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Eastern Gray Squirrel Ecology and Interactions with Western Gray Squirrels
Eastern Gray Squirrel Ecology and Interactions with Western Gray Squirrels
Aaron Johnston School of Forest Resources ∙ ∙University of Washington
Aaron Johnston School of Forest Resources ∙ ∙University of Washington
Photo: Rod GilbertPhoto: Mary Linders
Eastern Gray Squirrel
Photo: Mary Linders
Verts and Carraway (1998)
Eastern Gray Squirrel Introductions
Western Gray Squirrel
Photo: Rod Gilbert
Verts and Carraway 1998
Current Distribution of Western Gray Squirrels
Linders and Stinson (2007)
KLICKITAT COUNTY
PUGET TROUGH
NORTH CASCADES
Objective: Investigate competition
• Are they competing? – Test for competitive effects
• How are they competing?– Describe and compare
components of the niche
Niche
Diet
Shelter
Habitat Behavior
Use of time
Use of space
Niche
ENVIRONMENTAL GRADIENT
AB
UN
DA
NC
E
Resource Partitioning
ENVIRONMENTAL GRADIENT
AB
UN
DA
NC
E
Competitive Exclusion Principle
ENVIRONMENTAL GRADIENT
AB
UN
DA
NC
E
Photo: David J. Slater
InterferenceExploitation
Competition
Patch 1Patch 2
Patch 3
Ideal Free Distribution
Patch 1Patch 2
Patch 3
Equilibrium
Density Dependent Habitat Selection
DENSITY
HA
BIT
AT
QU
ALI
TY
Photo: Danielle Reese
Methods
Utilization Distributions
Measuring Spatial Overlap
0.5 Km
EASTERN WESTERN
0
10
20
30
40A
RE
A (
Ha
)
FEMALE GRAY SQUIRREL HOMERANGES
t15 = 5.36, P = 0.0001
EASTERN WESTERN E/W W/E
-5
0
5
10
% O
VE
RL
AP
FEMALE-FEMALE SPATIAL OVERLAP
F3,30 = 2.89, P = 0.052
Utilization Distributions
0.5 Km
1 Km
Eastern Western
DIS
TAN
CE T
O W
ETLA
ND
(m)
Distance to Wetland
P < 0.001, df = 33
Shrub Cover
WesternEastern
% S
hrub
Cov
er
P = 0.007, df = 33
Shrub Height
Shru
b H
eigh
t (m
)
Eastern Western
P < 0.001, df = 33
Western Gray Squirrel Habitat
Eastern Gray Squirrel Habitat
ENVIRONMENTAL GRADIENT
AB
UN
DA
NC
EEastern Western
H0: There is no difference between eastern and western gray squirrels in their selection of habitat.
GIS Layers
Habitat Plots
Nest Plots
Habitat Analysis
Methods: Habitat measurements
Habitat Plot
OVERSTORY
COMPOSITION STRUCTUREDIVERSITY
UNDERSTORY
F7,152 = 8.6, P < 0.001
ebh enh enl ebl wnl wbh wbl wnh2.64 2.58 1.97 1.77 1.25 1.13 1.04 0.98
Total Understory
ebh ebl enh enl wbh wbl wnh wnl
01
23
4
Methods: Removal Experiment
• Randomized block design– Site = Experimental unit– Removal treatment
assigned randomly to a set of sites in 2009 and another set in 2010
1 Km
Eastern gray squirrel Western gray squirrel
Wetland
Trap
BEFORE AFTER
-0.1
0.4
0.9
1.4
% O
VE
RL
AP
OVERLAP BEFORE AND AFTER EASTERN GRAY SQUIRREL REMOVAL
t16 = 0.133, P = 0.896
Hmmm…
SummarySummary
• Territorial behavior and possible interspecies avoidance
• Differential habitat selection
• More to come on resource use and removal effects
• Territorial behavior and possible interspecies avoidance
• Differential habitat selection
• More to come on resource use and removal effects
Photo: Brett PetersPhoto: Brett Peters
Photo: ODFWPhoto: ODFW
Photo: Danielle Reese
AcknowledgementsWDFW – Gene Orth, Matt Vander Haegen, Caitlin McIntyre, AnnMarie Prince, Mary Linders
Fort Lewis – Todd Zuchowski, Dave Clouse
Nature Conservancy – Cheryl Fimbel, Sanders Freed
Volunteers – Danielle Reese, Val Filer, Sara Gregory, Amy Stratton, Scotty Hardwick, Cindi Perez, Tadd Wheeler, Rachel Lipsky, Jesse McCarty
Committee – Steve West, Matt Vander Haegen, John Marzluff, Josh Lawler, Jim Kenagy
Photo: Danielle Reese
