Geoscience Reference
In-Depth Information
alterations.to.the.environment,.led.to.rising.land.and.ocean.temperatures.of.approxi-
mately.0.6°C..The.Intergovernmental.Panel.on.Climate.Change.(IPCC).has.produced.
emission.scenarios.that.suggest,.across.the.range.of.possible.scenarios,.a.temperature.
increase.of.1.4°C.to.5.8°C.by.2100.(Houghton.et.al..2001)..Warming.is.likely.to.be.
more.pronounced.on.land.and.at.higher.latitudes.compared.to.oceans.and.equato-
rial. regions.. Precipitation. is. expected. to. increase. in. higher-latitude. temperate. and.
polar.regions.and.in.the.tropics,.with.decreases.in.the.subtropics..These.long-term.
trends.are.accompanied.by.an.increased.likelihood.of.extreme.weather.events..These.
extreme.events.may.prove.to.be.as.important.as.or.more.important.than.changing.
averages.in.terms.of.direct.impacts.on.species.distribution.and.diversity.(Easterling.
et.al..2000).
The. climatic. conditions. of. the. recent. past. and. near. future. should. be. considered.
within.the.broader.context.of.climatic.changes.over.longer.time.scales,.ranging.from.
millenia.to.millions.of.years..Barnosky.et.al..(2003).used.paleoclimatic.reconstruc-
tions.and.the.mammalian.fossil.record.to.examine.the.rate.of.climatic.changes.and.
the. nature. of. species. responses. to. those. changes. under. different. rates. of. warming.
and.over.three.different.timescales.(350.years,.10,000-20,000.years,.and.4.million.
years)..We.focus.only.on.salient.climatic.data.presented.by.the.authors..Barnosky.et.
al..(2003).conclude.that.the.current.rate.of.warming.is.within.the.range.of.warming.
seen.in.the.past—for.example.during.the.rapid.warming.that.followed.the.last.ice.age..
However,.if.the.IPCC.predictions.are.accurate,.at.some.point.during.this.century.the.
rate.of.warming.is.likely.to.exceed.that.of.any.period.within.the.past.65.million.years.
m
ammalian
r
esponse
p
roCesses
What.can.organisms.in.general.and.terrestrial.mammals.in.particular.do.in.the.face.
of.such.unprecedented.changes.in.climatic.conditions?.The.answer.depends.both.on.
the.severity.of.direct.and.indirect.effects.of.climatic.changes.and.on.the.physiology.
and.behavior.of.the.organisms.in.question..For.some.mammals,.climatic.conditions.
are. rarely. directly. limiting. factors,. due. to. either. broad. climatic. tolerances. or. the.
ability. to. behaviorally. regulate. the. climate. they. experience.. For. these. mammals,.
biotic.factors.such.as.food.availability,.competition,.and.predation.may.control.spe-
cies.diversity.and.distribution..Although.climate.may.not.have.direct.effects.on.such.
species,.there.might.still.be.indirect.effects.due.to.changes.in.the.diversity.and.dis-
tribution.of.food.sources,.predators,.or.competitors..For.other.mammal.species.with.
narrower. physiological. tolerances. to. temperature. or. precipitation,. there. may. be. a.
direct. response. to. climate. change.. In. such. cases,. individuals. and. populations. can.
either.disperse.in.order.to.ind.more.favorable.conditions,.adapt.in.situ.physiologi-
cally.or.behaviorally,.or.go.locally.extinct..Both.local.extinction.and.dispersal.away.
from.unfavorable.habitats.will.result.in.range.alteration..However,.the.genetic.conse-
quences.are.quite.different..Species.that.are.capable.of.dispersing.may.maintain.their.
genetic.diversity..In.the.case.of.local.extinction,.overall.population.size.declines.and.
genetic.diversity.may.be.lost.(Dalén.et.al..2007;.but.see.Ray.2001).
It.is.presumed.that.the.likelihood.of.adaptation.or.dispersal.as.opposed.to.extinc-
tion.depends.both.on.the.tolerances.and.plasticity.of.the.species.in.question.and.on.
the. rapidity. and. magnitude. of. climate. change.. The. evolution. of. novel. adaptations.
