Sharing recources in a tiny Mediterranean Island? Comparative diets of Chalcides ocellatus and Podarcis filfolensis in Lampione

2010·5.3 MB·English

by  Miguel A Carretero

0
Bonn zoological Bulletin Volume 57 Issue 2 pp. 111-118 Bonn, November 201
Sharing resources in a tiny Mediterranean island?
Comparative diets of Chalcides ocellatus and Podarcisfilfolensis in Lampione
&
Miguel A. Carretero1-*, Pietro Lo Cascio2, Claudia Corti3-1 Salvatore Pasta4
'CIBIO, Centro de Investigacao em Biodiversidade e Recursos Geneticos, Campus Agrario de Vairao,
P-4485-661 Vairao, Portugal; E-mail: [email protected]
2Associazione "Nesos", Via Vittorio Emanuele 24, 98055 Lipari (ME), Italy; E-mail: [email protected].
3Museo di Storia Naturale dell'Universita di Firenze, Sezione di Zoologia "La Specola'1 Via Romana 17,
,
1-50125, Firenze, Italy; E-mail: [email protected]
4via VF. 19, 60/A, 1-90126, Palermo, Italy; E-mail: [email protected]
Corresponding author: E-mail: [email protected] tel.[phone] fax.[phone]
Abstract. The insular lizard microcommunity inhabiting the Lampione islet (Pelagian islands, S Italy) is constituted by
a skink (Chacides ocellatus) and a lacertid lizard (Podarcisfilfolensis). Their diet composition (taxa and sizes) during
spring-early summerwere analysedbased on 131 faecal pellets, which could be individually assigned to alizard species
andsex (onlyinP.filfolensis). ThedietofC. ocellatuswasbiasedtowardshardpreyofmediumto largesizes(Coleoptera,
insect larvae). Podarcisfilfolensis displayed a more diverse prey spectrum including Fonnicidae, Coleoptera, insect lar-
vae and minorprey not consumed by the skink, but restricted to the small items; differences between sexes were mini-
mal. Both specieswerepartiallyherbivorous. EvidenceofcannibalismwasfoundforP.filfolensisandC. ocellatuspreyed
upon P. filfolensis. Pseudocommunity analysis does not support community structure but instead points to convergence
in trophic strategies between both species due to insular conditions. Evolutionary history, rather than resource partition-
ing, seemsresponsible forthe moderate trophic overlaps recorded andeven may explain whyboth species coexist under
the harsh conditions ofthis tiny islet.
Keywords. Diet; Chacides ocellatus; Podarcisfilfolensis; community ecology; islands; Lampione.
INTRODUCTION
Fordecades, lizards have constituted fruitful model organ- recentmeta-analysis concludedthat lizards ofmost (80%)
isms forstudies in community ecology, dietbeing the most communities worldwide do not partition their food re-
studied ecological dimension (see review by Luiselli sources but are randomly organised in the trophic niche
2008). Many ofthe initial and current studies are focused axis (Luiselli 2008). Instead, increasing evidence is
on the most complex assemblages, namely those in trop- demonstrating that the influence ofevolutionary history
&
ical or desert areas (Arnold 1984; Pianka 1986; Vitt on the lizard trophic traits is stronger than previously
& &
Caldwell 1994; Vitt Carvalho 1995; Vitt Zani 1998; thought. Specifically, niche conservatism rather than
Vitt et al. 2000; Akani et al. 2002, amongst many others), species interactions accounts formany trophic differences
where environmental stabilitycould allow interspecific re- between the community components (Brooks & McLen-
lationships promoting detectable community structure nan 2002; Webb et al. 2002; Vitt et al. 2003; Vitt & Pi-
&
(Winemiller Pianka 1990). In contrast, studies on lizard anka 2005; Mesquita et al. 2007; Espinoza et al. 2008).
assemblages inhabiting temperate regions are less abun-
dant (but see Perez-Mellado 1982; Strijbosch et al. 1989; Withinthis context, lizards inhabiting small Mediterranean
Polio & Perez-Mellado 1991; Carretero & Llorente 1993; islands constitute an apparent paradigm ofsimplicity. On
&
