42.3 Factors That Limit Population Size | |
| 5. Environmental resistance counters unrestrained growth by increasing mortality rates and/or reducing birthrates. | |
| 6. In response to environmental resistance, the population may stabilize at its carrying capacity, the number of individuals an environment can indefinitely support. After a period of exponential growth, a population may overshoot the carrying capacity and crash. Alternatively, density-dependent factors may slow growth so the population size levels off at the carrying capacity, producing an S-shaped logistic growth curve. | |
| 7. Environmental resistance includes density-independent factors, which kill a fraction of the population regardless of its size. Density-dependent factors, which have a greater effect on large populations, can also regulate population size. | Essential Study Partner
Regulation of Growth Rate |
| 8. Populations that regularly increase and decrease in size have a boom and bust cycle. | |
| 9. Different life histories reflect a trade-off between the number of offspring and parental investment. K-selected species invest heavily in rearing relatively few young. In contrast, r-selected species produce many offspring but do not expend much energy on each. | Essential Study Partner
Life Histories
Essential Study Partner
Life History Strategies |
