Living with Your Food: Geckos in Termitaria of Canta˜ O L

Home , Gymnodactylus, Gymnodactylus amarali

Journal of Zoology. Print ISSN 0952-8369 Living with your food: geckos in termitaria of Canta˜ o L. J. Vitt1, D. B. Shepard1, J. P. Caldwell1, G. H. C. Vieira2, F. G. R. Franc¸a2 & G. R. Colli2

1 Sam Noble Oklahoma Museum of Natural History and Department of Zoology, University of Oklahoma, Norman, OK, USA 2 Departamento de Zoologia, Universidade de Bras´ılia, Bras´ılia, DF, Brazil

Keywords Abstract ectotherm thermoregulation; diets; microhabitat specificity, lizard ecology, We tested three non-exclusive hypotheses that the lizard, Gymnodactylus carvalhoi, termitaria. lives in termitaria to avoid thermal extremes, to avoid predators, or because of an abundance of food (dietary specialist). We first confirm that these geckos are Correspondence restricted to termitaria in the region studied. Body temperatures (Tb) of geckos Laurie J. Vitt, Sam Noble Oklahoma averaged below environmental temperatures during day outside of termitaria and Museum of Natural History, 2401 above outside temperatures at night; Tb averaged only slightly higher than Chautauqua Avenue, Norman, OK 73072, temperatures inside termitaria. We conclude that thermal constraints in Cerrado USA. Tel: +1 405 325 5002; Fax: +1405 habitats lacking rocks restrict Gymnodactylus to termite nests. High frequencies of 325 7699 tail loss and the presence of many potential predators within termitaria suggest Email: [email protected] high encounter rates with predators, indicating that predation pressure does not restrict these geckos to termite nests. Dietary data indicate that G. carvalhoi is a Received 11 August 2006; accepted termite specialist. Published data indicate that other Gymnodactylus species and 27 September 2006 populations are also termite specialists, even though several live primarily outside termitaria (in crevices and under rocks). An evolutionary history of termite doi:10.1111/j.1469-7998.2006.00273.x specialization and low thermal requirements in the clade (Gymnodactylus) predis- pose them to feed on termites within the termitaria.

Introduction We examined the ecology of Gymnodactylus carvalhoi (Gekkonidae), a lizard that appears to be almost entirely Energy gained by an organism from food is used for restricted to termite nests constructed of hard-packed soil in maintenance, growth and, if sexually mature, reproduction some areas of the Brazilian Cerrado. The vast grasslands (Congdon, Dunham & Tinkle, 1982; Congdon, 1989; known as Cerrado experience both daily and seasonal shifts Schwarzkopf, 1994; Doughty & Shine, 1997). To maintain in temperature and moisture (Franco, 2002). Little rainfall a positive energy balance, energy gain resulting from prey and high temperatures characterize a prolonged dry season ingestion must exceed energetic costs of searching for, extending from about May through October, depending pursuing and capturing prey. However, this simplified view upon locality. The wet season is characterized by sporadic, of predator–prey interactions excludes potential risk sometimes intense rainfall and less extreme temperatures. associated with foraging behavior (e.g. Shine, Schwarzkopf Frequent fires affect vegetation structure as well as nutrient & Caley, 1996). Foraging individuals may increase fluxes (Miranda, Bustamante & Miranda, 2002). Reptile and their exposure to predators (direct fitness cost) or may be amphibian diversity is high in Cerrado (Colli, Bastos & constrained in their ability to harvest available prey because Araujo, 2002) and many species use termite nests as refugia. of predation risk (Stamps, 1977; Werner et al., 1983; In habitats where lizards have been studied, Cerrado con- Cooper, 1997; Cooper et al., 2003). In addition, physiologi- tains from 22 to 75 termite species in four families (Colli, cal constraints may limit an individual’s ability to forage Constantino & Costa, 2006), many of which live in large, in some habitat patches or during certain times (e.g. Grant, compacted terrestrial termitaria (Lacher et al., 1986). Many 1990). Terrestrial ectotherms are primarily constrained additional Cerrado termite species are known (Mathews, by their inability to tolerate changes in moisture and 1977; Gontijo & Domingos, 1991; Constantino, 1998, 2005). temperature (Shine, 1988; Congdon, 1989; Hutchison & Termites are important in tropical ecosystems for a wide Dupre, 1992; Qualls & Andrews, 1999), which affect range of reasons, varying from food sources for amphibians behavioral and physiological processes (Huey & Stevenson, and reptiles (e.g. Vitt & Colli, 1994; Colli et al., 2006) to 1979; Troyer, 1987; Van Damme, Bauwens & Verheyen, production of atmospheric gases (Zimmerman et al., 1982). 1991). These constraints may restrict individuals to micro- In both Australian deserts and Brazilian Cerrado, lizard habitats that meet the physiological requirements of the diversity is correlated with termite diversity (Morton & species. James, 1988; Pianka, 1989; Colli et al., 2006). Nevertheless,

