Download Reproductive ecology of Bombina variegata: characterisation of

Reproductiveecologyof Bombinavariegata: characterisation
of spawningponds
Heinz-Ulrich
Jonas
Barandun,
Reyer*
of
Winterthurerstrasse
CH-8057
Switzerland
Institute,
Zürich,
190,
Zürich,
University
Zoological
was
inadynamic
sites
habitat
The
useofspawning
Abstract.
byBombina
variegata
analysed
containing
aswell
aspermanent
were
avariety
ofdifferent
Cool
orshadowy
notused
forspawning
at
ponds
ponds.
were
numbers
increased
with
water
both
that
when
all.Among
theephemeral
used,
egg
ponds
temperature,
areas
within
numbers
inponds
between
different
were
also
of
and
ponds.
Egg
higher
among
ponds
compared
than
inthose
forshorter
orlonger
Ponds
ofintermediate
duration
with
intermediate
duration
persisting
periods.
with
larvae
ofcompeting
anuran
were
densities
and
arborea,
moderate
calamita)
species
(Hyla
Bufo
predator
more
often
than
short-lived
with
nopredators
and
This
ofspawn
used
competitors.
ponds
pattern
deposition
larval
toselect
sites
and
toavoid
can
beinterpreted
asanattempt
(warm
water)
allowing
rapid development
The
sites
with
numbers
ofnewts
and
invertebrate
selection
critera
seem
to
predators
(permanent
ponds).
high
are
and
desiccation
more
for
larval
survival
than
and
duration
beadaptive,
because
important
predators
pond
remain
conditions
forBombina
asthe
Yet,
highly
unpredictable
variegata,
competitors.
optimal
reproductive
aremainly
determined
conditions.
ofspawning
characteristics
and
ponds
byclimatic
Consequently
dynamics
chances
oftadpoles
can
within
afew
orweeks,
onrainfall
and
survival
days
depending
evaporation.
change
Introduction
hasa strong
influence
onoffspring
survival.
Thechoice
ofa spawning
byanurans
pond
occurs
before
Butmortality
rates
difInmost
mortality
metamorphosis.
highest
species,
sitesdepending
onpredation
ferdramatically
rate,riskofdesiccation,
among
spawning
andlarval
Banks
andBeebee,
1983;
conditions,
density
(Smith,
1987).
feeding
Rapid
because
it reduces
theexposure
totheserisksof
larval
isadvantageous
development
isenhanced
lowlarval
andsufbyhightemperature,
density,
mortality.
Development
ficient
foodsupply
Inorder
tomaximize
their
1980;
Riis,1991).
(Pawlowska-Indyk,
areconsequently
toavoid
adultanurans
short-lived
as
success,
expected
reproductive
orponds
withhighdensities
ofpredators
orcompeting
anuran
larvae
wellascoolponds
Banks
andBeebee,
1983;
1987).
(Smith,
author.
*Corresponding
144
orlakes
aregenerally
coolandcharacterized
Permanent
and
ponds
byhighdiversity
which
caneatlarge
numbers
oftadpoles.
larval
abundance
ofpredators
Thus,
mortality
Thishighmortality
isusually
ratemaybethe
(Licht,
1974).
ponds
highinpermanent
inpermanent
orlakes(Duellreason
regularly
spawn
whyfewanuran
species
ponds
andsurvival
inbothdurable
manandTrueb,
1986).
mayaffect
growth
Competition
under
stable
andtemporary
butismorepersistent
conditions.
When
ponds,
exposed
arewarm
andhighly
which
favours
tosunshine,
deproductive
temporary
ponds
quick
Buttemporary
Thus,
1987).
(Williams,
ponds
posetheriskofdesiccation.
velopment
interms
conditions
oftemperature,
andpredation
which
offer
better
productivity,
ponds
ofdesiccation
Thisposes
worse
interms
areusually
risk,andviceversa
(Smith,
1983).
ofoptimal
sites:
theanimals
areforced
totrade-off
adilemma
fortheselection
spawning
andlowpredation
riskwithhighdesiccation
ofrapid
risk.
theadvantages
development
whether
therearereasons
toassume
thatindividuals
Inthisarticle,
weinvestigate
related
tothedilemma
described
above.Under
onfactors
the
choose
a pondbased
wehypothesize
areassessed,
thatponds
with
thatthese
densities
assumption
qualities
high
aswellascoolandephemeral
areavoided.
orcompetitors
ofpredators
ponds
is a suitable
model
tostudy
Theyellow-bellied
toadBombina
variegata
organism
andunpredictable
conditions.
