Society for the Study of Amphibians and Reptiles
Predator Mediated Patch Use by Tadpoles (Hyla regilla): Risk Balancing or Consequence of
Motionlessness?
Author(s): Sarah J. Kupferberg
Source: Journal of Herpetology, Vol. 32, No. 1 (Mar., 1998), pp. 84-92
Published by: Society for the Study of Amphibians and Reptiles
Stable URL: http://www.jstor.org/stable/1565484
Accessed: 24-04-2015 21:35 UTC
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Vol.32, No. 1, pp. 84-92, 1998
Journal
of Herpetology,
Copyright1998Societyforthe Studyof Amphibiansand Reptiles
PredatorMediated Patch Use by Tadpoles (Hyla regilla):
Risk Balancing or Consequence of Motionlessness?
SARAH J. KUPFERBERG1
Departmentof IntegrativeBiology,Universityof California,Berkeley,California94720, USA
ABSTRACT.-TOquantify the impact of garter snakes (Thamnophishydrophilus,formerly T. couchii)on
tadpole prey (Hyla regilla),I experimentallyexamined whether: (1) gartersnakes have greaterimpact on
tadpole numbers or on behavior;(2) tadpole patch choice follows the rule of minimizing the ratio of mortality risk, iL, to foraging gain, g; and (3) predator-inducedresourceavoidanceinfluencesalgal production.
In replicatedenclosed pools constructedon gravel bars of a northernCaliforniariver,gartersnakes did not
significantlyreducethe numberof tadpolesbut did alterpatchchoice.Tadpolesspent less time in high food
quality algae mats (Cladophora
glomeratawith epiphyticdiatoms)and moretime in low food qualitypatches
(Zygnematalesalgae mats and sediments) when gartersnakes were presentthan when they were absent In
mortalityrisk experiments,however, there were no significantdifferencesin the numbers of tadpoles consumed among patch types, and gartersnakes were not size selective. Therefore,patch choice did not follow
the rule of minimizing /Ag. The change in patch choice was likely a consequenceof the sublethal effect of
garter snakes in which tadpole activity is decreased.For negatively buoyant tadpoles, decreasedactivity
results in sinking away from floating algal resources.This apparentresourceavoidanceby tadpoles did not
affect algal mass over the relatively short durationof the experiments.
For anurans, many factors affect the transition
from tadpole to frog: temperature, nutrition,
competition, predation, and environmental variability. These factors are summarized by two all
encompassing parameters, A, risk of mortality,
and g, growth rate, which have been used in
recent models to predict optimal sizes at which
ontogenetic changes in niche should occur (Werner and Gilliam, 1984), and to predict patch
choice in the presence of a predator (Gilliam
and Fraser, 1987; Abrahams and Dill, 1989; Gotceitas, 1990). The basic premise of risk-balancing
models is that growing prey confront tradeoffs
between gaining energy and avoiding predation. Foraging in a rich habitat may provide
great energetic gain but may entail predation
risk, whereas staying in a refuge may entail risk
of starvation or slow growth, making transition
to the next life stage unlikely. When animals occupy habitats which minimize the ratio (,/ g),
population growth is maximized.
Adaptive behaviors that decrease vulnerability to predators, such as decreased activity levels, can also cause patterns of distribution
among patches that appear to follow the ,//g
rule. In addition to influencing shifts in habitat
use, predation risk can decrease prey activity
(Lawler, 1989; Werer, 1991; Semlitsch and Reyer, 1992; Skelly, 1995). Immobility can decrease
the chance of attack by visual predators (Brodie
et al., 1974; Caldwell et al., 1980; Feder, 1983;
Peterson and Blaustein, 1992) and increase survival time (Azvedo-Ramos et al., 1992). For negatively buoyant prey in aquatic environments,
however, this predator avoidance behavior could
be misinterpreted as risk-balancing patch choice
if motionlessness causes prey to sink away from
floating or suspended algal food resources.
