Supranivean travel of snowshoe hares on Niwot Ridge
Marieta BialekEBIO 4100Winter Ecology Spring 2012
Layout of Presentation
IntroductionBackground
Snowshoe Hare, Relevance to Winter Ecology,
Question
Hypotheses
Methods
Results
Discussion
Key References
Snowshoe Hare Lepus Americanus of the Rocky Mountains
• Hare populations more heterogeneous in rocky mountain regions
• Important Habitat: Lodgepole pine forests and engelmann spruce-subalpine fir forests
• Threat: Climate change affecting precipitation (snow) and thus biotic communities (Ellsworth, Reynolds 2006)
Relevance to Winter Ecology
In winter hares are main prey biomass for many predators
Consume a large amount of woody forage all winter
Constantly deposit fecal pellets on the surface which eventually reach the forest floor, affecting soil nutrient content
Snow conditions (i.e., depth and density) play an important role in the types of predators that hunt hares during the winter
Thus may influence predation risk (Ellsworth, Reynolds 2006)
Coevolution with the lynx for snow travel – morphological adaptations
Cont.
SnowMorphological adaptation to snow: feet
Mechanism: Reduced snow loading facilitates movement over snow
Question
• Does the top layer of snow density significantly limit the travel of snowshoe hare?
How does the stride length effect the depth of the track?
How does the density of the snow effect the depth of the track?
Is there a significant relationship between the density of the snow and stride length?
Null Hypothesis: There is no significant relationship between stride, density of snow, and the depth of a traveling hare track
Multiple Hypotheses and reasoning
H1The depth of the track will increase as stride increases, due to force pushing down on snow to jump further
H2Tracks will be deeper at lower densities because at lower densities snow is harder to move through
H3Strides will be longer at higher densities because less energy is lost to the snow and more can be used for the jump
MethodsMaterials: flotation, snow density tools (from the snow pit kit)
Two locations: Up Niwot Ridge Road between MRS and Cable Gate
Around the mountain research station
Recorded measurements after fresh snowfall on two different days
Only recorded tracks of larger hares
Picked tracks between areas of forage where hare clearly has a destination, moving swiftly
For each track:Measure stride, depth (hind feet), density of top layer
Limitations in the methods
LimitationsUncertainty how long after the snowfall the hair traveled through over snow, in which conditions could have changed
Only two days of measurements, after it snowed
Time (more time, more data, greater range of densities to work with)
Little variation in snow density (range 0.079 g/cm)
Hypothesis 1
Figure 1: Plot of all tracks, depth as a function of stride
R squared = 0.07492
P-value = 0.1589
Figure 2: Only strides > 85 cm
R squared = 0.03066
P-value = 0.2808
Not significant
Discussion possible conclusions
Figure 1: Slower = shorter stride, more time to sink
Data not significant, because not a significant range of densities: need more data
Implications
Top layer conditions do not have a significant effect on snowshoe hare travel – they are just too well adapted
Perhaps the snow conditions are more important in how they effect supranivean predators
Snow conditions (i.e., depth and density) play an important role in the types of predators that hunt hares during the winter. Thus may influence predation risk
(Ellsworth, Reynolds 2006)
Future study: same experiment for hare predators
Future Research
Over a longer period of time, conditions can be assessed, (amount of last snowfall (cm), type of snow (i.e. sugar snow, crust, wet melt, powder)
Effect of snow conditions on snowshoe hare travel – what conditions are optimal for the snowshoe hare? Can they move faster on a solid crust than on fresh snow? (measure speed)
Studies have shown that hare travel is more efficient on snow than bare ground…
Key ReferencesAttributes of forest strips used by snowshoe hare in winter within clear-cut boreal landscapes. Potvin, François, Normand Bertrand, Jean Ferron. 2005. Canadian Journal of Forest Research, 35:(10) 2521-2527
Ecology of Snowshoe Hares in the Central Rocky Mountains. Dolbeer, Richard, William R. Clark. 1975.The Journal of Wildlife Management, 39(3): 535-549
Effect of moonlight on winter activity of snowshoe hares. Gilbert, B., Stan Boutin. 1991. Arctic and Alpine Research, 23:(1) 61-65
-methods
The Geometry of a population cycle: a mechanistic model of snowshoe hare demography. Kingi, Aaron and William Schaffer. 2001. Ecology, 82(3): 814-830
Snowshoe Hare (Lepus americanus): A technical conservation assessment. Ellsworth, Ethan and Timothy Reynolds. 2006. USDA Forest Service, Rocky Mountain Region.
Key article