Transcript POPULATION DYNAMICS

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Growth rates can be linear, exponential, or
S-shaped
Linear growth: growth is steady
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If graphed it’s a straight line
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Exponential growth: as population gets
larger, it grows faster because there are more
individuals able to reproduce
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when graphed results in a J-shaped curve
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S-shaped growth: population levels off
when certain limiting factors are met
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If resources are plentiful, there are more
births than deaths and carrying capacity can
be temporarily exceeded
Overshooting carrying capacity can lead to
mass die-offs as resources run out
Deaths exceed births and population again
falls below carrying capacity
● Carrying capacity was overshot and population dropped, then grew again, etc.
● Overall the growth pattern is S-shaped
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2 types: rapid and slow
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Rapid life history:
Mature quickly
 Reproduce early in life
 Produce lots of offspring
 Short life span
 Small size
 Example: rabbit, mosquitoes
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Slow life history:
Mature slowly
 Reproduce later in life
 Produce few offspring
 Long life span
 Large size
 Example: elephants, sea turtles, pandas
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Any biotic or abiotic factor that affects a
population and limits its growth.
The factor may be too little in quantity or too
much.
Each species has a range of tolerance for
each limiting factor
Every population thrives in an optimal range of abitoic factors.
Beyond this range, one finds fewer and fewer numbers of
these organisms.
Often, the range is shown for each factor, and this is known as
the range of tolerance.
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1. Density-dependent factors
depend on the population
size/density
 As
the population grows the
effect of the limiting factor
increases
Examples of Density Dependent
a. Predation: an interaction between species in
which one species uses another species as food
follows a predictable cycle of population changes
over time
Lynx (predator)
Why is the lynx population always lower than the hare population?
Lynx is higher up on the food chain; energy is lost between the herbivores and
the carnivores
Examples of Density Dependent
b. Competition: fighting for resources
 if population size is low, resources will build up
 as resources are used, population increases
 increased population =increased competition and
population size drops
c. Crowding: fighting for space
 as crowding increases, stress increases
 Stress results in:
 Increased aggression
 Lower fertility
 Lower parental care
 Lower resistance to disease
Density-independent: does not
depend on population density
the factor affects individuals the
same regardless of population
density
Usually abiotic factors
 Temperature
 Volcanic eruptions
 Flooding/ Drought
 pesticides