WINTERTIME MAMMAL ACTIVITY – SPECIFIC ENVIRONMENTAL CONTROLS
Brian Inglis
EBIO 4100-570 - Winter EcologyMountain Research Station Spring ’12 CU Boulder
Drawing courtesy of Marieta
Question…
What are the dominant environmental factors controlling the distribution/abundance of overwintering mammals in the upper-montane and sub-alpine regions of Colorado?
Possible AnswersAll together now!….
Snow
Cold
Radiation
Energy
Wind
Predation
Motivation
Food availability is an extremely influential variable in the wintertime --More so in the mountains?
Ecology 101 Vegetation as food chain supplier for all (Carnivores too)
How far will an organism go to get its food? Depends on the obstacles
“snow cover alone does not fully explain the upper range limit of wombats… wombat occurrence is influenced by local habitat features (topography, soils, vegetation) in combination with maximum snow depth.” (Matthews et Al., 2010)
Diurnal radiation fluctuations and impact force from wind create ice crusts and packed layers suitable for travel
“…occupation was also positively associated with percent forest cover. …a reflection of the importance of proximal forest for weather and predator protection.”(Roger et Al., 2007)
What I Care About...
In what ways do aspect and vegetation density affect the presence of supranivean mammals in the winter?
My Specific Hypotheses:H 1: Vegetation density affects the abundance of mammal tracks
•Denser stands more conducive to winter activity food availability and protection
H 2: Aspect affects the abundance of mammal tracks
•Southern-facing hillsides more abundant in supranivean mammals
•benefits of radiation and wind.
Methodology
2 Sites 3 Aspects 4 Total Transects
Make a straight-line transect across terrain with constant aspect
At crossing track, noted species, snow depth and distance to nearest above-snow tree/vegetation
Ranked vegetation distances into four categories at 1.5m intervals (0-150cm, 151-300cm, 301-450cm, 451cm +)
Ranked snow depths similarly into 5 categories (Bare, 1-30cm, 31-60cm, 61-90cm, 91-120cm)
Analyze
Site Descriptions
Two transects of NORTH aspect
Average Altitude: 2877 m (9440’) A.S.L.
Vegetation: Lodgepole and Limber
Pine, Englemann Spruce, Aspen, Sub-Alpine Fir
Animals Found: Mtn. Cottontail, Coyote,
Tree Squirrel, Weasel
One SOUTHWEST facing transect, one SOUTHEAST facing
Average Altitude: 2621 m (8600’) A.S.L.
Vegetation: Ponderosa and
Lodgepole Pine, Englemann and Blue Spruce, Aspen
Animals Found: Mtn. Cottontail, Coyote,
Tree Squirrel, Moose
Mountain Research Station Grounds - Fourmile Creek
Tahosa Valley – Near Meeker Park, CO
Not Important:
….two-factor analysis of variance without replacement…. H01: The
differences in the number of tracks from one site to another is due to random chance
H1: The differences in the number of tracks from one site to another is due to distance from vegetation
ANOVA Results: Df Sum of Squares Mean of Squares F value P Value
Distance Class 1 1251.3 1251.3 74.48 0.0001Reject null H 01
Aspect 2 15.5 7.8 0.461 0.6510Can’t reject null H 02
DistanceClass:Aspect 2 4.4 2.2 0.132 0.8788Can’t reject null H 03residuals 6 100.8 16.8
….two-factor analysis of variance without replacement…. H02: The
differences in the number of tracks from one site to another is due to random chance
H2: The differences in the number of tracks from one site to another is due to slope aspect
ANOVA Results: Df Sum of Squares Mean of Squares F value P Value
Distance Class 1 1251.3 1251.3 74.48 0.0001Reject null H 01
Aspect 2 15.5 7.8 0.461 0.6510Can’t reject null H 02
DistanceClass:Aspect 2 4.4 2.2 0.132 0.8788Can’t reject null H 03residuals 6 100.8 16.8
….two-factor analysis of variance without replacement…. H03: any
interaction between aspect and vegetation density is due to random chance
H3: aspect has some control over the density of vegetation present
ANOVA Results: Df Sum of Squares Mean of Squares F value P Value
Distance Class 1 1251.3 1251.3 74.48 0.0001Reject null H 01
Aspect 2 15.5 7.8 0.461 0.6510Can’t reject null H 02
DistanceClass:Aspect 2 4.4 2.2 0.132 0.8788Can’t reject null H 03residuals 6 100.8 16.8
Conclusions
Analysis of variance Strong positive
correlation between vegetation density and mammal tracks P-value of 0.0001
No discernible influence of aspect on mammal activity P-value of 0.65 Look at the longer-
term bigger-picture
Hard to gauge the snow’s role Support or Sink
Specific animal analysis
Subnivean controllers
Not a complete 360⁰Vegetation density biasedSite differences
Final Thoughts…
Wintertime mammal activity not directly controlled by one factor
Aspect SCREWP
Vegetation P…. E…. W….
Vegetation density may/may not be dependent upon aspect relation between
two may be random, statistically Mammal
abundance as a result not clear
References
Matthews, A., Spooner, P. G., Lunney, D., Green, K. and Klomp, N. I. (2010), The influences of snow cover, vegetation and topography on the upper range limit of common wombats (Vombatus ursinus) in the subalpine zone, Australia. Diversity and Distributions, 16: 277–287. doi: 10.1111/j.1472-4642.2010.00638.x
Roger, Erin, Shawn W. Laffin, and Daniel Ramp (2007), Habitat Selection by the Common Wombat (Vombatus Ursinus) in Disturbed Environments: Implications for the Conservation of a ‘common’ Species. Biological Conservation 137.3: 437-449. doi: 10.1016/j.biocon.2007.03.001
Statistics run in R and Microsoft Excel Topographic images courtesy of USGS 7.5’-minute
series quadrangles “Ward”, “Allenspark” and “Longs Peak”
Expert Photography by Brian Inglis