Population

Reproduction, births, natality (B)

Mortality, death (D)

Emigration (E)Immigration (I)

Population growth

Adult survival, juvenile survival, and fecundity are what we need to estimate λ, the intrinsic population growth rate.

Winter Wren

Reserve Changing Developed

La

mb

da

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Sink / declining

Stable population

Source/ growing populations

Landscape Species Fecundity var Adult se Juv se λ Upper λ *Developed American Robin 0.59 0.08 0.4 0.15 0.13 0.08 0.5416 0.962

Bewick's Wren 0.92 0.88 0.29 0.14 0.08 0.05 0.4526 0.9243Dark-eyed Junco 1.37 0.15 0.5 0.17 ** 0.7543 1.158Song Sparrow 1.13 0.46 0.54 0.03 0.21 0.04 0.827 1.022Spotted Towhee 0.57 0.12 0.5 0.06 0.18 0.05 0.6563 0.8795Swainson's Thrush 0.40 0.07 0.46 0.07 0.16 0.05 0.5719 0.7886Winter Wren 1.23 0.08 0.35 0.19 0.11 0.08 0.5823 1.207

Changing American Robin 0.89 0.16 0.55 0.12 0.18 0.08 0.7606 1.102Bewick's Wren 0.78 1.33 0.32 0.08 0.08 0.03 0.4566 0.7325Dark-eyed Junco 1.10 0.38 0.47 0.09 0.14 0.05 0.6924 0.9812Song Sparrow 1.23 0.21 0.54 0.02 0.18 0.03 0.8125 0.9273Spotted Towhee 0.82 0.46 0.55 0.03 0.18 0.03 0.7475 0.9013Swainson's Thrush 0.40 0.07 0.53 0.04 0.17 0.04 0.6368 0.7744Winter Wren 0.61 0.33 0.38 0.08 0.1 0.03 0.5016 0.7522

Reserve American Robin 0.80 0.13 0.71 0.22 0.31 0.23 0.9666 1.443Bewick's Wren 0.84 0.16 0.14 0.06 0.03 0.02 0.2435 0.4885Dark-eyed Junco 0.55 0.50 0.5 0.17 0.15 0.09 0.6308 1.176Song Sparrow 0.81 0.37 0.51 0.06 0.16 0.04 0.6962 0.9349Spotted Towhee 0.74 0.15 0.54 0.06 0.18 0.04 0.724 0.9245Swainson's Thrush 0.50 0.06 0.59 0.1 0.21 0.08 0.7332 0.9873Winter Wren 0.61 0.09 0.54 0.12 0.18 0.08 0.6974 1.057

* Upper 95% CI Limit of parameters used for calculating λ

** Changing Juv survival estimate used in calculating λ

Apparent Survival

From Oleyar et al. (in prep)

No obvious response in growth rate by landscape.

Spotted Towhee

Reserve Changing Developed

La

mb

da

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Song Sparrow

Reserve Changing Developed

La

mbd

a

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Declining λ outside of reserves?American Robin

Reserve Changing Developed

La

mb

da

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Swainson's Thrush

Reserve Changing Developed

La

mb

da

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Winter Wren

Reserve Changing Developed

La

mb

da

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Possible sink during development for some species followed by recovery as subdivision ages?

Dark-eyed Junco

Reserve Changing Developed

La

mb

da

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Bewick's Wren

Reserve Changing Developed

La

mb

da

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Num

ber

dete

cted

with

in

50m

dur

ing

10m

ins

0.0

0.5

1.0

1.5

2.0 Winter WrenAmerican RobinSwainson's Thrush

Num

ber

det

ect

ed

with

in

50

m d

uri

ng

10

min

s

0.0

0.5

1.0

1.5

2.0

1999 2000 2001 2002 2003 2004 2005 2006 2007

Num

ber

det

ect

ed

with

in

50

m d

uri

ng

10

min

s

0.0

0.5

1.0

1.5

2.0

Year

Reserves

Developed

Changing

How do these projections match up with what we see out there?

•Winter Wren numbers high and ‘stable’ in reserves, low and/or declining elsewhere

•Robin numbers ‘stable’ but low in reserves, highest in developed residential areas

•Are developed landscapes ecological traps for Robins?

