/Allee effects: at very low densities growth can be negative, so populations below a threshold keep shrinking even without added mortality.

Step-by-step reasoning:
1. Identify equilibria on the figure: points A and C (and a high-stock right crossing) are zeros of natural growth. Between A and C the curve dips below the axis; at B (inside that dip) the red curve is clearly below the horizontal axis, indicating negative growth at that stock size.
2. Locate F: F is at a stock size where the red curve lies above the horizontal axis (between C and the high-stock crossing). That means the natural growth rate there is positive.
3. Removing hunting means harvest mortality is set to zero, so the population trajectory follows the sign of the natural growth curve alone.
4. Therefore: if current stock X = B, natural growth is negative → population will continue to shrink even after hunting is banned. If current stock X = F, natural growth is positive → population will grow once hunting is stopped.

Why other choices are incorrect:
- The first option reverses the signs for B and F.
- The third and fourth state the same outcome for both X values, but the graph shows opposite signs of growth at B and F so they cannot both behave identically.

Conclusion: We should expect the population to continue shrinking if X = B currently, but grow if X = F, matching the provided answer.

Using Fig. 4, suppose lawmakers are concerned about the survival of a species and pass a law that bans hunting of that species from now on. Provided the law is successfully enforced, we should: Fig. 4 Population Model单项选择题

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