Population Dynamics
Class Notes
3 Population Characteristics
1. Population density – number of organisms per
unit area
3 Population Characteristics
2. Spatial distribution – based on
dispersion, which is the spacing pattern of
a population within a certain area.
a. Uniform
b. Clumped
c. Random
What do the 3 distribution types look like?
3 Population Characteristics
3. Population Ranges –
organisms are able to
live only in certain
habitats
Ex:The iiwi only lives
on the Hawaiian islands.
Population-Limiting Factors
1. Density-independent factors – any
factor that does not depend on the
density of a population
–
–
–
Typically abiotic
Natural weather events – tornado, tsunami,
drought
Results of human activities – pollution
Population-Limiting Factors
2. Density-dependent factors – any factor that
depends on the population density
– Typically biotic
– Disease – spreads easily in dense populations
– Competition – limited resources
– Parasites-parasites spread like disease
Review
1. The Black Death killed 75 million people at the
beginning of the 20th century. Which size was
the population most likely at that time?
a. Small population, spread out
b. Small population, close together
c. Large population, spread out
d. Large population, close together
d. Large population, close together
Review
2. Which of the following is an example of a
density-independent factor? More than one
is correct.
a. Flood
b. Parasites
c. Deforestation
d. Competition
A and C
Population Growth Rate
• To compute how fast a population is
growing, these must be known:
– Birth rate
– Death rate
– Immigration: when organisms come into a
population
– Emigration: when organisms exit a
population
Models for Population Growth
1. Exponential Growth Model – population
growth with no environmental limits
•
Unlimited resources – food, space, mates
Exponential Growth
• Lag phase – slow
growth period
• J-shaped curve –
exponential growth
J-curve
Lag phase
Models for Population Growth
2. Logistic Growth
Model – population
growth slows,
birth rate is less than
death rate
• S-shaped curve
Lag
phase
Carrying capacity
Logistic Growth
• Carrying capacity – the maximum number of
organisms an environment can support longterm
C.C.is limited by the resources available.
This model explains why and how populations
stabilize.
Review
3. What is emigration?
When organisms exit or leave a population
Review
4. Which model – exponential or logistic – is
more realistic for a population?
Logistic – typically resources are limited in
an environment
R-strategists
Characteristics of R-strategists:
• Small organisms
• Short lifespan
• Produce many offspring
• Expend little energy to raise offspring
R-strategists Examples
K-Strategist
Characteristics of K-strategists:
• Larger organisms
• Longer life span
• Produces few offspring
• Time is invested in care of young
K-Strategist Examples