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1 This article was downloaded by: On: 7 March 00 Access details: Access Details: Free Access Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, 7 4 Mortimer Street, London WT JH, UK Italian Journal of Zoology Publication details, including instructions for authors and subscription information: Food habits of the green lizard, Lacerta bilineata, in central Italy and a reliability test of faecal pellet analysis Francesco Maria Angelici a ; Luca Luiselli a ; Lorenzo Rugiero a a Dipartimento di Biologia Animale e dell'uomo, Università di Roma La Sapienza, Roma, Italy To cite this Article Angelici, Francesco Maria, Luiselli, Luca and Rugiero, Lorenzo(997) 'Food habits of the green lizard, Lacerta bilineata, in central Italy and a reliability test of faecal pellet analysis', Italian Journal of Zoology, 64:, 67 7 To link to this Article: DOI: 0.080/ URL: PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan or sublicensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

2 Ital. J. Zool., 64: 677 (997) Food habits of the green lizard, Lacerta bilineata, in central Italy and a reliability test of faecal pellet analysis FRANCESCO MARIA ANGELICI Dipartimento di Biologia Animale e dell'uomo, Università di Roma "La Sapienza", viale dell'università, I0085 Roma (Italy) LUCA LUISELLI Dipartimento di Biologia Animale e dell'uomo, Università di Roma "La Sapienza", via Alfonso Borelli 50, I006 Roma (Italy) LORENZO RUGIERO Dipartimento di Biologia Animale e dell'uomo, Università di Roma "La Sapienza", viale dell'università, I0085 Roma (Italy) ABSTRACT Food habits of the green lizard (Lacerta bilineata) were studied in some Mediterranean sites of the vicinities of Rome (Latium, central Italy), by means both of stomach dissection of individuals found already dead in the field and faeces analysis of living individuals. The taxonomic diet composition of the lizards was accurately described by both methods, thus demonstrating the reliability of faecal pellet analysis as an noncruel method to study lizard diets. However, by using the faeces analysis technique, it is difficult to measure the exact food intake rate (items / unit of time) as well as the size distribution of prey ingested by lizards. There was a remarkable ontogenetic change in the taxonomic diet composition of green lizards: adults essentially consumed beetles and isopods, whereas juveniles fed mainly upon orthopterans, spiders, and Rhynchota. Cannibalism and predation upon small vertebrates (lizards) were very rare events. It is suggested that (i) agerelated differences in microhabitat frequented could explain the dietary differences between young and adult lizards due to different availability of the various prey categories in the various microhabitats, and that (ii) adults and juveniles partition their habitats to reduce intraspecific interference competition. KEY WORDS: Lacerta bilineata Lacertidae Diet Stomach content analysis Faecal pellet analysis Ontogenetic change Intraspecific competition Cannibalism Mediterranean habitat Italy. ACKNOWLEDGEMENTS We thank Dr. Massimo Capula (Zoológica! Museum, Rome) and one anonymous reviewer for having critically commented upon earlier drafts of this manuscript. Part of the data given here were collected by Dr. Ernesto Filippi (University of Rome "La Sapienza"). (Received January 997 Accepted 9 Muy 997) INTRODUCTION Conservation is one of the central aims of the contemporary zoologist community. Killing of specimens for biological analyses is therefore no longer acceptable in the study of endangered species or populations, but it is still unethical even when the taxa under study do not actually suffer a serious decline in numbers. This view is now fortunately widespread among herpetologists, and, as a consequence, several alternative methods of analysis to killing have been experimented and utilized during the recent years. With respect to dietary analyses of freeranging lizard populations, "stomach flushing" a very popular method in batracological research (e.g., see Fraser, 976; Joly, 987; LeClerc & Courtois, 99) has occasionally been used with positive results (Legier & Sullivan, 979; James, 990). However, the most popular bloodless method has been analysis of faecal pellets (FPA) (e.g. In den Bosch, 986; Strijbosch, 986; Capula & Luiselli, 994a, b; Capula et ah, 99). The success of FPA amongst lizard ecologists depends, apart from on its innocuousness for the examined specimens, (i) on the facility with which faeces can be obtained from lizards captured in the field, and (ii) on the