Journal of Zoology 272 (2007) 321–328 c 2007 The Authors. Journal compilation c 2007 The Zoological Society of London 321 Geckos in termitaria L. J. Vitt et al. termite diversity in the Cerrado does not appear to drive ably. In some instances, we worked on individual nests for lizard diversity (Colli et al., 2006). more than 10 min before finding and capturing a gecko. To We first establish that the Cerrado endemic gecko, determine whether the time necessary to find geckos influ- G. carvalhoi, is restricted to termite nests in the study area. enced their Tb, we made two relevant comparisons. First, Next, we ask why G. carvalhoi is restricted to termite nests because we often found more than one gecko in a nest, we even though no other sympatric lizard species are. We used an ANOVA to compare Tb between all geckos caught analyze temperature, tail loss frequency and dietary data to first, second or third. This included geckos caught in nests determine whether temperature, predation, diet or a combi- containing only a single gecko (they would be the first). nation of these factors account for the restriction of these Second, we used a paired t-test to compare Tb of only those lizards to termite nests. Finally, we comment on evolution geckos with paired values (e.g. two geckos captured con- within the genus Gymnodactylus and consider the evolution secutively in the same nest). If time to capture affected gecko of microhabitat specialization in an ecological and historical Tb, then we would expect geckos caught later relative to context (e.g. Vitt et al., 2003; Vitt & Pianka, 2005). others to have higher Tb. To gain more insight into temperature fluctuations of the Methods thermal environments on and within termite nests, we selected four moderately large termitaria and monitored Field data collection temperature every 10 min over a 13-day period (October 7–19) with electronic dataloggers (TidBits; Onset Computer The study took place at the Parque Estadual do Cantaõ, Corp.). A single TidBit was placed on the top of each nest to located just east of the Araguaia River in western Tocantins provide time series of surface temperatures. Three TidBits state, municipality of Caseara, Brazil (approximate coordi- with strings attached were dropped into holes in each nest. nates are: 09118033.200S 49157027.600W). The study area is Because these lizards live inside nests and are sometimes part of the Cerrado Biome, consisting of open grasslands active on nest surfaces, we consider these to estimate with stunted trees and large numbers of termite nests. We operative temperatures (Te) in representative gecko micro- used drift-fence arrays with a combination of pitfall and habitats. We did not attempt to validate the use of TidBits funnel traps to sample most lizards and snakes in the area. for two reasons: (1) several recent studies have shown that We also methodically broke apart 50 termite nests over a TidBits are useful as proxies for copper models of small- period of 8 days; subsequent observations revealed that bodied lizards (Vitt & Sartorius, 1999; Shine & Kearney, termites immediately began