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