Geoscience Reference
In-Depth Information
Niche hypervolume
Species'
populations
Niche centroid where optimal
conditions hold and abundance
is predicted to be maximal
Temperature
Distance to niche
centroid
FIGURE 4.3
Relationship.between.abundance.and.distance.to.niche.centroid..This.is.the.
conceptual.basis.for.predicting.spatial.patterns.of.abundance.
(i.e.,. an. “area-area. curve”).. They. derived. a. series. of. functions. that. successfully.
predicted.abundance.from.occurrence.data.at.local.scales,.but.the.model.was.not.
accurate.at.large.spatial.scales..As.an.improvement.of.previous.attempts.to.model.
abundance. patterns. from. occupancy. data,. Hui. and. McGeoch. (2007). developed.
the.“droopy-tail”.model.(DTM),.which.captures.the.logistic.relationship.between.
occupancy.and.abundance.more.accurately.than.alternative.models,.across.all.spa-
tial.scales.tested.
However,.looking.for.an.explanation.of.biogeographic.patterns.of.abundance.in.
the.geographic.domain.(i.e.,.as.a.consequence.of.landscape.coniguration).may.be.
misleading,.because.despite.the.fact.that.spatial.autocorrelation.exerts.an.important.
effect.on.the.distribution.of.abundance.(Brown.et.al..1995),.the.well-known.pattern.
of.species'.higher.abundance.at.the.center.of.the.geographic.range.compared.to.at.the.
periphery.(“the.abundant-center.hypothesis”).seems.to.be.incidental.and.not.a.gen-
eral.rule.(Sagarin.et.al..2006)..Local.population.abundance.is.largely.explained.by.
the.extent.to.which.local.niche.conditions.are.met.(Brown.1984)..If.this.is.true,.mod-
els.that.evaluate.the.suitability.of.sites.conferred.by.niche.conditions.should.relect.
abundance.patterns.to.some.degree..VanDerWal.et.al..(2009).tested.the.abundance-
suitability.relationship.using.a.probabilistic.niche.model.(Maxent),.interpreted.as.a.
suitability.surface,.and.local.abundance.for.69.vertebrate.species..They.found.a.posi-
tive.relationship.between.suitability.and.observed.abundance.for.most.species,.and.
concluded. that. such. a. modeling. approach. provides. reliable. information. on. spatial.
patterns.of.the.upper.limit.of.abundance.(VanDerWal.et.al..2009).
The.possibility.of.modeling.the.spatial.patterns.of.abundance.is.exciting..The.key.
seems.to.be.in.the.analysis.of.the.internal.structure.of.the.ecological.niche..Maguire.
(1973).demonstrated.that.optimal.conditions.for.a.species.are.found.near.the.niche.
centroid. in. environmental. space,. where. birth. rate. is. maximized. and. death. rate. is.
minimized..Thus,.abundance.should.be.highest.in.sites.where.niche-centroid.condi-
tions.are.met.(Figure 4.3)..Preliminary.tests.of.this.idea.have.yielded.very.promising.
results.(Díaz-Porras.2006),.but.further.testing.is.necessary.