reconstructing their nests. Be- 2001; Vitt et al., 2005) and (2) the most relevant TidBit fore opening each nest, we measured nest width on x and y temperatures were those within the termitaria where axes at ground level and height at the center. Nests approx- most physical variables affecting lizard temperatures (wind imate the shape of elliptical cones; thus, we used these speed, insolation, lizard posture) were at best only mini- measurements to estimate the volume of nests based on the mally relevant. We broke apart these four nests after our formula for an elliptical cone: temperature-sampling period; all contained Gymnodactylus. To aid in interpretation of our temperature data, we V ¼ðpÞðaÞðbÞðh=3Þ assembled data on body temperatures of other Neotropical where a is the x axis of the base, b is the y axis of the base and lizards (L. J. Vitt, A´vila-Pires, S.S. Sartorius & P.A. Zani h is the nest height. We recognize that our volume estimates publ. data and unpubl. data) collected by some of the are minimal estimates because the tops of nests are rounded authors. off rather than peaked like cones, and nests varied in the extent to which they extended underground. Laboratory data collection We recorded the location of each nest with respect to trees (in full sun, partly shaded, fully shaded, hereafter, nest We collected 69 G. carvalhoi from 25 termitaria for morpho- aspect). We counted all nest openings large enough for a logical and diet analyses. These were taken back to our field small vertebrate to enter. We measured four surface tem- laboratory and humanely euthanized within 1–2 h after peratures of each nest (approximating N, E, S and W) using capture. We measured snout–vent length (SVL), unregener- TM a Rayteks ST Pro (Raytek Corp., Santa Cruz, CA, USA) ated portion of the tail (tail base) and regenerated portion of hand-held infrared noncontact thermometer. We recorded the tail (if any) to 1 mm with a plastic rule, and head width temperatures inside of up to three holes entering the nests. (widest point), head length (from the anterior edge of the For these, we attempted to obtain temperatures as deep in tympanic opening to the snout), head height (at deepest the nest as possible. We then broke apart each nest and point), body width and height (mid body), hindleg length recorded all vertebrates encountered within the nest. We from the body anterior to the limb to the tip of the longest recorded the number, sex and relative size of Gymnodactylus toe and foreleg length from the body posterior to the limb to in each termitarium, when present. When Gymnodactylus the tip of the longest toe to 0.01 mm with digital calipers for were found, we captured them and immediately took cloacal each individual lizard before fixation. We weighed lizards to temperature (Tb) with a Miller–Weber rapid register ther- 0.01 g on Acculab digital balances (Acculab, Edgewood, mometer. The time lag between first disturbing a nest as we NY, USA). Tail measurements allowed us to calculate tail broke into it and the time we found geckos varied consider- loss frequency within the population. By using only lizards