Theanimal
is
under
siteselection
conflicting
spawning
inagricultural
or
known
tospawn
insmall,
ponds,
nowadays
mostly
sunny,
temporary
Buta wide
ofpond
isusedforspawning,
habitats
industrial
1987).
(Bauer,
range
types
created
wheel
tovegetated
from
depressions
persistent
ponds.
newly
ranging
Methods
site
Study
ina military
area
areaislocated
north-east
ofZurich,
Thestudy
Switzerland,
training
mixed
forest
withlittle
About
onethirdoftheareaisa closed
forarmoured
vehicles.
Theremaining
areaisa scarcely
herbaceous
open
vegetated
sheep
pasture
vegetation.
toa ca.10haareawiththehighest
ofboth
onclay.Thestudy
wasrestricted
density
created
when
vehicles
the
areartificial,
andtoads.
Allexisting
compress
ponds
ponds
theshape
ofponds
winter
andearly
soil.Vehicle
changed
mainly
during
spring
activity
from
toSeptember,
theannual
single
sampling
period
April
ponds
every
year.During
atleast1989,
At18sites,
have
existed
since
were
disturbed
occasionally.
ponds
although
have
theirshapes
changed.
repeatedly
werestudied
ineachyearofthestudy.Fifteen
Intheopenarea,44to46ponds
intheforest.
Theforest
were
allcompletely
were
situated
other
ponds
temporary
ponds
dried
out.Adults
and
ofthese
small
andwithout
shaded,
onlyrarely
vegetation;
eight
intheforest
butnocalling,
norspawn
was
were
found
subadults
ponds
mating,
regularly
were
notincluded
intheanalyses.
rainpuddles
everrecorded.
These
Ephemeral
ponds
145
which
dried
outwithin
twodaysafterrainhadstopped
were
alsonotincluded
inthe
because
noadequate
habitat
measures
could
betaken.
analyses,
Since
onhuman
rainfall
andevaporation,
dynamics
activities,
pond
depended
mainly
within
differences
between
were
aslarge
asbetween
ecological
ponds
spawning
periods
within
wetreated
asindependent,
even
when
Therefore,
ponds
periods.
ponds
theywere
used
inmore
thanonespawning
Thisresults
ina totalof302ponds
forwhich
period.
dataareavailable.
Forsome
ofthem
thedatasetonreproduction
andpond
characteristics
isnotcomplete.
sizes
candiffer
between
Therefore,
sample
analyses.
characteristics
Description
of pond
Data
were
collected
from
28April
to6September
1991
andfrom
5May
to16September
ofpotential
1992.
activities
(i.e.,aftersignificant
During
periods
reproduction
rainfall)
andnumbers
ofadultanurans
andBufo
(Bombina
variegata,
Hylaarborea
calamita)
were
recorded
twice
aweek;
andnumbers
ofneweggswere
noted
Both
presence
daily.
in 1991and1992,
therewerefourseparate
In1991:19-24
spawning
phases.
May,
3-10June,16-30
25-31
7-9June,
24-29
June,
June,10-13
July.In1992:
July,22-25
these
canbegrouped
intofivenon-overlapping
combined,
July.Forbothyears
phases
seasonal
19-24
3-10
16-30
10-13
June,
June,
May,
periods:
Julyand22-31
July.Tadpole
numbers
were
recorded
infourcategories
Inaddition
> 1000.
to
of 0,< 100,
100-1000,
adult
andjuvenile
wemeasured
thefollowing
sixpondcharacteristics
anurans,
during
eachspawning
period:
areaofponds
wascalculated
from
measurements
withatapemeasure
1-3
(1)Surface
Areas
from
0.1
wheel
toabout
(a small
daysaftermaximal
filling.
