Download Population Ecology

Chapter 52
Population Ecology
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Overview: Earth’s Fluctuating Populations
• To understand human population growth
– We must consider the general principles of
population ecology
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 52.1: Dynamic biological processes
influence population density, dispersion, and
demography
• A population
– Is a group of individuals of a single species
living in the same general area
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
PopuIation
size
Emigration
Deaths
Figure 52.2
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Deaths and emigration
remove individuals from a
population.
Patterns of Dispersion
• Environmental and social factors
– Influence the spacing of individuals in a
population
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A clumped dispersion
– Is one in which individuals aggregate in
patches
– May be influenced by resource availability and
behavior
(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.
Figure 52.3a
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A uniform dispersion
– Is one in which individuals are evenly
distributed
– May be influenced by social interactions such
as territoriality
(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.
Figure 52.3b
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A random dispersion
– Is one in which the position of each individual
is independent of other individuals
(c) Random. Dandelions grow from windblown seeds that
land at random and later germinate.
Figure 52.3c
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Demography
• Demography is the study of the vital statistics
of a population
– And how they change over time
• Death rates and birth rates
– Are of particular interest to demographers
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Survivorship Curves
• A survivorship curve
– Is a graphic way of representing the data in a
life table
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The survivorship curve for Belding’s ground squirrels
– Shows that the death rate is relatively constant
Number of survivors (log scale)
1000
100
Females
10
Males
1
0
2
Figure 52.4
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
4
6
Age (years)
8
10
• Survivorship curves can be classified into three
general types
Number of survivors (log scale)
– Type I, Type II, and Type III
1,000
I
100
II
10
III
1
0
Figure 52.5
50
Percentage of maximum life span
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
100
Reproductive Rates
• A reproductive table, or fertility schedule
– Is an age-specific summary of the reproductive
rates in a population
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 52.2: Life history traits are products of
natural selection
• Life history traits are evolutionary outcomes
– Reflected in the development, physiology, and
behavior of an organism
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Species that exhibit semelparity, or “big-bang”
reproduction
– Reproduce a single time and die
Figure 52.6
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Species that exhibit repeated reproduction
– Produce offspring repeatedly over time
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Parental care of smaller broods
– May also facilitate survival of offspring
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
“Trade-offs” and Life Histories
• Organisms have finite resources
Figure 52.7
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
RESULTS
100
Male
Female
Parents surviving the following winter (%)
– Which may
lead to tradeoffs between
survival and
reproduction
EXPERIMENT
Researchers in the Netherlands studied the
effects of parental caregiving in European kestrels over 5 years. The
researchers transferred chicks among nests to produce reduced broods
(three or four chicks), normal broods (five or six), and enlarged broods
(seven or eight). They then measured the percentage of male and
female parent birds that survived the following winter. (Both males and
females provide care for chicks.)
80
60
40
20
0
Reduced
brood size
Normal brood
size
Enlarged
brood size
CONCLUSION
The lower survival rates of kestrels with larger broods indicate
that caring for more offspring negatively affects survival of the parents.
• Some plants produce a large number of small
seeds
– Ensuring that at least some of them will grow
and eventually reproduce
(a) Most weedy plants, such as this dandelion, grow quickly and
produce a large number of seeds, ensuring that at least some
will grow into plants and eventually produce seeds themselves.
Figure 52.8a
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Other types of plants produce a moderate
number of large seeds
– That provide a large store of energy that will
help seedlings become established
(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.
Figure 52.8b
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 52.3: The exponential model
describes population growth in an idealized,
unlimited environment
• It is useful to study population growth in an
idealized situation
– In order to understand the capacity of species
for increase and the conditions that may
facilitate this type of growth
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Per Capita Rate of Increase
• If immigration and emigration are ignored
– A population’s growth rate (per capita
increase) equals birth rate minus death rate
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Zero population growth
– Occurs when the birth rate equals the death
rate
• The population growth equation can be
expressed as
dN 
rN
dt
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Exponential Growth
• Exponential population growth
– Is population increase under idealized
conditions
• Under these conditions
– The rate of reproduction is at its maximum,
called the intrinsic rate of increase
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Exponential population growth
– Results in a J-shaped curve
2,000
dN
 1.0N
dt
Population size (N)
1,500
dN
 0.5N
dt
1,000
500
0
0
Figure 52.9
10
5
Number of generations
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
15
• The J-shaped curve of exponential growth
– Is characteristic of some populations that are
rebounding
Elephant population
8,000
6,000
4,000
2,000
0
1900
1920
Figure 52.10
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
1940
Year
1960
1980
• Concept 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Carrying capacity (K)
– Is the maximum population size the
environment can support
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 52.5: Populations are regulated by a
complex interaction of biotic and abiotic
influences
• There are two general questions we can ask
– About regulation of population growth
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• What environmental factors stop a population
from growing?
