Population Ecology

population

ecosystem

community

biosphere

organism

Life takes place in populations

Population

group of individuals of same species in

same area at same time rely on same

resources

interact

interbreed

Population Ecology: What factors affect a population?

Why Population Ecology? Scientific goal

understanding the factors that influence the size of populations

Practical goal

management of populations increase population size

endangered species

decrease population size

pests

maintain population size

fisheries management

maintain & maximize sustained yield

Characterizing a Population

Describing a population

population range

pattern of spacing

density

size of population

1937

19431951

19581961

196019651964

1966 1970

1970

1956

Immigrationfrom Africa

~1900

Equator

range

density

Population Spacing

Dispersal patterns within a population

uniform

random

clumped

Provides insight into the

available resources

& social interactions of

individuals in population

Clumped Pattern (most common)

Clumped dispersion

Individuals in patches

Due to resource location

or

social behavior

Figure 52.3a

(a) Clumped. For many animals, such as these wolves,

living in groups increases the effectiveness of

hunting, spreads the work of protecting and caring for

young, and helps exclude other individuals from their

territory.

Uniform

Clumped patterns

May result from

Territoriality or

scarce, but

Uniform resources

Random dispersion

Positions independent of other

individuals

Resources not scarce

Figure 52.3c

(c) Random. Dandelions grow from windblown seeds

that land at random and later germinate.

Density and Dispersion

Density

The number of

individuals per unit

area or volume

Dispersion

The pattern of

spacing among

individuals within

the boundaries of

the population

Births and immigration add individuals to a

population.

BirthsImmigration

PopuIation

size

Emigration

Deaths

Deaths and emigration remove individuals

from a population.

Ways to Count a Population

Direct Count – Count Every Individual

Indirect Count – count every individual in a hive, burrow,town, etc. and then count the number of hives, burrows, etc. Only works for certain clumped organisms

Quadrat – LETS TRY IT

Mark Recapture – LETS TRY IT

Which way gives the best estimate depends on the type of organism being studied

Abiotic factors

sunlight & temperature

precipitation / water

soil / nutrients

Biotic factors

other living organisms

prey (food)

competitors

predators, parasites,

disease

Intrinsic factors

adaptations

Factors that affect Population Size

Life table

Species Survival Strategies

Factors that affect growth & decline of

populations

females males

Survivorship curves Graphic representation of life table

Belding ground squirrel

The relatively straight lines of the plots indicate relatively constant

rates of death

Survivorship curves What do these graphs

tell about survival &

strategy of a species?

0 25

1000

100

Human(type I)

Hydra(type II)

Oyster(type III)

10

1

50

Percent of maximum life span

10075

Su

rviv

al

per

tho

usan

d

I. High death rate in

post-reproductive

years

II. Constant mortality

rate throughout life

span

III. Very high early

mortality but the

few survivors then

live long (stay

reproductive)

Life strategies & survivorship curves

0 25

1000

100

Human(type I)

Hydra(type II)

Oyster(type III)

10

1

50

Percent of maximum life span

10075

Su

rviv

al

per

tho

usan

d

K-selection

r-selection

Reproductive strategies

K-selected

late reproduction

few offspring

invest a lot in raising offspring

primates

coconut

r-selected

early reproduction

many offspring

little parental care

insects

many plants

K-selected

r-selected

Trade-offs: survival vs. reproduction

The cost of reproduction

increase reproduction may decrease

survival

age at first reproduction

investment per offspring

number of reproductive cycles per lifetime

Natural selection

favors a life

history that

maximizes lifetime

reproductive

success

Trade offs

Number & size of offspring

vs.

Survival of offspring or parentr-selected

K-selected

“Of course, long before you mature,

most of you will be eaten.”

Parental survival

Kestrel Falcons:

The cost of larger

broods to both male

& female parents

Population growth

change in population = births – deaths

Exponential model (ideal conditions)

G = riN

N = # of individuals

r = rate of growth

ri = intrinsic rate

G = # of new Individuals

growth increasing at constant rate

intrinsic rate = maximum rate of growth

every pair has

4 offspring

every pair has

3 offspring

African elephant

protected from hunting

Whooping crane

coming back from near extinction

Exponential growth rate Characteristic of populations without

limiting factors

introduced to a new environment or rebounding from a catastrophe

K =

carrying

capacity

Logistic rate of growth

Can populations continue to grow

exponentially? Of course not!

effect of

natural controls

no natural controls

What happens as N approaches K?

500

400

300

200

100

0200 10 30 5040 60

Time (days)

Nu

mb

er

of

cla

do

cera

ns

(per

200 m

l)

Maximum population size that environment can support with no degradationof habitat

varies with changes in resources

Time (years)1915 1925 1935 1945

10

8

6

4

2

0

Nu

mb

er

of

bre

ed

ing

male

fur

seals

(th

ou

san

ds)

Carrying capacity

What’s going on with the plankton?

Regulation of population size

Limiting factors

density dependent

competition: food, mates,

nesting sites

predators, parasites,

pathogens

density independent

abiotic factors

sunlight (energy)

Rainfall

Natural Disasters

swarming locusts

marking territory

= competition

competition for nesting sites

Changes in Carrying Capacity

Population cycles

predator – prey

interactions

At what population level is thecarrying capacity?

K

K

Introduced species

Non-native species

transplanted populations grow

exponentially in new area

out-compete native species

loss of natural controls

lack of predators, parasites,

competitors

reduce diversity

examples

African honeybee

gypsy moth

zebra mussel

purple loosestrifekudzu

gypsy moth

Zebra mussel

ecological & economic damage

~2 months

reduces diversity

loss of food & nesting sites

for animals

economic damage

Purple loosestrife

1968 1978

reduces diversity

loss of food & nesting sites

for animals

Bright blue marble spinning in space

Ecology

biosphere

ecosystem

community

population

Studying organisms in their environment

organism