322 Journal of Zoology 272 (2007) 321–328 c 2007 The Authors. Journal compilation c 2007 The Zoological Society of London L. J. Vitt et al. Geckos in termitaria with complete tails in a regression of SVL versus tail length, using 60 arrays containing a total of 240 traps (12 720 trap we were able to generate estimates of original tail lengths for days), only one Gymnodactylus was caught in a trap. Among all individuals with broken or regenerated tails to determine 73 individuals captured in this study, one was in a pitfall the relative position of tail breaks. Most tail breaks occur trap, two were underneath a pile of boards in a field, one was along cleavage planes in vertebrae (Arnold, 1984), but some on the ground away from a termite nest at dusk and the secondary tail breaks occur within the regenerated portion remainder (94.5%) were found on or inside termite nests. lacking vertebrae. Lizards were fixed in 10% formalin and Several additional geckos (not collected) were observed given unique individual tags. Lizards were later transferred during the day inside termite nests through holes in the to 70% ethanol for permanent storage in the Herpetology nests, and several others were observed at dusk or at night Collection of the University of Brasılia´ (CHUNB) and the on or inside termite nests. Those on termite nests immedi- Sam Noble Oklahoma Museum of Natural History ately fled into the nests when approached. Among the (OMNH). 50 nests opened during the day, 25 (50%) contained geckos. Within 1 month following fixation, the stomachs were From one to four geckos occurred in nests containing removed from geckos, prey were identified to family when geckos (Fig. 1). Among the 25 nests containing geckos, possible and each prey item was measured for length and 14, 10 and one were in sun, partial shade or shade, width. When invertebrate prey are compressed in lizard respectively. Among nests not containing geckos, 16, 8 and stomachs, their shape approaches that of a prolate spheroid. one were in sun, partial shade or shade, respectively. The We used the formula for a prolate spheroid to estimate the 50 termitaria averaged 61.3 2.3 cm in height (h), volume of individual prey items: 101.9 3.4 cm in long base diameter (a), 92.2 3.3 cm in 3 short base diameter (b) and 0.695 0.083 m in volume. The 4 length width 2 number of holes varied from one to 27 (mean=11.4 0.8). V ¼ p 3 2 2 Termitaria containing geckos had the same number of holes opening to the outside as termitaria without geckos (11 1.0 using the program BugRun, a 4th Dimensions-based ana- and 11.6 1.3, respectively, Mann–Whitney U-test, lysis that produces dietary summaries, calculates mean prey Z=0.01, P=0.99). The number of holes was not signifi- size (length, width and volume) for each lizard, estimates cantly correlated with nest volume (r=0.24, n=50, stomach volume based on total prey volume and calculates P=0.10). We used multiple logistic regression to test niche breadth using the inverse of Simpson’s (1949) diversity whether nest volume, the number of holes and nest aspect measure (see Pianka, 1973, 1986): were good predictors of gecko presence/absence. Gecko 1 presence/absence could not be predicted by nest volume 2 2 b ¼ Pn (w =2.07,d.f.=1, P=0.15), the number of holes (w =0.49, 2 2 pi d.f.=1, P=0.48) or nest aspect (w =0.44,d.f.=2,P=0.80). i¼1 External and internal nest temperatures, based on con- where p is the proportional utilization of each prey type i. tinuous temperature monitoring with TidBits, varied on an Niche breadth values (b) vary from 1 (exclusive use of a hourly and daily basis (Fig. 2), with temperatures inside the single prey type) to n (even use of all prey). We log10 nests being considerably lower during the day but higher at transformed all quantitative data to normalize distributions night. Temperatures taken on termitaria surfaces and inside for further analyses. We used linear regression to determine whether prey size and number of prey eaten varied with lizard body size 25 (log10 SVL). To determine whether prey size or number of prey eaten differed between sexes, we used an ANCOVA 20 with log10 SVL as the covariate and sex as the class variable. We also plotted log10 stomach volume with log10 SVL to determine the relationship between stomach volume and 15 lizard size, and to estimate the relative fullness of the lizards sampled (see Huey, Pianka & Vitt, 2001). We made the 10 assumption that a line roughly parallel to the regression No. of nests slope that intersects upper values approaches the relation- 5 ship between full stomachs and lizard body size.

