Transcript Population dynamics

Population growth
Reproduction, births, natality (B)
Immigration (I)
Population
Mortality, death (D)
Emigration (E)
Adult survival, juvenile survival, and fecundity are what we
need to estimate λ, the intrinsic population growth rate.
1.8
Winter Wren
1.6
Source/ growing populations
1.4
Lambda
1.2
Stable population
1.0
0.8
0.6
0.4
Sink / declining
0.2
0.0
Reserve
Changing
Developed
Landscape
Developed
Changing
Apparent Survival
se
Juv
0.15
0.13
0.14
0.08
0.17
**
0.03
0.21
0.06
0.18
0.07
0.16
0.19
0.11
Species
American Robin
Bewick's Wren
Dark-eyed Junco
Song Sparrow
Spotted Towhee
Swainson's Thrush
Winter Wren
Fecundity
0.59
0.92
1.37
1.13
0.57
0.40
1.23
var
0.08
0.88
0.15
0.46
0.12
0.07
0.08
Adult
0.4
0.29
0.5
0.54
0.5
0.46
0.35
American Robin
Bewick's Wren
Dark-eyed Junco
Song Sparrow
Spotted Towhee
Swainson's Thrush
Winter Wren
0.89
0.78
1.10
1.23
0.82
0.40
0.61
0.16
1.33
0.38
0.21
0.46
0.07
0.33
0.55
0.32
0.47
0.54
0.55
0.53
0.38
0.12
0.08
0.09
0.02
0.03
0.04
0.08
0.71
0.14
0.5
0.51
0.54
0.59
0.54
0.22
0.06
0.17
0.06
0.06
0.1
0.12
Reserve
American Robin
0.80
0.13
Bewick's Wren
0.84
0.16
Dark-eyed Junco
0.55
0.50
Song Sparrow
0.81
0.37
Spotted Towhee
0.74
0.15
Swainson's Thrush
0.50
0.06
Winter Wren
0.61
0.09
* Upper 95% CI Limit of parameters used for calculating λ
0.04
0.05
0.05
0.08
λ
0.5416
0.4526
0.7543
0.827
0.6563
0.5719
0.5823
Upper λ *
0.962
0.9243
1.158
1.022
0.8795
0.7886
1.207
0.18
0.08
0.14
0.18
0.18
0.17
0.1
0.08
0.03
0.05
0.03
0.03
0.04
0.03
0.7606
0.4566
0.6924
0.8125
0.7475
0.6368
0.5016
1.102
0.7325
0.9812
0.9273
0.9013
0.7744
0.7522
0.31
0.03
0.15
0.16
0.18
0.21
0.18
0.23
0.02
0.09
0.04
0.04
0.08
0.08
0.9666
0.2435
0.6308
0.6962
0.724
0.7332
0.6974
1.443
0.4885
1.176
0.9349
0.9245
0.9873
1.057
se
0.08
0.05
** Changing Juv survival estimate used in calculating λ
From Oleyar et al. (in prep)
1.8
Song Sparrow
1.6
No obvious response in
growth rate by landscape.
1.4
1.0
0.8
0.6
0.4
0.2
0.0
Reserve
Changing
Developed
1.8
Spotted Towhee
1.6
1.4
1.2
Lambda
Lambda
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Reserve
Changing
Developed
1.8
1.8
Winter Wren
1.4
1.4
1.2
1.2
1.0
0.8
0.8
0.6
0.4
0.4
0.2
0.2
0.0
Reserve
1.8
Changing
Developed
American Robin
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Reserve
Changing
Reserve
Changing
Developed
Declining λ outside of
reserves?
1.6
Lambda
1.0
0.6
0.0
Swainson's Thrush
1.6
Lambda
Lambda
1.6
Developed
1.8
Dark-eyed Junco
1.6
Possible sink during
development for some
species followed by
recovery as subdivision
ages?
1.4
1.0
0.8
0.6
0.4
0.2
0.0
Reserve
Changing
Developed
1.8
Bewick's Wren
1.6
1.4
1.2
Lambda
Lambda
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Reserve
Changing
Developed
•Are developed landscapes
ecological traps for Robins?
Number detected within
50m during 10mins
•Robin numbers ‘stable’ but low
in reserves, highest in
developed residential areas
Number detected within
50m during 10mins
•Winter Wren numbers high and
‘stable’ in reserves, low and/or
declining elsewhere
2.0
2.0
Number detected within
50m during 10mins
How do these projections
match up with what we see
out there?
2.0
Winter Wren
American Robin
Swainson's Thrush
Reserves
1.5
1.0
0.5
0.0
Changing
1.5
1.0
0.5
0.0
Developed
1.5
1.0
0.5
0.0
1999
2000
2001
2002
2003
Year
2004
2005
2006
2007
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
Definitions
• Population regulation: the tendency of population
sizes to stay within a certain range
# of
Animals
(N)
time
Carrying capacity
Carrying capacity (k): the number of
organisms that can be supported by a given
area; the actual number of organisms
fluctuates near this
# of
Animals
(N)
k
time
Population fluctuations
Carrying capacity (k)
k
N
N
time
Classic growth curve,
unlimited resources
time
Classic growth curve,
limited resources (k)
Population fluctuations
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
Carrying capacity
Rabbits exceeded k
No rabbits
Rabbit-proof fence
Population regulation: food
High food addition
Low food
addition
Townsend’s vole
No food
added
Shaded area is winter
Population regulation: food
Population size
Population cycles: Ex. peaks in lynx populations
show time lag behind peaks in snowshoe hare
populations
Snowshoe hare
Lynx
Time (years)
Population regulation: climate
Population regulation: competition
• 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
Inter- or Intraspecific competition?
Exploitation or Interference competition?
Population regulation: competition
Niche
A portion of the feeding
niche of the Blue-gray
Gnatcatcher
(Smith & Smith 1998)
Foraging height (m)
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
Prey length (mm)
Interspecific Competition
• 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.
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
Ermine
Arctic fox
Wolf
Snowy Owl
Predation in Natural Communities
Almost all animals have significant predatorsexceptions 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 Relationships
Response to Prey
Functional Response
• Tendency of the predator to eat more of a prey
species as the prey become more abundant
Predator-Prey Relationships
Prey Attacked
Attacked
## Prey
Functional Response
80
80
60
60
40
40
20
20
00
00
20
20
40
40
Prey
Prey Density
Density
60
60
Predator-Prey Relationships
Response to Prey
Numerical Response
• Number of predators increases with an increase in the
density of prey animals
Predator-Prey Relationships
Numerical Response
(Buckner and Turnock 1965)
Sawfly Juveniles
Sawfly adults
Birds
High Density
(N/km2)
5,280,000
Low Density
(N/km2)
98,800
507,500
11,600
58.1
31.1
Annual cycle of a prey population
Percentage of Population
100
Energy shortages
Energy shortages
Accidents
Disease
Accidents
Predation
Disease
Predation
J
F
M
A
M
J
J
A
S
O
N
D
Population Cycles
Population Cycles
Adaptations to cyclical prey cycle?
Dispersal
Prey switch
Reproduction
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 century
Responsible 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 caribou
Caribou 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)