Transcript Limits to Growth Notes

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Limiting factor = a factor that causes a
population growth to decrease.
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Diagram on page 124 in textbook
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Density-Dependent limiting factor = a
limiting factor that depends on population
size.
These factors only become limiting when the
population reaches a certain size.
These factors operate strongly when the
population is large & dense.
Examples – competition, predation,
parasitism, and disease.
This illustrates how predation can affect the
population growth. The moose population was also
affected by changes in food supply, and the wolves
were also affected by disease.
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Density-Independent limiting factors = affect
all populations in similar ways, regardless of
the population size.
Examples – Unusual weather, natural
disasters, seasonal cycles, certain human
activities, i.e. cutting down forests, and
damming rivers.
In response to these factors, many species
show a crash in population size & then
rebuild.
Some species are extinguished.
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The size of the human population tends to
increase with time.
For most of human existence, the population
grew slowly due to lack of food, disease, &
death rates were so high.
About 500 years ago, the human population
began growing more rapidly due to industry,
agriculture, improved sanitation, &
healthcare.
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Demography = the scientific study of human
population
Birthrates, death rates, and age structure of a
population help predict why some countries
have higher growth rates.
Over the past century, population growth has
slowed… this is because of a dramatic change
in birth & death rates (demographic
transistion)
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Population growth depends on how many
people of different ages make up a given
population.
Demographers can predict future growth by
using models called age-structure diagrams
or population profiles.