Download Population Ecology

Population Ecology
Basic Ecology Terms:
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Ecology - the study of relationships between organisms
and their environment.
Population - a group of interacting individuals of the
same species.
Community - a group of interacting populations.
Ecosystem - a functional environmental unit, consisting
of a biotic community and the abiotic (nonliving) factors
on which the organisms depend.
Biosphere - the total of all ecosystems. In other words,
all the area on Earth where life is found.
Population Ecology
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What is a population: a group of organisms, of a single species that
live in a given area.
Do populations (numbers of individuals) go up, down, or stay
constant?
Yes
How can a populations growth rate be zero?
Birth and death rates need to be the same.
What factors caused such abrupt
changes in the deer population?
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The number of
organisms in a
particular area is
directly related to the
productivity of the
area.
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Primary productivity in an ecosystem - the
rate at which solar energy is converted into
organic compounds. The units of productivity
are kilocalories per square meter per year.
Gross primary productivity - the total
amount of energy produced, including the
energy used by the plants for their own
respiration.
Net primary productivity - the rate at which
plants store energy that is not used in plant
respiration.
Factors which control population growth
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Density Dependent
Factors: These factors
effect large/dense
populations.
1. Competition
2. Predation
3. Crowding/stress
4. Parasitism
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Density Independent
Factors: These factors
effect individuals regardless
of how large the population
is.
1. Weather
2. Pollution
Density dependent factors
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Competition: When populations become
crowded, organisms compete with each other
for food, water, space etc.
Predation: Predator-Prey relationships (316)
Crowding and stress: Need room to hunt,
space for nesting, or may need a territory of
a certain size.
Stress: eating their own
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Population: Is a group of organisms, of a single
species that live in a given area.
Growth rate: A change in population size can be
positive, negative or zero.
Why populations grow: Idea conditions ( ?, ?, ?)
- They are reproducing faster than the death rate.
Exponential growth: As long as ideal conditions
continue, the larger a population will get, and the
faster it grows.
Example: Bacteria
Zero population growth: Birth and death rates are the
same.
Population density: number of organisms in a given
area.
Growth, reduction, constant
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Populations change based on the
conditions they are faced with.
Under ideal conditions: Plenty of food,
shelter and space populations will grow
exponentially (fast).
Example bacteria on a petridish in the
incubator.
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Do graphing problem
Graphing Problem
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Graph the following population and label the
following areas on your graph.
1. Slow Growth
2. Exponential growth (fast growth)
3. Slows Growth
4. Carrying capacity
Rabbit population on a 100 acre plot.
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Year 1
Year 2
Year 3
Year 4
Year 5
Year 6
10
12
14
19
27
29
Year 7 32
Year 8 30
Year 9 31
Year 10 30
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Why does the population level off and not continue to grow?
How come human population hasn’t leveled off?
What would you expect to happen to the rabbit population if 25 of
the 50 acres became a housing development?
What do you think would happen to the predator population?
What would you expect to happen to the rabbit population if a
severe wind storm destroyed part of the habitat?
Identify density dependent and independent factors above.
Stages of Population Growth
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Population growth is best explained with a Growth with Limits
Curve.
Growth with Limits Curve (4 steps): This is under ideal conditions
1. Growth starts off slow
2. Exponential growth (fast growth)
3. Growth slows
4. Growth levels off to carrying capacity
Carrying capacity: is the number of individuals that can survive
over a long period of time in a given environment.
By reducing the size of a habitat we lower the carrying capacity. By
reducing the numbers of anyone population we reduce the carrying
capacity of that habitat for other populations. If we reduce the
number of anyone population in a food web other are affected
(interdependence).
Population Size and Density:
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To begin to study a population, the size of the
population (number of individuals) is
determined.
For the size of a population to have meaning,
the area covered by the population must be
known.
Density - the number of individuals per area
unit
Distribution Patterns: To give a better picture of population density,
distribution within the area needs to be known.
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Random distribution:
each individual has an
equal chance of being
found at any place in a
given area. This is a
hypothetical condition
that might never occur in
nature because resources
are not randomly
distributed.
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Uniform distribution:
animals are evenly
spaced throughout
the habitat. This can
at least be
approached in nature.
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Clumped distribution:
animals are found in
areas where
resources are found.
This is by far the
most common
distribution pattern in
nature.
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Population Age Structure: The age structure
can tell more about population dynamics than
either density or distribution.
Functional age classes: because of the
difference in life spans, the ages of these groups
can be very different from one group of animals
to another.
Prereproductive: too young to reproduce.
 Reproductive: able to reproduce.
- Postreproductive: too old to reproduce.
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Population age profile - an estimation of the number of
individuals in each age class.
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When the number of prereproductive individuals forms a high
percentage of the population, the population is likely to be increasing in
size.
A stable population has a fairly even number of individuals in each age
class.
When the number of postreproductive individuals is large, the
population is declining. There are too few individuals maturing to
provide population replacement.
A species with a short life span will show all three types of age profiles
during one seasonal cycle.
Natality - the ratio of the number of births in a given time to the
total population.
Mortality - the ratio of the number of deaths in a given time to the
total population.
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Population density - the number of individuals in a population in a given
area at a given time.
Carrying capacity - the maximum number of individuals that an
ecosystem is capable of supporting.
As population numbers increase, certain factors in the environment become
limits to growth. All living things need a certain amount of space in which to
live, food, water, and oxygen.
