Table Of Content1994. TheJournal ofArachnology 22:185-189
EFFECTS OF FISH ON THE GROWTH AND SURVIVAL
OF TWO FISHING SPIDER POPULATIONS
(DOLOMEDES TRITON; ARANEAE, PISAURIDAE)
Chester R. Figiel, Jr. and Gary L. Miller: Department ofBiology, University of
Mississippi, University, Mississippi 38677 USA
ABSTRACT. Our objectives were to determine ifDolomedes triton from two populations, one with fish
predators and one without, differed in growth and survival. Using a 2 x 2 randomized block design, equal
numbersofspiderswererearedoverasix-weekperiodinartificialpoolsinthepresenceandabsenceofanatural
predator, thebluegillsunfish, Lepomismacrochirus, (Perciformes: Centrarchidae). Neitherspiderbodysizenor
spidersurvivaldifferedbetweenpopulations.Survivalofspidersinpoolswithfishwasnotsignificantlydifferent
from spiders in fishless pools. However, spider body size was significantly smaller in pools containing fish
comparedtospidersinpoolswithoutfish.Nosignificantinteractionbetweenpopulationsourceandthepresence
of fish was detected. We suggest two mechanisms for the reduction in spider body size: interference (i. e.,
avoidance offish) and exploitativecompetition with fish forfood resources. The reductionin spiderbody size
isimportantbecauseoftherelationshipbetweenspidersizeandreproductivesuccess(largerfemalesmayproduce
agreaternumberofoffspringthan smallerfemales; largermales may copulatewith more femalesthan smaller
males). Because these spiders are found in wetlands areas where sunfish occur, our results suggest that these
spidersmayadjusttocompetitor/predator-richenvironmentsthroughcompromisesingrowthanddevelopment.
Predators can directly influence the structure (Rayor & Uetz 1990). In addition, smaller spi-
anddynamicsofaquatic communitiesbydiffer- ders may be more vulnerable to predatory en-
ential predation on species (Wilbur 1980). In- counters with conspecifics (Bleckmann & Barth
directly, predatorpresencecaninfluencepreyby 1984). Predators may modify these life history
alteringpreymorphology, lifehistory, orbehav- traits by influencing spider activity, exploiting
ior (reviewed in Kerfoot & Sih 1987; Lima & food resources or by altering spider habitat use
Dill 1990). For example, prey behavioral pat- (vanBerkum 1982;Rayor&Uetz 1990;Riechert
terns may change in response to predator pres- & Hedrick 1990). Van Berkum (1982) hypoth-
ence and subsequentlyaffectcompetitive orfor- esizedthat Trechaleamagnificaspidersmayfor-
agingtacticsoftheprey(Morin 1983; Werneret age noctumally to avoid predation risk during
al. 1983; Poweretal. 1985; Gilliam etal. 1989). the day, in spite ofthe greater prey abundance
Thesebehavioral modificationscanchangewith available during the day. Riechert & Hedrick
respect to ontogenetic development ifthe pred- (1990) examined predator assessment of two
ator-prey relationship is based on body size dif- populations of Agelenopsis aperta spiders and
ferences (see Werner & Gilliam 1984). Thus a determined that the population exposed to pre-
predator-prey relationship early in prey devel- dationpressureexhibitedalongerlatencyperiod
opment may be altered to a competitive rela- to return to a foraging mode following a preda-
tionshipthroughtime.Understandingtheeffects toryencounter.Fewstudies,however,havemea-
ofcompetitorsandpredators on thebehaviorof sureddirectlytheeffectsofpredatorpresenceon
interacting species can identify the mechanisms spiderforagingactivity orfeedingrates in terms
ofselection that are responsible for differences ofgrowth, body size, mating, or reproduction -
within populations in life history traits (e. g., traits that are closely related to fitness (but see
growth, reproductive success). Rayor & Uetz 1990).
In many species ofspiders, growth and body The objectives ofthis study were two-fold: 1)
sizearedirectlyrelatedtoreproductivepotential to examine the effects of fish presence on the
(e.g., numberofeggsproduced)andmatingsuc- growth and survival of the fishing spider, Do-
cess (Fritz & Morse 1985; Smith 1990; Brady lomedes triton (Walckenaer), and 2) to test for
1993), andarealso indirectlyrelatedto survival differences in growth and survival between two
185
186 THEJOURNALOFARACHNOLOGY
populations of spiders: one population from examine the main effects and interactions be-
ponds containing fish, and one population from tween fish presence and population source. We
locations that lacked fish. randomly assigned the four treatment combi-
nations within each offour replicate blocks for
EXPERIMENTAL SYSTEM
a total of 16 pools. Pools [within size ranges of
Dolomedes triton is a widely distributed spe- natural ponds inhabited by these spiders (CRF
cies in the United States and Canada, foraging pers. obs.)], were placed in an outdoor fenced
on or near the surface ofponds or slack water enclosure on the Edward J. Meeman Biological
areas ofstreams and rivers, and use the water’s Station(EJMBS)inShelbyCo.,Tennessee,which
surfacetocapturepreyorescapepredation(Car- exposed them to natural photoperiod, seasonal
ico 1973). Attack behavior by these spiders can rainfall and temperature. Pools were filled with
be elicited by water surface waves generated by tapwateron22July 1992andwindowscreening
prey(Bleckmann&Barth 1984;Bleckmann 1985; was placed over pools to prevent frogs and in-
Bleckmann & Lotz 1987). The sensory ecology sects from colonizing them and prevent spiders
ofD. triton spiders, with regards to foraginghas from escaping. We added logs, detritus, floating
been examined (Bleckmann & Barth 1984; sponges,andleaflittertopoolstoprovidehabitat
Bleckmann & Rovner 1984; Bleckmann 1985), complexity, refuge, and substrates for spiders.
