Yehudah L. Werner 1

1997 Asiatic Herpetological Research Vol. 7. pp. 153-165 Varied and Fluctuating Foraging Modes in Nocturnal Lizards of the Family Gekkonidae 1 - 2 3 4 Yehudah L. Werner Shigeru Hidetoshi Okada , Ota , Gad Perry and Shoji TOKUNAGA5 Department ofEvolution, Systematics and Ecology, The Alexander Silberman Institute of Life Sciences, The Hebrew University ofJerusalem. 91904 Jerusalem, Israel; Kagoshima Environmental Research & Services, 2-7 Masago-cho, Kagoshima-shi, Kagoshima 890, Japan; Tropical Biosphere Research Center and Department of Biology. University of the Ryukyus, Nishihara, Okinawa 903-01 .Japan; Department ofZoology, University of Texas, Austin, TX 78712-1064. USA; Department ofPublic Health. School of Medicine, Kyushu University, 3-1- 1 Maidashi, Higashi-ku, Fukuoka SI 2. Japan Abstract. -Heliothermic lizards have been used as model organisms in studies of foraging mode, although their behavior is generally complicated by thermoregulation. Tropical nocturnal gekkonid lizards could be better models than temperate diurnal lizards. In several recent reviews, gekkonids have been considered to be sit-and- wait (ambush) predators. Observation of Gekko hokouensis, G. japonicus and Teratoscincus roborowskii in the field on warm nights revealed that by the measure of moves-per-minute they are sit-and-wait (SW) predators but by the measure of percent-time-moving G. hokouensis is widely-foraging (WF), as is Coleonyx variegatus, according to the literature. The behavior of individuals of all three species combines to varying extent both SW and WF modes. This observation accords with recent reports of foraging behavior in G. gecko and Stenodactvlus doriae. Reexamination of the original literature sources quoted in recent reviews showed that these sources had already qualitatively described many geckos as either WF or mixed strategists. The fluctuating foraging mode of geckos presumably enables these noctural visual predators to locate stationary prey and. without wasting locomotor energy, to locate mobile prey. The option to employ both SW and WF modes may depend on the absence of competition. Although geckos as a group had been believed to be SW predators, their relative clutch mass (RCM) had often been believed to be as small as in WF lizards. More recently, several geckos were shown to have larger RCMs. Hence geckos, rather than having a paradoxically low RCM. are in fact intermediate between SW and WF lizard groups in both RCM and foraging mode. Key words: Reptilia, Lacertilia, Gekkonidae, Gekko hokouensis, Gekko japonicus, Teratoscincus roborowskii, China, Japan, foraging mode, nocturnality. relative clutch mass. Introduction assumptions that there is little intraspecific or intra individual variation in foraging behavior. Ever since they were first coined by Pianka (1966). Lizards have been used often as models for study- the terms "sit-and-wait" (SW) and "widely foraging" ing the foraging behavior of animals in the field. The (WF) have been used extensively to describe foraging two commonest coins for and behavior. Often they have been considered alternative quantification compari- son have been the time PTM) and states of a dichotomy (Pianka. 1986; McLaughlin. "percent moving"! "movements minute" (MPM, see below) 1989; Etheridge and Wit. 1993; and references in per (Huey and Pianka, 1981; et al., Pietruszka, 1986). while some authors have viewed Perry 1990). them as extremes of a continuum (Pianka. 1974:203; Going by such yardsticks, the foraging mode, Pietruszka, 1986; Perry et al., 1990). Although Vitt either SW or WF. is usually considered typical of a and Congdon (1978) and Vitt (1990) recognized the whole lizard family. Thus, Agamidae, Anguidae and possibility of a continuum of foraging modes, their lguanidae (s.L), unless herbivorous, are SW foragers, papers highlight differences between SW and WF liz- whereas almost all Lacertidae, Scincidae, Teiidae and ards. Implicit in the use of these terms (or the equiva- Varanidae are WF (Huey and Pianka. 1981; Dunham lent "ambush" and "active" foragers) are the et al.. 1988; Green and King, 1993; Cooper. 1994a, b). Vol. 7, p. 154 Asiatic Herpetological Research 1997 The studies underlying this classification obvi- ments per minute", the average number of times, ously presuppose that the observations quantified had during one minute, that a lizard changed its locomo- been free of socially-motivated (Regal, 1983:1 16) and tory state from "stationary" to "moving"; PTM, "per- of thennoregulation-related (Anderson, 1993) behav- cent time moving" percentage of the total time, that ior. Whereas it is relatively easy to account for the the animal spent locomoting; percra. percents of ra; former (Kingsbury, 1989), it is often difficult to com- ra. rostrum-anus ("snout- vent") length (Werner, pletely exclude the latter when observing diurnal 1971); RCM. relative clutch mass, ratio of total clutch poikilotherms such as lizards. Nocturnal lizards such mass to total maternal mass, including the clutch (Vitt as geckos can thus provide superior models of forag- and Price, 1982); SD, standard deviation; SW, "sit- ing mode if observed in a climate with stable night and-wait" predator; WF, "widely ranging forager". temperatures approximating those preferred by the lizards. Data Collection Environmental factors such as illumination can affect The Gekkonidae have traditionally been consid- the of nocturnal 1979: ered SW predators (Pianka. 