Transcript Wrangell Red-backed Vole Density Spring 1999

Endemic Small Mammals of
Southeastern Alaska: Evolutionary
Diversity, Ecology, & Conservation
Winston P. Smith
USDA Forest Service, PNW Research Station
Forestry Sciences Laboratory
Juneau, AK 99801-8545 USA
Acknowledgments:
____________________________________________________________________
WRANGELL, THORNE BAY and CRAIG Ranger
Districts, Tongass National Forest.
UAM: Joe Cook, Steve MacDonald, Chris Conroy,
John Demboski, Karen Stone, and Amy Runck.
SPECIAL THANKS:
Jeff Nichols, field crew leader and analytical
support;
Scott Gende, analytical support and comments on
presentation and completion reports.
Lillian Petershoare and JFSL Library.
Background – Setting:
_________________________________________________________________
 Unique attributes
- dynamic recent geological history
- naturally fragmented and isolated habitat
- largest NF and largest remaining
temperate rainforest
- spatial and temporal heterogeneity
 Limited information on natural history
 Depauperate small mammal fauna
 High potential for endemism
Background – Planning:
_________________________________________________________________
 Extensive clearcut logging since 1954:
- 50% of most productive forest on some
islands – 40+% of some watersheds
- >300 yrs to develop old forest features
 TLMP - endemic small mammals ranked as
highest risk of extinction;
 Conservation strategy
- metapopulation framework
- lacks empirical foundation
Land Mammal Fauna
_________________________________________________________________
87 islands + 24 mainland localities
45 land mammal species 65 small (<10kg) mammal taxa:
15 endemic
11 confined
36 widely distributed, 3 unknown;
Mammal fauna – nested structure with varying
genetic divergence:
- colonization rather than extinction;
- significant relationship between isolation
and species richness;
- competition influenced similar species
(e.g., bears, shrews);
Land Mammal Fauna
_________________________________________________________________
- neo-endemics (flying squirrel) and paleoendemics (marten);
- number of endemics on outer
islands suggests glacial refugia;
- some taxa have affinities with eastern NA
forms (e.g., flying squirrel, marten);
Most species – Upper Lynn Canal;
Most endemics – Mainland Subregion;
Ermine show highest degree of endemism with
5 subspecies representing 3 clades. (map)
Mustela erminea
Distribution in SE Alaska
MacDonald and Cook 1996
M. e. arctica
Juneau
M. e. salva *
N
M. e. alascensis
M. e. celenda
M. e. seclusa
.
Peromyscus keeni1
Distribution in SE Alaska
MacDonald and Cook 1996
*Island Endemics
P. k. algidus
*P. k. sitkensis
Juneau
*
N
*P. k. hylaeus
*P. k. oceanicus
1Hogan et al. 1993
.
P. k. macrorhinus
Island Biogeography
Processes: colonization & extinction
Variables: island size, distance from mainland, vagility
island
island
island
island
immigration
Continent
island
island
island
Community Dynamics
and Structure
S=7
S=4
island
island
Continent
S=9
S=3
island
S = 14
island
island
S=3
equilibrium
Extinction
S = 12
Species Richness (S)
Colonization
island
S=5
island
Island area
Faunal Extinctions
island
island
island
N
island
Glacial Advance
Continent
island
island
island
Regional Colonization
island
island
island
N
island
Glacial Retreat
Continent
island
island
island
Photo by P. Myers
Southern red-backed vole
Natural History: Red-backed vole
__________________________________________________________
Nearctic Distribution - in SE Alaska,
southern mainland and nearshore islands;
Mesic forest habitat specialist;
Omnivorous, but primarily eats fungi
(mycophagous) in the Pacific Northwest;
Sensitive to overstory removal and fire in
western coniferous forests;
Influenced by landscape context, but little
evidence of edge effects.
