Geoscience Reference
In-Depth Information
latitudinal. gradients.. This. means. that. a. species'. distribution. might. more. quickly.
reach. equilibrium. within. a. new. climate. by. using. elevational. gradients. rather. than.
latitudinal. ones,. all. else. being. equal.. In. addition,. Peterson. (2003). and. Guralnick.
(2006a). argued. that. mountain. and. latland. species. would. show. different. patterns.
of. range. expansion. and. contraction. under. warming. scenarios.. In. particular,. wide-
ranging.latland.species.likely.shift.their.ranges.farther.than.mountain.species.under.
warming..During.warming.episodes,.as.favorable.habitats.expand.northward,.North.
American. mountain. species. follow,. extending. their. northern. range. boundaries..
Southern. geographic-range. boundaries,. on. the. other. hand,. remain. relatively. static.
due. to. topographic. heterogeneity. and. the. resulting. ability. of. mountain. species. to.
track.favorable.conditions.by.simply.moving.up.elevational.gradients..Flatland.spe-
cies.are.not.able.to.select.habitats.along.elevational.gradients,.leading.to.latitudinal.
range.shifts.and.potential.range.contractions,.depending.on.the.dynamics.of.northern.
and.southern.range.boundaries.
Distributional. dynamics. and. population. connectivity. are. greatly. affected. by.
topography..For.cold-adapted.species.living.in.mountainous.areas,.continued.warm-
ing. may. cause. populations. to. retreat. upward. in. elevation.. Upward. range. shifts.
have. two. important. consequences.. First,. the. total. area. occupied. by. the. species.
decreases. because. mountains. typically. narrow. from. base. to. peak,. which. can. lead.
to.fewer.available.resources.and.lower.population.sizes.and.ultimately.local.extinc-
tion.(Figure 5.1,.especially.B;.see.also.Sekercioglu.et.al..2008)..Second,.previously.
contiguous.populations.are.divided.when.lowland.routes.are.no.longer.suitable.for.
dispersal.(Figure 5.1—note.the.loss.of.lowland.connections.in.A.and.B.during.warm-
ing).. Loss. of. lowland. habitats. cuts. off. gene. low. between. populations. (Ditto. and.
Frey.2007).and.can.lead.to.more.stochastic.extinctions.of.small.populations.that.can.
no. longer. be. recolonized.. Alternatively,. surviving. populations. may. become. better.
adapted.to.local.conditions..Evidence.for.local.adaptation.in.North.American.mam-
mals. comes. from. Guralnick. (2006b),. who. showed. that. there. is. more. variation. in.
experienced.climate.in.the.southern.portions.of.ranges.occupied.by.mountain.species.
than.in.the.northern.portions..The.persistence.of.populations.in.these.southern.areas.
likely. relects. long-term. adaptation. to. these. variable. local. conditions.. In. contrast,.
northern. populations. in. the. Holarctic. are. recent. immigrants. that. colonized. newly.
suitable.habitat.as.continental.ice.sheets.receded.during.warming.in.the.latest.Late.
Pleistocene. (18kya-10kya). and. Holocene. (10kya-present).. These. populations. most.
likely.do.not.represent.the.whole.of.the.gene.pool.found.in.the.South.and.thus.may.
be.tracking.a.subset.of.climatic.conditions.as.they.disperse..In.latland.areas,.such.
as.eastern.North.America,.warming.is.more.likely.to.cause.a.whole-cloth.shift.of.
distributions.toward.the.North,.at.both.range.edges..At.the.same.time,.warming.is.
not.as.likely.to.cause.vicariance,.and.gene.low.from.the.center.of.ranges.to.the.edges.
may.limit.the.potential.for.local.adaptations.
Mountain.orientation.may.also.be.an.important.factor.affecting.mountain.species.
response.to.warming..In.the.Americas,.most.mountain.chains.are.oriented.approxi-
mately. North-South,. which. means. that. elevation. and. concomitant. temperature.
gradients. are. generally. oriented. East-West,. perpendicular. to. latitudinal. gradients..
Therefore,. mammal. species. tracking. climatic. changes. along. elevational. gradients.
move.perpendicularly.to.those.tracking.climatic.changes.along.latitude..In.Europe,.