relative facility with which prey remains contained in the faeces can be identified under binocular light. However, in the faeces only small fragments of prey may be found, making the study of food size almost impossible (Strijbosch, 986). Moreover, as tests of the reliability of the method in picturing the diet composition of a given species are scarce, it cannot be excluded that 'soft' food remains easily identifiable in stomachs, but not so in faeces, thus seriously affecting the conclusions of studies based on FPA. Strijbosch (986) compared diet data obtained from faeces of Lacerta vivípara from the Netherlands with diet data available in the literature obtained from analysis of stomach contents of conspecifics from other European regions. He found that the diet composition of the various lizard populations was relatively similar, thus assuming that FPA is a suitable technique for dietary studies. The procedure used by this author for determining the reliability of FPA, however, is not completely convincing, although his conclusion may well be right. In fact, for testing the reliability of FPA, the best procedure consists in comparing the dietary data recovered from both FPA and stomach dissection by using the same lizard specimens or, at least, lizards belonging to the same population. On the basis of the above considerations, we decided to test the reliability of FPA, and for this selected the European green lizard as the study species. This lizard, previously named Lacerta viridis, is now renamed Lacerta bilineata according to Rykena (99). This oviparous lacertid, widely distributed in western Europe as well as in the Mediterranean basin (Arnold & Burton, 978), was selected for the following 'practical' reasons:

3 68 F. M. ANGEUCI, L. LUISELU, L. RUGIERO () it is widespread and easily caught in central Italy (Corsetti & Capula, 99), including suburban areas of Rome (cf. Cignini & Zapparoli, 995) that have regularly been surveyed by us for field studies on snake biology; () it was frequently found already dead in the field (mainly in springtime, usually squashed by cars), thus providing a good opportunity to analyse stomach contents without killing specimens specifically for the purpose of this study, and () it is a relatively wellknown species (cf. Kitzler, 94; Weber, 957; Saint Girons, 977; Korsos, 98, 984; Bradshaw et al., 987, 99; Saint Girons & Bradshaw, 989; Saint Girons et al, 989), whose food habits are, however, completely unknown as far as the Mediterranean region is concerned. This could appear surprising if we consider that the amount of recent papers on food habits of western European lizards has dramatically grown, including also studies on largesized lacertids closely related to L. bilineata (see Busack & Visnaw, 989; Castilla et al., 99; Hernandez et al., 99). In the present paper we address the following issues: (i) is the analysis of faeces a suitable technique for determining the taxonomic composition of a lizard species' diet? (ii) What does the green lizard feed upon in the Mediterranean environment of central Italy? (iii) Is there any difference in the diet composition of adult and young L. virtáis? (iv) If so, what are the reasons for this difference? MATERIALS AND METHODS Study area Data given here were collected in some localities situated very close to the urban centre of Rome (0 to 00 m a.s.l.), all with identical climatic conditions and identical vegetation structure, i.e. grassy zones with bushes (Rubus, Cytisus) and stony spots at the borders of Quercus cerris and Q. frainetto woods. This habitat type, in which green lizards are fairly common, is very rich in terms of reptile fauna. Nine different taxa (including L. bilineata in the count) are frequently found: Podareis muralis, P. sicula, Chalcides cbalcides, Hierophis viridiflavus, Elapbe longissima, Natrix natrix, Vípera aspis, and Testudo hermanni. Methods Diet data given in the present paper were collected from March to July, from 990 to 996, and come from analyses of both stomach contents of dead individuals and faecal pellets of live individuals. Both dead and living lizards were sexed and measured for snoutvent length (SVL, to the nearest millimetre) before the beginning of the procedures of identiflying the food eaten. For this study all the specimens with < 80 mm SVL were considered as juveniles. In this species, in fact, the minimal size at sexual maturity is ca. 8 mm SVL (Saint Girons et al, 989). Stomach contents of 46 L. bilineata ( males and 4 females) were analysed after dissection of the body and removal of the gut. All these