Chapter 4, Problem 17A

Summary Introduction

To analyze:

Explain how density-dependent factors can limit a specific population with two examples.

Introduction:

Density-dependent factors: any factor in the environment that depends on the number of members in a population per unit area. These factors are mostly biotic factors such as predation, disease, parasites, and competition.

Explanation of Solution

Two examples of how two different-density factors can limit a specific population are the following:

1. Disease: When population size increases and population density is high, the disease is transmitted easily and quickly from one person to another because contact between individuals is more frequent. In high-density area mortality rate is high. Because of the high mortality rate, population size decreases and hence limits the size of a specific population. Example: Recent coronavirus pandemic. 
2. Competition: As the population density increases, competition between organisms for resources like food and space increases. Competition for insufficient resources results in a decrease in population size in an area due to death or to individuals leaving the area. Example: Intra-species competition in Lemmings.

Conclusion

Density-dependent factors limit the population size by negatively affecting the population growth at higher densities.