14.3 Factors Affecting Population Change

1. 14.3 Factors Affecting Population Change

2. The role of Density • Generally, dense populations have lower birth rates, higher death rates, and slower growth rates than less dense populations • Density-dependant factors are factors that limit population growth • 4 factors are significant: disease, predation, parasitism and competition

3. Intraspecific competiton:As the number of raccoons in the forest increases, the availability of nesting sites limits population growth. • Disease: Overpopulating rabbits in Australia were finally controlled by a disease spread through the population. A higher mortality rate was recorded in regions with large populations than small populations.

5. Mangrove trees are often seen in the Florida everglades, their roots alternately exposed to the air, or submerged in water. Few tree species can survive such varied exposure. Mangroves can grow outside of the swamp, but rarely do. What are the ecological reasons for the unusual habitat of the mangrove. • decreasing interspecific competition - while the swamp conditions are not optimal, there must be enough benefit to living where other trees cannot live very well - the advantages of more available sunlight, space, nutrients outweigh the disadvantages of immersion/exposure

6. Predation • An ecological relationship in which one animal kills and eats another • Humans raise cattle for food, caring for them until they are slaughtered. This relationship can ultimately be described as predation • Predation is beneficial to one species, but usually lethal to the other • Wolves kill and eat deer. The wolves starve if no deer are present. The deer overpopulate and starve if their numbers increase. The relationship between wolves and deer is predation

7. The minimum viable population size • A population is considered at risk of becoming extinct when its number falls below the minimum viable population size • Low densities in populations can mean less genetic variation and less opportunities to mate

8. The Allee effect • Neanderthals may have died out when their birth rate became too low to offset their death rate.

9. Density independent factors • These factors limit population sizes through factors such as human intervention ( habitat destruction) or climate related events (droughts, floods, hurricanes)

10. Limiting Factor • Of all the resources that a population requires for growth, the one that is in shortest supply is the limiting factor • It determines how much the population can grow.