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

62
Data analyses
Thermal mapping
We measured power consumption 46 times in 38 sites (4 "den", 6 "ground open", 12
"ground covered" , 3 "deciduous", 5 "conifer open", 8 "conifer covered"), and col!ected 1012
hours of data with both mounts. We averaged power consumed by the mounts over one-hour
periods to match measures of Tc that were averaged over the same period. To insure that the
mean power consumed referred to relatively stable meteorological conditions, we excluded
one-ho ur periods during which Tc variation was > 3°C. This 3°C threshold allowed us to
remove most directional changes in Tc. Following this sampling strategy, we calculated me an
power consumption during 886 one-hour periods (mount 1: 494 h, mount 2: 392 h) . We
tested during calibration periods whether mounts had similar power consumption when
exposed to similar thermal conditions. We placed the two mounts 2 m apart (similar position)
in a "ground open" microhabitat and continuously recorded power consumed by the mounts.
We ran four calibration trials and calculated power consumption during 46 one-hour periods
covering a wide range of Tc (from -I8.2°C to +4.2°C). We tested for differences between the
two mounts using a paired t-test.
Our sampling design included repeated measurements of power consumption made on
the same site on different occasions and for a given site and occasion, repeated measurements
made at different hours. Therefore, we used general linear mixed models with normal
distributions (proc MIXED, SAS software version 9.1, SAS 2002), including occasion of
measurement as a random effect for a given site (because we used some sites on several
occasions), and hour of measurement as a repeated effect for a given site and occasion
(bec au se measurements closer in time are more correlated th an measurements further apart).
We fitted Tc, microhabitat as fixed effects to test whether the power consumed by mounts
was different between microhabitats (our variable of interest) when adjusting for Tc. We also
fitted Tcx microhabitat as a fixed effect to test whether the relationship between power
consumed and microhabitat differed according to Tc (e.g. to test whether the microhabitat
offering the best microclimate was the same at cold and wann Tc). When testing the effect of
microhabitat (as a main effect or in interaction with Tc), we first considered ail microhabitats
sampled (i.e. microhabitat had six modalities, Table 4.1, model 1) and then considered groups
of microhabitats that we expected to offer similar thermal conditions (i.e. microhabitat had