ranged
depression)
50m2,butvaried
inseveral
asaconsequence
ofdesiccation.
daily
ponds
Consequently,
thesizedataareonlyapproximate.
wasmeasured
duration
ofdayseachpond
contained
(2)Pond
water,
bythenumber
fromthebeginning
ofa spawning
Insome
thisrepresents
an
cases,
starting
period.
overestimate
withrespect
tolarval
because
inirregularly
desurvival,
shaped
ponds,
wasa gradual
withlarge
siccation
ofponds
thewhole
process
parts
drying
longbefore
wasdry.However,
wascompletely
betaken
asan
pond
onlythedaya pond
drycould
With
measure
fordesiccation.
a
operational
tadpole
development
taking
upto60days,
of70dayswastaken
asthemaximum
duration
forsuccessful
pond
necessary
durability
development.
were
measured
onsunny
in1991
on31May,
(3)Maximum
pond
temperatures
days,
23June,
and29July,
in1992
on26Juneand30July.
cover
wasestimated
asthepercentage
ofthesurface
areacovered
(4)Vegetation
by
andSparganium
erctum.
emergent
plants,
mainly
Glyceria
sp.,Alisma
plantago-aquatica
Inmost
cover
overthesesaon.
ponds,
vegetation
changed
markedly
newts
T vulgaris)
werepredators
oneggsandsmall
(5)Adult
(Triturus
alpestris,
Thepresence
ofnewts
wasrecorded
andvisually
tadpoles.
bydipnet
sampling
during
inthreecategories:
none(never
visit;theirabundance
every
perpondwasestimated
146
individuals
andregularly
orsingle
few(1-2individuals
times),
(several
many
observed),
noted).
invertebrates
were
ontadpoles
Aeschnidae,
(Libellulidae,
Dytismainly
(6)Predators
Thepresence
and
Notonectidae,
1989).
(Engelhardt,
cidae,
Nepidae)
Hydrophilidae,
fornewts.
inthesame
wasrecorded
ofinvertebrates
abundance
wayasdescribed
Statistics
ofBombina
numbers
torelate
statistics
Weusedunivariate
variegata
eggsperpond
thataremost
characteristics
tofivepond
variables)
(independent
variable)
(dependent
water
andnumbers
ofadult
relevant
forlarval
duration,
temperature
pond
performance:
Inorder
totestforinterandotheranurans,
insects
respectively.
newts,
predacious
variables
thesefiveandthreeadditional
actions
(seasonal
independent
period,
among
theeight,
andforreducing
areaandvegetation
surface
correlating
cover)
potentially
weperformed
a princiofindependent
number
factors,
toa smaller
variables
composite
A
lowest
varimax
rotation.
with
eigenvalue
(PCA)
subsequent
analysis
palcomponent
tobeextracted;
ofprincipal
thenumber
fordetermining
ofI wasused
(PCs)
components
variables
andPCswere
between
< 10.4501
("zero
loadings")
ignored
original
loadings
factors
theresulting
(Aspey
andonlyloadings10.5501
>_ wereusedforinterpreting
a precondition
for
oforiginal
distribution
Normal
variables,
andBlankenship,
1977).
variables
inanyoftheeight
didnotexist
(all
most
multivariate
independent
techniques,
arequite
ButPCAs
oftheKolmogorov-Smirnov-test).
Lilliefors-modification
P < 0.05;
and
ofnormality
from
theassumption
deviations
1973;
robust
(Balthazart,
Aspey
against
noruseofSpearman,
rather
than
datatransformation
andneither
1977)
Blankenship,
scores
weusedfactor
ofourPCA.
theoutcome
Peason
correlations
Therefore,
changed
thescores
toeggoccurrence
data.Werelated
onuntransformed
fromthePCAbased
andtoeggnumber
ofadiscriminant
by
(log-transformed)
analysis
(yesorno)bymeans
means
ofamultiple
analysis.
regression
tests
results.
Allstatistical
withtherespective
Further
details
ofthetestsaregiven
5.0(Systat,
Version
forWindows,
withSystat
were
Inc.)anda significance
performed
level
ofP = 0.05wasusedthroughout.
