Post on 22-Dec-2015
Chapter 52 (pgs. 1151- 1172) Population Ecology
AP minknow•How density, dispersion, and demographics can describe a population.•The differences between exponential and logistic models of population growth.•How density-dependent and density-independent factors can control population growth
• Characteristics of Populations• 1.Define the scope of population ecology • 2.Define and distinguish between density and dispersion. • 3.Explain how ecologists measure the density of a species. • 4.Describe conditions that may result in the clumped dispersion,
uniform dispersion, and random dispersion of populations. • 5.Describe the characteristics of populations that exhibit Type I,
Type II, and Type III survivorship curves. • 6.Describe the characteristics of populations that exhibit Type I,
Type II, and Type III survivorship curves.
• Life History Traits• 7.Define and distinguish between semelparity and iteroparity. • 8.Explain how limited resources affect life histories. • 9.Give examples of the trade-off between reproduction and survival.
• Population Growth• 10.Compare the geometric model of population growth with the logistic
model. • 11.Explain how an environment's carrying capacity affects the intrinsic rate
of increase of a population. • 12.Distinguish between r-selected populations and K-selected populations. • 13.Explain how a "stressful" environment may alter the standard r-selection
and K-selection characteristics.• Population-Limiting Factors• 14.Explain how density-dependent factors affect population growth. • 15.Explain how density-dependent and density-independent factors may
work together to control a population's growth. • 16.Explain how predation can affect life history through natural selection. • 17.Describe several boom-and-bust population cycles, noting possible
causes and consequences of the fluctuations. • Human Population Growth• 18.Describe the history of human population growth. • 19.Define the demographic transition. • 20.Compare the age structures of Italy, Kenya, and the United States.
Describe the possible consequences for each country. • 21.Describe the problems associated with estimating Earth's carrying
capacity.
• Population ecology is the study of populations in relation to environment– Including
environmental influences on population density and distribution, age structure, and variations in population size
52.1: Dynamic biological processes influence population density, dispersion, and demography
A population
• A population– Is a group of
individuals of a single species living in the same general area
Density and Dispersion
• Density– Is the number of individuals per unit area
or volume
• Dispersion– Is the pattern of spacing among
individuals within the boundaries of the population
Density: A dynamic perspective.• Determining the density of
natural populations– Is possible, but difficult to
accomplish
• In most cases– It is impractical or impossible to
count all individuals in a population
• Density is the result of a dynamic interplay– Between processes that add
individuals to a population and those that remove individuals from it
Births and immigration add individuals to a population.
Births Immigration
PopuIationsize
Emigration
DeathsDeaths and emigration remove individuals from a population.
Patterns of Dispersion
• Environmental and social factors– Influence the spacing
of individuals in a population.
– There are three different Patterns of Dispersion
• Clumped Dispersion• Uniform Dispersion• Random Dispersion
• A clumped dispersion– Is one in which individuals aggregate in
patches– May be influenced by resource availability and
behavior
Figure 52.3a
(a) Clumped. For many animals, such as these wolves, living in groups increases the effectiveness of hunting, spreads the work of protecting and caring for young, and helps exclude other individuals from their territory.
• A uniform dispersion– Is one in which individuals are evenly
distributed– May be influenced by social interactions
such as territoriality
Figure 52.3b
(b) Uniform. Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors.
• A random dispersion– Is one in which the position of each individual
is independent of other individuals
Figure 52.3c(c) Random. Dandelions grow
from windblown seeds that land at random and later germinate.
Life Tables
• A life table– Is an age-specific summary of the survival pattern of a
population– Is best constructed by following the fate of a cohort
Survivorship Curves• A survivorship curve
– Is a graphic way of representing the data in a life table
Figure 52.4
1000
100
10
1
Num
ber
of s
urvi
vors
(lo
g sc
ale)
0 2 4 6 8 10
Age (years)
Males
Females
• Survivorship curves can be classified into three general types– Type I, Type II, and Type III
Figure 52.5
I
II
III
50 10001
10
100
1,000
Percentage of maximum life span
Num
ber
of s
urvi
vors
(lo
g sc
ale)
Many species fall somewhere between these basic types of survivorship curves.
