Download Population Dynamics - Amazing World of Science with Mr. Green

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A group of individuals of the same species
found in the same area (habitat) at the same
time and which are capable of interbreeding.
The African Elephant in the bush of Liwandi
The bottlenose dolphins of the Indian River
Lagoon
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Sea otters keystone species in Pacific kelp forests
Daily consume 25% body weight in urchins &
molluscs
Population > 1 million before settlers arrived
1700’s hunted to near extinction – 1000 in the
Aleutians, AK only 20 off California
In 1971 A-bomb test in AK used sea otter
population to assess bomb’s power  1000’s died
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1973 Endangered Species Act passes, 1976 Marine
Mammal Conservation Act
1989 1000’s died in Exxon Valdez Oil spill
Otters recovering in most places after 1970’s
The spring 2008 survey found 2760 sea otters,
down 8.8-percent from the record 2007 spring
survey.
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Why are they declining now?
New Threats?
Pollution Effects
- Shellfish magnify
toxins
- Reduce disease
resistance
- Reduce fertility
Increased Predation
- Killer Whales
- Switch to otters
when other food
is scarce
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Populations are dynamic – change in
response to environment
◦ Size (# of individuals)
◦ Density (# of individuals in a certain space)
◦ Dispersion (spatial pattern of individuals)
 Random, Uniform, Clumped  based on food
◦ Age distribution (proportion of each age)
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Changes called Population dynamics
◦ Respond to environmental stress & change
Clumped
(elephants)
Uniform
(creosote bush)
Random
(dandelions)
Clumped is most common because resources have a patchy
distribution.
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4 variables govern changes in population size
◦ Birth, Death, Immigration, emigration
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Variables are dependent on resource
availability & environmental conditions
Population change = (Birth + Immigration)–
(Death + Emigration)
POPULATION SIZE
Growth factors
(biotic potential)
Abiotic
Favorable light
Favorable temperature
Favorable chemical environment
(optimal level of critical nutrients)
Biotic
High reproductive rate
Generalized niche
Adequate food supply
Suitable habitat
Ability to compete for resources
Ability to hide from or defend
against predators
Ability to resist diseases and parasites
Ability to migrate and live in other
habitats
Ability to adapt to environmental
change
© 2004 Brooks/Cole – Thomson Learning
Decrease factors
(environmental resistance)
Abiotic
Too much or too little light
Temperature too high or too low
Unfavorable chemical environment
(too much or too little of critical
nutrients)
Biotic
Low reproductive rate
Specialized niche
Inadequate food supply
Unsuitable or destroyed habitat
Too many competitors
Insufficient ability to hide from or defend
against predators
Inability to resist diseases and parasites
Inability to migrate and live in other
habitats
Inability to adapt to environmental
change
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Capacity for growth = Biotic potential
Rate at which a population grows with
unlimited resources is intrinsic rate of increase
(r)
High (r) (1)reproduce early in life, (2)short
generation time, (3)multiple reproductive
events, (4)many offspring each time
BUT – no population can grow indefinitely
Always limits on population growth in nature
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Environmental resistance = all factors which
limit the growth of populations
Population size depends on interaction
between biotic potential and environmental
resistance
Carrying capacity (K) = # of individuals of a
given population which can be sustained
infinitely in a given area
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Carrying capacity established by limited resources
in the environment
Only one resource needs to be limiting even if
there is an over abundance of everything else
Ex. Space, food, water, soil nutrients, sunlight,
predators, competition, disease
A desert plant is limited by…
Birds nesting on an island are limited by…
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(r) depends on having a certain minimum
population size MVP – minimum viable
pop.