I studied tradeoffs between predation risk
and foraging gain in a three trophic level system: garter snake predators, tadpole prey, and
algal resources. In western North America, Pacific treefrogs (Hyla regilla) and garter snakes
(Thamnophisspp.) are extremely common in a
wide range of aquatic habitats. Preliminary observations of western aquatic garter snake
(Thamnophishydrophilus,formerly T couchii) distribution and feeding on tadpoles in northern
California rivers suggested that snakes were
concentrated around algal patches where tadpoles were foraging. To quantify the impact garter snakes have on tadpole prey, I conducted a
series of replicated field experiments. Specifically, I examined whether: (1) garter snakes have
greater impact on tadpole numbers or on behavior, (2) tadpole patch choice follows the rule
of minimizing // g; and (3) predator induced
resource avoidance influences algal production.
STUDY SYSTEMNATURAL HISTORY
I conducted this research in the South Fork
Eel River (Angelo Coast Range Reserve, Mendocino Co., California), where western aquatic
garter snakes and Pacific treefrogs are common.
Garter snakes have long been considered important predators of tadpoles because tadpoles
can make up a significant proportion of their
gut contents (Fitch, 1965; Arnold, 1992; Lind
and Welsh, 1994). Garter snakes which forage at
aquatic/terrestrial margins may differentially
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TADPOLE PATCH CHOICE
prey upon metamorphicanurans (Arnold and
Wassersug,1978;Jones, 1990) when locomotion
is hindered by both tail and legs being present
(Wassersug and Sperry, 1977). Some garter
snakes, however,are specialized for underwater
foraging (Drummond, 1983; Schaeffel and de
Queiroz, 1990)and consume tadpoles of all freeswimming stages (Drummondand MaciasGarin particular,
cia, 1989). Thamnophis
hydrophilus
has visual system modifications, including a
large degree of pupil constriction,allowing it to
focus under water at greaterdistances than other snakes (Schaeffeland De Queiroz, 1990).
and
In the South ForkEel River,T.hydrophilus
the
in
are
two
found
habitats,
adjacent
tadpoles
main channel and stranded side pools. During
the low flow season the main channelbecomes
lentic and overgrown with the green alga ClaTurfs of algae break off from
glomerata.
dophora
rock substratesto form large floatingmats. Garter snakes often bask on and foragein the warm
sunlit algae mats which contain invertebrates,
fish, and tadpoles. Gartersnakes also forage in
shallow, turbid side pools that are cut off from
the river channel and support high densities of
tadpoles. Tadpoledistributionis very patchy.In
1 m wide transectsurveys across side pools and
adjacentriver channels,density routinelyvaries
from 0-35/m2 between adjacent m2 plots (Kup-
ferberg,unpubl. data).
In the main channel and sidepools, algal
foods availableto tadpoles vary greatlyin quality in large part due to the presenceof nutritious
epiphytic diatoms. Tadpoles fed epiphytized
usually the dominant alga
Cladophora
glomerata,
in the main channelof the river,metamorphose
significantlyfasterand weigh significantlymore
than tadpoles fed Mougeotia(Kupferberget al.,
1994) or Spirogyra(unpubl.data).Mougeotiaand
Spirogyra,members of the chlorophyte order
Zygnematales,have thick mucilaginoussheaths
which prevent colonization by diatom epiphytes. These algae are found in side pools and
dominate in years when hydrologic conditions
are poor. Growth rates (slopes
for Cladophora
from linear regressions of growth data from
Kupferberget al., 1994; and unpubl. data) on
these foods are 28 mg/day for epiphytized Cladophora,12.3 mg/day for Mougeotiaand Spirogyra,and 7.1 mg/day for tadpoles eating seston
and diatom films on rocks.
MATERIALS AND METHODS
Predation trials were conducted in replicate
pools excavated on a gravel bar, six pools in
1990,and 24 pools in 1991.Pools were 1 m wide
with sloping sides. Waterdepth was 20 cm at
the center.Pools were enclosed by circularfences 2 m diameter,46 cm high, with a 23 cm overhang made of shade cloth. To preventcarryover
85
effects of predatorchemicalcues (Petrankaet al.,
1987; Feminellaand Hawkins, 1994), I cleaned
pools between trials by bailing out water and
allowing them to refill by ground water intrusion. Pools were excavated to compensate for
decreasingwater table height when necessary.