Results
thistimespan,
19Mayand31July.Within
laidbetween
were
activity
spawning
Eggs
withheavy
indistinct
butoccurred
wasnotuniformly
distributed,
synchronized
periods,
for302ponds.
inpress).
Werecorded
andReyer,
rainfall
activity
spawning
(Barandun
densities
from
found
ofthemwenever
In197(= 65%)
ranged
eggs,intheothers,
tobeinfluenced
islikely
surface.
0.1to61eggs/m2
bya combination
Spawning
pond
thanbysingle
rather
Nevertheless
ofdifferent
variables,
pondqualities.
ecological
147
ofunivariate
toillustrate
thedatadistribution
andto
(1)helps
knowledge
relationships
results
from
multivariate
interpret
subsequent
(2).
analyses
based
onsingle
variables
1 Analyses
)
ecological
ofeggs(dependent
Infig.la-e,thenumber
the
variable)
perpondisplotted
against
fivepondcharacteristics
thataremost
forlarval
variables)
(independent
important
perfomance
riskofdesiccation),
(a):pondduration
(representing
(b)water
temperature
ofdevelopment),
densities
(c)newtand(d)invertebrate
(influencing
speed
(affecting
and(e)number
ofother
larval
anurans
forfood).
predation)
(representing
competition
between
thedependent
andeachindependent
variable
weretested
with
Relationships
regression
analyses.
ofthemonitored
varied
fromthree
(a)Pondduration
(fig.la): Theduration
ponds
Within
thesamepond,
dessication
ratevaried
theseason,
daystoperennial.
during
onweather
andvegetation.
There
wasnolinear
between
depending
relationship
egg
number
andpondduration
r2 = 0.001),
buta tendency
forponds
of
(P = 0.543,
tocontain
thehighest
intermediate
duration
number
rz= 0.034;
2nddegree
(P= 0.008,
While
theloweggnumber
indurable
active
polynomial
regression).
ponds
mayreflect
asaresponse
tohigher
avoidance
inthese
thelow
predation
pressure
(seebelow),
ponds
inponds
duration
doesnotseem
number
ofveryshort
toresult
from
because
avoidance,
inalmost
inseven
toads
Amore
isthat
cases,
spawned
dryponds.
likely
explanation
short-term
cannot
beused
asfrequently
forspawning
asmore
durable
ones.
Thus,
ponds
ineggnumbers
attherightendofthedistribution
thedecrease
curve
seems
toindicate
anadaptive
thedecrease
attheleftenda constraint.
response,
varied
bothwithin
andamong
(b)Temperature
(fig.lb): Water
temperature
markedly,
Onsunny
could
increase
than10°C
within
twohours
ponds.
days,
temperature
bymore
inopenshallow
almost
constant
atthebottom
orinvegetation.
parts,butremained
warmer
wereonaverage
s: 31.9 2.3°C)
± thanponds
which
(x:::!::
Spawning
ponds
were
notused
wasa significant
between
2.4)andthere
positive
relationship
egg
number
andwater
r2= 0.030).
Theimportance
ofwarm
water
(P= 0.003,
temperature
forspawning
isalsosupported
observations:
none
oftheshadowy,
First,
bytwoother
coolponds
intheforest
waseverusedforreproduction.
in16cases
where
the
Second,
distribution
wasrecorded
inthermally
ofspawn
spatial
heterogeneous
ponds,
eggswere
found
13times
inthewarmer
andonly3times
inthecooler
Thisissignificantly
parts.
different
from
anequal
distribution
Binomial
test,one-tailed).
(P= 0.011,
andinvertebrate
larvae
ofthefirstseasonal
(c,d)Predators
(fig.Ic,d): Newts
generationoccurred
inponds
untilabout
mid-June.
