Geoscience Reference
In-Depth Information
Weight across models
Weight per model
FIGURE 5.3
Relative.support.for.each.of.12.potential.predictors.of.pika.extinction.within.
the.system.described.in.Figure.5.2.(Beever.et.al.,.in.press)..Relative.support.is.shown.in.the.
form.of.rescaled.Akaike.weights,.derived.from.an.information-theoretic.analysis.(Burnham.
and.Anderson.2002)..Predictor.descriptions:.
∑
.represents.cumulative.or.average.metrics.cal-
culated.from.the.prevailing.climate,.0-60ybp;.
Δ
.represents.changes.in.each.metric.over.two.
periods,.30-60ybp.versus.0-30ybp;.
τ
.represents.recent.climate.metrics.calculated.from.ther-
mal.sensors.
in situ
.during.2005-2006;.AveSumT.=.average.summer.temperature.(average.of.
the.daily.minima.and.maxima.for.June.1-August.31),.a.potential.metric.of.chronic.heat-stress;.
Days. <. -10°C,. 0°C. =. number. of. daily. minima. below. -10°C. and. 0°C,. potential. metrics. of.
acute.cold-stress;.Days.>.28°C.=.number.of.daily.maxima.above.28°C,.a.potential.metric.of.
acute.heat-stress..Because.the.number.(
n
).of.models.itted.varied.across.predictors.(4.≤.
n
.≤.
27),.raw.weights.(dark.bars).are.contrasted.with.weights.per.model.itted.(light.bars)..Weights.
were.rescaled.to.sum.to.1.0.(Beever.et.al..2010).
and.survival.over.extended.fasting.periods.(Humphries.et.al..2004)..These.adapta-
tions. have. allowed. arctic. species. to. exploit. a. largely. uninhabitable. region. of. the.
world,.and.yet.these.same.traits.may.put.species.at.risk.as.arctic.climates.change.
For.polar.bears.(
Ursus maritimus
).and.other.arctic.mammals,.survival.is.tightly.
linked.to.annual.temperature.luctuations.and.subsequent.effects.on.sea-ice.stability.
(Laidre.et.al..2008;.Stirling.et.al..1999;.Derocher.et.al..2004)..Sea.ice.serves.a.criti-
cal.role.in.the.annual.energetic.balance.of.polar.bears,.whose.primary.food.source.is.
seal.pups.hunted.along.the.ice-sea.edge.(DeMaster.and.Stirling.1981)..This.hunting.
occurs.in.spring.and.continues.until.sea.ice.melts.(DeMaster.and.Stirling.1981)..The.
energy.stores.accumulated.must.sustain.individuals.throughout.the.summer.fasting.
period.(DeMaster.and.Stirling.1981).