Populations fluctuate due to

• Density dependent factors– Ex: Predation, competition, habitat availability

– change population growth in predictable ways

– N is driven by population density

• Density independent factors– Random or Stochastic events

– Ex. Weather, accidents

– Breeding

14 aug 2007

time

# ofAnimals

(N)

Definitions

• Population regulation: the tendency of population sizes to stay within a certain range

time

# ofAnimals

(N)

k

Carrying capacity (k): the number of organisms that can be supported by a given area; the actual number of organisms fluctuates near this

Carrying capacity

Population fluctuationsCarrying capacity (k)

Classic growth curve,unlimited resources

Classic growth curve,limited resources (k)

time time

N N

k

Example of unlimited growth:Australian rabbit (European hare)

• 1859: 24 hares introduced (for human food?)• 1865: over 20,000 hares were harvested, actual population much greater.• Mid-1800’s to mid-1900’s: major problem with too many hares; caused habitat destruction and reduction in native mammals• 2000: still present, local problems

Population fluctuations

No rabbitsRabbits exceeded k

Rabbit-proof fence

Carrying capacity

High food addition

Low food addition

No food added

Shaded area is winter

Townsend’s vole

Population regulation: food

Population cycles: Ex. peaks in lynx populations show time lag behind peaks in snowshoe hare populations

Pop

ulat

ion

size Snowshoe hare

Lynx

Time (years)

Population regulation: food

Population regulation: climate

• Competition – demand by 2 or more individuals of the same or different species for a common resource

• Between 2 individuals of same species: Intraspecific• Between 2 individuals of different species: Interspecific

• Limited supply of resource: Exploitation• Not limited but interaction detrimental: Interference

Population regulation: competition

Inter- or Intraspecific competition?Exploitation or Interference competition?

Population regulation: competition

Niche: an n-dimensional hypervolume which includes the range of biological and physical conditions under which an organism can exist, including the resources that an animal must exploit for growth and reproduction

A portion of the feeding niche of the Blue-gray Gnatcatcher (Smith & Smith 1998)

Prey length (mm)

Fo

rag

ing

he

igh

t (m

)

Niche

• Food sources (both what and where)

• Nest or Den sites• Interspecific competition can

lead to resource partitioning, and expression of a ‘realized niche’ versus a species ecological niche.

Interspecific Competition

Predator-Prey Relationships

What are predators?

• Animals that kill and eat other animals (prey)• At or near the top of the trophic pyramid

Major predators of the Arctic NWR

Polar Bear Grizzly Bear

Wolf

Ermine

Arctic fox Snowy Owl

Predation in Natural Communities

Almost all animals have significant predators- exceptions are:

Herbivores: Top predators:

Bison Grizzly bear

Elephant Lions

Rhinoceros Polar bear

Hippopotamus Killer Whale

Human Attitudes and Predators

• Human perspectives– Little Red Riding Hood

– The Three Little Pigs

• Human persecution

Why?

• Domestication of animals• Protection• Entertainment

Overcoming History

• Old attitudes die hard

• Urban residents and predators

Predator-Prey RelationshipsResponse to Prey

Functional Response• Tendency of the predator to eat more of a prey

species as the prey become more abundant

Predator-Prey Relationships

Functional Response

0

20

40

60

80

0 20 40 60

Prey Density

# P

rey

Att

ac

ke

d

0

20

40

60

80

0 20 40 60

Prey Density

# P

rey

Att

ac

ke

d

Predator-Prey RelationshipsResponse to Prey

Numerical Response• Number of predators increases with an increase in the

density of prey animals

Predator-Prey RelationshipsNumerical Response

(Buckner and Turnock 1965)

High Density

(N/km2)

Low Density

(N/km2)

Sawfly Juveniles 5,280,000 98,800

Sawfly adults 507,500 11,600

Birds 58.1 31.1

Annual cycle of a prey populationPerc

en

tag

e o

f Pop

ula

tion

Energy shortages

Accidents

Disease

Predation

Predation

Disease

Accidents

Energy shortages

J F M A M J J A S O N D

100

Population Cycles

Population Cycles

Adaptations to cyclical prey cycle?

Dispersal Prey switchReproduction

Isle Royale

Isle Royale

• Size: 45 miles long x 9 miles wide• Protection: National Park established in 1940

Wilderness designation in 1976

National Biosphere Reserve 1980• A location of a long term study of the relationships

between the moose and gray wolf

Historically, two large ungulates occupied Isle Royale:

Woodland Caribou Moose

Isle Royale

Settlers arrived in late 19th centuryResponsible for fire and forest cutting

Moose cross ice from Minnesota and establish early 20th century

Fires change old-growth coniferous forests to younger deciduous forests

Moose outcompete woodland caribouCaribou became extinct on the island

Wolves arrive 1950 by crossing ice

Wolf Response to Moose

Functional Response: lots of moose• Possible because wolves are cooperative hunters

Numerical Response: lots of moose• wolves reproduce well

• Immigration is unlikely since it depends on Lake Superior freezing (uncommon)

Moose Response to the Wolf

• Most vulnerable moose are the very young and the old (infirm)

• Most killed moose show signs of malnutrition and disease (i.e. they are more vulnerable)

• Males most vulnerable: go into winter in relatively poor shape because of rut

Wolf Population

Three major factors that control the wolf population:

1. Moose numbers

2. Linear dominance hierarchy in wolf population

3. Genetic diversity (inbreeding effects)