Below MVP
◦ 1 – some individuals may not find mates
◦ 2 – genetically related individuals reproduce
producing weak or deformed offspring
◦ 3 – genetic diversity may drop too low to enable
adaptation to environmental changes –
bottleneck effect
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Exponential growth  starts slow and proceeds
with increasing speed
◦ J curve results
◦ Occurs with few or no resource limitations
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Logistic growth  (1) exponential growth, (2)
slower growth (3) then plateau at carrying
capacity
◦ S curve results
◦ Population will fluctuate around carrying capacity
© 2004 Brooks/Cole – Thomson Learning
Population size (N)
Population size (N)
K
Time (t)
Exponential Growth
Time (t)
Logistic Growth
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In rapid growth population may overshoot
carrying capacity
◦ Consumes resource base
◦ Reproduction must slow, Death must increase
◦ Leads to crash or dieback
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Carrying capacity is not fixed, affected by:
◦ Seasonal changes, natural & human catastrophes,
immigration & emigration
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Density Independent Factors: effects regardless
of population density
Mostly regulates r-strategists
◦ Floods, fires, weather, habitat destruction, pollution
◦ Weather is most important factor
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Density dependent Factors: effects based on
amount of individuals in an area
Operate as negative feedback mechanisms
leading to stability or regulation of population
External Factors
◦ Competition, predation, parasitism
◦ Disease – most epidemics spread in cramped conditions
Internal Factors
◦ Reproductive effects  Density dependent fertility,
Breeding territory size
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Over longer time spans populations cycle
Canadian lynx & Snowshoe hare - 10 year cycles
Once thought that predators controlled prey #’s
 Top down control
Now see a negative feedback mechanism in place
 community equilibrium
Population size (thousands)
160
140
Hare
120
Lynx
100
80
60
40
20
0
1845
1855
1865
1875
1885
1895
Year
1905
1915
1925
1935
5,000
Moose population
Wolf population
3,000
100
90
80
2,000
70
60
50
40
1,000
30
20
500
10
0
1900 1910
1930
1950
Year
1970
1990
2000
1999
Number of wolves
Number of moose
4,000
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Two idealized categories for reproductive patterns but
really it’s a continuum
r-selected & K-selected species depending on
position on sigmoid population curve
r-selected species: (opportunists) reproduce early,
many young few survive
◦ Common after disturbance, but poor competitors
K-selected species: (competitors) reproduce late, few
young most survive
◦ Common in stable areas, strong competitors
Carrying capacity
K
Number of individuals
K species;
experience
K selection
r species;
experience
r selection
Time
r-Selected Species
cockroach
dandelion
Many small offspring
Little or no parental care and protection of offspring
Early reproductive age
Most offspring die before reaching reproductive age
Small adults
Adapted to unstable climate and environmental
conditions
High population growth rate (r)
Population size fluctuates wildly above and below
carrying capacity (K)
Generalist niche
Low ability to compete
Early successional species
K-Selected Species
elephant
saguaro
Fewer, larger offspring
High parental care and protection of offspring
Later reproductive age
Most offspring survive to reproductive age
Larger adults
Adapted to stable climate and environmental
conditions
Lower population growth rate (r)
Population size fairly stable and usually close
to carrying capacity (K)
Specialist niche
High ability to compete
Late successional species
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Most organisms somewhere in the middle
Agriculture  crops = r-selected, livestock =
K-selected
Reproductive patterns give temporary
advantage
Resource availability determines ultimate
population size
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1.
2.
3.
Different life expectancies for different species
Survivorship curve: shows age structure of
population
Late loss curve: K-selected species with few
young cared for until reproductive age
Early loss curve: r-selected species many die early
but high survivorship after certain age
Constant loss curve: intermediate steady
mortality
Percentage surviving (log scale)
100
10
1
0
Age
1.
2.
3.
4.
5.
6.
7.
