Geoscience Reference
In-Depth Information
shifts. for. multiple. species. over. a. relatively. small. geographic. area. have. the. beneit.
of.comparing.species.with.different.natural-.and.life-history.characteristics.as.they.
respond. to. a. relatively. homogeneous. change.. Such. studies. allow. us. to. understand.
which. traits. may. make. certain. species. more. sensitive. than. others. to. changing. cli-
matic.conditions..The.other.approach.is.to.focus.on.single.species.that.are.known.to.
be.thermally.sensitive.and.thus.likely.impacted.by.climate.change.more.rapidly.than.
others..By.studying.single,.sensitive.species.over.a.broad.geographic.range,.we.can.
gain.a.better.understanding.of.the.landscape.or.climatic.factors.determining.range.
edges.and.how.changes.in.such.factors.could.affect.other.species'.ranges.over.longer.
time.scales..Single-species.and.multispecies.studies.have.been.informative.and.laid.
the.foundation.for.gaining.a.mechanistic.understanding.of.distributional.shifts..We.
elaborate.on.a.few.key.studies.in.the.remainder.of.this.section.
Multiple Species within a Limited Geographic Area
Multispecies.mammal.distribution.studies.often.focus.on.either.elevational.or.lati-
tudinal. range. shifts. driven. by. temperature. change.. Moritz. et. al.. (2008). undertook.
an.elevation-based.study.spanning.a.central.portion.of.the.Sierra.Nevada.mountain.
range.of.California..Revisiting.the.“Yosemite.transect”.studied.by.Joseph.Grinnell.
and.colleagues.from.1914.to.1920,.Moritz.et.al..assessed.changes.in.the.elevational.
ranges.of.43.small.mammals.over.the.past.century..The.transect.spans.elevations.60-.
to.3300-m.above.sea.level..This.region.has.experienced.substantial.climatic.change.
in. the. past. century,. with. average. minimum. monthly. temperature. increasing. 3.7°C.
over.that.period..Using.occupancy.modeling.techniques,.the.authors.found.that.most.
species'. ranges. shifted. upward. an. average. of. ~500. m,. but. results. were. quite. vari-
able. among. species.. Elevation. shifts. occurred. more. frequently. for. high-elevation.
species.than.those.typically.dwelling.at.low.elevations;.however,.certain.life-history.
traits.appear.to.increase.the.probability.of.upward.range.shift.for.some.low-.to.mid-
elevation.species..In.a.post-hoc.analysis.of.10.low-.to.mid-elevation.species,.Moritz.
et. al.. found. that. species. with. shorter. life. spans. and. larger. litter. sizes. were. more.
likely. to. exhibit. upper. range. limit. expansion.. Lower. limits. shifted. upward. more.
frequently.than.upper.limits,.leading.to.range.contraction.for.many.high-elevation.
species..Range.collapse.(simultaneous.increase.in.low.limits.and.decrease.in.high.
limits).occurred.for.only.two.species..Despite.some.clear.trends,.there.was.a.great.
deal.of.variation.in.species.response,.even.among.closely.related.species.(e.g.,.those.
in.the.genus.
Peromyscus
).
Overall,.the.results.of.Moritz.et.al..(2008).provide.some.of.the.most.informative.
data.to.date.on.mammal.elevational.shifts.due.to.climate.change..The.conclusions.
remain.correlational,.primarily.due.to.the.nature.of.this.study.as.a.one-time.resurvey.
of.the.Yosemite.region,.rather.than.a.continuous.monitoring.program.of.species.and.
climate.within.this.study.area.over.the.last.century..Despite.these.limitations,.this.
study.has.the.advantage.of.land.use.stability,.in.that.the.majority.of.the.study.area.is.
in.Yosemite.National.Park,.which.has.been.under.land.use.protection.since.before.
the.Grinnell.surveys.were.conducted..This.scenario.allows.for.the.isolation.of.cli-
mate.change.impacts.from.those.resulting.from.other,.typical.human.disturbances.
such.as.agricultural.and.urban.development..While.most.places.are.not.similarly.iso-
lated.from.human.land.use.impacts,.studies.such.as.Moritz.et.al.'s.allow.us.to.isolate.
