Question

The graphs shown represent the relationship between population size ($N$) and population growth rate $\frac{dN}{dt}$. Which one of the following growth curves represents a density-dependent population that experiences a strong Allee effect?
\includegraphics[width=0.5\linewidth]{44.png}

• A. P
• B. Q
• C. R
• D. S

Hint:

To identify an Allee effect: 1. Look for negative growth at very small population sizes.
2. A strong Allee effect includes a critical threshold population size below which the population declines.
3. Growth peaks at intermediate population sizes before declining near carrying capacity.

Answer 1

The Correct Option is A

Step 1: Understand the Allee effect. The Allee effect describes a phenomenon where a population’s growth rate decreases when the population size is very small. This occurs due to challenges such as difficulty finding mates or cooperative behaviors not being effective at low densities. A strong Allee effect results in a critical population size below which the population declines to extinction. Step 2: Identify the characteristics of the growth curve. A population with a strong Allee effect will exhibit: 1. Negative growth ($\frac{dN}{dt}<0$) for very small $N$, as the population cannot sustain itself. 2. Positive growth ($\frac{dN}{dt} > 0$) as $N$ increases beyond a critical threshold. 3. A peak in growth rate at an intermediate population size. 4. Declining growth ($\frac{dN}{dt} \to 0$) as the population approaches carrying capacity. Step 3: Analyze the graphs. Graph P: Correct. This graph represents the strong Allee effect, showing negative growth for small $N$, a critical threshold, and a peak at intermediate $N$. Graph Q: Incorrect. This graph shows logistic growth, which does not include negative growth at small $N$. Graph R: Incorrect. This graph shows continuous positive growth rates at all population sizes, inconsistent with the Allee effect. Graph S: Incorrect. This linear growth pattern does not capture the density-dependent dynamics of the Allee effect.