0 Results 01234 No. Gymnodactylus Lizard microhabitats, Tb and thermoregulation Figure 1 Frequency distribution showing number of geckos Gymno- dactylus carvalhoi found in each of 50 termitaria sampled. When nests Our pitfall trapping established that G. carvalhoi rarely contained more than two geckos, additional individuals were juve- move about on the ground. During 53 days of trapping niles.

Journal of Zoology 272 (2007) 321–328 c 2007 The Authors. Journal compilation c 2007 The Zoological Society of London 323 Geckos in termitaria L. J. Vitt et al.

60 − In/bottom x = 35.3 ± 0.39 °C 40 In/mid (26.8−61.8 °C) 50 Surface n = 196 30 40 20

30 10 No. of records

20 0 2530 3540 4550 5560 65 Surface temperatures (°C) 10 60 40 − x = 33.3 ± 0.31 °C 50 30 (27.0−49.4 °C) n = 138 40 20

10 30 No. of records 0 2530 3540 4550 5560 65

C) 20 ° Hole temperatures (°C) 10 Figure 3 Frequency distributions of temperatures recorded with the 60 Rayteks noncontact thermometer on the surfaces and in the holes of termitaria. 50 Temperature (

40 remains true when only gecko pairs from the same nest were compared (paired t =0.26, P=0.80). Because these geckos 30 7 were captured during the day, comparisons with termitaria 20 temperatures are only relevant during those time periods. Nevertheless, G. carvalhoi was able to maintain Tb close to 10 the upper limit of Te inside nests, likely by positioning 60 themselves in exit holes or other nest areas where temperatures were slightly higher. 50 An ANOVA on species’ mean Tb revealed significant differences among lizard families (families represented by 40 less than three species were excluded; F5,60 =17.0, Po0.001). Gekkonid Tb were not significantly different 30 from those of gymnophthalmids, scincids, polychrotids or tropidurids. Teiid lizards had higher Tb than polychrotids, 20 gymnophthalmids and gekkonids (Po0.05, post-hoc Games–Howell test). However, because most of the lizards 10 represented (Fig. 4) occur in more mesic habitats (e.g. 0000 0400 0800 1200 1600 2000 0000 rainforest), we divided species into those living in closed Hour of day (forest), open (e.g. caatinga, Cerrado) and both habitats Figure 2 Daily march of temperatures on surface, inside approxi- (e.g. Ameiva ameiva occurs nearly everywhere in tropical mately the middle, and inside near the bottom of four termitaria based Brazil). A comparison of Tb for lizards in these categories s on continuous monitoring with TidBit digital temperature recording revealed significant differences among categories (F2,63 devices. Repeated bars to the right of each panel depict ranges of Tb =18.7, Po0.0001). Tb of lizards in closed habitats was for geckos captured inside of the 50 nests that were opened, and the lower than those in open habitats (Po0.05, post-hoc continuous line across each panel indicates the mean value. Games–Howell test), and Tb of lizard species using both open and closed habitats was intermediate (P40.05, post- hoc Games–Howell test). Our sample of species’ means did holes before we broke apart nests varied considerably not allow a two-way ANOVA, so these results should be depending on exposure, but surface temperatures overall taken only as suggestive (i.e. we cannot sort out the relative were higher than temperatures inside holes (Fig. 3). effects of phylogeny and habitat type). Most relevant is that The mean Tb of 31 captured geckos was 31.3 0.2 1C Tb of G. carvalhoi in Cerrado (31.3 0.2 1C), Gymnodactylus (28.3–33.8 1C). The order of capture (first, second or third) geckoides in caatinga (32.5 0.6 1C) and Gymnodactylus did not affect gecko Tb (F2,28 =0.7, P=0.49) and this amarali in Cerrado [30.2 0.5 1C(SE calculated from SD)]

324 Journal of Zoology 272 (2007) 321–328 c 2007 The Authors. Journal compilation c 2007 The Zoological Society of London L. J. Vitt et al. Geckos in termitaria

by family by habitat 14 38 37 12

C) 36 10 °

35 8 34 6 33 No. of lizards 4 32 31 2

30 0 29 10 20 30 40 50 60 70 80 90 100

Mean body temperature ( Per cent of original tail lost 28 Figure 5 Frequency distribution of percent of tail lost in Gymnodacty- 27 lus carvalhoi with missing or regenerated tails. Both Teiidae

Scincidae Table 1 Dietary summary for Gymnodactylus carvalhoi from the Gekkonidae

Tropiduridae Canta˜o region of Brazil based on analysis of 60 stomachs containing Polychrotidae Open habitats

Closed habitats prey.

