Transcript Population Ecology

Population Biology
BCOR 012
Chapter 53
February 25 and 27, 2009
Population Ecology
Chapter 52
I. Characteristics of Populations
A. Introduction
B. Two important characteristics of populations are density and the
spacing of individuals (= dispersion)
C. Demography
II. Life Histories
A. Natural selection favors strategies that maximize and individual’s
fitness.
B. Reproductive strategies
C. Trade-offs between reproduction and survival
Population ecology is concerned with:
• measuring changes in population size and
composition
• identifying the ecological causes of such
fluctuations
Population Ecology
Study of populations in
relation to the environment
Influences of environment
on population:
Density
Distribution (dispersion)
Age structure
Size
From Chapter 23:
So what is a population?
A population is a set of individuals of the same species
that live close
enough together
to interbreed.
in a particular
geographic
area.
Density – the number of individuals
per unit area
Aerial census of African water buffalo in the Serengeti
Dispersion – the spacing among individuals
within the population boundaries
Factors which influence population
density and dispersion?
Ecological needs of species
Structure of the environment
Interactions between individuals
Demography
Study of the vital
statistics of populations
and how they change
over time
~ Birth and Death rates
Demography is the study of factors that affect the growth and decline of
populations. Populations increase as a result of births and
immigration; they decrease as a result of deaths and emigration.
A life table follows fate of a cohort from birth to death
Type I
Few offspring with good care
(mammals)
Death rate low until older ages
Type II
Intermediate (rodents, annual
plants)
Death rate constant
Type III
Many offspring with little care
(marine invertebrates, long-lived
plants)
Initial death rate high, then low
Idealized
survivorship curves
Reproductive rate
The other key demographic
factor determining size
changes in populations
without immigration or
emigration
Reproductive table ~ agespecific reproduction rates
(Birth Rates)
Population Ecology
Chapter 52
I. Characteristics of Populations
A. Introduction
B. Two important characteristics of populations are density and the
spacing of individuals (= dispersion)
C. Demography
II. Life Histories
A. Natural selection favors strategies that maximize and individual’s
fitness.
B. Reproductive strategies
C. Trade-offs between reproduction and survival
Life history - the set of traits related to reproduction, including
frequency of reproduction, number of offspring, investment in
parental care, etc.
Reproductive Strategies
Semelparous reproduction (big-bang) – A life history strategy
in which the organism reproduces but once and then dies.
Iteroparous reproduction – repeated reproduction over the
course of the life span
White tailed deer - an iteroparous species
Giant palm of Madagascar
Fitness involves both individual survival and the
production of viable offspring that will live to reproduce
themselves.
Q. Therefore, why not a life history strategy that involves early
reproductive maturity, frequent reproduction, and many offspring
per brood?
Trade-offs between reproduction and survival:
Survivorship vs. brood size in European kestrel
Organisms whose young are subject to high mortality rates often
produce large numbers of small offspring. In other species, fewer
and larger offspring are produced.
r-selection: short life span, high
reproductive output, high juvenile
mortality, limited parental investment
K selection: long life span,
low reproductive output,
low juv. mortality, high
parental investment
Population Ecology
Chapter 52
III. Population Growth
A.
Exponential Growth
B.
Logistical Growth
IV. Population Limiting Factors
A.
Density dependence
B.
Population fluctuations
C.
Boom and bust cycles
V. Human Population Growth
A.
Earth’s carrying capacity
B.
What can you do?
Population Growth
Growth rate results from
processes that add and
remove individuals
+ Births
− Deaths
+ Immigration
− Emigration
Growth curve for a population growing exponentially
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
N is the population size
∆N
∆t
r is the per capita growth rate,
r = b - d, where b is the per
capita birth rate and d is the
per capita death rate
Kingfish, Louisiana, had a population of 1,100
individuals. They had a birth rate of 12/100, a death
rate of 8/100, and an emigration (individuals leaving
the population) rate of 2/100. How many people were
added to Kingfish's population in one year?
What is r?
r = (b+i) - (d+e)
r = 0.12 - (0.08+0.02) = 0.02
rN=(0.02)(1,100) = 22
good job!
Exponential
growth:
Populations
introduced to new
or unfilled habitat
Populations
rebounding after
catastrophe
Rebound of the whooping crane population
In the notation of differential calculus, population growth is
given as:
rN = dN
dt
(Note: here d is being used to symbolize very small
change. It does not refer to the per capita death rate!)
The maximum value of r, achieved under ideal growth conditions,
is called the intrinsic rate of increase. It is noted as rmaxN.
As b decreases and/or d increases, r, the per
capita growth rate, decreases.
The carrying capacity (K) of an environment
is the maximum population size that the
environment can sustain with no degradation
of the habitat.
As the population size (N) approaches carrying capacity (K), the
population growth rate approaches zero.
The Logistical Growth Equation
K - N
dN
dt = rmaxN  K 
By multiplying the exponential rate of increase rmaxN by
(K - N)/K, we reduce the actual growth rate of the population
as N increases.
The logistic model of population growth produces a sigmoid (S-shaped)
curve when N is plotted over time.
How well do actual populations fit the logistical model?
This laboratory population
of Paramecium grew according
a logistical model.
This laboratory population of
Daphnia overshot carrying capacity.
And this natural
population of song
sparrows fluctuated
considerably in
response to environmental stresses.
Population Ecology
Chapter 52
III. Population Growth
A.
Exponential Growth
B.
Logistical Growth
IV. Population Limiting Factors
A.
Density dependence
B.
Population fluctuations
C.
Boom and bust cycles
V. Human Population Growth
A.
Earth’s carrying capacity
B.
What can you do?
Density-dependent factors limiting population
growth
• Plants: light, nutrients, water
• Animals: food, water, nesting/breeding
sites
• Increased predation
• Accumulation of waste in the
environment
• Increased transmission of disease
• Stress
Density-dependent limits on population growth are
examples of negative feedback, a primary mechanism
of self-regulation whereby the product of a process
slows or stops that process.
A non-biological example: your home heating system!
When your thermostat senses that room temperature has
fallen, it signals the furnace to come on. The product of
furnace activity, heat, accumulates until the desired temp.
is reached. The thermostat, sensing the accumulating
heat in the room, then signals the furnace to shut off.
So what is an example of a density independent factor?
Floods, for example: factors that have nothing to do
with the size of the population in question.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Fluctuation in a moose population on Isle Royale,
Lake Superior
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Ten-year population cycles in the snowshoe hare and lynx.
Population Ecology
Chapter 52
III. Population Growth
A.
Exponential Growth
B.
Logistical Growth
IV. Population Limiting Factors
A.
Density dependence
B.
Population fluctuations
C.
Boom and bust cycles
V. Human Population Growth
A.
Earth’s carrying capacity
B.
What can you do?
The human population is growing exponentially
Where is K???
Age-structure pyramids for the populations of Afghanistan,
the United States, and Italy
In the United States, our
ecological footprint is large.
So what can you do about it?
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Live sustainably
Use resources wisely
Eat more vegetable protein and less meat
Support global family planning efforts
Work for peace and justice