HERPETOLOGICAL JOURNAL, Vol. 4, pp. 145-150 (1994)

EFFECTS OF BODY TEMPERATURE ON THE PREDATORY BEHAVIOUR OF THE LIZARD PSAMMODROMUS AL GIRUS HUNTING WINGED AND WINGLESS PREY

JOSE A. DiAZ

Departamento de Biologia Animal I (Vertebrados), Facultad de Biologia, Un iversidad Complutense, 28040 Madrid, Sp ain

The thermal dependence of predation success in the Mediterranean lacertid lizard Psammodromus algirus was studied using two types of prey (winged and wingless fl ies) that differed in their ability to escape predation at all Tbs (body temperatures) tested (25-27°C, 29- 320C, and 34-37°C). Both number of failures and handling time decreased significantly at higher Tbs, and capture success was much higher fo r wingless flies; in fact, low Tbs were associated with a significant increase in capture success only in the case of winged flies. At low Tbs, winged fl ies could be efficiently seized by lizards only if pursued from a short distance. The attack distance was therefore larger for the less mobile (and less detectable) wingless flies at low Tbs, which suggests a trade-off between attack distance and capture success under conditions of impaired locomotor performance. Results of this study show that the escape abilities of prey are crucial to evaluate the effects of temperature on the performance of reptiles as predators.

INTRODUCTION evaluate the role of predatory efficiencyas a selective forceleading the evolution of behavioural thermoregu­ The body temperature (Tb) of reptiles affects their behaviour by influencingbiochemical and physiologi­ lation in reptiles (A very et al., 1982). The experiments cal mechanisms (Dawson, 1975), but the ecological reported here were designed to analyse to what extent and evolutionary implications of such thermal depend­ the escape abilities of prey influence the thermal de­ ence are best revealed at the level of organismal pendence of predation success in a Mediterranean performance (Huey & Stevenson, 1979; Huey, 1982, diurnal basker. For this purpose, I employed two types 1991 ). The increased efficiency ofmuscula r contrac­ of prey (winged and wingless flies) and offered them to tion and neuromuscular coordination at higher lizards whose Tb had been previously fi xed. The par­ ticular issues addressed were (1) Do the escape temperatures (Putnam & Bennett, 1982; Marsh & : Bennett, 1985), for instance, leads to higher sprint abilities of prey influence the effects of lizard Tb on speeds (Bennett, 1980) that improve the ability to cap­ predation success?; (2) What aspects of the feeding ture prey and the ability to escape predation (Christian system (e.g. handling time or attack distance) have & Tracy, 1981; Avery, Bedford & Newcombe, 1982; larger sensivities to Tb and/or prey fleeing abilities? ; Van Damme, Bauwens & Verheyen, 1991 ). These and (3) Considering the data available about Tbs of ac­ abilities, in tum, directly affect Darwinian fi tness tive lizards, how good are the performance levels of lizard predation expected under field conditions? (Huey, 1991 ). It is therefore not surprising that diurnal lizards use behavioural means to achieve relatively METHODS high and constant body temperatures (Cowles & Bogert, 1944 ), even if such thermoregulatory behav­ The predator of choice was Psammodromus algirus, iour entails costs in time, energy or predation risk a medium-sized lacertid lizard (adult snout-vent (Huey, 1974; Huey & Slatkin, 1976). length: 60-85 mm; mass: 6- 14 g) that actively searches Within this context, one central aspect of the ther­ for a variety of arthropod prey (Diaz & Carrascal, mal biology of lizards that has received relatively little 1990, 1993) and most frequently inhabits broad-leaved attention is the thermal dependence of predation suc­ (both deciduous and evergreen) forestswith a well de­ cess (though see Greenwald, 1974; Avery et al., 1982; veloped undergrowth of shrubs (Diaz & Carrascal, Avery & Mynott, 1990; Van Damme et al., 1991). 1991). It is a shuttling heliotherm (Diaz, 1991) whose Most of the work on this subject has been carried out microhabitat selection is strongly related to ther­ using experimental (and often clumsy) prey whose be­ moregulatory behaviour (Diaz, 1992). haviour bears little resemblance with tlie predator Animals used in the experiments reported here were avoidance tactics of arthropods under more natural nine adult lizards (mean [±SD] snout vent length of field conditions (Edmunds, 1974; Curio, 1976; Endler, 74.3±5.02 mm, and mean [±SD] body mass of 1986). Without using fast-fleeingprey, it is difficultto 9.9±2.26 g) collected in an open forest of Quercus 146 J. A. DIAZ