In all experiments,I stocked pools with ten
H. regillatadpoles that had been collected as
eggs and reared on mixed algal diets in flow
through 12 1 bucket enclosures in the river at a
density of 10 tadpoles/bucket. Garter snakes
were caughtby hand, kept without food for 2448 h, and then randomlyassigned to enclosures.
If mean size varied significantly among treatments, snakes were reassigned.Juvenilesnakes
were used in the experimentsbecause snakes of
that size naturally spend 50% of their time in
similar pool habitats (Lind and Welsh, 1994).
Snake size ranged from 20 to 33 cm SVL.Trial
durationvaried from experimentto experiment
in part because of weather.Snakesoften did not
forage on cool or cloudy days.
Patch Choice,ExperimentsI, II.-For Experiment I, in 1990,six replicateponds were stocked
with tadpoles and 250 g damp mass Cladophora
and 250 g Mougeotia.
Algae were spun in a salad
spinner 50x before weighing to attain uniform
watercontent (Hay 1986).After one day a garter
snake was added to each of three randomlychosen pools. Tadpolelocationand the numbersurviving were spot checked4-6 times/d on days
2, 5, and 6. The mean proportionin each algal
type and in the gravel sediment on each day
was calculated. Continuous observations of
snake and tadpole behavior were made at the
end of the experimentby transferringa garter
snake that was an effective predatorin another
enclosure to a previously snake free enclosure.
In 1991, I observed patch choice with varying
duration of snake exposure (Experiment II).
Twenty four pond enclosureswere stockedwith
and 260 g
weighed tadpoles, 260 g Cladophora,
of Mougeotia.After 1, 4, and 7 d, a gartersnake
was added to each of four randomly chosen
ponds. Twelve replicate ponds did not receive
garter snakes. Mean garter snake size did not
differ among treatments.On day 9 tadpole feedMougeoing activity and location in Cladophora,
tia, or sediment, was spot checked at 1000 h,
1400 h, and 1600 h. Four observers rotated
among the pools. After the final spot check,tadpoles and algae were harvested and weighed.
Tadpoleresponse variableswere the number of
survivors, tadpole growth, proportion actively
feeding, and proportionin each substratetype.
In ExperimentI, repeated measures MANOVA tested the null hypotheses that (1) tadpoles
do not alter habitat use in response to garter
snakes (snake effect); (2) tadpole behavior was
the same on successive days of observation(date
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86
SARAH J. KUPFERBERG
0.8-
(a) 1990
Cladophora
*I
II Mougeotia
sediment
0.6-
0.4.
a
0.2.
CO
co
a o.
0Q
no snake (n=3)
C
o 0.8
0
t0
o
snake (n=3)
(b) 1991
0.6-
Q.
.z
0.4-
0.2
0.0 -
no snake
(n=12)
3 days of snake 6 days of snake 9 days of snake
(n=4)
(n=4)
(n=4)
FIG. 1. Average patch use by Hyla regilla tadpoles in the presence or absence of Thamnophisbased on spot
check observations in Experiments I(a) and Experiment II(b). Error bars are + 1 SE. Significance of snake effects
summarized in Tables 1 and 2.
effect); (3) tadpole response to snakes was consistent on successive dates (snake x date interaction). In Experiment II, one-way ANOVAs of
data from the three snake present treatments
tested the null hypothesis that survival, growth,
patch use, feeding activity, and algal mass did
not differ in relation to duration of snake exposure. Upon acceptance of that null hypothesis, data from snake present enclosures were
pooled and compared to snake absent enclosures using sequential Bonferroni (Rice 1989)
adjusted t-tests.
Patch Specific Mortality Risk, Experiments IIIV.-To determine the relative risk of predation
in different patches, survival was measured in
enclosures stocked with only one type of algae.
In 1990, I conducted Experiment III, which had
two treatments, Cladophoraor Mougeotia (N = 3
replicates/treatment). In 1991, I repeated the trial, Experiment IV, with three treatments, sediment only, Spirogyrawith access to sediment, or
Cladophorawith access to sediment (N = 8 replicates/treatment). Survival was measured after
four days. To assess whether the gravel and pebble sediment provided an important refuge
from predation, I conducted Experiment V in
which the sediment was covered with a liner
made of shade cloth. Treatments were (1) shade
cloth liners only; (2) sediment only; (3) Cladophora with a liner covering the sediment; and (4)
Spirogyrawith a liner covering the sediment (N
= 6 replicates/treatment). Survival was censused after five days.
