Biology 213 Chapter 53
Introduction to Ecology:
Population Ecology Part 1
You will be able to…
• List various fields of study in Ecology
• Explain what factors change
populations
• Calculate population rate changes
• Compare and contrast densitydependent to density-independent
factors
Ecology:
Oikos = home
Ology = study of
Integrates all biological fields
1. Organismal ecology: physiology, behavior,
interactions with environment
2. Population ecology: factors affecting groups
of individuals in an area.
3. Community ecology: interactions between
species in an area
4. Ecosystem ecology: biotic and abiotic
interactions; E flow & chem. Cycles
5. Landscape ecology: exchange of E &
materials across multiple ecosystems
6. Global ecology: biosphere: regional
exchange of E & materials affecting entire
functioning & distribution of organisms
wotldwide.
Ecology & evolution: changes in environment
impacting populations’ alleles over time.
Ecology & environmental issues
Complexity of Nature:
Why are some species present in an area?
Dispersal difficulties (accessibility?)
Behaviour limits distribution (habitat preference)?
Biotic factors: competition/parasitism/predation/etc
Abiotic factors:
Chem: H2O, O2, pH, salinity, nutrients
Phys: Macro & micro climate: Temp, light, fire,
soil composition, moisture
• Estimate: one million years to get from 2.5 million
to human population of ~ 5 million people in 6000
B.C. (2x)
• population did not reach 500 million until almost
8,000 years later -about 1650 A.D (100x)
• doubled roughly once every thousand years or so
• reached a billion ~ 1850, doubling in 200 years
• reached two billion around 1930 – doubling in 80
years
• 1970’s it reached 4 billion ~ 40 year doubling time
• Today’s population ~ 7 billion
What factors have allowed human population
to increase so rapidly?
Ecologists study population trends rather than
individual organisms.
Properties of populations include
•
•
•
•
•
•
Population size
Population density
Patterns of dispersion
Demographics
Population growth
Limits on population growth
• Population density
– # individuals of a species per unit
at a given time
• Population dispersion (spacing)
– How are individuals distributed in a habitat?
– Why would this be important to know if you
were studying a population?
– What does a dispersion pattern tell you?
Individual members
distributed in a # of
different ways:
• Clumped -
• Uniform • Random -
Why would a clumped population pattern form?
individuals _____________ to each other,
or __________________________________.
What factors encourage a
uniform population pattern?
individual organisms actively _____ each other
or all _________________________________
What abiotic or biotic features would
encourage a random population pattern?
Rare in nature - occurs in absence of strong
attractions or repulsions among individuals.
Dispersion patterns and density
may change over time
Habitat changes: food, nutrients, water,
sunlight (plants)
Age / size / developmental stages change:
• Four factors that produce
changes in population size
Natality: birth rate
Mortality rates
Mortality rate of cheetahs
Increased Infant
Mortality
• Is the cheetah
dangerously inbred?
• Majority of deaths in
wild due to predation.
• Future for cheetah
population?
How a population changes:
D in # of individuals
in a certain period of time
N=
r=
How a population changes:
D in # individuals / time
N = # individuals
r=
* Per 1,000 individuals
Growth rate =
Example: N = 300,000 humans:
3,000 births + 1,500 deaths in one year
r = (birth rate) – (death rate)
Example: N = 300,000 humans:
r = (birth rate) – (death rate)
r =
r =
Example: N = 300,000 humans:
r = 0.005 x 100 = 0.5% increase
rN = 0.5 x 300,000
rN =
If r is positive, increase in pop.
If r is negative, pop. is decreasing
If r = 0, population is stable
Are there other factors besides
birth and death
and
size of a population
that can change a population?
Immigration
• What causes
immigration
biologically?
– Favorable factors
Factors encouraging immigration:
New environment made available
–Natural disasters large and small
–Competitive or predatory species goes
extinct / moves away
–Climate change or new resources
–Hitch-hiking (“alien” species)
Less competition in new area
Succession after a disaster
Immigrants have an opportunity to invade:
Reduced competition
Factors that encourage
successful immigration:
Distribution methods:
• dispersal is at or near ground level vs.
aerial dispersal
• dispersers actively engage in searching,
or not
• dispersers able to orient toward preferred
habitat from some distance,
or not
Wind dispersing Golden Orb spiders
Emigration
Unfavorable Factors:
*Excessive competition: mates or food
*Lack of resources
*Disease
*Avoidance of in-breeding
Population change includes
immigration and emigration:
r = (birth rate) – (death rate) plus
(immigration – emigration)
e.g. Example: N = 300,000 humans:
3000 births + 1500 deaths in one year
3,000 immigrated into the area
9,000 emigrated out of the area
r = (b – d) + (i – e)
b – d = (10/1000) – (5/1000) = 0.005
i – e = 1/1000 – 3/1000
= 0.001 – 0.003 = -0.002
r = (b – d) + (i – e)
= (0.005) + (-0.002) = 0.003 x 100 = 0.3%
Growth rate: rN = (0.3%)(300,000)
= 900 more people in the population
Intrinsic rate of increase (rmax)
Maximum rate at which species or
population can increase under ideal
conditions
• Exponential population growth
Exponential population growth
According to Malthus:
• Population, when unchecked, increases in a
geometrical ratio.
