Geoscience Reference
In-Depth Information
environmental. data,. mechanistic. models. also. require. information. regarding.
physiological. tolerances. to. critical. variables. that. are. speciic. for. each. species.
(Helmuth. 2009;. Kearney. and. Porter. 2009).. Their. main. advantage. over. niche.
models.is.that.mechanistic.models.unveil.the.processes.underneath.distributional.
patterns.. That. is,. they. provide. an. explanation. not. only. of.
what
. environmental.
variables.are.critical.for.delimiting.a.species'.distribution,.but.also.
how
.and.
why
.
the. species. will. respond. to. changes. in. environmental. conditions. (Morin. et. al..
2007;.Kearney.et.al..2009).
Both. ENMs. and. mechanistic. models. have. advantages. and. limitations..
Consequently,.attempts.to.take.the.best.from.each.of.the.two.modeling.approaches.
and.produce.hybrid.models.are.starting.to.emerge,.with.promising.results..For.exam-
ple,. Crozier. and. Dwyer. (2006). developed. a. population-dynamic. model. to. analyze.
potential.range.shifts.of.the.skipper.butterly.(
Atalopedes campestris
).in.which.ambi-
ent.temperature.determines.population.growth.asymmetrically.across.seasons..Their.
results.indicate.differential.response.to.climate.change.during.summer.and.winter,.
and.an.overall.reduction.in.spatial.distribution..In.another.study,.Morin.and.Thuiller.
(2009). compared. range-shift. predictions. from. an. ENM. and. a. mechanistic. model.
for. 15. tree. species. in. North. America.. They. observed. that. niche. models. predicted.
higher.extinction.and.colonization.rates.than.did.the.mechanistic.model,.but.found.
that.the.two.approaches.identiied.generally.similar.trends.of.shifts.and.areas.of.local.
extinction..This.comparison.allows.the.quantiication.of.differences.between.the.two.
approaches.and.thus.the.assessment.(and.ultimately.reduction.of).uncertainty..This.is.
possible.because.the.two.modeling.processes.are.based.upon.different.assumptions;.
hence,.identifying.the.same.sites.that.are.prone.to.species.extinction.with.the.two.
approaches. is. complementary. and. provides. more. conidence. in. the. results. (Morin.
and.Thuiller.2009).
Spatially.explicit.mechanistic.and.hybrid.models.are.in.the.early.stages.of.devel-
opment,.but.their.potential.is.crystal.clear..It.is.desirable.to.have.stronger.interdisci-
plinary.collaboration.among.physiologists,.ecologists,.biogeographers,.and.computer.
scientists..Such.collaboration.could.be.used.irst.to.harvest.all.valuable.physiologi-
cal. and. demographic. information. from. the. literature. generated. from. centuries. of.
empirical.ield.and.experimental.research,.and.then.to.develop.tools.that.allow.the.
integration.and.analysis.of.spatial,.ecological,.and.physiological.data.to.derive.reli-
able.predictive.distributional.models.
PREDICTING SPECIES' ABUNDANCE AT THE RANGEWIDE SCALE
A.general.biogeographic.pattern.in.nature.is.that.population.numbers.vary.drasti-
cally. across. species'. ranges,. with. the. majority. of. places. holding. relatively. few.
individuals.and.only.some.sites.containing.orders.of.magnitude.more.individuals.
(Brown.et.al..1995)..Because.ENMs.use.either.presence.or.presence.and.absence.
data,.associated.predictive.maps.are.typically.not.expected.to.contain.any.infor-
mation.regarding.the.geographic.variation.in.abundance..However,.a.few.attempts.
have. been. made. to. predict. the. distribution. of. abundance. from. occurrence. data,.
with. quite. interesting. results.. He. and. Gaston. (2000). proposed. a. model. based. on.
the.relationship.between.the.area.of.the.sampling.unit.and.the.area.of.occupancy.