One way ANOVAs of the number of tadpoles
surviving in Experiments III, IV, and V tested
the null hypothesis that predation risk does not
vary among patch types. Data from Experiments IV and V were combined and a two way
ANOVA tested for the effects of sediment, algal
mats, and an interaction between sediment and
algal mats on tadpole survival.
Size SpecificMortality Risk, ExperimentVI.-To
determine whether there was a relationship between predation risk and tadpole size, I used
groups of tadpoles varying in mass in Experiment VI. The range of mean tadpole size among
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87
TADPOLE PATCH CHOICE
TABLE
1. RepeatedmeasuresMANOVAfor the arc
sin squareroot transformedproportionof tadpolesin
Cladophora
patchesin Expt.I. Data summarizedin Fig.
la.
Source
Wilk's
Mean Lambdf
square da
F
P
Analysis of Differences(MANOVA)
1.4 0.38
Date
0.52 2,3
0.68 2,3
0.72 0.56
Date x Snake
Analysis of Totals(ANOVA)
Betweensubjects
1.3
1
65
0.001
Snake
4
Error
0.02
the groups of tadpoles (N = 14) was 40-350 mg.
The sediment bottom of each enclosure was
lined with shade doth. Survival after 29 h was
correlated with mean tadpole mass using Spearman's rank correlation coefficient.
RESULTS
The main effects of garter snakes as tadpole
predators were sublethal, influencing patch
choice, feeding and growth. Tadpole use of high
food quality Cladophorapatches decreased in the
presence of garter snakes (Fig. 1) in Experiments I (Table 1) and II (Table 2). Continuous
observations revealed that in response to garter
snake foraging, tadpoles left Cladophoraand
moved to low food quality sediments and Mougeotia (Fig. 2). In Experiment II, there were no
significant effects of duration of snake exposure
among the three garter snake treatments, so
data were compared on a snake present vs. absent basis (Table 2). Garter snakes did not significantly reduce tadpole numbers (Fig. 3a), but
significantly decreased tadpole growth by 28%
(Fig. 3b). This difference in tadpole size among
treatments did not likely alter the predator prey
on five
TABLE2. Effectsof Thamnophis
hydrophilus
measures of Hyla regillatadpole response and one
measure of algal response in Expt. II. Data are summarized in Fig. lb and Fig. 3. * Asterisksindicatesignificance using the sequential Bonferronitechnique
(Rice, 1989). Table-widea = 0.05. t Proportiondata
were arc sin squareroot transformed.
Variable
Survival
Growth
Proportionin Cladophorat
Proportionin sedimentt
Proportiontadpoles activet
algal damp mass
df
T
P
1
1
1
1
1
1
-1.7
-5.1
-2.7
4.4
-2.9
0.52
0.10
0.00005*
0.013*
0.00026*
0.009*
0.61
relationship because there was no correlation
between tadpole size and risk of being eaten by
a garter snake in ExperimentVI (Fig. 4). Tadpoles were 56% less active in the presence of
gartersnakes (Fig. 3c). Decreased feeding activity did not result in any differences in the
amount of algal foods remaining at the end of
the experiment(Fig. 3d).
Patches of Zygnematales algae, Cladophora,
and sediment did not differsignificantlyin their
value as refuge from snake predation (Fig. 5a)
in Experiments If (T = .78, P = .5), IV (Fz20 =
1.7, P = .21), or V (F320= 1.2, P = .35). When
data from ExperimentsIV and V are combined
(Fig. 5b) and analyzed with a two way ANOVA,
there is a significant effect of the presence or
absence of algae as cover, a significanteffect of
access to sediment, and no significant interaction between algae and access to sediment (Table 3).
DISCUSSION
Gartersnakes changed patch use by tadpoles
in a manner similar to predator avoidance
among fishes in which vulnerable size casses
1-0
[] seliment
,0.8
0.61
o*
'
_
CLadophora
. 0.4
. 0.2
0.0
time(mins)
forFIG.2. Continuousobservationof Hyla regillatadpole patch use before, during, and after Thamnophis
aging activity in one representativeenclosure.Single arrowindicatestime of gartersnake additionand double
arrowindicatesremoval.Numbersin parenthesesindicatenumbersof tadpolesremaining.Tadpoleswere taken
by the snake in Cladophora.
