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Population Dynamics
Vocab
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Ecosystem includes biotic and abiotic factors.
Population – group of interacting individuals of
the same species that inhabit a set geographic
area.
Community – consists of two or more
populations of different species occupying the
same geographic area.
Factors Affecting Population Size
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Birth and immigration increase a population size
while death and emigration decrease it.
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Given unlimited habitat factors, the capacity for
reproduction under ideal conditions is called
biotic potential. Why don’t organisms meet
their biotic potential?
Factors Affecting Rate of Population
Increase
1 – age at which species is reproductively mature
2 – number of young produced
3 – frequency of births
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Exponential growth results in a j-shaped curve.
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There are two factors that affect the shape of
the curve: the reproductive rate per individual
and the initial population.
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Limited environmental resources limit
exponential growth flattening the j-shaped curve
into an s-shaped curve fluctuating around the
carrying capacity.
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Carrying capacity is the number of individuals an
environment can support for a prolonged period
of time.
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Carrying capacity changes as the environment
changes.
What is the carrying capacity of this
species?
Limiting Factors
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Density – dependent factors are those whose
effect increases as the population increases:
competition, disease, parasites, and food.
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Disease will spread more quickly through more
dense populations.
Density – independent factors are those that
affect all populations regardless of their density.
Most density – independent factors are abiotic:
temperature, flood, drought, storms, and habitat
disruption.
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Gause's Rule (Competitive Exclusion
Principle): Two species cannot live the same
way in the same place at the same time
(ecologically identical species cannot coexist in
the same habitat). This is only possible through
evolution of niche differentiation (difference in
beak size, root depths, etc.).
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Interspecific Competition refers to the
competition between two or more species for
some limiting resource.
This limiting resource can be food, nutrients, space,
nesting sites-- anything for which demand is greater
than supply.
 When one species is a better competitor, this
competition negatively influences the other species
by reducing population sizes or growth rates.
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Intraspecific Competition refers to the
competition within members of the same
species for some limiting resource.
The result of intraspecific competition is
natural selection.
Home Range vs. Territory
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Home range – area individuals travel during the
span of a year
Territory – area individuals secure for breeding
purposes and will defend.
- Territory is smaller than HR
- Territory is within HR
- As habitat quality increases, HR decreases
Population Biology
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Ecologists have used the two variables, "r" and
"K“, to define end members in the spectrum of
animal behavior.
"r"-selected species
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"r"-selected species rely on a high intrinsic
population growth rate in order to succeed.
These are "weedy" species which disperse
quickly to find newly opened environments,
have very many offspring (but small – only a
very small portion of the parents reproductive
resources are devoted to any single juvenile), and
are generally poor competitors.
"K"-selected species
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"K"-selected species are just the opposite. They
are weak dispersers, have high parental
investment , few offspring, and are strong
competitors.
r & K species
r →high potential rate of reproduction
→ population fluctuates greatly in relation to
carrying capacity
K → low potential rate of reproduction
→ population is more stable with less
fluctuation
r
K
Body size
Smaller
Larger
Life span
Shorter
Longer
Age of first breed
Younger
Older
Parental investment
Lower
Higher
Position in the food
chain
Population stability
Lower
Higher
Less
More
Population turnover
More
Less
Number of offspring
Higher
Lower
Juvenile mortality
Higher
Lower
** These are general trends and there are exceptions in each of these categories
Record Holders:
Oldest recorded Quahog (clam):
220 years
Oldest recorded Tortoise:
152 years
Oldest recorded Human:
120 years
Oldest recorded
Giant Salamander:
55 years
Oldest recorded Queen Ant:
18 years
Oldest recorded Housefly:
29 days