pyrenaica oaks at the northern slope of the Sierra de la flieshad their wings removed by cutting their base. The Morcuera (40°35'N, 3°53 'W, province of Madrid, dichotomy between these two types of prey seemed an Central Spain). Upon arrival at the laboratory, lizards appropriate .oneunder the experimental conditions em­ were housed in leaf-litter filledterraria (100 x 50 x 30 ployed, because even winged fliescould eventually be cm) with a 60-W bulb providing heat for8 hr per day captured (after several trials, if necessary) due to the and allowing lizards to maintain temperatures within limited distance they could fly in the feeding enclo­ previously reported field activity ranges (20-38°C; sures. In addition, defence against predators is assumed Carrascal & Diaz, 1989; Diaz, 1992). Food to be a basic functionof insect flight,and dipterans, that (mealworms, blowflies and wasp larvae) and water are among the more efficientinsect fliers, make a small were supplied ad libitum. but evenly distributed contribution to the diets of more The experiments on predatory behaviour were car­ than 90 species of desert lizards (Pianka, 1986). This ried out in a 90 x 50 x 40 cm wooden cage with a probably reflects the fact that rapid movements not transparent wall allowing direct observation of lizards, only favour predator avoidance, but also elicit the at­ and whose floor had been ruled with a I 0 x I 0 cm grid tack response of visually-guided predators such as to facilitate recording attack distances. A few dead insectivorous amphibians and reptiles (Freed, 1988; branches were used to provide environmental com­ Diaz & Carrascal, 1993). In addition, dipterans have plexity. Illumination was natural daylight been shown to make a major contribution to the diet of complemented with an additional bulb inside the cage. at least some populations of P. algirus (Carretero & I took advantage of natural fluctuations in temperature, Llorente, 1993 ). together with the effects of varying the power of the The four prey (two winged and two wingless flies) bulb used (40, 60, or I 00 W) and its distance from the were subsequently introduced into a matchbox that was substrate (15-30 cm), to manipulate the thermal envi­ allowed to warm up for a few minutes under a 60-W ronment in such a way that the operative temperatures bulb. At the same time, an individual lizard was placed monitored using copper models (Bakken & Gates, in the experimental cage and given 5 min to habituate 1975; Bakken, 1992) fell within one of three distinct to the fe eding environment and have its Tb equilibrated temperature ranges, hereafter referred to as low (25- within the range selected (low, moderate, or high); the 270C), moderate (29-32°C), and high (34-37°C). lizards were allowed to sit under the bulb and warm up Models were copper cylinders with a small hole allow­ before the experiment was started. The sequence of ing insertion of the sensing tip of an electronic digital temperatures for each individual was deliberately non­ thermometer (precision of ±0. 1 °C) that were placed systematic to prevent within-subject order effects. under the bulb to mimic the location of "basking" liz­ Following this interval, the matchbox containing the ards. Model verification was obtained by comparing flies was simultaneously opened and thrown into the equilibration temperatures of models against those experimental cage, as farfrom the predator as possible. taken from anesthetized P. algirus under varying con­ An obvious problem of this experimental protocol, but ditions of radiant heating. In addition, cloaca) one which is impossible to solve in a study involving temperatures measured aftereach trial (see below) con­ ectotherms, is that flytemperatures in the terrarium firmed the accuracy of operative temperature copper cannot be controlled, so that results could reflect in thermometers (mean Tb±SD in °C, n, range; low tem­ part the physiology of the flies, notjust of the lizards. perature: 26.1±0.47, 17, 25.4-27.0; moderate: Anyway, results (see below) showed that temperature 31.0±0.97, 17, 29.4-32.5; high: 35.9±0.79, 20, 34.4- effects onthe escape behaviour of fliesdid not compen­ 37.2). These ranges were realistic considering available sate forthe reduced predation success of lizards at low data about body temperatures in the field (Carrascal& temperatures. Diaz, 1989; Diaz, 1992) and preferred body tempera­ Lizard behaviour was observed for the next five tures, that is, temperatures lizards would attempt to minutes or, alternatively, until all prey had been cap­ achieve in the absence of physical and biotic restric­ tured. A stop watch (±0. 1 s precision) was used for tions (Licht, Dawson, Schoemaker & Main, 1966); in measuring handling times, defined as the time elapsed P. algirus, mean selected Tb is about 35.2°C (unpub­ between the firstseiz ure of a prey by a lizard, and the lished data). firstcomple te closure of the jaws afterit had been swal­ Experimental prey were commercially supplied lowed. All observations were dictated to a tape blowflies(Calliphora sp.) with an average body length recorder, so that the following variables could be noted of I 0.4 mm and an average head width of 3.1 mm. All when transcribing the tapes: (I) thermal regime (low, flies were offered to the lizards within two days after moderate or high temperature); (2) type of prey their emergence from pupae, thus eliminating differ­ (winged or wingless) being attacked; (3) number of at­ ences in escape ability that could have been acquired in tacks, i.e. chases and jaw closures in an obvious attempt previous encounters with predators. Flies were kept in to catch a prey; (4) number of captures (ranging be­ refrigerated chambers at 4°C until the moment they tween one and four); (5) number of failures (attacks were taken out, in groups of four, for lizard feeding. minus captures); and (6), when attack was successful Immediately after extraction, two randomly chosen (that is, when it led to prey capture), attack distance (± I TEMPERATURE EFFECTS ON LIZARD PREDATION 147

