Download Population Biology - Salisbury Composite High

12/7/2009
Population Biology
Definition
A population is a
group of organisms
of the same species,
interbreeding or
closely related
through
interbreeding and
evolving as a unit.
Review
Community: a group
of interacting plants
and animals forming
an identifiable group
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Review
Biosphere: the
entire part of the
earth where
organisms are
found
Review
Habitat: the place
where an organism
naturally lives or
grows
Review
Niche: position or
function of an
organism in its
community – its
occupation
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Population Size Calculations
Simplest
calculations involve
changes in
populations over a
time period in a
defined space.
gr= N/ t
Ex) What is the growth rate?
Initial Population
20 gulls move in
(immigration)
0 gulls move out
(emigration)
32 chicks hatch
(natality)
10 chicks die
2 adults die
Time
200
20
0
32
-10
-2
1 year
Total
240
Annual Increase of +40 birds per year
Density
Formula:
D = N/A or N/V
Density
equals number of organisms
divided by area (or volume or space)
Eg.
200 bison in a 100 acre pasture is a
density of 2 bison per acre
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Rate of Change
Often
R
uses density
=
D/
t
Rate
of density change equals change in
density over change in time.
Example
In 1996 there were 10 Grizzly Bears in a
10 000 ha forest. In 2005 there are only 8.
What is the rate of density change?
R=
D/
t
R = 0.0008 – 0.001 / 2005 – 1996
R= - 0.0000222 bears/ha/y
Per Capita Growth Rate
Or
cgr
amount that a population changes
per individual over a set period of time
The
Cgr
=
N /N
capita growth rate = change in
number divided by initial population size
Per
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CGR
A lynx population was 19 per 10 000 sq. km in
1991. In 1993 it was 3 per 10 000 sq. km.
What was the cgr of this population from
1991 to 1993?
Cgr = N/ N
= -16 / 19
= - 0.84 per lynx
Distributions of Populations
Can
be clumped – more individuals
together than apart
Often involves cooperation among group
members (eg. Herd, pack)
Distribution of Populations
Can
be random – not seen often in
nature
Organisms have no effect on each other
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Distribution of Populations
Can be uniform: evenly distributed
Usually due to competition between
individuals
Territories, etc.
Open Populations
Are
those where organism can enter or
leave
Often have S-shaped curves
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Closed Populations
True
closed populations are rare
On islands, isolated communities
Population Growth Graphs
typically
have
numbers on
vertical axis
and time on
horizontal
axis
Logistic Growth
S shaped
curves are
typical of
stable
populations
.
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Eg.
Wild
Horses on
reserve land
in AB
Exponential Growth
J
shaped curve (initially) occurs with
short-lived populations that rapidly
deplete their environment
Eg.
Flies on a carcass
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Overshoots
Result
when k is
greatly exceeded
and the
environment
deteriorates
Carrying Capacity
Is the number of
organisms a habitat
can sustain over
the long term
“k”
Influenced by Biotic
Potential and
Environmental
Resistance
Biotic Potential
maximum
number of offspring produced
capacity of offspring to survive to reproduce
number of times per year an organism
reproduces
age at which offspring are reproductively
mature
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Generally speaking, smaller, simpler
organisms have a higher biotic potential than
larger organisms.
Environmental Resistance
limiting factors on a
population
Availability of resources
(food, water, space, etc.)
Competition for resources
with other organisms
Intra-specific – within a
species
Inter-specific – between
a species
Predators
Disease
Climate change
Environmental Resistance
Puts
brakes on biotic potential (B) –
maximum reproductive rate
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Environmental Resistance
Environmental Resistance
B
K
Environmental Resistance
Limiting Factors on Populations
Law
of the Minimum: if any one of many
needed nutrients/limiting factors is
reduced below the required levels, the
population growth rate declines
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Limiting Factors
Can
be density independent – those that
will affect a population regardless of its
size
Eg. Cold winter
Limiting Factors
Can
be density dependant – those that
increase when the population size
increases
Eg. Disease
Predation
Food Supply
Gause’s Law
Competitive
exclusion
No
two species can remain in
competition for a limited resource
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Other Graphs
Survivorship
curves
Other Graphs
Age
distribution pyramids
Population Histograms
are graphs showing the composition by
age and gender of a population at a
specific time. Population histograms have
the following characteristic shapes:
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R and K Population Strategies
This
is a continuum
Most populations fall between these two
extremes
K Selection
k-selected
species is one that typically
has:
Stable environmental conditions
Slow growing individuals
Low reproduction rate (B)
Parental care of offspring
R- Selection
An
R-selected species is one that
typically has:
Unpredictable environment
Small individuals with short life spans
Reproduce at a high rate
Little or no parental care
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Life History Patterns
Some
organisms undergo regular
patterns of growth and decline known as
population cycles
Small rodents, rabbits, lemmings often
cycle every 1 – 4 years
Population Cycles
Can be due to
fluctuations in food
supply, predation, or
both
Predator - Prey Cycles
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Chaos Theory
Used
by population biologists to study
the general trends in populations
Small uncertainties in short-term
prediction of individual events may be
magnified to such an extent that complex
systems become quite unpredictable
Chaos
The
‘butterfly effect”
This is the sensitivity of a system to the
initial conditions
Change any starting parameter slightly
and the resulting changes magnify until
the result is very different from the initial
prediction
Technologies
Include:
Radio collars
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Technologies
Sampling methods
Quadrats –
counting organisms
in defined areas
Transects –
counting organisms
that touch line
Technologies
Mark/recapture
studies
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Symbiotic Relationships
Symbiosis
– a relationship between two
individuals of different species.
Parasitism
– one species lives in or on
another where it obtains food and
resources. The host is usually harmed by
the relationship. Ex. Tapeworm
Many
parasites are r-selected
Eg. Tapeworm
Commensalism
– one species lives on
or near another, but while one species
benefits, the other is unaffected.
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Mutualism
– two species that live in
close association with one another,
where both benefit from the relationship.
Ex. honeybee and flower
Ex. shark and remora
Ecological Succession
Ecological
succession – is the gradual
and orderly change of a community as it
is either developed from bare land or
replaced by another community.
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Succession
Primary
Succession – the gradual
colonization of an area that has not
supported an ecosystem before. (from
bare rock)
PrimarySuccession
Secondary
Succession – the
colonization of an area that once
supported an ecosystem that was
destroyed by fire, flood, etc.
Exploring Time Gallery Display
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Pioneer
Community – is the first
species to appear during succession.
Climax Community – is the final stable
community that results at the end of
succession.
Generalizations about
Succession:
Species composition changes more quickly
at earlier stages.
Total number of species increases
dramatically at early stages, levels off at
intermediate phases and declines at the
climax stage.
Food webs develop in complexity as
succession progresses.
Total biomass increases during succession
and levels off at the climax stage.
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