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88
SARAH J. KUPFERBERG
10-
(a)
5(b)
8'
T
.>c
O1
*
40- '
E
30::I
-
20"
0u3
I:
m1
#e
0)
10-
X
c0
{:3
0-
0
)
3
5
9
0
(c)
._
200-
3
(d)
]Mougeotia
5
9
QACladophora
o
? .20150-
0a
T
T
O .10'
co
E
c8
Bill
^%:? (^
Tl
I I.;1
I-?--~
0
0
.VQ
1100_
50g100:::::l??:?i:?i:?:::::::::i::i::j
j
50-
I:
0
.
iE
3
5
9
0
%
^6<
</
^<% 4
0
3
.- -
5
,
9
Days of exposure to gartersnakes
FIG.3. Survival(a), averageper capitagrowth (b), and activitylevel (c), of Hylaregillatadpolesexposed to
gartersnakes for a period of time varyingfrom 0-9 days (ExperimentII). (d) Damp mass of algae at the end
of ExperimentII.Columnshadingin (a), (b),and (c) indicatessignificantsnakeeffects;statisticsaresummarized
in Table2. Errorbars are +1 SE.
segregate among habitats and avoid resources
(Kerfoot, 1987; Mittelbach and Chesson, 1987;
Power, 1984). The avoidance of algal resources I
observed erroneously suggested that tadpoles
were making tradeoffs between energetic gain
and foraging risk by taking refuge in a low resource patch. Because there were no significant
differences in risk, .L, among the patch types,
tadpoles were not minimizing the ratio of /l/g
(using the mean risk of mortality from Experiment V, 49.4%, and growth rates reported in the
introduction, i/ gcldophora= 1.8, / / gzygnematales
4.0, and //geiment = 7.0%/mg/d). Cladophora
patches, which were preferred in the absence of
garter snakes here, and in other predator-free
cafeteria food preference experiments (Kupferberg, 1997), were not inherently risky. In fact
algae provided important cover and protection
as indicated by the low survival in predation
trials where no algae mats were present. Active
feeding, however, was the probable risk factor,
and was the aspect of behavior which tadpoles
modified in the presence of predators.
My observation that tadpoles moved less in
the presence of snakes indicates that the tradeoffs made between mortality and growth (Wer-
12- R2 = 0.002
10..
C,
C
0
6-
c)
9
49
n
,
0.0
0.1
0.2
0.3
0.4
tadpolemass (g)
FIG.4. Survivalof tadpolesafter29 hours of snakeexposurein ExperimentVI was independentof tadpole
size.
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TADPOLE PATCH CHOICE
10
(a)
89
Zygnematales
0m Cladophora
8-
0)
C
c
sediment
lineronly
-
T T
6.
..
:3
=tC=
0-
III
v
IV
Experiment
(b)
-*
aT
O
free access to sediment
sediment covered with a shade-cloth liner
0)
C: 6
.,
i
03
4-
a)
0o
0
Absent
Present
Algae
FIG.5. (a) Mortalityrisk in patches of differenttypes. In ExperimentIII shade cloth liners blockedaccess
to sediment in the algal treatments.(b) Data from ExperimentsIII and IV combined.Cladophora
and Zygnematalestreatmentswere pooled. Histogramswith the same letterare not significantlydifferentfromeachother.
TABLE3. Two way ANOVAof survival data com-
bined from Expts IV and V. Data from Spirogyraand
treatmentswere pooled becausetherewere
Cladophora
no significantdifferencesin survival.
Source
MS
Sedimentaccess (liner
present vs. absent) 40.11
Algal mat (presentvs.