Biotic potential - the rate at which a population will grow if all individuals
survive and reproduce at their maximum capacity. This is a theoretical
number that is never realized in nature. While the term is not usually
applied to human populations, health and census data are available for such
calculations.
Realized intrinsic rate of growth - a measure of the difference between
natality (birth rate) and mortality (death rate).
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r=n-m
Since environmental conditions are rarely ideal, the maximum growth rate is
almost never achieved in nature. For this reason, the realized intrinsic rate
of growth more closely represents the actual growth of organisms in nature
than does the biotic potential.
Mathematical Models of Population
Growth :
1. Exponential growth model:
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A population could reach its biotic potential,
the maximum growth rate of which a
population is physiologically capable, if these
conditions are met:
environmental conditions are ideal
 there are no restrictions on reproduction
 mortality rate is kept extremely low
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Realized intrinsic rate
of growth is measured
by the difference
between natality (birth
rate) and mortality
(death rate).
r=n-m
(rate = natality mortality)
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Since environmental
conditions are rarely
ideal, the maximum
growth rate is almost
never achieved in nature.
For this reason, the
realized intrinsic rate of
growth more closely
represents the actual
growth of organisms in
nature than does the
biotic potential.
No growth in a population
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Zero population
growth is reached
when r = 0, natality
equals mortality, and
population size
remains constant,
even though
individuals are being
born and are dying.
2. Logistic growth model:
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Environmental resistance - the combination of
many factors that tend to prevent exponential
growth.
Exponential growth begins to slow because of a
combination of declining birthrate and increasing
death rate. Eventually, the population stops growing
as it fluctuates around zero population growth at the
habitat's carrying capacity - the maximum
population density that the environment can support
for an extended time.
Population Changes Based On
Carrying Capacity
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r-selected species capable of very rapid
population growth,
approximating an
exponential growth
pattern followed by a
crash in the adult
population .
Population Changes Based On
Carrying Capacity
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K-selected species have more or less
stable populations
adapted to exist at or
near carrying capacity
in relatively stable
habitats.
Mathematical models
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These two mathematical models help
us understand, but not necessarily
precisely describe, how populations
actually grow. Both models make
important simplifying assumptions that
do not actually relate to nature.
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The exponential model assumes that
populations grow without being
influenced by environmental resistance.
While the logistic model may seem
more realistic, it makes several
assumptions:
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Assume the carrying capacity is
constant.
Assume each individual affects the
growth of the entire population by
increasing environmental resistance as
soon as it is born.
Assume the number of offspring
produced by an individual relates
directly to the resources available at the
time of birth.
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Population Control:
Two things can be said about populations:
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Population density varies from habitat to
habitat.
No population increases indefinitely.
Assignment
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Explain how the percentage of each functional age
class found in a population determines the health of
most populations.
In a population of 100,000, there are 900 deaths and
2,000 births in one year. Calculate the natality and the
mortality in this population.
What is the realized intrinsic rate of growth in the
population in question #2?
What is the best example of a euryecious species you
can think of?
What two things can always be said about
populations?
Assignment
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Use the following information to answer the
final multiple choice questions.
Susan got a two cubic foot aquarium for her
birthday. With the help of a pet store, Susan
set up the aquarium complete with 4 female
guppies, 1 male guppy, and 10 snails. She
provided plenty of food and kept the aquarium
clean and supplied with air. After 6 months,
Susan's aquarium contained 50 guppies and
150 snails.
1.
Snail population density in the aquarium at the end of 6 months was
1.
2.
3.
4.
2.
The population growth rate for snails during the 6 months was
1.
2.
3.
4.
3.
2.
3.
4.
10
30
40
60
guppies
guppies
guppies
guppies
Susan will know that her guppy population has reached the carrying capacity of her tank
when
1.
2.
3.
4.
5.
150 snails
140 snails
25 snails/month
14 snails/snail/6 months
In the 7th month, Susan noticed that 40 guppies were born and 30 died. The guppy
population size at the end of the 7th month was
1.
4.
150 snails/cubic foot
25 snails/cubic foot
75 snails/cubic foot
150 snails
guppies are no longer born
guppies no longer die
the guppy birth rate equals the death rate
there is no longer room for guppies to swim
The snails may start getting sick and some may die. Disease is an example of a (an) ___
population control.
1.
2.
3.
4.
fatal attraction
exponential
density-independent
density-dependent
Human Population
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Human Population: Slow growth for most of our existence
why?
1. harsh 2. food
3. predators 4. parasites
*** until recently, only half of the children survived
About 300 yrs ago population increased: why?
1. agriculture
2. industrial revolution
3. better health care
 Growth is still exponential: about 180 people every minute, which
means 92 million more people every year.
 Page 320 What/how will human population be slowed?
Demographic transition:
Demographic transition: is a change in rate
resulting from a change in birth rate.
Three stages:
1. High birth rate and high death rate: Slow
population growth ( both are high)
2. Improved living conditions: food production
increases, medical advances, thus death rate
decreases (increased population)
3. Birth rate decreases: why? more children are
living, birth and death rates reach a balance.
Future population growth: is the most important
factor in determining the health of the earth.
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Restricted or logistic
population growth can
be expressed by the
following equation:
d N / d t = r N x (K - N)
/K
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d - means an
instantaneous change
in
N - the number of
individuals already in a
population
t - a unit of time
r - realized intrinsic rate
of population growth
K - carrying capacity