as has theircourtship behavior(Roland & Rov- We seined L. macrochirus {X = 43 mm total
ner 1983; Bleckmann & Bender 1987), and prey length ±2.4 mm SD) from a pond located on
use (Zimmermann & Spence 1989). theEJMBStoserveasourmodelpredator. Blue-
The bluegill sunfish, Lepomis macrochirus, is gillsunfishthissizecanvigorouslyattack,injure,
syntopic with D. triton over most ofits range. and consume D. triton (CRF pers. obs.). Two
These sunfish have a diverse diet and will eat a fish were used per pool (0.8 fish per m^ ofpool
wide variety of arthropods including D. triton surface area; within range ofdensities offish in
(CRF pers. obs.). These sunfish and D. triton natural ponds. Hall & Werner 1977). Likewise,
often occupy the same microhabitats of ponds the treatment level ofZ). triton (four spiders per
(e. g., shallow shoreline areas) because ofinter- pool) is within the range of spider densities in
actions with larger predatory fish (Werner et al. naturalpondsin Mississippi(1.6 spidersperm^,
1983; CRF pers. obs.). CRFunpubl. data). Spidersand fishwereplaced
METHODS in pools on 17 August 1992. Hyla chrysoschelis
tadpoles were used as prey for spiders and fish
WemeasuredgrowthandsurvivalofD. triton and were collected from nearby ponds. We sup-
collectedfromtwopopulations: SavannahRiver plementedpreyinpoolsbyaddingcrickets{Ach~
Plant, Aiken County, South Carolina (SC) and etusspp.) from a commercial colony. Eitherfive
the University of Mississippi Biological Field similar-sized crickets or five similar-sized tad-
Station,LafayetteCounty,Mississippi(MS).Spi- poles were added to all pools once every five
ders were collected from two SC ponds on 31 days. Spidersreadilycaptureandconsumethese
July 1992andfromthreeMSpondson3 August prey in the lab. The experiment was terminated
1992 to ensure local population replication. We on 28 September 1992 and all spiders and fish
chose these two populations to ensure that gene were preserved in alcohol.
flow between the populations was low or non- Spiderbodysizewasdeterminedbymeasuring
existent. Additionally, we chose SC ponds be- thecarapacelengthonpreservedspecimens. Re-
cause they have lacked fish forat least 20 years, sponse variables in the experimental treatments
(J. Pechmannpers. comm.),whiletheMSponds were mean growth (increase in length ofcara-
have had fish present for the last 40 years, L. pace, measured to the nearest 0.5 mm) and sur-
macrochirus Pimephales promelas (flathead vival (the number ofsurviving spiders divided
,
minnows) and Micropterus salmoides (large- by initial number) foreach pool. Proportions of
mouth bass) (B. Knight pers. comm.). surviving individuals from the initial number
Spiders (Xcarapace length at the start ofthe were arcsine transformed, and body size data
experiment ± SD:Xsc = 3.5 mm ±0.1 mm,Yms were log transformed before analyses.
= 3.5 mm ±0.2mm)wererearedinthepresence
RESULTS
andabsenceofL. macrochirusinartificialponds
(plastic wading pools, 1.52 m diameter, 22 cm Survival was not correlated with body size at
deep). We used a 2 x 2 factorial experiment to the end of the experiment (r = -0.224), thus
FIGIEL& MILLER^GROWTH AND SURVIVALOFDOLOMEDES TRITON 187
Table L—Summary ofthe two-way analysis of variance on body size (carapace length) and survival of
Dolomedestritonfromtwo populationsrearedinthepresenceandabsenceoffish, Lepomismacrochirns. Body
sizedatawerelogtransformedand percentsurvivaldatawerearcsine square-roottransformedbeforeanalysis.