cm), defined as the distance between the lizard's snout more frequently than expected by chance (equal pro­ and the location of the fly when the lizard started mov­ portions of 0.5 for each prey type: t8 = 2.38, P < 0.05), ing towards the prey before seizing it. In addition, the whereas no significant deviations from random were behaviour of both prey types (percentage of time im­ found at moderate and high Tbs (18 = 1.06 and t8 = 0.78, mobile vs. percentage of time walking or flying) was respectively; P > 0.1 in both cases). monitored in a series of two minutes observations of DISCUSSION randomly selected flies (10 winged and 10 wingless) that were released two at a time into the empty experi­ Perhaps the most remarkable finding of this study is mental cage. that the effects of body temperature on the predatory Afterending a trial, the lizard was taken out from the efficiency of lizards were more clear-cut for winged experimental cage and its Tb was immediately meas­ prey than forwingless ones (Fig. 1). A number of pre­ ured (±0. 1°C) with a Miller-Weber cloaca! vious studies have shown that reptilian handling times quick-reading mercury thermometer. All lizards were increase as Tb decreases (Avery et al., 1982; Avery & successfullytested (a trial was successful when it led to Mynott, 1990; Van Damme et al., 1991). These in­ the capture and consumption of at least one prey) at creases are probably due to a reduction in each temperature range at least twice, always in differ­ neuromuscular coordination at tissue or lower levels ent days. Individual data were averaged for each trial, (Putnam & Bennett, 1982; Marsh & Bennett, 1985) and, in order to avoid pseudoreplication (Hurlbert, that would also affect sprint performance and hence 1984), trial means were averaged over experimental ability to chase fast-moving prey (Huey & Stevenson, subjects within temperature ranges. Mean (±SD) 1979; Huey, 1982). number of replicates per lizard was 3.00±0.62 at each The unsuccessful attempts to feed at low tempera­ (1974) temperature interval (range 2-4, n = 27). Data on cap­ tures are similar to Greenwald's observations ture efficiency, handling times, and attack distances on strike efficiencyin gopher snakes and to the results were analysed using repeated measures two-way (tem­ reported by Avery et al. (1982) and Van Damme et al. perature by type of fly) analyses of variance, after (1991) with Lacerta vivipara. These later authors, having checked their conformity with the assumptions however, could not demonstrate a decrease in capture ofANOVA.

a RESULTS 3 Wingless flies spent significantly less time moving

(t = 2.42, = 10 P < 0.05) n for both series of data, than 2 I 28 ± 22 % 53 ± 25 %, did winged flies(mean ± SD: vs. t ..... t respectively). The body temperature of lizards influ­ 0 1 enced both capture efficiencyand handling time (Figs. 0 � c: I a & 1 b ), since warmer lizards had higher capture suc­ i i

= 4.23, P < 0.05) cess (number of fa ilures: F2 16 and b = 3.67, P < 0.05). shorter handling times (F21� The 12 winged-wingless condition had no significant effect on �f 10 handling time (F, 8 = 2.85, P > 0.1 ), but lizards were clearly more successful in capturing winged flies F ( 8 , 8 �I = 183.79, P < 0.001). No interaction was fo und be­ 6 ]' tween the effects of prey type and Tb on capture success or handling time (P > 0.1 in both cases), though the effect of Tb on number of failures was significant for c

= 5 winged flies (F216 3.68, P < 0.05) but not for wingless 6 = t ones (F 2. 4, P > 0.1). The attack distance, that 216 0 � was smaller for winged fl ies (F = 9.08, P < 0.05), i ,.8 varied significantly with Tb (F216 = 6.48, P < 0.01) be­ 5 cause at low temperatures attack distances were much 0- reduced for winged flies; there was a marginally sig­ t

nificant interaction (F216 = 3.49, P = 0.055) between the effects of Tb and type of prey on attack distance 26 31 36 Tb C'C l (Fig. le). The proportion of trials in which first capture was a FIG. I. Mean (±2SE) number of (a) unsuccessful capture winged fly (ranging between 0/2 and 4/4 fo r each ex­ attempts, (b) handling time (in s), and (c) attack distance (in perimental subject at each Tb range) tendea to increase cm), according to body temperature and type of prey (winged 2; vs. wingless flies). Solid and white bars represent winged and at higher Tbs (Fig. repeated measures ANOVA wingless prey, respectively. n = 9 data (means of two to four model with linear contrast: F, 8 = 5.12, P = 0.053). At replicates per individual lizard) for each prey type - T b low Tbs, lizards captured wingless flies in first place combination. 148 J. A. DIAZ