(map)
Clethrionomys gapperi
Distribution in SE Alaska
MacDonald and Cook 1996
*Island Endemics
Juneau
*
N
C. g.
stikinensis
*C. g. wrangeli
*C. g. solus
C. g. phaeus
C. g. saturatus
Prince of Wales Flying Squirrel
Markedly different from
PNW populations
Nocturnal, active yearround
1 litter (2-4 young)/year
Reputed old-growth
habitat specialist
Mycophagist in PNW
Vulnerable to isolation
in managed landscapes
(map)
Glaucomys sabrinus
Distribution in SE Alaska
MacDonald and Cook 1996
G. s. zaphaeus
G. s. alpinus
•
*
N
G. s. griseifrons
.
Juneau
Research
Objectives:
___________________________________
1. Estimate density of red-backed voles and
flying squirrels among habitats;
2. Contrast seasonal abundance, age and
sex composition, body condition,
survival, and reproductive condition of
voles and squirrels among habitats;
3. Examine habitat use and density relative
to microsite and stand-level vegetative
and structural features.
Study
Area
(voles):
________________________________________________
Wrangell Island
4 habitats:
- 3 unmanaged habitats in largely
unmanaged landscapes;
- thinned young growth stands within
watershed with ~40% POG clearcut .
Gap-Phase Old-Growth Forest
Structurally heterogeneous, vertically and
horizontally - large (>150 cm), old (>800 yr) trees.
Northerly
exposure
<500 m
elevation
Fine scale
disturbance
Sitka
spruce/
western
hemlock
Multi-Cohort Old-Growth Forest
Southerly exposure;
Catastrophic disturbance
per 100-200 yr;
Heterogeneous stands of
even-aged patches ;
Uniform diameter, dense
canopy forest: 100-102 ha.
Unmanaged Peatland-scrub/
Mixed-conifer Forest
Structurally complex,
biologically diverse
communities.
Spatially heterogeneous:
from open muskeg to
forest over a scale of
101 – 102 m.
2 replicates in 1
watershed.
Thinned Young
Growth (25 yr-old)
-pre-commercial thinning
2-3 yr prior to study initiation;
-2 replicates within the same
watershed.
Dense understory of
herbaceous and woody
plants and slash.
Study
Design:
______________________________________
Two replicates each of 4 habitats;
 Replicates within the same
watershed but >800 m apart;
1-ha grid (11 X 11) + 8
assessment lines per replicate
with 2 traps per station (n = 242);
Live trap spring 1999-2000 and
early autumn 1998-2000.
Study
Area
(squirrels):
_________________________________________________
North-Central Prince of Wales Island
2 habitats: 1) POG (mostly gap-phase)
and 2) peatland-scrub/mixed-conifer;
1) two ends of a continuum of forest cover;
2) peatland-scrub/mixed-conifer - little
commercial, but potential ecological value.
Study
Design:
____________________________________________
Three replicates each of 2 habitats in
largely unmanaged landscapes;
Replicates in the same watershed but
>1 km apart;
13-ha grid (10 X 10 array of traps);
Live trap spring and early autumn
1998-2000.
RESULTS:
Demography
Mean Effective Area Sampled:
Wrangell Red-backed Voles
First estimates for red-backed voles, which
precludes comparison of density with earlier
studies;
Effective area sample was an order of
magnitude larger than grid;
Effective area sampled was significantly
greater in gap-phase old-growth than in
other habitats – relative comparisons among
habitats are therefore invalid.
Wrangell Red-backed Vole Density
Spring 1999 - 2000
Density higher in 1999 than 2000 with
significant differences in multi-cohort and
gap-phase old-growth;
Density lower in peatland/mixed-conifer in
both years but significant only in 1999.
Wrangell Red-backed Vole Density
Autumn 1998 - 2000
Density higher in 1998 than 1999 or 2000
with significant differences in all habitats;
Peatland/mixed-conifer consistently had
lowest densities of voles with significant
differences in 1999 and 2000;
Some evidence that thinned YG may
serve as a habitat sink.