Thesecond
invertebrate
larval
generation
didnotbecome
fortadpoles
before
theendofJuly.So,eggs
andtadpoles
were
dangerous
from
lateJune
tobesafefrom
tolateJuly,
butnotfrom
likely
aquatic
predators
predation
148
characterist
inrelation
toseasonal
and
seven
ofeggs
1. Total
number
pond
period
perpond
Figure
boxes
25-75%
Vertical
lines
show
lines
medians.
solid
horizontal
90%,
Diamonds
ranges.
means,
represent
variable
areavailable.
data
ontherespective
forwhich
ofponds
Nrefers
tothenumber
149
which
alsowere
observed
toeattadpoles
and
crows,
(herons,
gulls),
occasionally
bybirds
aheron
took79outof81largetadpoles
within
one
Inonenearly
drypond,
metamorphs.
canalsoeliminate
alleggsortadpoles
from
newt
orinvertebrate
Asingle
hour.
predator
time.
With
such
dramatic
effects
ofpredation
onreproductive
within
ashort
asmall
pond
withpredators
toavoid
forspawning.
beexpected
toads
could
success,
ponds
Contrary
wasnotrelated
toaquatic
foreither
tothisexpectation,
predator
density
eggnumber
bothP > 0.450,
df= 2).Eggnumber
could
not
larvae
newts
orinvertebrate
(ANOVA;
because
theoccasional
visits
ofbirds
toponds
could
berelated
toterrestrial
predation,
bequantified.
notreliably
other
anuran
usedthestudied
for
species
ponds
(fig.le): Two
(e)Anuran
competitors
started
attheendof
arborea.
Both
calamita
andHyla
species
breeding
Bufo
spawning:
Bombina
inearly
weeks
before
onetothree
did,butstopped
variegata
breeding
April,
timeduring
thebreeding
atany one
Bombina
continued
untilAugust.
while
Thus,
July,
tolaytheireggsintoponds
withor
adults
hadthechoice
Bombina
season,
variegata
isnotaffected
fromother
without
tadpoles.
Apparently,
spawning
bysuch
competition
were
inthesame
theirmales
occurred
Allthreespecies
together
pond;
competition.
several
andBombina
within
30cmofeachother
observed
hours,
during
pairs
calling
calamita
orHyla
beside
werefound
tospawn
directly
simultaneously
spawning
Bufo
number
andthe
between
There
wasnosignificant
arborea.
Bombina-egg
relationship
P = 0.877,
df= 4);eggswere
andHyla-tadpoles
ofBufocombined
(ANOVA;
density
laidintoponds
containing
upto100tadpoles/m2.
onvariable
combinations
based
2)Analyses
univariate
totheabove
variables:
independent
According
among
(a)Relationships
inBombina
determinant
ofeggdistribution
is themajor
analyses,
pondtemperature
asmentioned
alsoseems
toexertsome
influence.
duration
However,
variegata;
pond
a multivariate
distribution
ofspawn
a deeper
approach,
requires
before,
understanding
effects.
We
andconfound
eachother's
variables
because
several
mayinteract
ecological
onthe
aprincipal
thisinteraction
(PCA)
analysis
component
byperforming
investigated
additional
characteristics
theunivariate
fivevariables
from
(surpond
analysis
plusthree
within
theseason;
andperiod
cover
facearea,vegetation
affecting
fig.If-h)potentially
withcuesastowhere
andwhen
tospawn.
thetoads
them
and,consequently,
providing
variables
tothree
correlated
reduced
theeight,
ThePCA
partly
original
independent
I
72.6%
ofthetotalvariance
component
factors,
(fig.2).Principal
together
explaining
ofpond
surface
andduration
ischaracterized
and,thus,canbe
byhighloadings
(PC1)
anuran
andlarvae
ofcompeting
Densities
ofinvertebrate
termed
size".
predators
"pond
thatthese
more
withthisfactor,
alsocorrelate
species
prefer
larger,
suggesting
species
2
desiccation.
toavoid
Principal
component
complete
mortality
through
ponds
permanent
ofperiod.
from
the
asindicated
Following
bythehighloading
"seasonality",
represents
scores
ofseasonality
reflect
factor
onPC2andtheirsigns,
otherloadings
increasing
150
aprincipal
based
ontheeight
2.Result
from
variables
offig.1.Names
ofthe
analyis,
Figure
component
are
initalics
above
thecircles,
variances
three
(PCs)
components
given
explained
principal
bytherespectiv
PCwithin
thecircles.
Numbers
above
thelines
PCs
and
variables
refer
tofactor
connecting
original
loadings
ones
lines.
