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publishing as Benjamin Cummings
Ecology - Study of interactions
among organisms and their
environment
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ECOSYSTEM LEVEL
• Biosphere Eucalyptus forest
COMMUNITY LEVEL
All organisms in
• Ecosystems
eucalyptus forest
POPULATION LEVEL
Group of flying foxes
ORGANISM LEVEL
• Community Flying fox
Brain
Spinal cord
ORGAN SYSTEM LEVEL
Nervous system
• Population ORGAN LEVEL
Brain
Nerve
TISSUE LEVEL
Nervous
tissue
CELLULAR LEVEL
Nerve cell
MOLECULAR LEVEL Figure 1.1
Molecule of DNA
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• Population ecology is the study of populations in
relation to their environment, including
environmental influences on density and
distribution, age structure, and population size
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2011 Pearson Education, Inc.
Dynamic biological processes influence population
density, dispersion, and demographics
• A population is a group of individuals of a
single species living in the same general area
• Populations are described by their boundaries
and size
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2011 Pearson Education, Inc.
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
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2011 Pearson Education, Inc.
Density: A Dynamic Perspective
• In most cases, it is impractical or impossible
to count all individuals in a population
• Sampling techniques can be used to estimate
densities and total population sizes
• Population size can be estimated by either
extrapolation from small samples, an index of
population size (e.g., number of nests), or the
mark-recapture method
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2011 Pearson Education, Inc.
• Mark-recapture method
– Scientists capture, tag, and release a random
sample of individuals (s) in a population
– Marked individuals are given time to mix back into
the population
– Scientists capture a second sample of individuals
(n), and note how many of them are marked (x)
– Population size (N) is estimated by
sn
N
x
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2011 Pearson Education, Inc.
• Density is the result of an interplay between
processes that add individuals to a population and
those that remove individuals
• Immigration is the influx of new individuals from
other areas
• Emigration is the movement of individuals out of
a population
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2011 Pearson Education, Inc.
Figure 53.3
Births Deaths
Births and immigration Deaths and emigration
add individuals to remove individuals
a population. from a population.
Immigration Emigration
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Population Ecology
• Population- how to measure?
• Growth rates: J shaped, S shaped
• K, r, and reproductive strategies
• Human population
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• The dispersion pattern of a population refers
to the way individuals are spaced within
their area
– Clumped -
– Uniform:
– Random: no pattern
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Figure 53.4
(a) Clumped
(b) Uniform
(c) Random
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How do populations grow?
• Idealized models describe two kinds of
population growth
1. exponential growth
2. logistic growth
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• King’s chess game
• A J-shaped growth curve, described by the
equation G = rN, is typical of exponential
growth
– G = the population growth rate
– r = the intrinsic rate of increase, or an
organism's maximum capacity to reproduce
– N = the population size
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Figure 35.3A
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1500 high intrinsic
rate of increase
1000
Population size
low intrinsic
rate of increase
zero population
500 growth
r=0
negative intrinsic
rate of increase
r = -0.05
0
0 5 10 15 20
Time (years)
2. Logistic growth is slowed by population-
limiting factors
K = Carrying capacity is
the maximum
population size
that an environment
can support
Figure 35.3B
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• logistic growth curve
– K = carrying capacity
– The term
(K - N)/K
accounts
for the
leveling
off of the
curve
Figure 35.3C
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Multiple factors may limit population growth
declining birth rate or increasing death rate
• The regulation of growth in a natural
population is determined by several factors
– limited food supply
– the buildup of toxic wastes
– increased disease
– predation
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– About every 10 years, both hare and lynx
populations have a rapid increase (a "boom")
followed by a sharp decline (a "bust")
Figure 35.5
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• Survivorship curves plot the proportion of
individuals alive at each age
• Three types of survivorship curves reflect
important species differences in life history
Figure 35.6
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Evolution shapes life histories
• An organism's life history is the series of events
from birth through reproduction to death
• Life history traits include
– the age at which reproduction first occurs
– the frequency of reproduction
– the number of offspring
– the amount of parental care given
– the energy cost of reproduction
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• Principles of population ecology may be used
to
– manage wildlife, fisheries, and forests for
sustainable yield
– reverse the decline of threatened or
endangered species
– reduce pest populations
– IPM = Integrated Pest Management
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• Integrated pest management (IPM) uses a
combination of biological, chemical, and
cultural methods to control agricultural pests
• IPM relies on knowledge of
–the population ecology of the pest
–its associated predators and parasites
–crop growth dynamics
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The Spread of Shakespeare's Starlings
• In 1890, a group of Shakespeare enthusiasts
released about 120 starlings in New York's
Central Park
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• Today: over 100 million starlings, spread over
N. Amer.
Current
1955 Current
1955
1945
1935
1925
1945
1905
1915
1925
1935
1925
1935
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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Human Population
– Expanding and are virtually uncontrolled
– Harming other species
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THE HUMAN POPULATION
• doubled three times in the last three centuries
• about 6.1 billion and may reach 9.3 billion by
the year 2050
• improved health and technology have lowered
death rates
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• The history of human population growth
Figure 35.8A
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• The age structure of a population is the proportion
of individuals in different age-groups
RAPID GROWTH SLOW GROWTH ZERO GROWTH/DECREASE
Kenya United States Italy
Male Female Male Female Male Female
Ages 45+ Ages 45+
Ages 15–44 Ages 15–44
Under Under
15 15
Percent of population Percent of population Percent of population
Also reveals social conditions, status of women Figure 35.9B
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• The ecological footprint represents the
amount of productive land needed to support a
nation’s resource needs
• The ecological capacity of the world may
already be smaller than its ecological
footprint
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• Ecological footprint in relation to ecological
capacity
Figure 35.8B
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Per capita CO2 emissions Total CO2 emissions
(metric tons of carbon) (billion metric tons of carbon)
0 1 2 3 4 5 6 0 0.5 1 1.5
U.S. 5.48 U.S. 1.49
China 0.75 China 0.91
Russia 2.65 Russia 0.39
Japan 2.51 Japan 0.32
India 0.29 India 0.28
• What next?
Figure 35.8C
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Figure 2.10x
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