Transcript Population dynamics

A few more thoughts regarding predator prey / resource consumer
dynamics and population regulation:
Food webs
From: Bolen and
Robinson (2003)
A few more thoughts regarding predator prey / resource consumer
dynamics and population regulation:
Top-down vs Bottom-up regulation
From: Bolen and
Robinson (2003)
A few more thoughts regarding predator prey /
resource consumer dynamics and population
regulation:
Trophic cascade:Loss of key species in a
community sparks indirect effects and subsequent
changes to biological communities.
Classic example:
Kelp, Sea Otters, Sea Urchin
In this setting the sea otter is considered a keystone species
In this setting the sea otter is considered a keystone species
From Groom et al, 2006
Factors affecting population size and persistence:
a quick review
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Species life history characteristics
Density-dependent factors
Density-independent factors
Intraspecific and Interspecific relationships
AND…
• interconnectedness/interaction between populations
Interactions and interconnectedness of
populations
• Many species exist in more than 1 population
• Metapopulation = population of populations
– set of semi-isolated subpopulations, between which
movement is possible
– linked by immigration and emigration
– subpopulations disappear (extinction) and others appear
(colonization) through time
Metapopulation
Mountain Sheep in Southern CA (Bleich et al. 1990)
Subpopulations
Area temporarily unoccupied
Interpatch movement
Range of Total Population (within fenced highways)
What is Habitat?
What is Habitat?
Scale?
Habitat loss, fragmentation and alteration
Urban sprawl in eastern King County, Washington, USA
(1974  1998)
Habitat Loss & Fragmentation
• Overall loss of habitat (% cover)
• Isolates remaining habitat
• Increases edge habitat
interior
edge
Major causes
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overgrazing
deforestation
agriculture
fuelwood
urbanization
industry
pollution/contaminants
Stages of fragmentation
• stage 1: dissection
Stages of fragmentation
• stage 1: dissection
• stage 2: perforation
Stages of fragmentation
• stage 1: dissection
• stage 2: perforation
• stage 3: fragmentation
Stages of fragmentation
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stage 1: dissection
stage 2: perforation
stage 3: fragmentation
stage 4: attrition
**consider biological
processes operating at
different stages**
Stages of fragmentation
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stage 1: dissection
stage 2: perforation
stage 3: fragmentation
stage 4: attrition
Habitat for
species ‘x’
Matrix
Population and community-level consequences
of fragmentation
• interrupts ecological patterns and processes
– e.g. species interactions, behavior, dispersal, etc.
Population and community-level consequences
of fragmentation
• interrupts ecological patterns and processes
• reduced habitat patch area
– leads to small populations and/or disappearance of populations
Population and community-level consequences
of fragmentation
• interrupts ecological patterns and processes
• reduced habitat patch area
• edge effect
– impacts of non-habitat extend into habitat patch
– effective patch size is smaller
Edge Effects
• Increased nest parasitism
• Brown-headed Cowbird
• Increased nest predation
– Predators edge-affiliated: jays, ravens
• Barriers to movement
• Alter microclimate: drier and warmer
• Positive for some species, negative for
other species
Brown-headed
Cowbird
Steller’s Jay
Population and community-level consequences
of fragmentation
• interrupts ecological patterns and processes
• reduced habitat patch area
• edge effect
– impacts of non-habitat extend into habitat patch
– effective patch size is smaller
• size and edge effects
– role of edge area vs. shape
• Brood parasite
An eastern phoebe nest with a parasitic brown-headed cowbird chick. Courtesy of Jeffrey Hoover.
Songbird disappearance
• Eastern U.S.
• Artificial nests
Predation rates 70% in suburbs, 2% in Smokies
Population and community-level consequences
of fragmentation
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interrupts ecological patterns and processes
reduced habitat patch area
edge effect
increased patch isolation
– decreased successful movement (immigration and emigration)
– increased likelihood of local extinction
Processes operating between fragments
• dispersal
– increasing fragmentation decreasing colonization rates
– leads to decreasing # of species within patch
– increasing risk of local extinction of species within patch
Processes operating between fragments
• dispersal
• matrix
– disturbed/converted habitat surrounding fragments
– potential roles?
matrix
Persistence of populations
• In which directions would you predict net movement of
individuals?
• Which populations are more likely to persist? why? Disappear?
• What are the factors most important in determining a
population’s likelihood to persist?
• Which populations, if they disappear, are most likely to be
recolonized?
Grizzly bear
• 50,000 historic estimate
• Persecution and habitat
changes == about 1,200
wild grizzlies remain in
lower 48
Grizzly bear ecosystems
40-50
30-40
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<20
0?
>500
http://www.fws.gov/mountain-prairie/species/mammals/grizzly/
Y2Y
Yukon to Yellowstone Conservation Initiative
• Goal: maintain and sustain region to allow
wilderness, wildlife, native plants, and natural
processes to function as an interconnected web of life
• Partnerships of NGOs, businesses, foundations,
concerned citizens, scientists
• Based on science
• Balance area needs
Cascade Land Conservancy
In conjunction with members of
communities, work toward largescale conservation
• Habitat Lands
• Farmland
• Working Forests
• Parks, Trails and Open Spaces
• Shorelines and Estuaries