Transcript PowerPoint

Chapter 19- Populations
• A population is a group of organisms of the same species
living in the same place at the same time
• Millions of different populations all evolving according to
their own self interest in a particular environment.
• But each population is a part of the environment of its
neighbors, so any evolutionary change has a ripple effect.
A Population
• Group of organisms
of the same species
living in the same
place at the same
time
• Individuals may
come and go, but the
population can
remain the same
Population Growth
• Since each organism of a
population is governed by the
selfish gene, populations tend
to grow
• If unlimited resources are
present, growth will be
exponential
• It will proceed very quickly
for rapidly reproducing
organisms and more slowly
for slowly reproducing ones
• The curve, however, will
always be a “J” curve or an
exponential growth curve
Generation
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
# of bacteria
1
2
4
8
16
32
64
128
256
512
1024
2048
4096
8192
16,384
32,768
65,536
131,072
262,144
524,288
1,048,576
2,097,152
4,194,304
time
0
15min
30min
45min
1hr
75min
90min
105min
2hrs
3hrs
4hrs
5hrs
Population Growth 2
• Resources are never
unlimited, though.
• As population rises,
resources decline.
• If the growth is too rapid,
resources are rapidly
depleted and a population
crash can occur
• This pattern occurs often
with many populations
(including humans)
Gypsy moth caterpillar
Population Growth 3
• More often what happens
is that the resources
slowly decrease, the
growth rate slowly
decreases, and they meet.
• This point that they
oscillate around is the
carrying capacity of the
environment for that
particular organism
• So when would you
“harvest” these
individuals? (1,2,3,4,or 5)
S - shaped curve
Population Mortality
• Organisms differ on strategies of
reproduction and differ on types
of predation
• Those organisms that put much
care into their few young tend to
have good survivorship of young
• Those organisms that spread
their young all over tend to have
poor survivorship of their young
• A graphic representation of the
rates of survival at different ages
is called a survivorship curve
Population Density
and Dispersion
• Population density is
simply the number of
individuals measured per
unit of area or volume
• Additionally, the
population can clump in
different ways
– Random
– Clumped
– Regular
Growth Rate Limiting Factors
(effecting birth or mortality rates)
Density-Dependent
– Predation
– Increased competition
for scarce resources
– Sickness
– Others?...
Density-Independent
– Weather
Range of Tolerance is an important factor:
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•
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Ice Age
Global Warming
Flood
El Nino
Etc.
temperature, light,
salinity, nutrients, water
Human Growth Patterns
What are the causes that allow this to happen?
What are some possible consequences of this?
What are some possible results of the population boom?
What will the future look like?
Graph showing possible future population growth based on Total Fertility
Rate - the average number of children a woman has