Geoscience Reference
In-Depth Information
3000
m
2008
:
2569 m
1999
:
2474 m
Historical
:
2374 m
2000 m
FIGURE 5.2
Upslope.range.retraction.of.the.American.pika.(
Ochotona princeps
).on.moun-
tain.ranges.within.the.Great.Basin.ecoregion.of.the.western.United.States.(data.collected.by.
E..Beever.and.J..Wilkening)..The.average.minimum.elevation.of.25.populations.with.histori-
cal.records.(1898-1956).was.2374.m..By.2008,.nine.of.these.25.populations.had.gone.extinct,.
and. the. average. minimum. elevation. of. individuals. within. persisting. populations. had. risen.
nearly.200.m..Almost.half.of.this.rise.occurred.within.the.last.decade.(Beever.et.al..2012).
distributional. shifts.. First,. the. natural. history. of. many. arctic. and. alpine. mammal.
species.has.been.well.studied..Second,.the.habitats.of.these.species.are.typically.less.
disturbed.by.human.land.conversion.practices.compared.to.other.areas.
One.such.sensitive.alpine.mammal.is.the.American.pika.(
Ochotona princeps
),.a.
species.known.to.avoid.even.normal.summer.temperatures.by.retreating.into.crev-
ices.among.the.rocks.of.its.talus.habitat.(Smith.1974)..This.species'.speciicity.for.
alpine.talus.is.perhaps.driven.by.its.low.vagility.and.thermal.sensitivity.(Smith.and.
Weston.1990)..In.their.study.of.
O. princeps
.in.the.Great.Basin.region.of.the.United.
States,. Beever. et. al.. (2003). found. elevation. (serving. as. a. proxy. for. climate). to. be.
one. of. the. best. predictors. of. local. population. extirpations.. Six. of. 25. populations.
documented.before.1990.were.found.locally.extinct.in.surveys.from.1994.to.1999..
The. lower. elevational. limit. of. extant. populations. has. risen. dramatically. over. the.
last.century,.and.especially.during.the.last.decade.(Figure 5.2)..The.most.important.
predictor. of. population. extinction. was. the. maximum. elevation. of. talus. near. each.
site—potentially.a.local.refuge.or.source.of.rescue.through.recolonization..Extinct.
populations.tended.to.lack.this.elevational.refuge,.and.also.experienced.19.6%.less.
annual.precipitation.and.7.7-10.2%.higher.mean.daily.maximum.temperatures.dur-
ing.summer.(June.1-August.31),.based.on.PRISM.(Daly.et.al..1994).values.during.
1961-1990..In.addition,.extinct.populations.were.generally.located.on.smaller.habitat.
patches,.within.grazed.allotments,.and.closer.to.access.by.road.
The.correlational.nature.of.recent.climate.change.research.is.exempliied.in.this.
admittedly.“exploratory”.study.(Beever.et.al..2003)..While.elevation.may.be.a.rea-
sonable.proxy.for.climatic.variables,.it.is.less.clear.that.grazing.and.distance.to.roads.
are. appropriately. orthogonal. proxies. for. anthropogenic. drivers. of. local. extinction..
Because. roads. and. grazing. are. more. common. at. lower. elevations,. the. predictive.
ability.of.these.variables.may.relect.effects.of.elevation.rather.than—or.in.addition.
to—effects.of.human.activity.
