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Transcript of Chapter 53 Population Ecology. Copyright © 2008 Pearson Education, Inc., publishing as Pearson...
![Page 1: Chapter 53 Population Ecology. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview Population ecology is the study.](https://reader036.fdocuments.in/reader036/viewer/2022062321/56649e3a5503460f94b2bfd7/html5/thumbnails/1.jpg)
Chapter 53Chapter 53
Population Ecology
![Page 2: Chapter 53 Population Ecology. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview Population ecology is the study.](https://reader036.fdocuments.in/reader036/viewer/2022062321/56649e3a5503460f94b2bfd7/html5/thumbnails/2.jpg)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Overview
• Population ecology is the study of populations in relation to environment, including environmental influences on density and distribution, age structure, and population size.
• A population is a group of individuals of a single species living in the same general area.
![Page 3: Chapter 53 Population Ecology. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview Population ecology is the study.](https://reader036.fdocuments.in/reader036/viewer/2022062321/56649e3a5503460f94b2bfd7/html5/thumbnails/3.jpg)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
I. Population density, dispersion, and demographics
• Density = number of individuals per unit area
• Dispersion = pattern of spacing among individuals within boundaries of population.
• Density is result of processes that add individuals and that remove individuals.
![Page 4: Chapter 53 Population Ecology. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview Population ecology is the study.](https://reader036.fdocuments.in/reader036/viewer/2022062321/56649e3a5503460f94b2bfd7/html5/thumbnails/4.jpg)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• Immigration = adding new outside individuals
• Emigration = movement of individuals out
• Sampling techniques used to estimate densities and total population sizes.
– extrapolation from small samples, an index of population size, or the Mark-Recapture Method.
![Page 5: Chapter 53 Population Ecology. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview Population ecology is the study.](https://reader036.fdocuments.in/reader036/viewer/2022062321/56649e3a5503460f94b2bfd7/html5/thumbnails/5.jpg)
Population dynamics
Births
Births and immigrationadd individuals toa population.
Immigration
Deaths and emigrationremove individualsfrom a population.
Deaths
Emigration
![Page 6: Chapter 53 Population Ecology. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview Population ecology is the study.](https://reader036.fdocuments.in/reader036/viewer/2022062321/56649e3a5503460f94b2bfd7/html5/thumbnails/6.jpg)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
A. Patterns of Dispersion
• Clumped dispersion = individuals aggregate in patches. (influenced by resource availability and behavior)
• Uniform dispersion = individuals are evenly distributed. (influenced by social interactions such as territoriality)
• Random dispersion = individuals are independent of other individuals. (occurs in the absence of strong attractions or repulsions)
![Page 7: Chapter 53 Population Ecology. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview Population ecology is the study.](https://reader036.fdocuments.in/reader036/viewer/2022062321/56649e3a5503460f94b2bfd7/html5/thumbnails/7.jpg)
Patterns of dispersion within a population’s geographic range
(a) Clumped
(b) Uniform
(c) Random
![Page 8: Chapter 53 Population Ecology. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview Population ecology is the study.](https://reader036.fdocuments.in/reader036/viewer/2022062321/56649e3a5503460f94b2bfd7/html5/thumbnails/8.jpg)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
II. Demographics
• Demography = study of vital statistics of a population and how they change
– Death rates and birth rates
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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
A. Life Tables & Survivorship Curves
• Life table = age-specific summary of survival pattern of population.
• Follows the fate of a cohort (group of individuals of the same age)
• Survivorship curve = graph of data in a life table.
![Page 10: Chapter 53 Population Ecology. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview Population ecology is the study.](https://reader036.fdocuments.in/reader036/viewer/2022062321/56649e3a5503460f94b2bfd7/html5/thumbnails/10.jpg)
Survivorship curves for squirrels shows relatively constant death rate
Age (years)20 4 86
10
101
1,000
100
Nu
mb
er o
f su
rviv
ors
(lo
g s
cale
)
Males
Females
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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• Survivorship curves can be classified into three general types:
– Type I: low death rates early and middle life, increase among older age (humans)
– Type II: the death rate is constant (squirrels)
– Type III: high death rates for the young, slower death rate for survivors (Fish)
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Survivorship Curves
1,000
100
10
10 50 100
II
III
Percentage of maximum life span
Nu
mb
er
of
su
rviv
ors
(lo
g s
ca
le)
I
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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
B. Reproductive Rates
• Reproductive table (fertility schedule) = age-specific summary of reproductive rates in a population. (describes reproductive patterns of a population)
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III. Life history
• Life history comprises the traits that affect its schedule of reproduction and survival:
– age when reproduction begins
– How often it reproduces
– How many offspring are produced each time
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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
IV. “Trade-offs” and Life Histories
• Organisms have finite resources, which may lead to trade-offs between survival and reproduction.
– Animals small#, dandelions large# and coconuts more stored energy
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Variation in the size of seed crops in plants
(a) Dandelion
(b) Coconut palm
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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
V. Exponential model
• Study population growth in an idealized situation.
– helps understand the capacity of species to increase and the conditions that may facilitate this growth.
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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• Zero population growth = birth rate = death rate.
• Formula: Nt
rN
N = population size, t = time, and r = per capita rate of increase = birth – death
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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
VI. Exponential Growth
• Exponential population growth is population increase under idealized conditions.
– rate of reproduction is at maximum (intrinsic rate of increase)
• Results in a J-shaped curve
• Exponential Growth is not sustainable.