Gymnophthalmidae % Prey type No. % No. Volume Volume Freq. Figure 4 Means and SE of lizard Tb by family and among habitat types. See Supplementary Materials Table S1 for data and references. Crickets and grasshoppers 3 0.38 140.89 1.86 3 Termites 728 91.8 5881.58 77.76 53 Gekkonid mean Tb is similar to those of gymnophthalmids and Beetles 5 0.63 28.62 0.38 3 polychrotids, most of which live in tropical forest. Gekkonid Tb remain Homopterans 6 0.76 143.46 1.9 3 low regardless of habitat type. The mean Tb for Gymnodactylus carvalhoi from this study (open habitat) was 31.3 1C. Flies 4 0.5 119.77 1.58 1 Hymenopterans (non-ant) 2 0.25 0.63 0.01 2 Ants 27 3.4 351.42 4.65 16 Insect egg case 1 0.13 67.24 0.89 1 are considerably lower than mean Tb for lizards living in open habitats (34.3 0.8 1C), but higher than the mean for Insect larvae 3 0.38 193.65 2.56 2 all gekkonid species combined (29.5 0.8 1C). Springtails 1 0.13 0.58 0.01 1 Spiders 9 1.13 456.42 6.03 8 Millipedes 1 0.13 159.25 2.11 1 Tail-loss frequencies and position of tail Centipedes 2 0.25 19.34 0.26 2 breaks Pseudoscorpions 1 0.13 1.01 0.01 1 Fifty of 69 (72.5%) geckos had lost their tails at least once. SUMS 793 100.00 7563.86 100.00 — For geckos with unbroken tails, tail length was signiﬁcantly Niche breadths 1.18 1.63 2 correlated with SVL (adjusted R =0.93, F1,18 =254.8, No., number of individuals of a particular prey; Volume, total volume of Po0.0001); the relationship between unbroken complete that prey type in all lizards; Freq., number of individual lizards (out of a tail length and SVL was: tail length=1.29 (SVL)6.843. possible 60) containing a particular prey type. Percent of the tail broken off varied from 19.6 to 96.5%

(mean=70.9 3.2%), with nearly 20% of geckos losing 3 nearly the entire tail (Fig. 5; i.e. tail break occurring on the 0.72–1283.72) mm in volume. No relationship was found ﬁrst vertebral cleavage plane of the tail). between gecko SVL and mean prey volume (F1,56 =2.0, P=0.16) or number of prey (F1,56 =3.0, P=0.09). Larger geckos contained a larger total volume of prey (F =5.6, Lizard diets 1,56 P=0.02; Fig. 6). Sixty G. carvalhoi contained a total of 219 prey items in their stomachs, comprising 14 prey categories (Table 1). The diet Discussion was dominated numerically and volumetrically by termites, with only spiders and ants contributing much to the remain- Terrestrial termitaria are abundant in many areas of the der of the total diet. Fifty-three of the 60 geckos contained Brazilian Cerrado and provide refuge for a wide variety of termites. Low niche breadth values (Table 1) indicate that animals. The endemic Cerrado gecko G. carvalhoi appears G. carvalhoi is a termite specialist. Individual prey averaged largely restricted to these social insect nests in the Canta˜o 9.1 0.33 (range 0.80–35.41) mm in length, 3.28 0.11 region based on our sampling data. Our failure to trap more (range 0.61–11.19) mm in width and 79.7 8.65 (range than a single individual using terrestrial trap systems that

Journal of Zoology 272 (2007) 321–328 c 2007 The Authors. Journal compilation c 2007 The Zoological Society of London 325 Geckos in termitaria L. J. Vitt et al.

4 King, 1974; Colli et al., 2003). This behavior presumably estimated distracts predator attacks away from the head and body full stomach toward the expendable tail. Such displays may deter pre- 3 dator attacks rather than elicit them (Dial, 1986), but we have no evidence for this in G. carvalhoi. Raising the tail over the body in Coleodactylus brachystoma, another 2 Cerrado gecko, presumably makes lizards resemble sympatric scorpions, thereby reducing predation (Branda˜o& Motta, 2005). Lizard-eating snakes, large scolopendro- 1 morph centipedes, therophosid spiders and large amblypy- gids occur inside termitaria and are potential predators stomach contents volume

