In a population experiencing positive density dependent growth, which of the following would you expect to happen? – The population growth rate decreases as the population density increases – The population growth rate does not change as the population density increases. – The population growth rate increases as the population density increases
The Correct Answer and Explanation is:
Correct Answer:
The population growth rate increases as the population density increases.
Explanation:
Positive density-dependent growth occurs when the per capita growth rate of a population rises with increasing population density. This phenomenon often contrasts with the more common negative density dependence, where growth slows down as density rises due to resource competition, disease, and crowding.
In positive density dependence, a sparse population might suffer from limited opportunities for mating, reduced group defense against predators, or insufficient cooperative behaviors such as foraging. As population density increases, individuals may benefit from enhanced survival, reproduction, or foraging efficiency. This relationship is often described by the Allee effect, named after ecologist W.C. Allee, who observed that some populations require a minimum density to sustain growth and avoid extinction.
For example, certain species of animals that rely on group hunting or herding, like wolves or elephants, may face survival challenges at low densities. As their numbers grow, the efficiency of social behaviors improves, and the rate of reproduction or survival increases. Similarly, in plants that depend on cross-pollination, having more individuals nearby can improve pollination success, thereby raising reproductive rates.
This pattern continues until density becomes high enough to trigger negative feedback mechanisms such as resource depletion or increased disease transmission. Thus, positive density dependence often operates at low to intermediate densities, beyond which traditional negative density dependence dominates.
In summary, populations showing positive density-dependent growth experience an increase in growth rate with rising population density—particularly in cases where individual success depends on the presence of conspecifics for survival, reproduction, or other cooperative behaviors.
