Final answer:
The decrease in egg-laying as food resources become scarce among female fruit flies is an example of negative density dependence, as fecundity declines with increased population density and competition for limited food resources.
Step-by-step explanation:
The scenario in which female fruit flies lay fewer eggs as food resources become scarce is an example of negative density dependence. This is because the population's fecundity (egg-laying capacity) is inversely related to the population density. When resources such as food become limited due to a large population, competition for those resources increases, leading to fewer resources per individual, and thus, a reduced rate of egg production.
Density independence would imply that the number of eggs laid is unaffected by the population density and, instead, is influenced by factors such as weather events, pesticides, or other factors that affect a population regardless of its size. Delayed density dependence refers to when the effects of current population density are not immediately seen but have an impact on the population at a later time.
An experiment with fruit flies that were selected for resistance or susceptibility to DDT showed that selection led to a reduced rate of egg production compared to nonselected flies. This finding complements our understanding of negative density dependence in that selection pressures can also play a role in fecundity alongside environmental factors like resource availability.