Wrangell Red-backed Vole Population
Attributes among Habitats
Age and sex ratios were similar among
habitats;
Summer survival and percentage of
reproductive females were significantly
lower in YG than other habitats – winter
survival also was lower but not statistically
significant.
Prince of Wales Flying Squirrel
Seasonal Movements
Mean maximum distance moved was
similar between habitats and seasons,
averaging about 110 yards;
Home ranges also were similar between
seasons and and habitats and ranged
from about 5.5 acres to about 9.5 acres.
POW Flying Squirrel Density
Spring 1999 - 2000
Density (ha)
3
2
1999
2000
1
0
Upland-OG
Peatland-MC
Habitat
POW Flying Squirrel Density
Autumn 1998 - 2000
Density (ha)
5
4
3
2
1
0
Upland-OG
Peatland-MC
Habitat
Reproductive
1998
1999
2000
Female x 10
POW Flying Squirrel
Survival and Productivity
Percentage (%)
90
80
70
60
50
Upland-OG
40
30
Peatland-MC
20
10
0
Sum m er
Survival
Winter Survival %Reproductive
Population Attributes
Recruitm ent
Densities in the Pacific Northwest
Location
Density
Source
(ha)
Washington
0.50
Carey (1995)
Western Oregon
2.30
Rosenberg and
Anthony (1992)
SW Oregon
0.85
Witt (1992)
NE California
2.76 - 3.48
SE Alaska
Peatland-MC
Upland-OG
1.5 – 2.0
2.2 – 4.0
Waters and
Zabel (1995)
Smith and
Nichols (2002)
Why?
Hypotheses
Competitive release
Reduced predation pressure
Diet
RESULTS:
Habitat Relations
Logistic Regression Model – Spring 1999-2000:
Red-backed Voles
Deciduous shrub cover (+) within 1.5 meters
of the forest floor was the most significant
variable influencing vole microhabitat
selection overall:
by a factor of 2 in multi-cohort OG and 3 in
peatland/mixed-conifer.
Moss cover (-), density of stumps (+) and
density of small snags and saplings (+) were
correlates of microhabitat use in gap-phase,
thinned YG, and peatland/mixed-conifer.
Logistic Regression Model - Autumn 1999-2000:
Red-backed Voles
Deciduous cover again had the greatest
influence on microhabitat selection overall:
- cover between 0.3 – 1.5 m had 2-fold
(-) in gap-phase;
- cover < 0.3 m had 5-fold (+) in gapphase and 5-fold (-) in peatland/mixedconifer.
Discriminant Model- Spring 1999-2000:
Red-backed Vole
Model
Gap-Phase
Multivariate
Factor
N/A
Multi-cohort
N/A
Thinned YG
N/A
Peatland-MC
Moss, sapling, &
deciduous shrub
Discriminant Model- Autumn 1999-2000:
Red-backed Vole
Model
Gap-Phase
Multivariate
Factor
Vaccinium &
deciduous shrub
Multi-cohort
N/A
Thinned YG
Vaccinium & moss
Peatland-MC
Moss, sapling, &
deciduous shrub
Red-backed Vole Density &
Decayed Downed Wood
Explained about 90%
of variation in density
Decay IV
(volume/ha)
Red-backed Vole Density &
Conifer Seedling Cover
Explained about 85% of
variation in vole density
Conifer cover (%) <30 cm
Habitat Correlates of Density:
Red-backed Vole
Spring 1999-2000
Autumn 1999-2000
________________________________
________________________________
Decayed wood class IV (+)
Soft snags 10-49 cm dbh (-)
Coarse woody debris (+)
Decayed wood class III (+)
Conifer cover 0.3 –1.5 m (-)
Conifer cover <0.3 m (-)
Water ground cover (+)
Moss ground cover (-)
Trees 10-49 cm dbh (-)
Decayed wood class IV (+)
Soft snags 10-49 cm dbh (-)
Coarse woody debris (+)
Decayed wood class III (+)
Conifer cover 0.3 –1.5 m (-)
Conifer cover <0.3 m (-)
Trees 5-10 cm dbh (-)
Logistic Regression Model:
Northern Flying Squirrel
Density of trees >74 cm dbh and cover of
Vaccinium most influenced microhabitat use
during spring and autumn:
- in
peatland/mixed-conifer large tree density
increased capture probability by a factor of 3
during spring and 17 in autumn;
Most influential habitat feature in gap-phase
OG was ground cover of water was inversely
correlated with microhabitat use.