• Why do some populations show radical
fluctuations in size over time, while others
remain stable?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Population Change and Population Density
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Territoriality
• In many vertebrates and some invertebrates
– Territoriality may limit density
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Cheetahs are highly territorial
– Using chemical communication to warn other
cheetahs of their boundaries
Figure 52.16
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Oceanic birds
– Exhibit territoriality in nesting behavior
Figure 52.17
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Health
• Population density
– Can influence the health and survival of
organisms
• In dense populations
– Pathogens can spread more rapidly
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Predation
• As a prey population builds up
– Predators may feed preferentially on that
species
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Toxic Wastes
• The accumulation of toxic wastes
– Can contribute to density-dependent regulation
of population size
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Intrinsic Factors
• For some populations
– Intrinsic (physiological) factors appear to
regulate population size
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Population Cycles
• Many populations
160
Snowshoe hare
120
Lynx
9
80
6
40
3
0
1850
0
1875
Figure 52.21
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
1900
Year
1925
Lynx population size
(thousands)
Hare population size
(thousands)
– Undergo regular boom-and-bust cycles
• Boom-and-bust cycles
– Are influenced by complex interactions
between biotic and abiotic factors
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 52.6: Human population growth has
slowed after centuries of exponential increase
• No population can grow indefinitely
– And humans are no exception
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Global Human Population
• The human population
– Increased relatively slowly until about 1650
and then began to grow exponentially
5
4
3
2
The Plague
1
Figure 52.22
8000
B.C.
4000
B.C.
3000
B.C.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2000
B.C.
1000
B.C.
0
1000
A.D.
0
2000
A.D.
Human population (billions)
6
• Though the global population is still growing
– The rate of growth began to slow approximately
40 years ago 2.2
2
Percent increase
1.8
1.6
2003
1.4
1.2
1
0.8
0.6
0.4
0.2
0
1950
Figure 52.23
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
1975
2000
Year
2025
2050
Regional Patterns of Population Change
• To maintain population stability
– A regional human population can exist in one
of two configurations
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Zero population growth = High birth rates –
High death rates
• Zero population growth = Low birth rates – Low
death rates
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The demographic transition
– Is the move from the first toward the second state
Birth or death rate per 1,000 people
50
40
30
20
10
Sweden
Mexico
Birth rate
Birth rate
Death rate
Death rate
0
1750
1800
1850
Figure 52.24
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
1900
Year
1950
2000
2050
• The demographic transition
– Is associated with various factors in developed
and developing countries
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Age structure
– Is commonly represented in pyramids
Rapid growth
Afghanistan
Male
Female
8 6 4 2 0 2 4 6 8
Percent of population
Age
85
80–84
75–79
70–74
65–69
60–64
55–59
50–54
45–49
40–44
35–39
30–34
25–29
20–24
15–19
10–14
5–9
0–4
Slow growth
United States
Female
Male
8 6 4 2 0 2 4 6 8
Percent of population
Figure 52.25
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Age
85
80–84
75–79
70–74
65–69
60–64
55–59
50–54
45–49
40–44
35–39
30–34
25–29
20–24
15–19
10–14
5–9
0–4
Decrease
Italy
Female
Male
8 6 4 2 0 2 4 6 8
Percent of population
• Age structure diagrams
– Can predict a population’s growth trends
– Can illuminate social conditions and help us
plan for the future
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
80
50
Life expectancy (years)
Infant mortality (deaths per 1,000 births)
60
40
30
20
40
20
10
0
0
Developed
countries
Figure 52.26
60
Developing
countries
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Developed
countries
Developing
countries
Global Carrying Capacity
• Just how many humans can the biosphere
support?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Estimates of Carrying Capacity
• The carrying capacity of Earth for humans is
uncertain
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Ecological footprints for 13 countries
Ecological footprint (ha per person)
– Show that the countries vary greatly in their footprint
size and their available ecological capacity
16
14
12
New Zealand
10
USA
Germany
Japan Netherlands
Norway
8
6
UK
Spain
4
World
China
India
2
0
Australia
Canada
Sweden
0
2
4
6
8
10
12
Available ecological
capacity (ha per person)
Figure 52.27
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
14
16
• At more than 6 billion people
– The world is already in ecological deficit
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings