AP Biology

Ch. 53

Introduction to Ecology

and the Biosphere

population

ecosystem

community

biosphere

organism

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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?

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Why Population Ecology? Scientific goal

understanding the factors that influence the size of populations general principles

specific cases

Practical goal

management of

populations increase population size

endangered species

decrease population size

pests

maintain population size

fisheries management

maintain & maximize sustained yield

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Density: A Dynamic Perspective

In most cases, it is impractical or impossible to

count all individuals in a population

Sampling techniques can be used to estimate

densities and total population sizes

• Population size can be estimated by either

Extrapolation from small samples

Index of population size (e.g., number of

nests)

Mark-recapture method

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Mark-recapture method

Scientists capture, tag, and release a random

sample of individuals (s) in a population

Marked individuals are given time to mix back

into the population

Scientists capture a second sample of

individuals (n), and note how many of them are

marked (x)

Population size (N) is estimated by

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sn

x N

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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

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Characterizing a Population

Describing a population

population range

pattern of spacing

density

size of population

1937

1943 1951

1958 1961

1960 1965 1964

1966 1970

1970

1956

Immigration from Africa

~1900

Equator

range

density

Hey, I was

captured

last week and

got marked.

Ha ha! That has a

RFID tag Imbedded.

Expect to be

abducted and

measured periodically

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Population Range

Geographical limitations

abiotic & biotic factors temperature, rainfall, food, predators, etc.

habitat

adaptations to polar biome

adaptations to

rainforest biome

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Changes in range

Range expansions & contractions

changing environment

Woodlands

Grassland, chaparral, and desert scrub

15,000 years ago-glacial period

Alpine tundra

Spruce-fir forests

Mixed conifer forest

0 km

2 km

3 km

1 km Ele

vati

on

(km

)

Present Alpine tundra

Spruce-fir forests

Mixed conifer forest

Woodlands

Grassland, chaparral, and

desert scrub

aspen oak, maple white birch sequoia

result of competition

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Density is the result of an interplay between

processes that add individuals to a population and

those that remove individuals

Immigration- influx of new individuals from other

areas

Emigration - movement of individuals out of a

population

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Births Deaths

Immigration

Emigration

Births and immigration add individuals to

a population. Deaths and emigration

remove individuals from a population.

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At risk populations

Endangered species

limitations to range / habitat

places species at risk

Socorro isopod

Devil’s hole pupfish

Iriomote cat

Northern white rhinoceros

New Guinea tree kangaroo

Iiwi Hawaiian

bird

Catalina Island

mahogany tree

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Population Spacing

Dispersal patterns within a population

uniform

random

clumped

Provides insight into the

environmental associations

& social interactions of

individuals in population

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Clumped Pattern (most common)

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Uniform

Clumped patterns

May result from

direct interactions

between individuals

in the population

territoriality

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Random • The position of each individual is independent

of other individuals

• It occurs in the absence of strong attractions

or repulsions

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Population Size

Changes to

population size

adding & removing

individuals from a

population

birth

death

immigration

emigration

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Population growth rates

Factors affecting population growth rate

sex ratio

how many females vs. males?

generation time

at what age do females reproduce?

age structure

how females at reproductive age in cohort?

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Life table

Demography

Factors that affect growth & decline of

populations

vital statistics & how they change over time

Why do teenage boys pay high car insurance rates?

females males

What adaptations have led to this difference

in male vs. female mortality?

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Survivorship curves Graphic representation of life table

Belding ground squirrel

The relatively straight lines of the plots indicate relatively constant

rates of death; however, males have a lower survival rate overall

than females.

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Age structure

Relative number of individuals of each age What do these data imply about population growth in these countries?

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Survivorship curves

Generalized strategies

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

100 75

Su

rviv

al

pe

r th

ou

sa

nd

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)

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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

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Parental survival

Kestrel Falcons:

The cost of larger

broods to both male

& female parents

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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

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Populations in which individuals have a more

difficult time surviving or reproducing if the

population size is too small

Allee effect

Smaller populations suffer ever

decreasing reproductive success.

The smaller the group size, the

poorer their output of offspring per

individual . . . which leads to even

smaller populations, which have

even poorer reproductive outlooks . .

. and the whole scenario makes the

fight to restore populations a

challenging uphill battle.

Passenger pigeon and

African Wild Dogs

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Trade offs

Number & size of offspring

vs.

Survival of offspring or parent r-selected

K-selected

“Of course, long before you mature,

most of you will be eaten.”

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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

100 75

Su

rviv

al

pe

r th

ou

sa

nd

K-selection

r-selection

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Population growth

change in population = births – deaths

Exponential model (ideal conditions)

dN = riN dt

N = # of individuals

r = rate of growth

ri = intrinsic rate

t = time

d = rate of change

growth increasing at constant rate

intrinsic rate = maximum rate of growth

every pair has

4 offspring

every pair has

3 offspring

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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

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Regulation of population size

Limiting factors

density dependent

competition: food, mates,

nesting sites

predators, parasites,

pathogens

density independent

abiotic factors

sunlight (energy)

temperature

rainfall

swarming locusts

marking territory

= competition

competition for nesting sites

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Stability and Fluctuation

Long-term population studies have challenged

the hypothesis that populations of large

mammals are relatively stable over time

Both weather and predator population can

affect population size over time

For example, the moose population on Isle

Royale collapsed during a harsh winter, and

when wolf numbers peaked

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AP Biology

Wolves Moose

Year

Nu

mb

er

of

wo

lves

Nu

mb

er

of

mo

ose

1955 1965 1975 1985 1995 2005

50

40

30

20

10

0

2,500

2,000

1,500

1,000

500

0

Figure 53.18

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Population Cycles: Scientific Inquiry

Some populations undergo regular boom-and-

bust cycles

Lynx populations follow the 10-year boom-and-

bust cycle of hare populations

Three hypotheses have been proposed to

explain the hare’s 10-year interval

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AP Biology

Snowshoe hare

Lynx

Year

1850 1875 1900 1925

Nu

mb

er

of

hare

s

(th

ou

san

ds)

Nu

mb

er

of

lyn

x

(th

ou

san

ds)

160

120

80

40

0

9

6

3

0

Figure 53.19

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Hypothesis: 1 The hare’s population cycle

follows a cycle of winter food supply

If this hypothesis is correct, then the cycles

should stop if the food supply is increased

Additional food was provided experimentally

to a hare population, and the whole population

increased in size but continued to cycle

These data do not support the first hypothesis

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Hypothesis 2: The hare’s population cycle is

driven by pressure from other predators

In a study conducted by field ecologists, 90%

of the hares were killed by predators

These data support the second hypothesis

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Hypothesis 3: The hare’s population cycle is

linked to sunspot cycles

Sunspot activity affects light quality, which in

turn affects the quality of the hares’ food

There is good correlation between sunspot

activity and hare population size

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The results of all these experiments suggest

that both predation and sunspot activity

regulate hare numbers and that food

availability plays a less important role

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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 loosestrife kudzu

gypsy moth

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Zebra mussel

ecological & economic damage

~2 months

reduces diversity

loss of food & nesting sites

for animals

economic damage

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Purple loosestrife

1968 1978

reduces diversity

loss of food & nesting sites

for animals

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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?

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500

400

300

200

100

0 20 0 10 30 50 40 60

Time (days)

Nu

mb

er

of

cla

do

cera

ns

(p

er

20

0 m

l)

Maximum population size that environment can support with no degradation of 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

ma

le

fu

r s

ea

ls (

tho

us

an

ds

)

Carrying capacity

What’s going on with the plankton?

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Changes in Carrying Capacity

Population cycles

predator – prey

interactions

At what population level is the carrying capacity?

K

K

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Human population growth

What factors have contributed to this exponential growth pattern?

1650500 million

20056 billion

Industrial Revolution

Significant advances in medicine through science and technology

Bubonic plague "Black Death"

Population of… China: 1.3 billion India: 1.1 billion

adding 82 million/year

~ 200,000 per day! Doubling times

250m 500m = y ()

500m 1b = y ()

1b 2b = 80y (1850–1930)

2b 4b = 75y (1930–1975)

Is the human population reaching carrying capacity?

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Distribution of population growth

1

2

3

Time 1950 1900 2000

Developing countries

2050

4

5

6

7

8

9

10

11

0

Developed countries

Wo

rld

po

pu

lati

on

in

billio

ns

World total

uneven distribution of population:

90% of births are in developing countries

uneven distribution of resources:

wealthiest 20% consumes ~90% of resources

increasing gap between rich & poor

What is K for humans? 10-15 billion?

There are choices as

to which future path

the world takes…

the effect of income

& education

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Ecological Footprint 30.2

15.6

6.4

3.7

3.2

2.6

USA

Germany

Brazil

Indonesia

Nigeria

India

Amount of land required to support an individual at standard of living of population

2 0 4 6 8 12 10 14 16 18 20 22 24 26 28 30 32 34

Acres

uneven distribution:

wealthiest 20% of world:

86% consumption of resources

53% of CO2 emissions

over-population or over-consumption?

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Ecological Footprint

Based on land & water area used to produce all resources each country consumes & to absorb all wastes it generates

deficit surplus

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Any

Questions?

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Difficult to count a moving target

Measuring population density

How do we measure how many

individuals in a population?

number of individuals in an area

mark & recapture methods

sampling populations

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Evolutionary adaptations

Coping with environmental variation

regulators

endotherms

homeostasis

(“warm-blooded”)

conformers

ectotherms

(“cold-blooded”)

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Bright blue marble spinning in space

Ecology

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biosphere

ecosystem

community

population

Studying organisms in their environment

organism