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5-2 Limits to Growth
Limiting Factors
• Remember, primary productivity of an
ecosystem can be reduced by limiting
nutrients
• Limiting factors can determine carry
capacity
– Density Dependent Factors
– Density Independent Factors
1. Density-Dependant Factors
• Limiting factors that depend on population
size
• Density-dependent factors become limiting
only when population density reaches a
certain level
• Does not affect small, scattered
populations
1a. Competition
• Occurs when populations
become crowded
• When 2 species compete for
same resource, they are
under pressure to change
– Over time, evolve to occupy diff.
niches
1b. Predation
• Populations in nature are controlled by
predation
– Known as predator-prey relationship
• Isle Royale in Lake Superior
1c & 1d Parasitism & Disease
• Parasites are similar to predators
– weaken and kill hosts
• Large populations can be under
stress making them more
susceptible to diseases
• More members = easier to pass
“things” around
3. Density-Independent Factors
• Factors that affect
populations regardless of
their size
• Examples:
– Unusual weather (Draught,
Hurricanes)
– Season cycles
– Human activities (damming
rivers, forest cutting)
5-3 Human Population Growth
• Like the populations of many other
living organisms, the size of the human
population tends to increase with time.
• For most of human existence, the
population grew slowly
• Until fairly recently, only half the
children in the world survived to
adulthood.
• What caused human populations to
suddenly grow rapidly?
• Agriculture
• Industry/Medicine
• About 500 years ago, the human population
began growing more rapidly because of
agriculture and industry.
• With these advances, the human population
experienced exponential growth
Patterns of Population Growth
• English economist Thomas Malthus
observed that human populations were
growing rapidly.
• Malthus predicted that such growth
would not continue indefinitely.
• Malthus- war, famine, and disease
would limit human population growth.
Demographic Transition
• The scientific study of human
populations is called demography
• Demographic transition, a dramatic
change in birth and death rates.
• Ex: U.S., Japan, Europe
What are the 4 densitydependent limiting factors?
•
•
•
•
Predation
Disease
Competition
Parasitism
What are examples density
independent limiting factors?
• Storms
• Natural Disasters
• Human activity
What caused the human
population to grow rapidly?
• Agriculture
• Industry
• Medicine
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