Some invertebrates, such as crabs, show a “stair-stepped” curve, with increased mortality during molts.
52.2 Life histories are highly diverse, but they exhibit patterns in their variability.
• Life histories entail three basic variables:
– when reproduction begins– how often the organism reproduces– how many offspring are produced
during each reproductive episode.
• These histories are evolutionary outcomes reflected in the development, physiology, and behavior of an organism.
• Some organisms, such as the agave plant, exhibit semelparity. Big Bang Production. (then death)
• By contrast, some organisms exhibit iteroparity.
– They produce only a few offspring during repeated reproductive episodes.
• Some plants produce a large number of small seeds– Ensuring that at least some of them will grow
and eventually reproduce
Figure 52.8a
(a) Most weedy plants, such as this dandelion, grow quickly and produce a large number of seeds, ensuring that at least somewill grow into plants and eventually produce seeds themselves.
• Other types of plants produce a moderate number of large seeds– That provide a large store of energy that will
help seedlings become established
Figure 52.8b
(b) Some plants, such as this coconut palm, produce a moderate number of very large seeds. The large endosperm provides nutrients for the embryo, an adaptation that helps ensure the success of a relatively large fraction of offspring.
• In other words, how much does an individual gain in reproductive success through one pattern versus the other?
• The critical factor is survival rate of the offspring.• When the survival of offspring is low, as in highly
variable or unpredictable environments, big-bang reproduction (semelparity) is favored.
• Repeated reproduction (iteroparity) is favored in dependable environments where competition for resources is intense.
• In such environments, a few, well-provisioned offspring have a better chance of surviving to reproductive age.
What factors contribute to the evolution of semelparity versus iteroparity?
Population Growth is measured byPer Capita Rate of Increase
• If immigration and emigration are ignored– A population’s growth rate (per capita
increase) equals birth rate minus death rate
Growth rate = rN
It can be found using the equation---
dN
dt rN
Exponential Population Growth
• Exponential population growth– Results in a J-
shaped curve
Figure 52.9
0 5 10 150
500
1,000
1,500
2,000
Number of generations
Pop
ulat
ion
size
(N
)
dNdt 1.0N
dNdt
0.5N
•Exponential population growthIs population increase under idealized conditions
•Under these conditions•The rate of reproduction is at its maximum, called the intrinsic rate of increase
dNdt rmaxN
The J-shaped curve of exponential growth
• Is characteristic of some populations that are rebounding
Figure 52.10
1900 1920 1940 1960 1980
Year
0
2,000
4,000
6,000
8,000
Ele
phan
t pop
ulat
ion
52.4: The logistic growth model includes the concept of carrying capacity
Exponential growth– Cannot be
sustained for long in any population
• A more realistic population model– Limits growth by
incorporating carrying capacity
• Carrying capacity (K)– Is the maximum
population size the environment can support
The Logistic Growth Model
• In the logistic population growth model– The per capita rate of increase declines as
carrying capacity is reached
We construct the logistic model by starting with the exponential model
And adding an expression that reduces the per capita rate of increase as N increases
Maximum
Positive
Negative
0N K
Population size (N)
Per
cap
ita r
ate
of
incr
ease
(r)
The logistic growth equation
Includes K, the carrying capacity
dNdt
(K N)Krmax N
Table 52.3
• The logistic model of population growth– Produces a sigmoid (S-shaped) curve
Figure 52.12
dN
dt 1.0N Exponential
growth
Logistic growth
dN
dt 1.0N
1,500 N1,500
K 1,500
0 5 10 150
500
1,000
1,500
2,000
Number of generations
Pop
ulat
ion
size
(N
)
2. As N approaches K for a certain population, which of the following is predicted by the logistic equation? – The growth rate will not change. – The growth rate will approach zero. – The population will show an Allee effect. – The population will increase exponentially. – The carrying capacity of the environment will
increase.
