Geoscience Reference
In-Depth Information
In.Japan,.Kusano.and.Inoue.(2008).analyzed.long-term.data.sets.(12-31.years).for.
three.species.of.amphibians.and.found.that.all.populations.examined.for.these.species.
were.breeding.earlier.(Table 2.1)..The.date.of.irst.spawning.was.correlated.with.the.mean.
monthly.temperature.just.before.the.breeding.season.for.each.population.examined.
The.broad.pattern.emerging.from.available.breeding.studies.is.that.some.temper-
ate.zone.amphibian.populations.show.a.trend.toward.breeding.earlier,.whereas.oth-
ers.do.not..The.reasons.for.this.variation.are.not.known.
ENVIRONMENTAL CHANGES AND
EMERGING INFECTIOUS DISEASES
One. potential. consequence. of. global. warming. is. the. increased. spread. of. infectious.
disease.(Cunningham.et.al..1996;.Epstein.1997)..This.may.occur,.for.example,.if.ris-
ing.temperatures.affect.the.distribution.of.the.vectors.of.a.pathogen,.thereby.making.
vectors.more.abundant,.or.if.an.environmental.agent.renders.a.host's.immune.system.
more.susceptible..Changes.in.temperature,.precipitation,.acidiication,.pollutants,.and.
increased.UV-B.radiation.are.some.of.the.stressors.that.may.affect.the.immune.systems.
of.amphibians..Immune.system.damage.from.multiple.stressors.could.make.amphib-
ians.more.susceptible.to.pathogens.whose.ranges.may.change.due.to.global.warming.
(Blaustein.et.al..1994b;.Kiesecker.and.Blaustein.1995,.1997)..Thus,.rising.temperatures.
and.changes.in.precipitation.could.be.stressful.and.might.be.associated.with.disease.
outbreaks.in.amphibian.populations.(Pounds.et.al..1999;.Kiesecker.et.al..2001).
There.is.some.evidence.that.climate.change.may.inluence.disease.emergence.in.
amphibian.populations..On.a.local.scale,.an.experimental.ield.study.in.Oregon.by.
Kiesecker.et.al..(2001).illustrates.the.complex.interrelationships.among.environmen-
tal.change,.UV.radiation,.and.amphibian.population.declines,.and.it.parallels.a.tropi-
cal.study.by.Pounds.et.al..(1999)..Kiesecker.et.al..(2001).linked.ENSO.events.with.
decreased.winter.precipitation.in.the.Oregon.Cascade.Range..They.suggested.that.
less.winter.snow.pack.resulted.in.lower.water.levels.when.western.toads.(
A. boreas
).
breed.in.early.spring..Toad.embryos.developing.in.shallower.water.are.exposed.to.
higher.levels.of.UV-B.radiation,.which.results.in.increased.mortality.from.the.patho-
genic. oomycete.
Saprolegnia ferax
..
Saprolegnia
. infects. all. stages. of. amphibians.
and.has.been.documented.to.cause.extreme.mortality.in.developing.embryos.(e.g.,.
Blaustein.et.al..1994b;.Romansic.et.al..2007,.2009).
Pounds. et. al.. (2006). identiied. two. dynamics. that. are. global. in. nature:. climate.
change. and. the. spread. of. a. highly. virulent. pathogen. (discussed. in. Blaustein. and.
Dobson. 2006).. A. pathogenic. “chytrid”. fungus,.
Batrachochytrium dendrobatidis
(BD),.is.implicated.as.the.proximate.cause.for.
Atelopus
.population.crashes.and.spe-
cies.extinctions.in.tropical.America..BD.infects.the.mouthparts.of.tadpoles.and.the.
skin.of.adult.amphibians.(Longcore.et.al..1999)..It.has.been.associated.with.amphib-
ian.population.declines.around.the.world.(e.g.,.Berger.et.al..1998;.Mendelson.et.al..
2006)..Pounds.et.al..(2006);.(Vredenburg.et.al..2010;.Blaustein.and.Johnson.2010).
presented.a.mechanistic.explanation.for.how.climate.change.inluences.outbreaks.of.
BD.by.modifying.conditions.in.montane.areas.of.Central.and.South.America.where.
nighttime. temperatures. are. shifting. closer. to. the. thermal. optimum. for. BD,. while.