46.65
absent)
Sedimentaccess x Al0.16
gal mat
Error
7.25
df
F
P
1
5.53
0.023
1
6.43
0.015
1
0.022
0.884
43
ner, 1986) are manifest in activity level rather
than habitat use per se. Whereas motion associated with feeding can trigger attacks by visual
predators, natural and pharmacologically induced immobility has been shown to decrease
encounter rates with insect predators (Peterson
and Blaustein, 1992; Skelly, 1994). Similar reductions in encounter rates and attacks by garter
snakes are likely because they respond to moving prey more than static prey (Burghardt and
Denny, 1983). Hyla regilla, in particular, has a
strong motionlessness defense relative to other
less palatable tadpoles (Bufo and Rana) (Peterson
and Blaustein, 1992). For a negatively buoyant
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90
SARAH J. KUPFERBERG
tadpole, which H. regilla appears to be in this
system, the anti-predator behavior of being still
can be misinterpreted as patch choice if motionlessness causes it to sink away from floating or
suspended algal patches. Vertical movement
such as swimming from the bottom up to the
floating algae may be particularly risky as
aquatic garter snakes appear to visually cue in
on vertical components of movement (Macias
Garcia and Drummond, 1995). Because tadpoles
can control buoyancy by altering lung volume
(Gee and Waldick, 1995), it is also possible that
H. regillahas a distinct anti-predator behavior of
sinking to the bottom. Being less active and
spending more time on the bottom resulted in
a clear trade-off with growth; tadpoles were significantly smaller in the presence of garter
snakes.
Contrary to the expectation that tadpole susceptibility to predation would vary among microhabitats (Hews, 1995) and levels of food
availability (Anholt and Wemer, 1995), mortality
risk did not differ among Cladophora,Zygnematales, and sediment. Although garter snakes
appeared to move more effectively in mats of
Cladophora, susceptibility in Zygnematales
patches, where snakes bottom crawled below
the cloudy and mucilaginous algae, was similar
to susceptibility in Cladophora.
Rather than being
risky, each of these patches provided cover from
predation, as indicated by the significant decrease in survival in enclosures where cover was
entirely lacking. In other systems, Cladophora
serves as effective cover for salamanders (Holomuzki, 1989), and isopods use algae mats for
cover from green sunfish predators (Holomuzki
and Short, 1988, 1990). Cladophoramay therefore
be a preferred substrate for both cover and food
resources.
The marked preference for Cladophoraobserved in Experiment I was depressed in Experiment II probably due to increases in scale of
experimentation. In Experiment II, with 24 enclosures and four observers walking around the
gravel bar, tadpoles may have been reacting to
that movement the same way that they do to all
predators, by decreasing their activity. Whereas,
in Experiment I, with one observer and six enclosures, little walking was necessary.
I did not observe any indirect effects on algae
by garter snakes, although changes in community appearance and structure are possible
when foragers avoid resources to limit predation risk. Cascading trophic effects due to shifts
in prey behavior have been documented in a variety of aquatic habitats where the presence of
piscivorous fish affects the distribution, abundance, and size structure of planktivorous and
herbivorous fish (Power et al., 1985; Mittlebach
and Chesson, 1987; Turner and Mittlebach,
1990). The lack of an indirect effect of snakes on
algae in Experiment II, may have been due to
the short duration of the experiment or the large
quantities of algae stocked. Large amounts, 250260 g per algal type, were necessary to mimic
the algae's properties as habitat patches, large
floating mats. In smaller scale food choice experiments, where tadpoles were given only 5 g
of each algal type over a similar time period,
significant decreases in algal mass due to Hyla
grazing were detected (Kupferberg, 1997). Additionally, I did not examine the Cladophoramicroscopically. There may have been differences
in depletion of epiphytic diatoms among treatments which would not be detectable by gross
weight measurements.
The lack of a cascading trophic effect may
also have been due to ineffectiveness of garter
snakes in reducing tadpole numbers. Despite
the possibility that tadpoles can constitute significant portions of garter snake diets (Arnold,
1992; Lind and Welsh, 1994), snakes did not
consume many tadpoles in these experiments,
nor were they size selective. The high food availability of these experiments may have allowed
tadpoles to decrease their activity level, thus
avoiding predation. As Anholt and Werner
(1995) have shown, tadpoles are able to reduce
mortality from odonate predators by adaptively
decreasing activity level at high food levels but
not at low food levels because at low resource
levels the risk of starvation would be too great.
