Download Ch43 Lecture-Populations

6
Populations
Factors that Regulate Population Abundance and
Distribution
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Population size- symbol N- total number of individuals
within a defined area at a given time.
Population density- number of individuals/unit area
Population distribution- how individuals are
distributed with respect to one another.
Population sex ratio- the ratio of males to females
Population age structure- how many individuals fit into
particular age categories.
Populations Are Patchy in Space
and Dynamic over Time
Population distribution
Abundance varies on several spatial scales.
Geographic range—region in which a species is found
Within the range, species may be restricted to specific
environments or habitats.
Habitat patches are “islands” of suitable habitat separated by
areas of unsuitable habitat.
Factors that Influence Population Size
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Density-dependent factors- size of the
population will influence an individual’s
probability of survival.
Resources, space, food, water, etc
Density-independent factors- size has no
effect on the individual’s probability of
survival.
Disease, hunting, development
Populations Are Patchy in Space & Dynamic over
Time
Density of one species population may be related to density of
other species populations.
Concept 43.5 Extinction and Recolonization Affect
Population Dynamics
Small subpopulations in habitat patches are vulnerable to
environmental disturbances and chance events and may go
extinct.
Individuals from other subpopulations can recolonize the
patch if dispersal is possible.
Think oak trees, deer and tick populations.
Exponential Growth Model
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J-shaped curve- when graphed the exponential
growth model looks like this.
Concept 43.4 Populations Grow Exponentially, but
Not for Long. Why?
Population growth is multiplicative—(exponential) an ever-larger number
of individuals is added in each successive time period.
Logistic Growth Model
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Logistic growth- population growth is initially exponential,
but slows as the population approaches the carrying
capacity.
when graphed the logistic growth model produces an “S”.
Concept 43.4 Populations Grow Exponentially, but
Not for Long
Exponential growth has a constant doubling time.
The time it takes a population to double in size can be
calculated if r (rate) is known.
To calculate :doubling time=70/r, AKA , Rule of 70. Example
how many years will it take to double a population if rate
increase is 20%?
3.5 years
this graph shows
Rate –r slows when population
Reaches K=carrying capacity
Steady state
Variations of the Logistic Model
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If food becomes scarce, the population will experience
an overshoot by becoming larger than the spring
carrying capacity and will result in a die-off, or
population crash.
Reproductive Strategies
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K-selected species- the population of a
species that grows slowly until it reaches the
carrying capacity.
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Ex. elephants, whales, and humans.
R-selected species- the population of a
species that grows quickly and is often
followed by overshoots and die-offs.
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Ex. mosquitoes and dandelions
Which animal is a K?
Which is an r?
Math Practice
go to:
Population worksheet
& print this out to follow along
Concept 43.2 Births Increase and Deaths Decrease
Population Size
Change in population size depends on the number of births
and deaths over a given time.
“Birth–death” or BD model of population change:
Example” Population 200 = 1,000 births-800 deaths
t-time, =N=population, B=birth, d=death
Nt 1  Nt  B  D
Births Increase and Deaths Decrease Population Size
Population growth rate (how fast it is changing):
Δ= change, all other letters same as last slide
Example (easier than below) BR-DR/10 Why 10? express as %
Example 1000-800/10=20%
Nt 1  Nt  N  B  D
For the bottom equation example use the Worksheet to guide
you. This is rate change over time. Problem a. 300 Falcons
N
BD
BD
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 BD
T
(t  1)  t
1
Births Increase and Deaths Decrease Population Size
Per capita birth rate (b)—number of offspring individual produces
Per capita death rate (d)—average individual’s chance of dying
Per capita growth rate (r) = (b – d) = average individual’s
contribution to total population growth rate
If b > d, then r > 0, and the population grows.
If b < d, then r < 0, and the population shrinks.
If b = d, then r = 0, and population size does not change.
Problem b. Growth rate of falcons
(B-D)/N
Problem b. What is the per capita growth rate?
rmaxN
rmax (maximum that the per capita growth rate can be)
Use this formula much easier:
rmax=(B-D)/N
(50-30)/300 =.066, .067 X 100=6.7%/year
Extinction and Recolonization Affect Population
Dynamics
The BIDE model of population growth adds the number of
immigrants (I) and emigrants (E) to the BD growth model.
Nt 1  Nt  B  I  D  E
Example :
N=1,000
N=1,040
B=50
I=15
D=20
E=5
Problem d. Find the avg. rate of change 2013-2018
Average rate of change =slope
2013, 300
2018, 414
414-300/2018-2013= 22.8
Logistical Growth Rate Carrying capacity Kentwood
N=49,000
K=60,000
rmax=.9
Are they above or below K?
a. Below
b. What will be the population growth rate for 2013?
rmax N((K-N)/K)
(.9)(49,000)(60,000-49,000)/60,000)
8085 peeps/year
Concept 43.2 Births Increase and Deaths Decrease Population Size
Which of the following factors can explain a decline in
the size of a population through time?
a. Per capita birth rates b have decreased
b. Per capita death rates d have decreased
c. Per capita death rates d have increased
d. Both a and c
Examining the following graph, how would you describe the
population growth of Daphnia grown in the laboratory?
a. Up until day 60, growth appears to be exponential and
density-independent.
b. The population initially overshoots its carrying capacity.
c. The carrying capacity appears to be about 180 individuals.
d. Both a and b
Concept 43.3 Life Histories Determine Population
Growth Rates
Species’ distributions reflect the effects of environment on
per capita growth rates.
A study of temperature change in a lizard’s environment,
combined with knowledge of its physiology and behavior,
led to conclusions about how climate change may affect
survivorship, fecundity, and distribution of these lizards.
Concept 43.3 Life Histories Determine Population
Growth Rates
What’s the take away about resource acquisition?
The more we take, the more resources are available to us as
humans, the less available they are to other organisms.
This leads to stress on an community and can lead to death,
extinction, loss of diversity.
Concept 43.4 Populations Grow Multiplicatively, but Not for
Long
The human population is unique. It has grown at an everfaster per capita rate, as indicated by steadily decreasing
doubling times.
Technological advances have raised carrying capacity by
increasing food production and improving health.
Figure 43.9 Human Population Growth (Part 1)
Figure 43.9 Human Population Growth (Part 2)
Concept 43.4 Populations Grow Multiplicatively, but
Not for Long
Many believe that the human population has now overshot its
carrying capacity for two reasons:
Reduction in resources
• Technological advances and agriculture have depended on
fossil fuels, a finite resource.
• Reduction in the quality of resources
• Climate change and ecosystem degradation have been a
consequence of 20th century population expansion.
Competition
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Competition- the struggle of individuals
to obtain a limiting resource .
Mutualism
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Mutualism- A type of interspecific interaction where both species benefit.
Commensalism
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Commensalism- a type of relationship in which one species
benefits but the other is neither harmed nor helped.
Remora feeds on leftover food of shark
Keystone Species
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Keystone species- a species that plays a role in its community that is far more
important than its relative abundance might suggest.