10 0 on Gymnodactylus. If anything, crepuscular habits of G. carvalhoi while on the surface of nests could reduce Log predation by lizard-eating birds, most of which forage −1 during morning. Whether a social (e.g. Fox & Rostker, 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1982; Fox, Heger & Delay, 1990; Martin & Salvador, 1993) or demographic (e.g. Niewiarowski et al., 1997) cost of tail Log10 snout–vent length loss exists in G. carvalhoi remains unknown. Figure 6 Relationship of lizard body size [snout–vent length (SVL)] Te within termitaria remained relatively constant with total prey volume for Gymnodactylus carvalhoi. The slope of the throughout the day and was within the range of Tb observed relationship, log total prey volume=1.633(log SVL) – 0.836, is 10 10 in G. carvalhoi (Fig. 2). However, Te on termitaria surfaces significantly different from zero (t=2.36, P=0.02). Full stomach were much higher during the day and considerably lower volume is estimated as the line that intersects the highest points on during the night than gecko Tb, suggesting that thermal the regression. extremes (high and low) in the external environment con- tribute partially to the restriction of G. carvalhoi to termitar- proved effective for all other lizard and snake species, even ia. Although the underlying causes of low Tb in G. carvalhoi with 12 720 trap days, indicates that these geckos spend little remain unknown, our comparisons of Tb among lizard time moving about on the ground. Most likely, they move families and among habitat types shed some light on this. only when dispersing to find new nests to inhabit. Thus, we We conclude that G. carvalhoi is living in a microhabitat confirm that G. carvalhoi are restricted to termitaria as their (inside of termitaria) that buffers these lizards from external primary microhabitats in the Cantaõ region. Populations of temperature extremes that most gekkonids would not be able G. carvalhoi in some other areas of the Cerrado (e.g. Goias´ to tolerate. These findings are consistent with our temperature State), formerly referred to as Gymnodactylus geckoides data on termitaria and the rarity of these lizards in terrestrial amarali (see Colli et al., 2003 for ecological data and Vanzolini, traps. Thus, temperature is one reason why G. carvalhoi 2005 for most recent taxonomy), live in rock crevices and inhabits these social insect nests. However, other species and under rocks. Rocky habitats were not available at Cantaõ populations of Gymnodactylus live in non-exposed microhabi- as they are at some other Cerrado localities, so restriction to tats in open habitats (under rocks for G. geckoides and Goias´ termite nests may result from an absence of alternative appro- populations of G. carvalhoi; Vitt, 1995; Colli et al., 2003). In the priate refuges. Alternatively, restriction to rocks in some other Cantaõ region, surface rock microhabitats are not available. In areas may result from absence of appropriate termitaria. The caatinga where G. geckoides occurs and rocky areas of Goias,´ possibility also exists that G. carvalhoi as now delineated large termite nests are rare. represents more than a single taxon. The high frequency of geckos containing prey in their Our data on thermal ecology, tail loss and diets suggest stomachs, and the relative fullness of stomachs suggest that that a combination of thermal constraints, limited types of prey resources are easily available and that these geckos available refugia, and diet preferences explain the restriction maintain a positive energy balance (e.g. Huey et al., 2001). of these geckos to termite nests. The hypothesis that preda- All three measures of dietary importance, numbers, volumes tion risk plays a significant role in restricting these geckos to and frequencies of use, indicate that G. carvalhoi is, for the termitaria is not supported by our observations on tail loss. most part, a termite specialist. Because these lizards eat Although high frequencies of tail loss do not necessarily other invertebrates as well, the possibility exists that their indicate high predation rates (e.g. Schoener, 1979; Schoener apparent specialization on termites results from superabun- & Schoener, 1980), they do suggest that predator attacks are dance of termites in microhabitats in which geckos are quite common and that many geckos escaped at least one restricted. Spiders and ants, the only other prey categories attack by losing their tails. Tail loss may occur during contributing substantially to the diet, are also common in intrasexual encounters in some lizards (e.g. Vitt et al., 1974; termitaria. Termites dominate the diets of G. geckoides Vitt & Zani, 1997), but we have not observed such encoun- (caatinga) and Goias´ populations of G. carvalhoi (Cerrado) ters in Gymnodactylus. Individuals often raise their tails as a as well (Vitt, 1995; Colli et al., 2003). defensive display to expose the black and white-banded Open habitats in warm environments present numerous underside, similar to other lizard species (Congdon, Vitt & challenges to small terrestrial vertebrates, including high

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