Ch 36 Populations (1-3)
Population Dynamics
Population: a group of a particular species that uses the same resources and successfully interbreed
Population Density: # of individuals within a particular area
How large is the area?
How will you count them?
Good luck……
Population Dispersion
How are populations spread out?
Clumped Pattern
What pattern of dispersion would you expect a predator of this fish population to have?
Clumped Pattern
Uniform Dispersion
Random Dispersion
Ch 36 4-6
What Factors Influence Growth?
G = rN
G = growthr = instrinsic rate of increaseN = population size
Growth Rate Examples
• US = 2.1%
• Kenya = 3.9%
G = rN
If r is constant, growth rate would depend only on N
The larger the N, the faster the population growth
Exponential Growth (J curve)
The larger the N, the faster the growth rate
Fig. 36-4a
Time (months)
Pop
ulat
ion
size
(N
)
0 1 2 3 4 5 6 7 8 9 10 11 12
0
50
100
150
200
250
300
350
400
450
500Exponential Growth (J curve)
Logistic Growth (S curve)
G = rN (K-N)/K
Limited by K (carrying capacity)
Carrying capacity= maximum # individuals an ecosystem can hold
Fig. 36-4bb
Year
1915 1925 1935 1945
Bre
edin
g m
ale
fur
seal
s(t
hous
ands
)
0
2
4
6
8
10
Logistic Growth (S curve)
Try these…..
• G = rN (K-N)/K
When N is small in comparison to K, growth rate is high
Ex: N = 1000 K = 10,000 r = 2
• When N is large in comparison to K, growth rate slows
• Ex: N = 9000 K = 10,000 r = 2
• When N is larger than K, the growth rate is negative
If population size is 12,000 and K is 10,000 and r is 2…..
Other factors that affect logistic growth?
• Ecological limits
• Age distribution
• Immigration/emmigration
• Predation
Density Dependent Limiting Factors
They regulate growth rate depending on the number of species within the population:
Ex: Shelter, Food, Water, Competition for mates
Density Independent Factors
• They regulate growth rate and do not depend on the number of species within the population
• Ex. Fire, Drought
Lynx
Snowshoe hare
Lynx
pop
ulati
on s
ize
(tho
usan
ds)
Har
e po
pula
tion
size
(tho
usan
ds)
Year1850 1875 1900 1925
0
40
80
120
160
0
3
6
9
Boom Bust Cycle