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Fragmenting & degrading habitats
Simplifying natural ecosystems
Using or destroying world primary
productivity which supports all consumers
Strengthening pest and disease populations
Eliminating predators
Introducing exotic species
Overharvesting renewable resources
Interfering with natural chemical cycling and
energy flow
Environmental Stress
Organism Level
Population Level
Ecosystem Level
Physiological changes
Psychological changes
Behavior changes
Fewer or no offspring
Genetic defects
Birth defects
Cancers
Death
Change in population size
Change in age structure
(old, young, and weak may die)
Survival of strains genetically
resistant to stress
Loss of genetic diversity
and adaptability
Extinction
Disruption of energy flow through
Disruption
of biogeochemical
food chains
and webs
cycles
Disruption of biogeochemical
Habitat
cyclesloss & degradation
Lower species
species diversity
diversity
Lower
Less
complex
food
webs
Habitat loss or degradation
Lowercomplex
stabilityfood webs
Less
Ecosystem
collapse
Lower
stability
Ecosystem collapse
© 2004 Brooks/Cole – Thomson Learning
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Use dichotomous keys, field guides,
observe a museum collection, or consult an
expert
http://www.earthlife.net/insects/orderskey.html#key
Sample key for insect ID
http://people.virginia.edu/~sosiwla/Stream-Study/Key/Key1.HTML
Macroinvertebrate key
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Used for fish & wildlife populations
Traps placed within boundaries of study area
Captured animals are marked with tags, collars, bands
or spots of dye & then immediately released
After a few days or weeks, enough time for the
marked animals to mix randomly with the others in
the population, traps are set again
The proportion of marked (recaptured) animals in the
second trapping is assumed equal to the proportion of
marked animals in the whole population
Repeat the recapture as many times as possible to
ensure accuracy of results
Marking method should not affect the survival or
fitness of the organism
# of recaptures in second catch
Total # in second catch
=
# marked in the first catch
Total population (N)
Assuming no births, deaths, immigration, or emigration 
population size is estimated as follows (Lincoln Index)
N
= (# marked in first catch) (Total # in second catch)
# of Recaptures in second catch
MEMORIZE THIS EQUATION
50 snowshoe hares are captured in box
traps, marked with ear tags and released.
Two weeks later, 100 hares are captured
and checked for ear tags. If 10 hares in the
second catch are already marked (10%),
provide an estimate of N
N = (50 hares x 100 hares) / 10 = 5000 / 10
= 500 hares
**Realize for accuracy that you would
recapture multiple times and take an
average**
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2.
3.
4.
5.
6.
Used for plants or sessile organisms
Mark out a gridline along two edges of an area
Use a calculator or tables to generate two random
numbers to use as coordinates and place a quadrat
on the ground with its corner at these coordinates
Count how many individuals of your study
population are inside the quadrat
Repeat steps 2 & 3 as many times as possible
Measure the total size of the area occupied by the
population in square meters
Calculate the mean number of plants per quadrat.
Then calculate the population size with the following
equation
N = (Mean # per quadrat) (total area)
Area of each quadrat
This estimates the population size in an area
Ex. If you count an average of 10 live oak trees per square
hectare in a given area, and there are 100 square
hectares in your area, then
N = (10 X 100 hectare2) / 1 hectare2 = 1000 trees in the
100 hectare2
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Density = # of individuals per unit area
◦ Good measure of overall numbers
Frequency = the proportion of quadrats sampled
that contain your species
◦ Assessment of patchiness of distribution
% Cover = space within the quadrat occupied by
each species
◦ Distinguishes the larger and smaller species
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Necessary because populations may change
over time through processes like succession
But also because human activities may impact
a population and we want to know how
◦ Impacts include  toxins from mining, landfills,
eutrophication, effluent, oil spills, overexploitation
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Can still use CMR or quadrat method
Just do it repeatedly over time
Also could use satellite images taken over time
1. Do pre and post impact assessments in one
area
2. Measure comparable areas – one impacted, one
not at a given time
Overexploitation, Agricultural use, Global Warming have
Caused a decrease in Lake Chad’s area over last 50 years
Lake
Chad
Satellite
Images
Practice Problems
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In a mark – recapture study of lake trout
populations, 40 fish were captured, marked
and released. In a second capture 45 fish
were caught; 9 of these were marked. What
is the estimated number of individuals in the
lake trout population
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Woodlice are terrestrial crustaceans that live
under logs and stones in damp soils. To assess
the population of woodlice in an area, students
collected as many of the animals as they could
find, and marked each with a drop of fluorescent
paint. A total of 303 were marked. 24 hours
later, woodlice were collected again in the same
place. This time 297 were found, of which 99
were seen to be already marked from the first
time. What approximately, is the estimated
population of woodlice in this area?
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2.
3.
4.
5.
Dispersion patterns
Carrying capacity and limiting factors
r and K selection
Natural population cycles
Human effects
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http://www.otterproject.org