Geoscience Reference
In-Depth Information
the.nearest.10-mile.increment..Similarly,.we.typically.have.no.information.to.know.
whether.direction.was.straight.West.or.“West-ish.”.All.of.these.inaccuracies.produce.
a. degree. of. uncertainty. in. occurrence. data. that. has. been. demonstrated. to. impact.
distributional. patterns. of. species. (Rowe. 2005). and. also. niche. models. (Graham. et.
al..2008)..Georeferencing.techniques.that.incorporate.a.measure.of.uncertainty.have.
been.developed.(Wieczorek.et.al..2004;.Guo.et.al..2008),.and.formal.tests.are.under.
development.to.assess.the.degree.to.which.positional.uncertainty.biases.model.results.
(J..Wieczorek,.pers..comm.),.but.these.are.topics.that.clearly.demand.further.research.
Environmental.layers.constitute.the.other.fundamental.source.of.primary.data.for.
building. ecological. niche. models.. Transfer. of. niche. models. through. time. requires.
parallel.sets.of.climatic.layers.for.the.present.and.at.least.one.period.in.the.past.or.
the.future..Climatic.surfaces.in.the.present.are.interpolations.from.climatic.stations.
that.vary.in.their.degree.of.accuracy,.depending.on.the.spatial.dispersion.of.stations.
and.the.length.of.time.measuring.climatic.variables.(Hijmans.et.al..2005;.Mitchell.
and.Jones.2005)..For.past.and.future.modeling.scenarios,.the.most.widely.used.data.
sets.are.derived.from.General.or.Regional.Circulation.Models.(Randall.et.al..2007)..
Several.works.have.evaluated.different.aspects.of.environmental.layers.in.the.per-
formance.of.niche.models,.such.as.the.type.and.number.of.layers.used.(Thuiller.et.
al..2004;.Luoto.et.al..2007;.Randin.et.al..2009).and.the.spatial.resolution.of.the.envi-
ronmental.data.(Guisan.et.al..2007a,.2007b;.Trivedi.et.al..2008)..In.the.context.of.
climate.change,.important.efforts.have.focused.on.analyzing.uncertainty.generated.
by. climatic. scenarios. in. model. output. (Peterson. et. al.. 2004;. Araújo. et. al.. 2005a,.
2005b)..Similarly,.numerous.works.have.evaluated.uncertainty.associated.with.dif-
ferent. modeling. techniques. for. transferring. species. distributions. across. space. and.
time.(Pearson.et.al..2006;.Peterson.et.al..2007;.Barbosa.et.al..2009)..Results.indicate.
very. high. variability. among. scenarios. and. methods,. to. the. degree. of. considering.
ENM.of.little.help.for.guiding.conservation.actions.(Dormann.2007).
As.a.result.of.this.situation,.new.analytical.tools.have.been.implemented.to.analyze.
and.reduce.uncertainty.in.model.projections..Particularly,.ensemble.approaches.have.
been.developed.to.capture.variability.among.various.modeling.techniques.and.sce-
narios,.assess.uncertainty,.and.obtain.results.that.are.more.stable.and.robust.(Araújo.
et.al..2005b;.Araújo.and.New.2007;.Coetzee.et.al..2009;.Diniz.et.al..2009;.Buisson.
et.al..2010)..For.example,.Araújo.and.New.(2007).proposed.a.framework.for.gen-
erating.and.analyzing.model.ensembles,.demonstrating.that.the.ensemble.approach.
produces.more.reliable.results.compared.to.single-model.approaches..Without.doubt,.
ensemble.forecasting.is.an.approach.that.will.develop.more.fully.in.the.ield.of.niche.
modeling.in.the.coming.years;.in.fact,.computerized.tools.for.manipulating.and.ana-
lyzing.ensembles.have.already.been.developed.(Thuiller.et.al..2009).and.others.are.
about.to.appear.(M..Araújo,.pers..comm.).
m odel V alidaTion
In. addition. to. the. variability. in. forecasts. among. niche. models. due. to. input-data.
and.analytical-technique.idiosyncrasies,.another.issue.of.concern.is.the.evaluation.
of.model.accuracy..For.example,.if.we.produce.a.series.of.models.for.current.and.
future. scenarios.using. different.techniques. but.use. the. same. input.data.(i.e.,.same.
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