Geoscience Reference
In-Depth Information
increased.daytime.cloudiness.prevents.frogs.from.inding.thermal.refuges.from.the.
pathogen.
Climate.change.variation.determines.altitudinal.patterns.of.extinction..According.
to.Pounds.et.al..(2006).mid-elevation.montane.
Atelopus
.species.experience.higher.
rates.of.extinction.than.do.those.restricted.to.the.lowlands.or.to.the.highest.eleva-
tions.(where.there.are.fewer.extinctions),.because.these.sites.in.tropical.America.are.
thermal.refuges.from.the.pathogen..In.these.refuges,.temperatures.are.either.too.high.
or.too.low.for.optimal.growth.of.BD.
Several.earlier.studies.suggested.that.BD
was.an.emergent.pathogen.and.poten-
tially.the.sole.reason.for.amphibian.population.declines.in.the.tropics.(Berger.et.al..
1998;.Daszak.et.al..1999)..While.chytridiomycosis,.the.disease.caused.by.BD,.was.
a.relatively.common.condition.in.many.areas.experiencing.declines,.the.early.stud-
ies. presented. no. mechanisms. explaining. the. emergence. of. the. pathogen.. In. many.
cases,. it. was. unknown. if. BD
was. responsible. for. causing. declines. directly. or. if. it.
was. secondary. in. nature. and. is. associated. with. already. dead. and. dying. animals.
(McCallum. 2005).. Thus,. Pounds. et. al.. (2006). explain. this. “climate-chytrid. para-
dox.”.The.climate-chytrid.paradox.simply.states.that.the.climatic.conditions.favoring.
chytrid.growth.appeared.to.be.the.opposite.of.those.created.by.current.climate.trends..
Pounds.et.al.'s.(2006).discussion.of.this.paradox.explains.how.shifting.temperatures.
may.be.the.ultimate.trigger.that.sets.off.a.pathogenic.fungus.such.as.BD—a.likely.
contributor.to.
Atelopus
.extinctions.
Importantly,.Pounds.et.al..(2006,.2007).suggest.that.the.dynamics.discussed.above.
are.but.one.of.many.potential.scenarios.and.that.more.than.one.pathogen.may.be.involved.
in.amphibian.population.declines..Moreover,.they.suggest.that.more.than.one.stressor.
could.make.amphibians.susceptible.to.disease..Their.“climate-linked.epidemic.hypoth-
esis”.assumed.no.speciic.disease.or.mechanism.of.outbreak.(Pounds.et.al..2007).
Lips.et.al..(2008).tested.the.climate-linked.epidemic.hypothesis.by.reanalyzing.
data.on.declines.and.extinctions.of.
Atelopus
.species.in.the.same.region.where.Pounds.
et.al..(2006).conducted.their.research..They.found.no.evidence.for.the.climate-linked.
epidemic.hypothesis.and.suggested.that.BD.is.an.introduced.pathogen.that.has.been.
spreading. throughout. the. American. tropics. since. the. 1970s.. This. spatiotemporal.
hypothesis.suggests.that.BD.spreads.independently.of.climate.shifts.
The. points. made. by. Lips. et. al.. (2008). have. been. questioned. in. recent. papers..
For.example,.Lampo.et.al..(2008).demonstrated.that.some.of.the.assumptions.of.the.
spatiotemporal. hypothesis. are. inconsistent. with. data. on. extinctions. and. declines..
Moreover,. some. populations. have. a. lag. time. of. 7. years. between. pathogen. arrival.
and.amphibian.population.declines,.while.other.populations.crash.when.BD.arrives..
Thus,. Lampo. et. al.. (2008). reason. that,. at. least. in. some. populations,. population.
crashes.must.not.be.indicative.of.BD.arrival.
Parmesan. and. Singer. (2008). stated. that. the. Lips. et. al.. (2008). analysis. is. sta-
tistically. lawed.. They. conclude. that. Pounds. et. al.. (2006). show. spatial. patterns. of.
amphibian.extinctions.that.are.moderately.consistent.with.climate.change.being.the.
driver.and.that.Lips.et.al..(2008).show.spatiotemporal.patterns.of.amphibian.popu-
lation. declines. that. are. moderately. consistent. with. disease. spread. (BD). being. the.
driver..They.also.suggest.that.both.hypotheses.are.supported.by.numerous.studies,.
are.not.mutually.exclusive,.and.may.be.interactive.
