Question

A population of Drosophila melanogaster with 10,000 individuals and a carrying capacity of 20,000 follows the logistic growth equation. Suppose that 5,000 individuals of a competitor species, Drosophila simulans, are added to the population, and that this species has an α of 0.5. One would predict that this number of competitive individuals will decrease the D. melanogaster population growth rate by the same amount as the addition of _______ D. melanogaster individuals would.

1) 250
2) 750
3) 1,000
4) 2,500

Answer 1

The competitor species, Drosophila simulans, with an alpha (α) of 0.5, affects the population growth of D. melanogaster in a way that is equivalent to adding 2,500 individuals of D. melanogaster to the population.

Step-by-step explanation:

The addition of 5,000 individuals of a competitor species, Drosophila simulans, with an α of 0.5 would decrease the Drosophila melanogaster population growth rate by the same amount as the addition of 2,500 D. melanogaster individuals would.

The carrying capacity (K) is crucial in determining the growth rate of a population. Logistic growth equations typically include a term representing the interaction between these factors as the population nears its carrying capacity. In the given scenario, the competitive effect of D. simulans is considered half that of D. melanogaster (as α=0.5); thus, adding 5,000 individuals of the competitor species has the effect of adding half that number of D. melanogaster. Since the logistic growth rate is moderated by the expression K - N, where N is the current population size, this added effect essentially means that the carrying capacity for D. melanogaster is reduced as if their own population increased by 2,500 individuals. Therefore, the competitor species with an α of 0.5 has a similar effect on the carrying capacity and subsequent population growth rate as if an additional 2,500 individuals of D. melanogaster were introduced.