• Subsistence increases arithmetically.
Carrying capacity
–Carrying capacity (K) = largest
population maintained without
degrading environment they live in
–Changes as environment changes
• Logistic population curve
(S-shaped curve)
Carrying capacity and logistic population growth
Limiting
Factors
Density-dependent factors
–Regulate population growth by
affecting large proportion of
population as population rises:
Density-dependent factors
–What do you think would impact a
population as it got bigger?
• Predation
• Disease
• Competition
• Toxic wastes
Density-dependent factors and
negative feedback
• Density-independent factors
– Limit population growth but are not
influenced by changes in population
density: usually ABIOTIC
– Examples include natural disasters:
• Hurricanes
• Blizzards
• Forest fires
• Mudslides
• Volcanoes, tsunamis, and earthquakes
Limiting Factors
Biotic and abiotic,
Density dependent or independent
factors that limit a population’s growth:
What would be a limiting factor?
What can you think of that would be a
limiting factor?
Which are biotic and which are abiotic?
• increase death rate
• decrease birth rate
• limits immigration
• encourages emigration
• Any factors that slows population growth.
How are up & down cycles explained?
Can be very complex relationships and factors.
Biology 213 Chapter 53
Introduction to Ecology:
Population Ecology Part 2
You will be able to…
• Explain what factors change populations
• Calculate population rate changes
• Compare and contrast density-dependent
to density-independent factors
• Analyze human population patterns and
make predictions about future trends
• Semelparous reproduction
–Expend their energy in a
• Iteroparous reproduction
–Exhibit ________________________
throughout their lifetimes
Semelparity:
Expend energy to
reproduce in one big
effort
Most insects,
invertebrates,
many annual plants,
and some fish
What’s the advantage?
Iteroparous reproduction
• Expend energy to
reproduce in cycles
• Most vertebrates,
perennial plants.
• What’s the
advantage?
Species exhibiting an r strategy
–Emphasizes a high growth rate
–Organisms typically have
• small body size
• high reproductive rates
• short life spans
• inhabit variable environments
• Often
Species exhibiting a K strategy
–Maintains a population near
carrying capacity (K) of environment
–Species often have
• large body size
• low reproductive rates
• long life spans
• inhabit stable environments
• Often
• Survivorship curves
–Type I
• Mortality is greatest in old age
–Type II
• Mortality is spread evenly
across all ages
–Type III
• Mortality is greatest among
the young
Survivorship curves
Survivorship
curve for
a herring
gull
population
Source habitats:
–Preferred habitats
–Local reproductive success is
> local mortality
–Local individuals disperse from
source habitats to other regions
• Sink habitats
–Lower-quality habitats
–Individuals may suffer death or
poor reproductive success
–What would make an organism
move then?
Source & sink populations in a hypothetical
metapopulation
Human population growth
– World population reaches 7,000,000,000
6,668,926,425 by
Mayyear
20, 2008
The
2011
– Per capita growth rate declined from peak
in 1965 of about 2% per year
(doubling time 35 years)
– to 1.3% per year (doubling time of 54 years)
– birthrate necessary for zero population
growth is 2.1 births per woman
Human population growth:
exponential J-shaped curve so far
logistic population growth
Chapter 53 Clicker Question #4:
Often growth cycles of one population affects
the cycle of another. As moose populations
increase, wolf populations also increase. If we
consider the logistic equation for the wolf
population:
dN = rN (K-N)
dt
K
which of the above factors accounts for the
strongest impact on the moose population?
A. K
B. dN
C. rN
D. dt
Population characteristics
–Highly developed countries
• low birth rate
• low infant mortality
• low fertility rate
• long life expectancies
• high GNI PPP:
–GNI PPP per capita is the gross national
income in purchasing power parity
divided by mid-year population.
Population characteristics
–Developing countries
• high birth rate
• high infant mortality
• high fertility rate
• short life expectancies
• low GNI PPP
What trends do we see world-wide?
China and India’s populations increasing
Birth rate decline lags behind as death rate
decreases: e.g. in Mexico, 1900–2000
• Age structure influences
population dynamics
–Possible for country to have
replacement-level fertility and still
experience population growth
–Young age structure causes a
positive population growth momentum
as large pre-reproductive age group
matures
Age structure diagrams comparing
Kenya
to
USA
to Germany
15-to-40 range: reproductive rates are high
“Carrying-capacity" definition of
overpopulation:
• not population density, but #’s of people in
an area relative to resources capacity to
sustain human activities
• a condition of overpopulation might be
corrected with
no change in the number of people!
Ecological Footprint
• Developing countries tend to
have people overpopulation that
degrades the environment
• Developed countries have
consumption overpopulation that
degrades the environment
USA & Mexico
One week’s food supply.
One week’s food costs the American family $341.98
One week’s food
Egypt
Ecuador
Above: Bhutan
Below: Chad
One
week’s
food costs
the Chad
family
$1.23
•
•
•
•
China has 22 % of world’s population
India has 17 % of world’s population
Both nations are modernizing rapidly
USA uses has 4.4% of the world
population and uses 25% of world’s
energy resources
• What happens to global resources
when developing countries want to
enjoy a developed nation lifestyle like
ours?