Geoscience Reference
In-Depth Information
determine. the. range. limits. of. species. can. also. increase. the. reliability. of. modeled.
estimates.of.change..The.elevational.distributions.of.48.out.of.53.bird.species.sam-
pled. in. California. tracked. changes. to. temperature. or. precipitation. between. 1911-
1929. and. 2003-2008,. and. 77%. of. species. ranges. tracked. the. variable. predicted.
from. a. priori. models. of. species. range. sensitivity. to. climatic. variables. (Tingley. et.
al.. 2009).. Interestingly,. the. elevational. associations. of. species. inluenced. the. cli-
matic.factors.to.which.they.responded;.those.species.that.tracked.only.changes.to.
precipitation. occurred. in. the. lowlands. (mean. range. center. =. 916. m),. while. those.
tracking.only.temperature.were.associated.with.the.highlands.(mean.range.center.
=. 1944. m). (Tingley. et. al.. 2009).. The. observed. variation. in. range-limiting. factors.
may.relect.the.roles.of.precipitation.in.limiting.Net.Primary.Productivity.(NPP).at.
low.elevations,.and.of.energy.in.limiting.NPP.at.high.elevations.(see.also.Hawkins.
et.al..2003).
Ecophysiological.models.may.be.valuable.in.producing.testable.predictions.about.
how. the. elevational. ranges. of. species. will. respond. to. climate. change. (Hodkinson.
1999)..For.example,.for.low-elevation.margins.of.tropical.lowland.species.to.contract.
as.the.climate.warms,.current.species.distributions.must.be.situated.near.their.ther-
mal.optima,.and.this.is.suggested.by.evidence.for.tropical.ectotherms.(Deutsch.et.
al..2008).and.plants.(Clark.et.al..2003;.Feeley.et.al..2007)..Experimentally.derived.
indices. of. physiological. stress. caused. by. climate. warming. could. provide. quanti-
tative. assessments. of. extinction. risk. at. species'. low-elevation. range. margins. (e.g.,.
Bernardo.and.Spotila.2006),.but.the.capacity.of.species.to.expand.to.high.elevations.
may. depend. more. on. the. prior. availability. of. suitable. resources. or. conditions. for.
colonization.(e.g.,.Dullinger.et.al..2004;.Merrill.et.al..2008)..Future.species.ranges.
will.depend.both.on.the.ine-scale.effects.of.microclimate.on.growth,.survival.and.
fecundity,.and.the.landscape-scale.effects.of.land.use.on.the.distributions.of.suitable.
habitats..In.addition,.differences.in.the.environmental.cues.that.inluence.the.phenol-
ogy.of.interacting.species.may.determine.whether.species.are.able.to.track.otherwise.
tolerable.climatic.conditions.(for.examples.concerning.herbivorous.insects.and.their.
host.plants,.see.Hodkinson.1999)..In.practice,.models.based.on.topoclimatic.factors.
may.provide.reasonable.best-guess.predictions.of.species'.future.ranges,.especially.
where. climate. varies. over. a. ine. scale. and. relatively. large. areas. of. natural. habitat.
remain.. However,. available. evidence. suggests. that. even. over. steep. elevation. gra-
dients.there.may.be.a.greater.time.lag.in.upslope.colonizations.than.in.downslope.
extinctions.(Wilson.et.al..2007).
SYNTHESIS, FUTURE DIRECTIONS, AND CONSERVATION
There.is.now.strong.evidence.that.species.distributions.have.shifted.uphill.associ-
ated.with.recent.climate.change..There.are.indications.that.rates.of.range.contraction.
from.low-elevation.margins.may.be.keeping.closer.pace.with.climate.warming.than.
high-elevation. range. extensions,. which. may. be. constrained. by. habitat. availability..
A.number.of.studies.have.begun.to.identify.the.climatic.mechanisms.driving.these.
range. shifts,. and. to. predict. future. effects. of. climate. change. on. the. biodiversity. of.
elevational.gradients..In.particular,.recent.discussion.of.the.likely.impact.of.eleva-
tional. range. shifts. on. tropical. biodiversity. represents. an. important. contribution. to.