offbetween attack distance and capture success under 'C Q) Cl conditions of impaired locomotor performance. c: Though I did not compare distances forattacks that did j 80 � • and did not result in prey capture, lizards did in fact ::I � • ... • attempt to make long distance attacks on winged flies 2J 60 0 at low temperatures; these long distance attacks were t: ------at least partially responsible for the high number of .... ff · 4"- �.c: 0 failures on winged flies at low T s shown in Fig. 1. In 40 b � lizards, sprint speed exhibits a high thermal depend­ .... • "' Cii ence, with slower and clumsier movements at lower .. ... & .., 20 - Tbs (Bennett, 1980; Hertz, Huey Nevo, 1983; Avery ..... & Bond, 1989; Van Damme, Bauwens, Castilla & 0

� Verheyen , 1989; Van Damme et al., 1991). Reduced locomotor performanceat low T would have enhanced 26 31 36 b the escape abilities of winged flies by increasing the Tb c•c) time available for detecting lizards. This would have reduced the mean distance of successful attacks to FIG. 2. Proportion of trials in which fi rst successful capture winged prey at low temperatures, and would have in­ was a winged fly for each of the nine lizards tested at each creased the mean number of unsuccessful, long temperature range. The dashed line indicates the null distance attacks to such prey. hypothesis of equal number of first captures for both prey To what extent can the results obtained in this study types, and the circles show the mean values at each temperature range. be used to predict performance by field-active lizards under more natural conditions? According to a sample of302 field Tb readings in a nearby area (part of which have been reported elsewhere, see e.g. Carrascal & success at low Tb, probably because they employed Diaz, 1989; Diaz, 1992), most active lizards had Tbs crickets with their hind legs removed to prevent escape within the moderate and high ranges defined above from the terrarium. Results of the present study show (47.7 % of the readings between 28.6 and 33.5 °C, and that the escape abilities of prey are crucial to evaluate 33.1 % higher than 33.5 °C, respectively). However, the effects of temperature on the performance of rep­ 19.2 % of the Tb readings were at or below 28.5 °C, so tiles as predators. that a relatively large number of active lizards would The physical condition and vulnerability to preda­ be expected to show a diminished efficiency when try­ tion experienced by prey (e.g. wingless flies) may ing to capture flying prey. Although some of these low determine what defence tactics should be adopted Tbs probably correspond to lizards within the period of (Endler, 1991 ), for instance whether to freeze or flee morning warm-up, when reduced capture abilities (Bauwens & Thoen, 198 1). Alternatively, wingless might not be relevant, a high proportion of the winged flies could move less than winged ones as a conse­ prey (assuming similar thermal sensitivities formost quence of recent injury. Whatever the reasons for fly winged insects) would have effectively avoided lizard behaviour, immobility is useful as an antipredator de­ predation in the fi eld. In fact, casual observations of fence as long as predators rely on sensory modes that this and other lacertid species (e.g. wall lizards, detect motion (Edmunds, 1974; Endler, 1986), and liz­ Podarcis) suggest that attacks to diptera are likely to ards (including P. algirus; personal observation) often succeed only when launched from a very short dis­ do not detect objects outside their tongue-flicking tance. reach unless such objects are moving. Nevertheless, One final speculation is that improved ability to this antipredator strategy did not seem to be very effi­ capture fast-fleeing, winged prey is likely to evolve if cient in the case of wingless flies, as it could not such "difficult" prey become more common than "not­ compensate their reduced fleeing speed: wingless flies so-difficult" ones, which is the expected result of were in fact captured before winged fl ies at low Tbs stronger selection for prey defences than for predator (Fig. 2). counter-defences (Dawkins & Krebs, 1979; Endler, On the other hand, in a series of feeding trials with 1991 ). This suggests that reduced ability to capture P. algirus similar to the ones reported here, and allow­ fast-fleeing prey at low Tb may have been a major se­ ing for the effects of prey size, the attack distance was lective force leading to the evolution of behavioural larger for moving prey than forimmobile ones (Diaz & thermoregulation in reptiles (Avery et al., 1982). Re­ Carrascal, 1993). One should therefore expect attack sults of this study indicate that high Tbs (that were distance to be larger in the case of the more mobile close to the value of mean preferred Tb) not only im­ winged fl ies. However, no difference was found at prove predatory efficiency,but also widen the range of moderate or high Tbs, and the reverse was true at low prey that is actually available forli zards, because only Tbs: the attack distance decreased only in the case of at high Tbs can lizards counterbalance the escape abili­ the more difficultand mobile prey, suggesting a trade- ties of their more difficult and faster fleeing prey. TEMPERATURE EFFECTS ON LIZARD PREDATION 149

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