Positive
areindicated
relationships
bysolid,
negative
bybroken
newtdensity
andreduced
cover,
season,
increasing
vegetation
decreasing
progressing
PC3represents
"thermal
withhighfactor
scores
conditions",
Finally,
pondduration.
andhighvegetation
lowwater
cover.
Two
results
ofthisPCA
representing
temperature
distribution
ofnewts
wasbetter
First,
require
special
explanations:
explained
byseasonaduetotheirabsence
from
aftermid-June.
litythanbypondsize.Thisismainly
ponds
Newts
were
alsohighly
often
visited
mobile,
and,thus,
ponds
onlyduring
single
nights
than
were
lessrestricted
topermanent
invertebrate
one
Second,
ponds
predators.
although
would
thatwater
increases
from
toAugust,
temperature
April
expect
pond
temperature
wasnotrelated
toseasonality.
Theexlanation
liesinanopposing
probably
(i.e.,
cooling)
effect
ofvegetation
which
increases
withprogressing
season
(seePC3)
(seePC2).
151
1.Summary
ofrelationships
between
and
Table
statistics
conditions
described
activity
spawning
ecological
by
from
2.Table
statistics
from
thediscriminant
thethree
based
(PCs)
fig.
a)lists
principal
components
analysis
or
table
shows
statistics
from
the
ontheoccurrence
ofspawn
based
on
(yesno), b)
multiple
regression egg
inboth
from
theTables
included
butomitted
forreasons
ofclarity.
numbers.
Constants
were
tests,
between
actoecological
inrelation
factors:Therelationship
spawning
(b)Spawning
wastested
factors
extracted
intwoways:
andthethree
First,
ecological
bythePCA
tivity
between
withandwithout
wasusedtodistinguish
a discriminant
ponds
spawn,
analysis
wasperformed
ofeggnumbers;
a multiple
to
second,
regression
analysis
independent
ofthetwoanalyses
intable1.
PCs.Results
areshown
tothethree
relate
eggnumbers
wasnotsignificantly
related
topondsize(PC
Inbothcases,
1 and
) seasonality
spawning
conditions
Thissupports
thedominating
effect
withthermal
butincreased
(PC3).
(PC2)
Thediscriminant
function
from
thefirst
found
intheunivariate
oftemperature
analysis.
60%ofallponds,
102outof164without
and
classified
about
correctly
spawn
analysis
different
from
Thisissignificantly
66outof113withspawn.
(x2= 10.611,
expectation
Thediscrepancy
thateggnumbers
were
related
topond
duration
in
df= 1,P = 0.001).
inthis
PC1 orPC2(also
theunivariate
test,butnottoeither
duration)
representing
pond
thefactthatcalculation
ofprincipal
assumes
arises
from
components
analysis,
probably
duration
a linear
which
isnottrueforpond
(seefig.la).
relationship
Discussion
variable
selection
turned
outtobethemajor
of
Water
ecological
affecting
temperature
Theobserved
forwarm
and
sitesinBombina
variegata.
preference
ponds,
spawning
corroborates
oftypical
forwarmer
within
a pond,
descriptions
parts
previous
spawning
Itisalsoinaccordance
with
sitesasbeing
Grossenbacher,
1987;
1988).
(Bauer,
sunny
forhigher
water
found
inother
anurans,
(Kuhn,
temperatures
e.g.,Bufo
bufo
preferences
Wollmuth
etal.,1987;
etal.,
andvarious
Ranaspecies
1984;
(Sinsch,
Sj6gren
1993)
152
ofsuchpreference
is usually
Theadaptive
seenintheresulting
1988).
significance
andearlier
theanimals
faster
larval
toescape
the
metamorphosis,
development
allowing
withitshighpredation
anddesiccation
risksassoonaspossible
environment
aquatic
andBerven,
ForBombina
this
Newman,
1979;
1980).
however,
(Smith-Gill
variegata,
theadults'
forwarm
isnotsufficient
toexplain
because
successful
preference
ponds,
wasnotrelated
towater
oftheireggsandlarvae
buttopond
development
temperature,
inpress):
andReyer,
durable
duration
eggslaidinmore
(Barandun
ponds
produced
these
contained
more
eventhough
more
insects
newts,
metamorphs,
ponds
predacious
inBombina
thewell
known
trade-off
andother
anuran
between
Thus,
variegata,
species.
riskinsmall,
andhigher
and
desiccation
ususally
predator-free
ponds
competition
higher
Semlitsch
andReyer,
riskindurable
1983;
Woodward,
1983;
(Smith,
ponds
predation
Thisresult
toexplain
siteselection
isdecided
forthelatter.
