influence du climat et de la prédation sur l'utilisation de l'habitat et la ...

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3.2. Introduction
A growing number of studies indicates that climate affects population dynamics of
mammals (Krebs & Be11eaux 2006). Climate can have direct effects on individuals (for
example winter weather influences population dynamics through effects on locomotion
(Telfer & Kelsall 1984) or thermoregulation (Cook et al. 1998)); or indirect ones by affecting
species interactions. For example, deep snow may influence predator-prey relationships (Post
et al. 1999b, Hebblewhite 2005) and access to food resources (Turner et al. 1994, Post &
Stenseth 1999). Obviously, the different ways in which climate influences population
dynamics are complex and our understanding of mechanisms linking climate to population
growth rate is limited (Owen-Smith & Mills 2006). Because we can hardly manipulate
climate, testing specifically for changes driven by weather variations is plagued by
experimental difficulties. The two main approaches that have been used are 1) small scale
studies that aim at determining mechanisms linking weather variations and changes in
biological processes; and 2) large scale studies (i.e. data collected over long time periods
and/or large areas) that aim at correlating the observed climatic variability with changes in
ecosystem functioning. Both approaches have important drawbacks and Root and Schneider
(1995) suggested alternating studies performed on large and small scales to move ahead with
climate research. ln such cycles of analysis, large-scale studies would generate hypotheses
that wou Id be tested using small-scale studies.
The solar cycle is known to have an impact on weather (Sinclair et al. 1993) with
cascading effects on entire ecosystems (Verschuren et al. 2000, Hodell et al. 2001). For
instance, the reproductive output of snowshoe hares in Yukon was found to be cyclic and
highly correlated with sunspot numbers with a two years time lag (Stefan & Krebs 200 l,
Krebs & Be11eaux 2006). Possible mechanisms involved in this relationship include an effect
of solar activity on snow depth which might in turn affect food supplies (Krebs & Berteaux
2006) and lynx hunting success (Sten seth et al. 1999,2004). North American porcupine
(Erethizon dorsatum) populations in the Bas St. Laurent region of eastern Québec seem also
to be affected by the solar cycle. Klvana et al. (2004) found that an index of porcupine
abundance (porcupine feeding scars) was related to fluctuations in the solar cycle, winter