Population Ecology

Chapter 53

turtles

Population

Groups of individual of the same species that live in the same placeCharacteristics of populations1. Population range– Area where it occurs

2. Spacing patterns– Spacing of individuals

3. Size

Population range

No population is in all habitatsNo population is static1. Changing environment (receding glaciers)2. Expansion to new areas

Cattle egret

Current

1966

1970

1965 1960

1961

1958

1951

1943

1937

1956

1970

Population

DensityDispersionPattern of spacing

Spacing

1. Randomly spaced– Little interaction

2. Uniformly spaced– Competition for resources

3. Clumped spacing– Uneven distribution of resources– Social interactions (herd, flock, pride)

Dispersion (a) Clumped

(b) Uniform (c) Random

Demography

Statistical study of populationsGrows: births outweigh deathsShrinks: deaths outweigh birthsSex ratios (females > males)Generation time (birth to reproduce)ReproductionSurvivorship curves

Age structure

CohortGroup of individuals that are of the same ageFecundity: Birth rateMortality:Death rateAge structure# of individuals in a given cohort

Survivorship curve

1,000

100

10

10 50 100

II

III

Percentage of maximum life span

Nu

mb

er

of

su

rviv

ors

(lo

g s

ca

le)

I

Factors regulate populations

Cost of reproductionAge at first birthSemelparity:Single birth eventAnnuals/insectsIteroparity:Several births over several years

Factors regulate populations

Carrying capacity K:Maximum population an environment can sustainDensity-dependent effects Increase density decreased birth ratesLight, water, space, food, diseaseDensity-independent effects:Fire, volcano, cold

Carrying capacity

Snowshoe hare

Lynx

Nu

mb

er

of

lyn

x(t

ho

us

an

ds

)

Nu

mb

er

of

ha

res

(th

ou

sa

nd

s)

160

120

80

40

01850 1875 1900 1925

Year

9

6

3

0

Factors regulate populations

K-selection:Density dependent selectionr-selection: Density independent selection

Human growth

Density dependent factors

Competition for resources

Territoriality Intrinsic factors

Disease Predation

Toxic wastes 5 µm

Population pyramids

Fig. 53-26

Less indus-trialized

countries

Indus-trialized

countries

60

50

40

30

20

10

0 0

20

40

80

Lif

e ex

pec

tan

cy (

year

s)

Infa

nt

mo

rtal

ity

(dea

ths

per

1,0

00 b

irth

s)

Less indus-trialized

countries

Indus-trialized

countries

60

Ecological footprint

Log (g carbon/year)

13.49.85.8

Not analyzed

Energy use (GJ):

> 300 < 10150–300 50–150 10–50

Growth

Population growth rate N= change in population sizet = change in timeB=birth rateD=death rate

Growth

B=births during specified timeD= deaths during specified time b= annual per capita birth ratem (mortality)= per capita death rateN is population size

B bND mN

Growth

r = (per capita rate of increase)

r b – m

Nt

rN

Fig. 53-10

Number of generations

0 5 10 150

500

1,000

1,500

2,000

1.0N =dNdt

0.5N =dN

dt

Po

pu

lati

on

siz

e (N

)

Fig. 53-11

8,000

6,000

4,000

2,000

01920 1940 1960 1980

Year

Ele

ph

ant

po

pu

lati

on

1900

Table 53-3

Fig. 53-12

2,000

1,500

1,000

500

00 5 10 15

Number of generations

Po

pu

lati

on

siz

e (N

)

Exponentialgrowth

1.0N=dN

dt

1.0N=dN

dt

K = 1,500

Logistic growth1,500 – N

1,500

Fig. 53-13

1,000

800

600

400

200

00 5 10 15

Time (days)

Nu

mb

er o

f Paramecium

/mL

Nu

mb

er o

f Daphnia

/50

mL

0

30

60

90

180

150

120

0 20 40 60 80 100 120 140 160

Time (days)

(b) A Daphnia population in the lab(a) A Paramecium population in the lab