1992)
helps
whyspawning
andpredators.
ofcompetitors
small
is notaffected
Moreover,
choosing
bydensities
andinvertebrates
isnoguarantee
toescape
withnooronlyafewnewts
predation.
ponds
Thelackofaquatic
birds,
predators
maybecompensated
byhigher
predation
through
andVaira,
Avoidance
ofspawning
atthese
small
(cf.Crump
1991).
ponds
particularly
withhighpredator
densities
hasbeen
documented
forsome
other
inponds
anurans,
e.g.,
conditions
andWilbur,
under
but
forHylachrysoscelis
(Resetarits
1989),
experimental
andselecting
remain
unknown
and
thecuesusedforsearching,
(Ritke
discriminating,
Mumme,
1993).
ofpondduration
anddesiccation
forlarval
deWiththeoverwhelming
importance
it ispuzzling
thatthetoads
seem
topayonlylittle
inBonabina
variegata,
velopment
useanenvironmental
cueforeggdistothisfactor
attention
hand,
and,ontheother
ofreproductive
This
tribution
thatis a poorpredictor
success,
namely
temperature.
Interms
andbiological
reasons.
of
mayarisefrombothmethodological
discrepancy
measured
atother
thanthespawning
times.
In
were
often
characterisitics
method,
pond
forinstance,
sizeatthetimewhen
surface
measurements
were
drying
ponds,
quickly
thansizeatthetimeofspawning.
some
characteristic
wasoftenlarger
Also,
taken,
and/or
different
ofthepond.Thefinding
that
were
overlonger
parts
periods
averaged
wasnotuniform
with
totemperature,
indicates
that
within
respect
eggdistribution
ponds
unitforcharacterizing
conditions.
thepond
spawning
Spawning
maynotbeanadequate
hasalsobeenfound
inseveral
siteselection
within
heterogeneous
ponds
ecologically
Wollmuth
etal.,1987;
etal.,
other
1978;
Caldwell,
1986;
(Howard,
Sj6gren
amphibians
1988;
Warkentin,
1992;
Kuhn,
1988;
1993).
Waringer-L6schenkohl,
inourstudy
areaarehighly
because
conditions
Interms
ofbiology,
unpredictable,
pond
andpondduration
onweather
conditions.
A
bothwater
directly
depend
temperature
andextend
theduration
ofa pond
rainshower
canlower
byas
single
heavy
temperatures
willresult
inwarm
water
afewhotdays,
much
asthree
weeks;
causing
high
evaporation,
theexceptional
inJuly
asseenduring
andcanleadtocomplete
desiccation,
droughts
andAugust
of1991
and1992
andReyer,
inpress).
sizeand
(Barandun
Although
pond
information
about
these
cuesarefarfrom
timeoftheseason
offer
some
conditions,
pond
153
ofthermal
reliable.
Thisisillustrated
conditions
from
most
being
bytheseparation
(PC3)
andbytherelatively
lowcomponent
between
other
loadings
pondcharacteristics
pond
andPC2(seasonality),
Under
these
duration
andPC1
conditions
respectively.
(pondsize)
inwarm
ofintermediate
duration
willoften
result
ofunpredictability,
ponds
spawning
failure.
withheavy
rainfall
intotalreproductive
Yet,when
(Barandun
synchronized
a higher
itwill,onaverage,
fitness
thanspawning
incooler,
andReyer,
inpress)
yield
where
slow
andhighpredation
rates
areguaranteed.
development
ponds
permanent
students
and
friends
fortheir
inthefield
We
thank
themany
and
B.Anholt,
G.Guex,
help
Acknowledgements.
onthemanuscript.
and
R.D.
Semlitsch
forcritical
comments
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