Ecology
Notes
Populations – Chapter 5
Characteristics of Populations

Population – group of individuals of the same species that
live in the same area.
– 1. geographic distribution – the area inhabited by a
population (range)
Population Density
2. density – number of individuals per unit area.

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Area = L X W
Area = 2m X 1m
Area = 2 meters2
Population Density
= # individuals/area
Population Density
= 6/2 = 3 rabbits
per square meter
1
meters
2 meters
3. Growth – populations may stay constant
or change drastically from year to year.
4 factors affect population size

1.
2.
3.
4.
Natality – birth rate
Mortality – death rate
Immigration – movement of individuals IN
Emmigration – movement of individuals OUT
Average Annual Change
The average rise or fall in a
population per year. Can be positive
or negative
 Formula A.A.C.= change in
pop./years
 Sample Problem
What is the average annual change
of this monkey population?
2001 – Rainforest 125 monkeys
2001-2005 I=10, N=7, E=8, M=3
Change =+6
Average Annual Change =
+6/4yrs.=+1.5 monkeys/year

Exponential vs. Logistic Growth


Exponential growth –
population grows at a
constant rate…with
unlimited resources this will
occur.
Logistic Growth- occurs
when growth slows or stops.
The largest number of
individuals the environment
can support is called the
carrying capacity.
Limiting Factors

Limiting factors cause population growth
to decrease.
– Density dependent – a factor that depends on
population size. Occurs when populations are
large and dense.
 Competititon
 Predation
 Parasitism
 Disease
Density Independent Factors

A factor that affects all populations in
similar ways, regardless of population size.
– Unusual weather
– Natural disaster
– Seasonal cycles
– Human activity