specimens were found already dead in the field (usually squashed by cars but not too damaged). The prey items were spread in a Petri dish, and identified to the lowest taxon possible. The numbers of individuals of each prey type were recorded, and the proportional share of each prey type was estimated. Lizard specimens used for this analysis were then placed in 70 ethanol. Several of them were donated to Prof. B. Lanza, former director of the "La Specola" Zoological Museum, Florence. A total of 8 faeces of 9 L. bilineata ( young, and 6 adults, of which males and 9 females), were analysed using the methodology described earlier (cf. In den Bosch, 986; Strijbosch, 986) for determining any food residual. Faecal pellets were collected by placing the lizards into small cages until defaecation occurred. No faecal pellets were collected from the soil. Statistical procedures In the text the means are followed by ± one standard deviation. Analyses were done using SPSS (version 6.0, for Windows) statistical software. All tests were twotailed, with a set at 5. For the choice of the statistical tests we generally followed recommendations in Snedecor & Cochran (980), and Zar (984). Food niche breadth of each group of individuals was measured with a Simpson's (949) diversity index, whereas food niche overlap (O Jk ) between groups was calculated by using the symmetric equation of Pianka (97). The confidence intervals of these estimates are extremely difficult to assess, requiring complex bootstrap simulations (see Ricklefs & Lau, 980) or an appropriate statistical comparison (see Banley, 985). Therefore, our interpretation of these values is based on a comparison carried out by means of a nonparametric correlation matrix Mantel test. Data files were prepared for individual gut (or faeces) contents. These files were then randomly selected in order to determine a minimal sample representative of cumulative prey items (Margalef, 980). RESULTS Diet composition of adult Lacerta bilineata and the reliability of faeces analysis ' technique Diet data on adult L. bilineata, coming from both stomach and faeces analyses, are summarized in Table I. Over 90 of the diet is composed of terrestrial arthropods. Based on the total number of food items found in lizard guts, the bulk of the diet consists of isopods and beetles (mainly belonging to the Carabidae, Scarabaeidae, Tenebrionidae, Curculionidae and Staphilinidae families), accounting, respectively, for about 8 and 4 of the total diet (Table I). The relevance of these two taxa for adult L. bilineata diet is even more clear considering that isopods were found in 4, and beetles in about 45, of the lizards examined (differences between these frequencies: P > 0.5, X test with df). These nearly identical frequencies of occurrence could appear surprising in view of the total amount of beetles found in lizard guts (n = 08) being considerably higher than that of isopods (w = 88). However, the difference was mainly due to a single female lizard (88 mm SVL, and weighing 4.4 g) that had 9 small curculionid beetles (Byctiscus betulae) in the stomach. Other invertebrate categories were eaten by lizards much more rarely, and none of them exceeded 7 of the total diet. Small vertebrates (lacertid and scincid lizards) were also eaten by adult lizards, and, on the whole, they represented about.5 of the total dietary spectrum. Cannibalism also occurred, and both males and females were similar in terms of taxonomic diet composition (P > 0., X test with df = ). With regard to food size, we did not obtain complete data from our studied sample, either because most of prey ingested were too damaged for being measured when

4 DIET OF LACERTA BILINEATA IN CENTRAL ITALY 69 TABLE I Food composition of adult Lacerta bilineata from the vicinity of Rome, central Italy. Diet data come from both stomach content (first column, 46 individuals examined) and faecal pellet (second column, 6 individuals examined) analyses. For data in the second column, a total of 75 faecal pellets was examined in the laboratory. Pooled data are given in the third column. Prey taxon numbers in stomachs n n () numbers in faeces n «() pooled n () Oligochaeta Pulmonata Isopoda Araneidae Thysanura Mantodea Dermaptera Orthoptera Rhynchota Lepidoptera larvae Díptera Hymenoptera Coleóptera Terrestrial insect larvae Lacerta viridis juv. Podareis sicula juv. Chalcides chalcides Undetermined residues Total stomachs were dissected, or because examination of faeces hardly permits measurement of prey size. However, it was clear that adult L. bilineata fed on both large (i.e., small lizards, beetles of the genus Oryctes) and very small organisms (i.e., very small beetles such as Byctiscus betulae), without clearcut preference. Analysis of both faeces and stomach contents pictured the diet composition of adult L. bilineata in a very similar way (overlap between the two methods: 89.7). Also the values of food niche breadth obtained with the two methods were only slightly different (see Table III). Isopods and beetles were significantly more abundant than any other food category (P < 0.00, x test) in both the samples. Identification of prey types was facilitated when stomachs were dissected. This is reflected in the lower frequency of unidentified remains in the specimens dissected (less than 0) than in those examined for faeces (about 8, differences significant at P < 0.05, X test). The only remarkable difference between the two methods was that the mean number of prey items per specimen was significanly higher in lizards analysed by stomach dissection (x = 4.5, range: 0 9) than in those analysed by faeces collection (x =.08, range: 6) (differences between two groups: P < 0.000, oneway ANOVA). Two empty stomachs were found when dissecting lizards, while at least one prey item was found in all faeces examined. Diet composition of young Lacerta bilineata Faeces from young L. bilineata were collected and examined. A total of 74 food items was obtained, seven of which remained unidentified (Table II). The mean number of prey per individual was.9, ranging from to 4, which, with respect to adults, did not differ significantly when examined with the same method P> 0., oneway ANOVA), but was significantly lower (P < 0.000) when examined by dissection of stomachs. The diet was constituted almost exclusively by terrestrial arthropods, and the principal prey categories were Orthoptera, Rhynchota (Homoptera as well as Heteroptera) and Araneidae, accounting overall for over 60 of the total diet. Orthoptera remains were found in 54.8 of the faeces examined, Rhynchota in.58 and spiders in 9.0. Notably, isopods and beetles the most preyed taxa by adult lizards accounted together for about of the juvenile diet, and were found respectively in 6. and 6.45 of the individuals examined. Intersexual differences in terms of taxonomical diet composition of young lizards were not studied, while food niche breadth was wider than that found in adult lizards using both the study methods (Table III). DISCUSSION Reliability of the faeces analysis' technique One main conclusion that emerges from our study concerns with the reliability of faecal pellet analysis for studying lizard diets. This noncruel method provided a very similar picture of the green lizard diet to that obtained with stomach content analysis. Thus, our main

5 70 F. M. ANGELICI, L. LUISELLI, L. RUGIERO TABLE II Diet composition of young Lacerta bilineata from the vicinity of Rome, central Italy. The data relative to youngoftheyear were collected by examination of 4 faecal pellets from different specimens. Prey taxon n () Pulmonata Araneidae Isopoda Dermaptera Orthoptera Rhynchota Coleóptera Díptera Unidentified Total methodological conclusion supports previous observations on the reliability of the method (cf. Strijbosch, 987), and suggests that it should be selected for any kind of field alimentary study of lizard populations. The only remarkable difference detected between methods in the present study concerns the mean number of prey per individual, that was significantly higher in lizards analysed by stomach dissection than by faeces examination. Arguably, this relevant difference reveals an important limit of the technique of faeces analysis, i.e. that it is difficult (if not impossible) to readily measure the exact food intake rate (items / unit of time) in a given lizard population, other than also the size distribution of prey ingested by lizards. Diet of green lizards The diet of green lizards in Mediterranean habitats is composed essentially of arthropods, which is quite usual in Mediterranean lacertids, including both Podareis and Lacerta species (e.g. see: Pérez Mellado, 98, 98; In TABLE III Values of food niche breadth (calculated by Simpson's (949) formula) in juvenile and adult Lacerta bilineata analysed. For adults, specimens analysed both by stomach dissection and examination of faeces, are indicated. Agecategory Adults (stomach) Adults (faeces) Young Niche breadth den Bosch, 986; Pascual Gonzales & Peréz Mellado, 987; Pollo & Pérez Mellado, 988; Capula et al, 99; Capula & Luiselli, 994b). The fact that a wide variety of arthropods was preyed upon