800
600
400
200
0
Time (days)0 5 10 15
1,000
Nu
mb
er
of
Pa
ram
eci
um
/ml
The Logistic Model and Real Populations
• The growth of laboratory populations of paramecia– Fits an S-shaped curve
• Some populations overshoot K– Before settling down to
a relatively stable density
• Some populations– Fluctuate greatly
around K
180
150
0
120
90
6030
Time (days)0 16014012080 100604020
Nu
mb
er
of
Da
ph
nia
/50
ml
0
80
60
40
20
1975 1980 1985 1990 1995 2000
Time (years)
Nu
mb
er
of
fem
ale
s
The Logistic Model and Life Histories
• Life history traits favored by natural selection– May vary with population density and
environmental conditions
• K-selection, or density-dependent selection– Selects for life history traits that are sensitive
to population density• K-selection tends to maximize population size
and operates in populations living at a density near K.
• r-selection, or density-independent selection– Selects for life history traits that maximize
reproduction• r-selection tends to maximize r, the rate of
increase, and occurs in environments in which population densities fluctuate well below K, or when individuals face little competition.
Controversy
52.5: Populations are regulated by a complex interaction of biotic and abiotic influences
• In density-independent populations– Birth rate and death rate do not change with population density
• In density-dependent populations– Birth rates fall and death rates rise with population density
• Determining equilibrium for population density
Figure 52.14a–c
Density-dependent birth rate
Density-dependent death rate
Equilibrium density
Density-dependent birth rate
Density-independent death rate
Equilibrium density
Density-independent birth rate
Density-dependent death rate
Equilibrium density
Population density Population density Population density
Birt
h or
dea
th r
ate
per
capi
ta
(a) Both birth rate and death rate change with population density.
(b) Birth rate changes with populationdensity while death rate is constant.
(c) Death rate changes with populationdensity while birht rate is constant.
Density-Dependent Population Regulation
• Density-dependent birth and death rates– Are an example of negative feedback that regulates
population growth– Are affected by many different mechanisms
• Competition for Resources• Territoriality• Health (Disease/Parasites)• Predation• Toxic Wastes (think bacteria)
Competition for Resources• In crowded populations, increasing population
density– Intensifies intraspecific competition for resources
100 100
100
0
1,000
10,000
Ave
rag
e n
um
be
r o
f se
ed
s p
er
rep
rod
uci
ng
ind
ivid
ua
l (lo
g s
cale
)
Ave
rag
e c
lutc
h s
ize
Seeds planted per m2 Density of females
0 7010 20 30 40 50 60 802.8
3.0
3.2
3.4
3.6
3.8
4.0
(a) Plantain. The number of seeds produced by plantain (Plantago major) decreases as density increases.
(b) Song sparrow. Clutch size in the song sparrow on Mandarte Island, British Columbia, decreases as density increases and food is in short supply.
Territoriality• Cheetahs are highly territorial
– Using chemical communication to warn other cheetahs of their boundaries
Figure 52.16
Population Dynamics
• The study of population dynamics– Focuses on the complex interactions between
biotic and abiotic factors that cause variation in population size
Stability and Fluctuation• Long-term
population studies– Have
challenged the hypothesis that populations of large mammals are relatively stable over time
Figure 52.18
The pattern of population dynamics observedin this isolated population indicates that various biotic and abiotic factors can result in dramatic fluctuations over time in a moose population.
Researchers regularly surveyed the population of moose on Isle Royale, Michigan, from 1960 to 2003. During that time, the lake never froze over, and so the moose population was isolated from the effects of immigration and emigration.
FIELD STUDY
Over 43 years, this population experiencedtwo significant increases and collapses, as well as several less severe fluctuations in size.