MS
Sourceofvariation df Test ofsignificance
Body size
Population 1 0.00011 F- 0.165 F=0.6957
Fish presence 1 0.00948 F= 14.856 F=0.0023
Populationby fish 1 0.00001 0.017 F=0.9008
Error 12 0.00064
Total 15
Survival
Population 1 0.00428 F= 0.086 F=0.7778
Fish presence 1 0.03855 F= 0.771 F=0.4062
Population by fish 1 0.10709 F= 2.143 F= 0.1689
Error 12 0.04998
Total 15
growthdatawereanalyzedindependentlyofsur- Behavioral observationsofD. tritonplacedwith
vival data. Analysis showed there was no block L. macrochirusinlaboratoryaquariadetermined
effect and data from the four blocks were sub- thatthese spidersavoided bluegill sunfish byal-
sequently pooled for analysis. teringlocation in aquaria(CRFunpubl. data). If
Body size ofspiders was affected by the pres- this behavior influenced D. triton foraging time
ence offish (Table 1). At the end ofthe experi- or effort, as has been shown for other spiders
ment, spider body size was significantly smaller (van Berkum 1982; Riechert & Hedrick (1990),
mm
in pools containing fish (JTsc =4.85 ±0.21 this could account for the reduction in D. triton
mm; A'ms = 4.93 mm ±0.17 mm) compared to body size.
=
body size ofspiders in pools withoutfish {X^c Additionally, competition for prey between
5.45 mm ± 0.34 mm; = 5.50 mm ±0.45 sunfish and spiders probably resulted in a re-
mm). Body size did not differ between the SC duced food resource base for spiders, and sub-
population (5.15 mm ±0.41 mm) and the MS sequentlyresultedina reducedspiderbody size.
population (5.21 mm ±0.44 mm) at the termi- Although we did not directly measure food re-
nationoftheexperiment(Table 1).Nosignificant source levels in pools, sunfish can prey on tad-
interaction between population source and the polesandfloatingcrickets,andfoodresourcelev-
presence offish was detected (Table 1). el can be decreased in these pools due to fish
Spider survival did not differ between popu- presence (Figiel & Semlitsch 1990). Periodic
lations (Table 1). At the end ofthe six-week ex- searches for prey determined that no prey sur-
periment, the percent survival of spiders from vived in poolscontaining sunfish, whereas these
SCwas50.0% ±23%andfromMS46.9% ±22%. prey were available and abundant for spiders in
Survivalofspidersinpoolswithfish(Xsc=62.5% pools without fish. This suggests that the reduc-
±25%;Xms =43.8% ±14%)wasnotsignificantly tion in spider body size probably resulted from
differentcomparedto survivalofspidersin fish- exploitative competition between fish and spi-
lesspools(Xsc=37.5% ±14%;X^s= 50% ±29%) ders, with the additional pressure of predator
(Table 1). No significant interaction between avoidance. Because food resource levels for spi-
population source and the presence offish was ders in fishless pools were abundant, differences
detected (Table 1). in spider body size in natural conditions may
occur only when prey densities for spiders are
DISCUSSION
relatively high or fish densities are low.
Body size ofspidersdiffered significantlyafter It is difficultto determine reasons forthe lack
just 42 days and clearly indicates that fish pres- ofdifferences between populations in growth or
enceinfluencedspidergrowth. Twomechanisms survival, orin lack ofdifferencesin survival be-
could be responsible for these results: interfer- tween fish and fishless ponds, particularly con-
ence (i. e., spider avoidance offish) or exploit- sideringthattheSCpopulationshavelackedfish
ative competition with fish for food resources. in these ponds. With respect to survival, it is
188 THEJOURNALOFARACHNOLOGY
possiblethatmortalityrelatedtotheexperimen- lecting spiders. We thank G. Wein for access to
tal situation is high thereby masking effects of ponds in South Carolina and M. Kennedy and
the predator. A shorter experiment using larger theEdwardJ. MeemanBiologicalStationforthe
ponds might alleviate this problem ifit exists. useoffacilities.Weappreciatethecommentsand
However, there may be a biological basis for criticismsonearlierversionsonthismanuscript
the lack ofdifferences in growth and survival in from H. Farris, R. Holberton, and G. Stratton.
fish and fishless ponds. Conceivably, lack ofin-
terpopulational variation in growth or survival LITERATURECITED
resulted from selection forphenotypic plasticity
Bleckmann,H. 1985. Discriminationbetweenprey
in these life history traits. This may be an effec- andnon-preywavesignalsinthefishingspiderDo-
tive way for spiders to adapt to highly variable lomedestriton(Pisauridae),Pp.215-222,InAcous-
environments rather than favoring specific phe- tic and vibrational communication in insects (K.
notypes (Caswell 1983; Kaplan & Cooper 1984; Kalmring& N. Eisner, eds.), Parey Verlag, Berlin,
Petranka & Sih 1987). Potentially, therelatively Bleckmann, H. & F. G. Barth. 1984. Sensoryecol-
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enough for selection to influenced the behavior Behav. EcoL Sociobiol. 14:303-312.
Bleckmann, H. & M. Bender. 1987. Water surface
ofthese spiders. Additionally, there is an abun-
waves generated by the male pisaurid spider Do-
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lomedes triton (Walckenaer) during courtship be-
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