Transcript Population Dynamics

Population Dynamics
The study of factors within a
population that effect growth and
distribution of populations.
I. What is a population?
A.
A population is a group of the same
species living in the same given area.
1. Maple Trees in a deciduous forest
2. African Elephants in a particular
region of the jungle
3.Gnats in your kitchen
II. Characteristics that Effect
Population Dynamics
A. Geographic Distribution
 B. Population Size and Density
 C. Growth Rate
 D. Age structure
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A. Geographic Distribution
1. The range a population occupies
2. Dispersion with in the range
a. Clumped (humans in cities)
b. Uniform (tree in an orchard)
Geographical distribution of
the African Elephant
B. Size and Density
1. Size: The number of individuals in a
population
2. Density: The number of individuals in a
given area or volume such as
 100
buffalo km2
 100 mosquitoes m3
C. Growth Rate
*Determined by...
 1. number of births
 2. number of deaths
*Growth Rate = Births / Deaths*
a. if greater then 1 then population is growing
b. if less then 1 population is decreasing
c. if 1 the population is in equilibrium

3. number of individuals that leave or enter
the population
a. immigration(enter the population)
b. emigration (leave the population)
D. Exponential Growth
1. Occurs under ideal conditions
a. abundant food and space
b. no predators or disease
c. reproduction is at a constant rate
** A single bacteria cell can increase to
4,720,000,000,000,000,000,000 bacteria cell in
just one day if allowed to reproduce exponentially.
2. Exponential growth is expressed as a J-graph.
E. Logistic Growth
1. When a population’s growth stops or slows
after exponential growth due to
a. Limiting Factors: Factor that causes a population
to not grow exponentially
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Competition
Predation
Parasitism/Disease
Human Disturbances
Drought or other climate extremes
Limited Resources (nutrients, water, space…)
F. Density Dependent Limiting
Factor
1. effect population only after they reach a
certain level
2. Effect Large Dense Populations most
strongly
3. Do not effect scattered small populations as
much
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Factors include
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competition
predation
parasitism
 disease
G. Competition
1.Occurs among and between populations
a.Mates, Space, Food, Light, Water…
2. Niche: all the biotic and abiotic resources
used by and organism
a. The same population occupies the
same niche and therefore competes for
the same resources.
b. Competition between different
populations results in niche
overlapping.
c. No two species can occupy entirely the
same niche in the same place at the same
time.
H. Predation
*Important mechanism for population control
1. Predator population directly effects and follows prey
population.
2. When Predator population is down, prey is up, resulting in
a rise in predator and fall in prey and the cycle continues.
3. Example: Moose/Wolves of Isle Royale
I. Density Independent Factors
1. Effect all populations regardless of
population size
a. Unusual Weather
b. Seasonal Cycles
c. Certain Human Activities: Clear
cutting Forests, Damming rivers,
J. Carrying Capacity
1. The largest numbers of individuals of a
population an environment can sustain