Impacts of snow variability in the presence of supplemental feeding
on the spatial distribution of a large herbivore in an Alpine
environment
J. B. Ross, F. Cagnacci, W. Peters, F. Ossi, M. Ramanzin, E. Eccel, E. Cordano, F. Bianchini and P. R. Moorcroft
Winter, snow and animal movement
Food availability Snow layer
Winter climate is crucial for ungulate distribution in temperate and boreal ecosystems
Food accessibility (locomotion cost)
Movement responses at different spatiotemporal scales
D a ys w it h s n o w co ve r Elevation (m)
Less and more variable snow cover at low/intermediate altitudes T i n cr e a se ( ° C ) (m )
How does this environmental change affect ungulate
movement behavior?
December 2015, 1300 m, west TrentinoDecember 2017, aerial photo of Dolomites
Alteration resources distribution and phenology
• High ecological plasticity, with some populations living at the edges (Alps and Scandinavia)
Winter is LIMITING for populations living at the
edges (snow line) • Income breeder tactic scarce fat reserves + need for
continuous resource acquisition
[COMPLICATING FACTOR: Pervasive deployment of supplemental feeding]
• Highly sensitive to snow presence Partial migration AND 3rd order selection for shallow snowy spots + canopy cover
Roe deer: an excellent model species
Ideal to investigate the relationship between variability in limiting environmental conditions and changes in space use
Work goal and general predictions
• Examine if predicted roe deer winter distribution at the range altitudinal limit plastically changed over two decades in response to snow layer variability and modified supplemental feeding distribution
• P1: roe deer predicted winter distribution tracks snow variability • P2: supplemental feeding deployment mitigates snow cover effects on roe deer winter distribution, until a given limit
Two populations, and feeding sites….
•Strong development of supplemental feeding from historical to contemporary period
•Historical population (VHF data): 1999 – 2002
•Snow depth (ASD)
•Proximity to feeding stations (DistFS) •Canopy cover (CC)
Resource selection function (RSF) to predict roe deer winter habitat selection
(contemporary dataset)
The baseline model (from Ossi et al. 2014)
Spatial extension of the model
1. Canopy cover (CORINE)
2. Proximity to feeding stations
(ArcGIS raster 3D distance to closest FS)
Monthly winter maps (Nov to Apr) of
predicted habitat suitability for roe deer,
validated in space and time. 3. Snow depth (from GeoTOP
hydrological model; Endrizzi et al. 2014)
Low high suitability
Evaluating temporal changes in patterns of space use
• Weighted Kappa statistics (0: no agreement – 1: perfect agreement) to
compute the agreement between pairs of predictive winter distribution maps
• Subtractions maps to visualize predicted winter distribution changes over time
Portland – 102 ESA Annual Meeting 08/06-11/2017
Historical
Historical
Contemporary
Contemporary
Model results
•Snow depth avoidance ( = -0.021 ± 0.007, p < 0.01)β
•Selection for sites close to feeding stations ( = 91.803 ± 14.807, p < 0.001)β •Selection for canopy cover ( = -2.105 ± 0.362, p < 0.001)β
Winter distribution variability increased over time
Portland – 102 ESA Annual Meeting 08/06-11/2017
IH ID IC IH ID IC IH ID IC
IH ID IC
IH ID IC
IH ID IC
IH = intraperiod historical comparison
ID = interdecadal comparison
Portland – 102 ESA Annual Meeting 08/06-11/2017
….if snow occurs, of course!
IH ID IC IH ID IC IH ID IC
IH ID IC IH ID IC IH ID IC
P2: mitigation effect for feeding stations…
Overall, suitability increased from historical to contemporary period: an effect of feeding stations deployment?
April 2001 more suitable than April 2014: feeding stations compensate up to a given level…
Portland – 102 ESA Annual Meeting 08/06-11/2017
Take home messages…
• Roe deer track snow line changes (high plasticity)
• Habitat suitability increases with decreasing winter severity and deployment of supplemental feedings
• Range expansion following ‘new’ habitat availability? Altered migration patterns? Influence on forest community?
• Management concern 1: Snow variability is not equal to better conditions: take care of extreme events!
• Management concern 2: Feeding stations…do we really ‘need’ them? • if winter severity is decreasing, what is their role?
• if events are extreme, they may provide benefit only in the immediate surroundings, with controversial effects due to aggregation!