seems to suggest some opportunism in green lizard foraging habits, although data on prey availability in the wild should be collected before advancing firm conclusions on this issue. In any case, the opinion that lacertids are opportunist predators is widespread among lacertologists (cf. Avery, 966; Arnold, 987; Mou, 987; Diaz, 995). Italian green lizards fed only rarely upon caterpillars, whereas this kind of prey was very usual for Hungarian conspecifics (Korsos, 984). However, both Italian and Hungarian adults fed frequently upon beetles (cf. Korsos, 984), the same being true for green lizards from the island of Jersey (Perkins & Avery, 989) and for the closely related Lacerta schreiben from the Spanish Central System (Llórente & Pérez Mellado, 988). Especially puzzling issues are (i) the extremely low abundance of spiders and flies in the lizard diet (these are common prey for most of the other European lacertids studied to date), and (ii) the high abundance of isopods, as these arthropods are commonly avoided by many other species. Ideally, one would like to see the habitat sampled for all possible prey items and their relative abundance. In general, coleopteran taxa preyed on by Italian green lizards are from families which typically show clumped distributions (e.g. the curculionid Byctiscus betulae). The same prey types have frequently been found in Mediterranean lacertids with myrmecophagous habits (e.g. Acanthodactylus erythrurus, cf. Gil et al, 99) However, neither adults nor young Italian green lizards proved to feed frequently upon ants. Prédation upon vertebrates was an exceptionally rare event, but cannibalism was recorded. Cannibalism and intraspecific oophagy have already been detected in green lizards as well as in other large sized Mediterranean lacertids, both in captivity and in nature (Darevsky, 946; Laferrere, 970; Bruno & Maugeri, 977; Street, 979; Mitchell, 986; Mitchell & Groves, 99; Rugiero, 994). Other types of small vertebrates (e.g. snake offsprings, nesting birds and rodents), berries and drupes were not found in lizard guts, though they can be occasionally ingested by the species (Bruno & Maugeri, 977; Fretey, 987). Previous studies on L. bilineata from island of Jersey indicated that this species frequently feed upon large prey such as beetles and so their feeding rates may be very low (Perkins & Avery, 989; Avery & Tosini, 995). Our data are not in complete agreement with this finding, as central Italian green lizards appear to prey not only upon largesized arthropods, but also upon small invertebrates. However, the mean number of prey per stomach was relatively low both in adults and young green lizards, at least in comparison to that observed in other largesized lacertids from elsewhere, including e.g. the Spanish green lizard Lacerta schreiben (Llórente & Pérez Mellado, 988).

6 DIET OF LACERTA BLINEATA IN CENTRAL ITALY 7 Food niche overlap on taxonomical dietary composition between juvenile and adult green lizards was relatively low {O Jk = 0.5), thus indicating a relative ontogenetic shift in this species'diet. Adults fed primarily upon isopods and beetles, whereas juveniles essentially upon orthopterans. Ontogenetic taxonomic dietary shifts have rarely been observed in Mediterranean lacertids (cf. Diaz, 995), whereas this pattern is frequently found in other squamates, including snakes (cf. Luiselli & Agrimi, 99; Luiselli et al., 996). Conversely, separation along trophic dimensions between conspecifics of different ages ( = sizes) or between different species in Mediterranean lacertids is usually based simply on prey size, with smaller predators taking smaller prey (cf. Pollo & Pérez Mellado, 988, 99). As to why adult lizards feed upon prey types different from those preyed upon by juveniles, our conclusions are entirely tentative due to the limited data set. We have often observed slight differences in habitat utilization between juvenile and adult green lizards, with the former typically occurring in open grassy spots and the latter in wetter areas with more vegetation, spiny bushes etc. We suggest that (i) these microhabitat differences could explain the dietary differences between lizard ageclasses due to different availability of the various prey categories in the various microhabitats, and that (ii) the different habitats of adults and juveniles could serve to reduce intraspecific interference competition, involving territoriality, aggression and cannibalism (e.g. see Polis et al., 989), as observed by us in Italian green lizards. 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