Geoscience Reference
In-Depth Information
At.the.most.fundamental.level,.when.environmental.conditions.are.favorable.for.
a.species,.its.populations.grow.and.more.individuals.disperse.to.other.suitable.areas,.
thus.expanding.the.geographic.range..In.contrast,.when.conditions.become.unsuit-
able,. populations. may. respond. in. one. of. three. ways:. (1). if. they. are. preadapted. or.
their.genetic/phenotypic.plasticity.is.suficient,.they.can.survive.under.novel.condi-
tions.and.the.geographic.range.of.the.species.will.remain.more.or.less.constant;.(2).
if. adaptation. does. not. occur. but. the. dispersal. capacity. of. individuals. allows. them.
to. track. suitable. environments. across. space,. then. the. species'. range. will. shift;. or.
(3).when.neither.adaptation.nor.movement.is.possible,.populations.experience.local.
reductions.in.density.or.extirpations.and.the.species'.range.shrinks—in.the.extreme.
case,. the. range. will. collapse. ubiquitously. and. the. species. will. go. extinct. globally.
(Holt. 1990).. In. real. life,. however,. intrinsic. (e.g
.
,. dispersal. potential,. population.
growth. rate,. life. history). and. extrinsic. (e.g.,. interacting. species'. dynamics,. human.
facilitation.or.hindrance,.disease,.environmental.catastrophes).factors.and.processes.
complicate.the.fundamental-level.dynamics,.making.prediction.of.consequences.of.
contemporary.climate.change.on.species'.distribution.and.abundance.a.challenging.
endeavor.(Thuiller.2004).
PREDICTING SPECIES' DISTRIBUTIONS UNDER CLIMATE CHANGE
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CologiCal
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iChe
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odeling
Currently,. the. most. popular. approach. for. forecasting. species'. rangewide. distribu-
tional.shifts.due.to.climate.change.is.termed.Ecological.Niche.Modeling.(ENM),.also.
known.in.the.literature.as.Species.Distribution.Modeling.(SDM),.Habitat.Suitability.
Modeling.(HSM),.and.Climate.Envelope.Modeling.(CEM),.among.others..Ecological.
niche. models. are. logically. elegant. because. they. simply. look. for. nonrandom. rela-
tionships.between.species.occurrences.and.a.set.of.environmental.variables.that.are.
known.(or.assumed).to.constrain.species'.distributions..These.relationships.are.then.
used. to. produce. potential. distribution. maps.. Next,. those. environmental. combina-
tions.suitable.for.the.species.are.incorporated.in.a.spatially.explicit.manner.with.≥1.
climate.scenarios.for.the.future.(or.the.past).to.produce.a.new.map.representing.the.
species'. potential. distribution. under. such. altered. conditions. (Pearson. and. Dawson.
2003;. Guisan. and. Thuiller. 2005).. Further. Geographic. Information. Systems. (GIS).
manipulations.and.analyses.allow.spatially.explicit.quantiication.of.the.amount.of.
area.expected.to.be.added.or.lost.through.time.from.the.species'.range.(Figure 4.1)..
Several.works.have.addressed.the.assumptions,.strengths,.and.shortcomings.of.this.
modeling. approach. (e.g.,. Pearson. and. Dawson. 2003;. Guisan. and. Thuiller. 2005;.
Araújo.and.Guisan.2006;.Guisan.et.al..2006;.Heikkinen.et.al..2006;.Botkin.et.al..
2007;.Soberón.and.Nakamura.2009)..Here,.I.will.review.some.of.the.most.important.
ones.and.present.the.trend.of.current.research.and.perspectives.in.the.ield.
The. conceptual. simplicity. of. ENMs. dictates. that. they. must. rely. on. a. number.
of. assumptions,. the. tenability. of. which. has. been. questioned. by. numerous. authors.
(Araújo.and.Guisan.2006)..First,.species.are.assumed.to.be.at.equilibrium.with.cli-
mate.(i.e.,.they.occupy.all.climatically.suitable.areas.available.for.them).when.niche.
models.are.projected.onto.future.scenarios.(Araújo.and.Pearson.2005)..In.practice,.
