a few more thoughts regarding predator prey / resource consumer dynamics and population regulation:...

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

• 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

MetapopulationMountain Sheep in Southern CA (Bleich et al. 1990)

Range of Total Population (within fenced highways)

SubpopulationsArea temporarily unoccupied

Interpatch movement

What is Habitat?

What is Habitat?

Scale?

Urban sprawl in eastern King County, Washington, USA(1974 1998)

Habitat loss, fragmentation and alteration

edgeinterior

Habitat Loss & Fragmentation

• Overall loss of habitat (% cover)• Isolates remaining habitat• Increases edge habitat

Major causes• 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

• stage 1: dissection• stage 2: perforation• stage 3: fragmentation• stage 4: attrition

**consider biological processes operating at different stages**

Stages of fragmentation

• stage 1: dissection• stage 2: perforation• stage 3: fragmentation• stage 4: attrition

Matrix

Habitat for species ‘x’

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 speciesSteller’s Jay

Brown-headed Cowbird

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

• 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

http://www.fws.gov/mountain-prairie/species/mammals/grizzly/

<20

0? >500

40-50 30-40 ?

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

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