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44.5 Life History Patterns
There are examples that show how a density-independent factor can act.
Population size and growth can be influenced by various intrinsic factors.
The number of births per reproductive event, the age at reproduction, the life span, and the probability of living the entire life span are some of the factors that affect the population.
These particulars are part of the life history of the species.
Trade-offs can be found in life histories.
Each population can only capture so much of the available energy, and how this energy is distributed among its life span, reproduction events, care of offspring, and so forth has evolved over time.
The final life history of individual species is shaped by natural selection.
In mouth-brooding Frogs of South America, the male carries the baby in a vocal pouch under his mouth before releasing the froglets.
After the eggs hatch, the tadpoles wiggle onto the parent's back and are carried to water.
The midwife toad of Europe carries eggs around his hind legs and takes them to water when they are ready to hatch.
Density-independent factors keep populations in the lag phase of population growth in unpredictable environments.
Most energy goes into producing a large number of relatively small offspring, with little going into parental care.
Some of them will survive to reproductive age if they have more offspring.
Because of low population densities, density- dependent mechanisms, such as predator and competition, are unlikely to play a major role in regulating population size and growth rates most of the time.
There are not always clear-cut distinctions between life strategies.
Resources such as food and shelter are relatively scarce for these individuals, and those that are best able to compete have the greatest reproductive success.
Strategies, species that allocate the majority of their energy to their own growth and survival, as well as to their offspring.
They have a limited number of reproductive events and have a long life span.
When their normal way of life is destroyed, they become extinct.
Birds of prey, large mammals, and long-lived plants are some of the strategies.
The Florida panther is the largest mammal in Florida.
It requires a large range and few offspring, which require parental care.
The Florida panther is on the verge of extinction because it is not able to compensate for a reduction in its range.
Two male and four female deer were able to produce 160 offspring in 6 years.
The number of offspring could have reached 300 if the majority of female deer produced two young each time they reproduce.
The white-tailed deer population in the eastern United States was less than half a million a century ago.
When Europeans first colonized America, it was less than 200 million.
A reduction in natural predators and a readily available supply of food are to blame for the dramatic increase in population size.
Humans' killing of wolves and mountain lions has caused the natural predator of deer to be absent from most regions.
Deer hunting is banned in some urban areas.
In areas where deer populations have become too large, the deer suffer from starvation as they deplete their own food supply.
After deer hunting was banned on Long Island, New York, the deer population outgrew available food resources.
The animals were weak and sickly and their bones were visible through their skin.
A large deer population can cause a lot of problems.
A homeowner is sad to see new plants destroyed and evergreen trees damaged because of deer.
Over a million deer-vehicle accidents occur in the United States each year, resulting in over a billion dollars in insurance claims, thousands of human injuries, and hundreds of human deaths.
Over 3000 people are diagnosed with lyme disease each year and can lead to arthritis.
Deer overpopulation hurts both deer and humans.
There are less understory plants in forested areas that are overpopulated by deer.
The deer eat certain plants while leaving others alone.
Changing the number and diversity of trees in a forest can lead to a negative economic impact.
We need to learn how to properly manage deer populations.
Some states, such as Texas, have large land owners set aside a portion of their property for a deer herd.
They improve the nutrition of the herd and restrict the hunting of young bucks, but they allow hunting of does.
The result is a herd that is self-sufficient.
The white-tailed deer has a reproductive potential that can place it in conflict with human society.
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