Transcript 14.3 Factors Affecting Population Change

14.3 Factors Affecting Population
Change
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
• 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.
• 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
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
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
The Allee effect
• Neanderthals may have died out when their
birth rate became too low to offset their
death rate.
Density independent factors
• These factors limit population sizes through
factors such as human intervention ( habitat
destruction) or climate related events
(droughts, floods, hurricanes)
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.