RESULTS
CONCLUSION
1960 1970 1980 1990 2000
Year
Moo
se p
opul
atio
n si
ze
0
500
1,000
1,500
2,000
2,500
Steady decline probably caused largely by wolf predation
Dramatic collapse caused by severe winter weather and food shortage, leading to starvation of more than 75% of the population
Extreme fluctuations in population sizeAre typically more common in invertebrates
than in large mammals
Figure 52.19
1950 1960 1970 1980
Year
1990
10,000
100,000
730,000
Com
mer
cial
cat
ch (
kg)
of m
ale
cra
bs
(log
sca
le)
Fluctuating Wind pushing eggs out to sea
Cannibalism
Metapopulations and Immigration
• Metapopulations – Are groups of
populations linked by immigration and emigration
• High levels of immigration combined with higher survival– Can result in greater
stability in populations– Are groups of
populations linked by immigration and emigration
Mandarte island
Small islands
Nu
mb
er
of
bre
ed
ing
fe
ma
les
1988 1989 1990 1991Year
0
10
20
30
40
50
60
Population Cycles• Many populations
– Undergo regular boom-and-bust cycles
Figure 52.21 Year1850 1875 1900 1925
0
40
80
120
160
0
3
6
9
Lynx
pop
ulat
ion
siz
e (t
hous
and
s)
Har
e po
pula
tion
size
(t
hous
and
s)
Lynx
Snowshoe hare
Three main hypotheses have been proposed to explain the lynx/hare cycles.
•The cycles may be caused by food shortage during winter.
•The cycles may be due to predator-prey interactions.
•The cycles may be affected by a combination of food resource limitation and excessive predation.
Limiting Factors
Density Dependant Factors
Density Independent Factors
52.6: Human population growth has slowed after centuries of exponential increase
• No population can grow indefinitely– And humans are no exception
The Global Human Population
8000 B.C.
4000 B.C.
3000 B.C.
2000 B.C.
1000 B.C.
1000 A.D.
0
The Plague Hum
an
pop
ulat
ion
(bill
ions
)2000 A.D.
0
1
2
3
4
5
6 Increased relatively slowly until about 1650 and then began to grow exponentially
Global population Growth Rate• Though the global population is still growing
– The rate of growth began to slow approximately 40 years ago
Figure 52.231950 1975 2000 2025 2050
Year
2003P
erce
nt in
crea
se
2.2
2
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
1.8
Age Structure• One important demographic factor in present and future growth
trends– Is a country’s age structure, the relative number of individuals at
each age– Usually presented in Pyramids
Figure 52.25
Rapid growth Afghanistan
Slow growth United States
Decrease Italy
Male Female Male Female Male FemaleAge Age
8 6 4 2 0 2 4 6 8 8 6 4 2 0 2 4 6 8 8 6 4 2 0 2 4 6 8Percent of population Percent of population Percent of population
80–8485
75–7970–7465–6960–6455–5950–5445–4940–4435–3930–34
20–2425–29
10–145–90–4
15–19
80–8485
75–7970–7465–6960–6455–5950–5445–4940–4435–3930–34
20–2425–29
10–145–90–4
15–19
Infant Mortality and Life Expectancy
• Infant mortality and life expectancy at birth
– Vary widely among developed and developing countries but do
not capture the wide range of the human condition
Figure 52.26
Developed countries
Developing countries
Developed countries
Developing countries
Infa
nt
mo
rta
lity
(de
ath
s p
er
1,0
00
birt
hs)
Life
exp
ect
an
cy (
yea
rs)
60
50
40
30
20
10
0
80
60
40
20
0
Global Carrying Capacity
• Just how many humans can the biosphere support?
• It is complex and we just don’t know, but we have….
Ecological Footprint• The ecological
footprint concept– Summarizes the
aggregate land and water area needed to sustain the people of a nation
– Is one measure of how close we are to the carrying capacity of Earth
Figure 52.27
16
14
12
10
8
6
4
2
00 2 4 6 8 10 12 14 16
New Zealand
AustraliaCanada
Sweden
WorldChina
India
Available ecological capacity (ha per person)
SpainUK
Japan
GermanyNetherlands
Norway
USA
Eco
log
ica
l foo
tprin
t (h
a pe
r pe
rson
)
At more than 6 billion peopleThe world is already in ecological deficit