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Exponential Growth Model
Number of generations
0 5 10 150
500
1,000
1,500
2,000
1.0N =dNdt
0.5N =dN
dt
Po
pu
lati
on
siz
e (N
)
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The J-shaped curve of exponential growth characterizes some rebounding populations
8,000
6,000
4,000
2,000
01920 1940 1960 1980
Year
Ele
ph
ant
po
pu
lati
on
1900
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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
VII. Logistic model
• Exponential growth cannot be sustained for long in any population.
• Carrying capacity (K) = max population size the environment can support.
• In the logistic population growth model, the rate of increase declines as carrying capacity is reached.
• Logistic model of population growth produces a sigmoid (S-shaped) curve.
• Some populations overshoot K before settling down to a relatively stable density.
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Logistic Growth model
2,000
1,500
1,000
500
00 5 10 15
Number of generations
Po
pu
lati
on
siz
e (
N)
Exponentialgrowth
1.0N=dN
dt
1.0N=dN
dt
K = 1,500
Logistic growth1,500 – N
1,500
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The growth of laboratory populations fits an S-shaped curve which hovers around the Carrying Capacity of the area.
1,000
800
600
400
200
00 5 10 15
Time (days)
Nu
mb
er o
f P
aram
eciu
m/m
L
Nu
mb
er o
f D
aph
nia
/50
mL
0
30
60
90
180
150
120
0 20 40 60 80 100 120 140 160
Time (days)
(b) A Daphnia population in the lab(a) A Paramecium population in the lab
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VIII. Logistic Model and Life Histories
• LH traits favored by natural selection vary with pop density and env connditions.
• K-selection = density-dependent selection, selects for traits that are sensitive to population density.
• r-selection = or density-independent selection, selects for traits that maximize reproduction.
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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
IX. Population Change and Population Density
• Density-independent populations, birth and death rates do not change with population density.
• Density-dependent populations, birth rates fall and death rates rise with population density.
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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
X. Density-Dependent Population Regulation
• Density-dependent rates are an example of negative feedback that regulates population growth.
• They are affected by many factors (competition for resources, territoriality, disease, predation, toxic wastes, and intrinsic factors)
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Decreased reproduction at high population densities
Population size
100
80
60
40
20
0200 400 500 600300P
erce
nta
ge
of
juve
nile
s p
rod
uci
ng
lam
bs
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A. Territoriality
• Competition for territory may limit density.
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Territoriality
(a) Cheetah marking its territory
(b) Gannets
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B. Other Factors
• Dense populations, pathogens can spread more rapidly
• As prey builds up, predators feed preferentially on that species.
• Accumulation of toxic wastes can contribute to density-dependent regulation of population size.
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XI. Population Dynamics
• Population dynamics = interactions between biotic and abiotic factors that cause variation in population size.
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Changes in predation pressure can drive population fluctuations
Wolves Moose
2,500
2,000
1,500
1,000
500
Nu
mb
er o
f m
oo
se
0
Nu
mb
er o
f w
olv
es
50
40
30
20
10
01955 1965 1975 1985 1995 2005
Year
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Snowshoe hare
Lynx
Nu
mb
er
of
lyn
x(t
ho
us
an
ds
)
Nu
mb
er
of
ha
res
(th
ou
sa
nd
s)
160
120
80
40
01850 1875 1900 1925
Year
9
6
3
0
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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
XII. Human population
• Humans can not grow indefinitely
• Global population is still growing, the rate of growth began to slow during the 1960s.
• Most of the current global population growth is concentrated in developing countries.
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Human population growth
8000B.C.E.
4000B.C.E.
3000B.C.E.
2000B.C.E.
1000B.C.E.
0 1000C.E.
2000C.E.
0
1
2
3
4
5
6
The Plague
Hu
man
po
pu
lati
on
(b
illio
ns)
7
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A. Regional Patterns
• Regional human population can exist in one of two configurations:
– Zero population growth = High birth rate – High death rate
– Zero population growth =Low birth rate – Low death rate
• The demographic transition is the move from the first state toward the second state.
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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
B. Age Structure
• Relative number of individuals at each age.
• Age structure diagrams can predict a population’s growth trends.
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Age-structure pyramids for the human population of three countries
Rapid growthAfghanistan
Male Female Age AgeMale Female
Slow growthUnited States
Male Female
No growthItaly
85+80–8475–7970–74
60–6465–69
55–5950–5445–4940–4435–3930–3425–2920–2415–19
0–45–9
10–14
85+80–8475–7970–74
60–6465–69
55–5950–5445–4940–4435–3930–3425–2920–2415–19
0–45–9
10–14
10 10 8 866 4 422 0Percent of population Percent of population Percent of population
66 4 422 08 8 66 4 422 08 8
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C. Limits on Human Population
• Ecological footprint = summarizes the land and water area needed to sustain the people of a nation.
• Countries vary greatly in footprint size and available ecological capacity.
• Our carrying capacity could potentially be limited by food, space, nonrenewable resources, or buildup of wastes.
• Estimated CC of humans is 10-15 billion
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Review: Population Growth Curve
Number of generations
K = carrying capacityP
op
ula
tio
n s
ize
(N)
rmax NdNdt
=K – N
K
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You should now be able to:
1. Define and distinguish between the following sets of terms: density and dispersion; clumped dispersion, uniform dispersion, and random dispersion; life table and reproductive table; Type I, Type II, and Type III survivorship curves; semelparity and iteroparity; r-selected populations and K-selected populations.
2. Explain how ecologists may estimate the density of a species.
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3. Explain how limited resources and trade-offs may affect life histories.
4. Compare the exponential and logistic models of population growth.
5. Explain how density-dependent and density-independent factors may affect population growth.
6. Explain how biotic and abiotic factors may work together to control a population’s growth.