1986:48; Dunham et al.. activity geckos (Frankenberg. and Bouskila et 1988:513), and this view appears somewhat supported Frankenberg Werner, 1979; al., 1992; Petren et al., 1993). We therefore detail the circum- by recent observations on Gekko gecko (Stanner et al.. stances of the observations. in press). However, Coleonyx variegatus employs an intermediate stragtegy (Kingsbury. 1989) and some Observations were made at night by one observer others have recently been counted as active foragers carrying an electric torch with a removable cover of Thus it remains unclear whether (Cooper, 1994a,b). red cellophane paper (two layers). When the torch was the Gekkonidae are characterized by a given foraging held on the observer's forehead, Teratoscincus could as are other lizard families, if what that mode, and. so, be located on the ground by their reflecting reddish mode is. foraging eyeshine. With both Gekko species, which were observed on walls, this method was This issue is of particular interest because whereas mainly superflu- ous. at a distance for Tera- SW lizards usually have greater relative clutch masses Searching began (>20 m less for the Gekko with white (RCMs) than WF lizards (Vitt and Congdon, 1978). toscincus; species) light. The main observations from geckos tend to have RCMs similar to those of WF were made 3-10 m, on and situation, with red We Lizards (Vitt and Price, 1982: figs. 1 and 3). This depending species light. endeavoured to observe each individual for 30 min- putative paradox cannot be explained fully as an adap- the was and examined. tation of geckos to life in crevices (Vitt, 1981): small utes; finally gecko approached In all three some of the locomotion of the RCMs occur also in cursorial, arenicolous species of species, individuals was towards the hence geckos (Vitt and Price, 1982: Werner, 1989): in some observer, presum- the observer did not affect them of these this could be a phylogenetic constraint (Vitt. ably (following 1986: Stearns, 1992) but presumably at least in the Anderson. 1993). primitive group of Eublepharinae (Kluge. 1967: To enable prompt photography, the observer car- Werner. 1972) this would not be the case. Hence addi- ried a ready camera (Leica M3 with 135 mm lens) tional data on the foraging modes of geckos are with flash and mostly Agfachrome Professional 200 needed. ASA film. Air temperature was recorded with a Miller- Weber thermometer Therefore, we report here on the foraging behavior mercury ("Schultheis" 1 above also 1 of three nocturnal geckos in the eastern Asian sum- type) m ground (for Teratoscincus cm above and substrate was also mer, Gekko hokouensis, G.japonicus, and Teratoscin- ground, temperature taken). Illumination was recorded with a Lunasix-3 cus roborowskii . We pay particular attention to meter. intraspecific variation, which has been reported in the (Gossen) light foraging behavior of some other lizards (Pianka et al„ Observations and environmental data were 1979; Kingsbury. 1989: Perry. 1996). and to intra- recorded into a microcassette recorder (Panasonic individual variation, a topic which has not been RN-102). When the information was transcribed on addressed previously. paper, detailed time data were derived from a clock synchronized with recorded times. Because the speeds Materials and Methods of recording and playback varied with battery strength, care was taken to use equivalent batteries. Abbreviations and Definitions CV, coefficient of variation (standard deviation as percent of mean); FM. foraging mode: MPM, "move- 1997 Asiatic Herpetological Research Vol. 7, p. 155 32.7). We followed this methodology for approx. half the data of Gekko hokouensis, which included appro- priate time statements. In the remainder of G. hokouensis data, the observations had been grouped per half-minute periods, leaving precise durations unknown. These records were scanned automatically by the NOTITA computer program (N. Werner & H. Dreher, in MS) which con- structed a quantitative table, from which some sum- marising statistics were derived by the Microsoft Excel program. We do not use

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