To more fully understand how predators influence the impacts of tadpoles on algae will thus
require investigations at a number of resource
levels.
Acknowledgments.-M. Power, J. Patrusky, and
W. Sousa made many constructive comments on
earlier drafts of the manuscript. Valuable assistance in field work was given by L. Corelison,
R. Fewster, K. Grief, C. Lowe, K. Meier, M. Parker, M. Power, and S. Temple. I thank W. Sousa
and M. Power for comments on experimental
design. This research was made possible by NSF
BSR 9100123 to M. E. Power, and grants to SJK,
from Sigma Xi, Theodore Roosevelt Fund of the
American Museum of Natural History, and the
U. C. Natural Reserve System.
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Vol.32, No. 1, pp. 92-96, 1998
Journal
of Herpetology,
Copyright1998Societyfor the Studyof Amphibiansand Reptiles
A New Amphisbaenian from Cuba
RICHARD THOMAS1 AND S. BLAIR HEDGES2,3
'Departmentof Biology,PO Box 23360, Universityof PuertoRico,
San Juan,PuertoRico 00931-3360, USA
2Departmentof Biology,208 MuellerLab,PennsylvaniaState University,
University Park,Pennsylvania16802, USA
ABSTRACT.-A new species of Amphisbaena is described from the Cabo Cruz region of eastern Cuba. It
shares with two other Cuban species, Amphisbaena barbouri (new rank) and A. cubana, fusion of the second
supralabial and ocular scales. It is a pallid, long-tailed, xerophilic species associated with dry, coastal limestone habitats.
In the West Indies, amphisbaenians occur
only on the island banks of Cuba, Hispaniola,
and Puerto Rico (Schwartz and Henderson,
1991). Three species are currently recognized
from Cuba: Amphisbaenablanoides,A. palirostrata,
and A. cubana. The first two occur in western
Cuba and were placed in the genus Cadeauntil
recently (Hedges, 1996; Powell et al., 1996). A
fourth taxon, barbouri,was described as a subspecies of A. cubana(Gans and Alexander, 1962).
It has a peculiar distribution in west-central
Cuba in that it is known only from coastal or
near-coastal localities in the north (Havana-Matanzas) and south (Bay of Pigs-Cienfuegos).
Specimens from east and west (including Isla de
Juventud) of these areas are assigned to the
nominate subspecies (Schwartz and Henderson,
1991) and no morphologically intermediate
specimens are known despite the close proximity of some localities and apparent sympatry
at Soledad, Cienfuegos Province (Gans and Alexander, 1962). For these reasons (and, see below), we choose to recognize A. barbouriat the
species level.
During July, 1994, we collected along the
south coast of eastern Cuba ("Oriente") in the
provinces of Granma and Santiago de Cuba. Although the entire coast between Cabo Cruz in
the west and Cabo Maisi in the east is generally
dry, the areas near the two capes are more xeric
3Author for correspondence and reprints. E-mail:
[email protected]
than the intermediate coast. In the western xeric
area (Meseta de Cabo Cruz), between Cabo
Cruz and Boca del Toro, a series of limestone
terraces descends stepwise to the coast, and the
xeric scrub vegetation grows within solution
holes in the limestone. The conditions are very
reminiscent of the xeric, scrub-covered, terraced
limestone on the southern part of the Barahona
Peninsula in Hispaniola. Within a kilometer to
the west of Boca del Toro we collected four specimens of a distinctive, slender, pale species of
Amphisbaena.A fifth specimen of this new species, also from the Cabo Cruz region, was found
among specimens of A. cubanain the collection
of the University of Michigan Museum of Zoology.
MATERIALS AND METHODS
Scale counts were taken according to the criteria of Gans and Alexander (1962); measurements of head scales were taken with a dissecting microscope and digital readout micrometer
caliper. The count of total half-annular segments
of the head is a count of the segments dorsal to
the splitting of the second body annulus into
two half-annuli, which may be given as a total
count (the number of segments in anterior halfannulus + number of segments in posterior
half-annulus). Snout-vent length (SVL) and tail
measurements were taken to the nearest mm by
laying the specimen along a ruler. Other length
measurements were made with a digital readout micrometer caliper and recorded to the
nearest 0.1 mm. Drawings of head scalation
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