Transcript Population Limiting Factors

Chapter 14:
Populations
Section 14-2:
Why Populations Stop
Growing
Population Limiting Factors
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Population density = the number of
organisms in a given area
Density-dependent limiting factors are
those that operate more strongly on large,
dense populations than on small, lesscrowded ones
Species whose populations are controlled by
these factors tend to be more stable
Population Limiting Factors
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There are four density-dependent limiting
factors:
– Competition
– Predation
– Parasitism
– Crowding
Competition
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Individuals compete with each other for food, water,
space, sunlight, etc.
Only some individuals will get what they need to
survive and reproduce, some will only be able to
live and not reproduce, and others may starve to
death or die from lack of shelter
The more individuals in an area, the sooner they
will use up available resources
Can affect carrying capacity
Predation
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Most species exist as food for other
species, and in nature predators and their
prey usually coexist for long periods of time
Prey develop defenses against their
predators, and predators develop counter
defenses
Even with this accommodations, there is not
always a balance between predators and
prey
Predation
Parasitism
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A parasite is an organism that takes nourishment
from its host
Parasites weaken their hosts, cause disease, and
in some cases death – usually not right away
Because parasites are host-specific, they are more
effective when their hosts are present in large
numbers
Crowding of individuals helps parasites travel from
one host to another
Crowding
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Most organisms have a built in behavioral need for
a certain amount of space
If organisms become too over-crowded, they may
fight among themselves, leading to high levels of
stress, disrupting homeostasis of hormone levels
Can lead to a weakened immune system, or can
lead to changes in behavior that cause individuals
to neglect, kill, or even eat their own offspring
Population Limiting Factors
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Density-independent limiting factors do
not depend on population density or size
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Examples are weather and human activity