Discriminant Function Model:
Northern Flying Squirrel
Model
Multivariate
Factor
Spring
Peatland-MC
Understory
cover/structure
Large tree/ snag
density
Upland-OG
N/A
Autumn
Peatland-MC
Upland-OG
Large tree/ snag
density
Vaccinium
Squirrels/ha
Glaucomys sabrinus Density and
Live Trees >74 cm DBH
Explained about
65% of variation in
squirrel density
Trees >74 cm dbh/ha
Ecological Correlates of Density:
Northern Flying Squirrel
Spring 1998-2000
Autumn 1998-2000
_____________________________________________
______________________________________________________
Moss ground cover (+)
Decayed wood class I (+)
Decayed wood class I (+)
Decayed wood class IV (+)
Trees >74 cm dbh (+)
Trees 5-10 cm dbh (-)
Trees 10-49 cm dbh (-)
CONCLUSIONS
Endemism
____________________________________
Current taxonomy under-represents
diversity & complexity of mammal fauna;
High likelihood of undocumented endemic
taxa, especially on mainland;
Outer islands show greater divergence
and may contribute more genetic diversity;
POW flying squirrel differs markedly from
northern flying squirrel in PNW;
Habitat loss will increase extinction risks,
especially endemics of small islands.
Population
Ecology
____________________________________
Peatland-scrub/mixed conifer may support
breeding populations of flying squirrels,
but not red-backed voles;
Small HCAs likely large enough to support
breeding populations of flying squirrels;
Voles occur in thinned YG, but it may
function as a habitat sink;
Vole captures most often correlated with
deciduous cover, but relationship and
ecological impact varied among habitats CANNOT ignore habitat context;
Population
Ecology
____________________________________
Vaccinium - major component of “factors”
correlated with autumn vole captures in Young
Growth and Gap-Phase habitats;
Moss in YG during autumn may reflect vole
needs for moist microsite conditions;
POG is primary habitat of POW flying squirrel,
which may have a more general lifestyle than
populations in PNW;
Stand level - vole density directly related to
coarse woody debris and decayed downed
wood, inversely related to conifer cover and
dead saplings in the understory;
Population Ecology
____________________________________
Flying squirrel captures most influenced
by large tree and snag density and
Vaccinium cover in peatland/mixed-conifer
where it may be limiting;
Stand level - squirrel density related to
large tree density and decayed wood;
Inferences limited because of annual
population variability, its influence on
habitat use, and limited duration of study.
Management Implications
____________________________________
Select-harvest of POG likely have minimal
impacts to flying squirrel populations;
HOWEVER, select harvest of mixedconifer forests likely will markedly reduce
habitat capability for flying squirrels;
Viability risk for Wrangell Island vole and
POW flying squirrel likely less than
suggested from research on these species
elsewhere.
Information
Needs
____________________________________
Systematic inventory and genetic analysis
of mammals, especially on nearshore and
outer small (<100,000 acre) islands;
Statistically robust sampling protocols to
document “absence” of mammal taxa;
Long-term (>5 years) population data;
Study vole and flying squirrel populations
in managed stands;
Dispersal success of flying squirrels in
managed landscapes.
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_____________________________________________________________
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___________________________________________
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___________________________________________
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