a few more thoughts regarding predator prey / resource consumer dynamics and population regulation:...
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![Page 1: A few more thoughts regarding predator prey / resource consumer dynamics and population regulation: Food webs From: Bolen and Robinson (2003)](https://reader035.vdocuments.net/reader035/viewer/2022062519/5697bfbf1a28abf838ca343b/html5/thumbnails/1.jpg)
A few more thoughts regarding predator prey / resource consumer dynamics and population regulation:
Food webs
From: Bolen and Robinson (2003)
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A few more thoughts regarding predator prey / resource consumer dynamics and population regulation:
Top-down vs Bottom-up regulation
From: Bolen and Robinson (2003)
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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
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In this setting the sea otter is considered a keystone species
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In this setting the sea otter is considered a keystone species
From Groom et al, 2006
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Factors affecting population size and persistence: a quick review
• Species life history characteristics• Density-dependent factors• Density-independent factors• Intraspecific and Interspecific relationships
AND…• interconnectedness/interaction between populations
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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
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MetapopulationMountain Sheep in Southern CA (Bleich et al. 1990)
Range of Total Population (within fenced highways)
SubpopulationsArea temporarily unoccupied
Interpatch movement
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What is Habitat?
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What is Habitat?
Scale?
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Urban sprawl in eastern King County, Washington, USA(1974 1998)
Habitat loss, fragmentation and alteration
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edgeinterior
Habitat Loss & Fragmentation
• Overall loss of habitat (% cover)• Isolates remaining habitat• Increases edge habitat
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Major causes• overgrazing• deforestation• agriculture• fuelwood• urbanization• industry• pollution/contaminants
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Stages of fragmentation
• stage 1: dissection
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Stages of fragmentation
• stage 1: dissection• stage 2: perforation
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Stages of fragmentation
• stage 1: dissection• stage 2: perforation• stage 3: fragmentation
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Stages of fragmentation
• stage 1: dissection• stage 2: perforation• stage 3: fragmentation• stage 4: attrition
**consider biological processes operating at different stages**
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Stages of fragmentation
• stage 1: dissection• stage 2: perforation• stage 3: fragmentation• stage 4: attrition
Matrix
Habitat for species ‘x’
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Population and community-level consequences of fragmentation
• interrupts ecological patterns and processes– e.g. species interactions, behavior, dispersal, etc.
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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
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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
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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 speciesSteller’s Jay
Brown-headed Cowbird
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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
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• size and edge effects– role of edge area vs. shape
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• Brood parasite
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An eastern phoebe nest with a parasitic brown-headed cowbird chick. Courtesy of Jeffrey Hoover.
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Songbird disappearance
• Eastern U.S.
• Artificial nests
Predation rates 70% in suburbs, 2% in Smokies
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Population and community-level consequences of fragmentation
• 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
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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
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Processes operating between fragments
• dispersal• matrix
– disturbed/converted habitat surrounding fragments
– potential roles?
matrix
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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?
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Grizzly bear
• 50,000 historic estimate• Persecution and habitat
changes == about 1,200 wild grizzlies remain in lower 48
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Grizzly bear ecosystems
http://www.fws.gov/mountain-prairie/species/mammals/grizzly/
<20
0? >500
40-50 30-40 ?
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Y2YYukon 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
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Cascade Land Conservancy
In conjunction with members of communities, work toward large-scale conservation
• Habitat Lands• Farmland• Working Forests• Parks, Trails and Open Spaces• Shorelines and Estuaries
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