Capula Luiselli 1994; Carretero et al. 2006; Kuranova one hand, strong seasonality and impoverishedtrophicre-
et al. 2005; Rouag et al. 2007). This is probably because sources impose severe constraints to insularlizards (Perez-
&
these are composed ofless species but also because abi- Mellado Corti 1993), higher than those in adjacent
otic restrictions ofseasonal climates overcoming the role mainland, making lizardcommunities inhabitingMediter-
ofspecies interactions would make community structure ranean islets extremely poor when compared to those on
&
less expectable to appear (Barbault 1991). In fact, a big islands oron the continent (Mylonas Valakos 1990).
Bonn zoological Bulletin 57 (2): 111-118 ©ZFMK
112 Miguel A. Carretero et al.
On the other hand, the exposition to less potential com- Study lizards
petitors andpredators and subsequent increase inthe con-
specific density (Carretero 2004, 2006) may open new Two lizard species inhabitthe islet: the Maltese wall lizard,
&
possibilities forenlarging trophic niche (Perez-Mellado Podarcisfllfolensis (Bedriaga, 1876), (Squamata: Lacer-
Corti 1993; Carretero 2004). Nevertheless, evidence on tidae) and the Ocellated skink, Chalcides ocellatus
lacertid lizards indicates that the ecological response to (Forskal, 1775) (Squamata: Scincidae). The firstis a gen-
these shifted environmentalpressures isnotimmediate and uine insular species endemic to the Maltese Archipelago
some evolutionary time is needed to develop profound and two Pelagian islands, Linosa and Lampedusa, where
&
trophic adaptations (Perez-Mellado Corti 1993; Car- it is said to be introduced in early or recent time (Capula
retero 2004). Literature on the diet of Mediterranean 2006; Lo Cascio & Corti 2008). The Ocellated Skink,
lizards in small islands is abundant but usually focused Chalcides ocellatus, is widely distributed on the Sindian-
on a single species (reviewed inVan Damme 1999; Perez- Mediterranean area andis recorded forall the Pelagian is-
& &
Mellado Traveset 1999; Carretero 2004), studies atmul- lands (Turrisi Vaccaro 2006); the origin ofthe isletpop-
tispecies level being rare (Nouira 1983). ulation is probably related to the Pleistocene connections
between Lampione and the nearby North-African main-
Here, the diet composition ofa microinsular community land (see Grasso et al. 1985). The first data on the occur-
constitutedbytwo divergent lizard species is analyseddur- rence ofsuch species in Lampione were reportedby Lan-
ing spring-summer considering both inter- and intraspe- za & Bruzzone (1961). Population density is extremely
cific variation and compared to other populations ofthe high for both species, only for Podarcisfllfolensis being
same species. Moreover, the hypothesis of community estimated using standard methods (7500-8000 individu-
structure at the trophic level is specifically tested against als/ha, see Lo Cascio etal. 2006). From fieldobservations,
the null hypothesis ofrandom trophic overlap. the ratio ofapparent abundance between this species and
Chalcides ocellatuswas 3:1 approximately(Lo Cascio un-
published).
MATERIALAND METHODS
Study area Sampling and lab methods
Lampione (35°33'00"N-12°19'11"E) is a small islet lo- Field samplingwas carriedout during several visits in late
W
cated 17 km offthe coast ofLampedusa (Pelagian Is- spring/early summerof2004 and 2005, whenboth species
lands) and 110 km offTunisia, in the Channel of Sicily. show the peak of annual activity (Corti & Lo Cascio
The area is 0.021 km2 and the maximum altitude is 36 m 2002). Faecal pellets were obtained from adult Podarcis
a.s.l. From ageologicalpointofview, the islet is composed fllfolensis and Chalcides ocellatus; all the specimens were
mm
ofdolomitised carbonates belonging to formations ofthe measured (snout-ventlength, SVL) to thenearest 0.1
Tunisian offshore, and its definitive isolation from North using adigital calliper, sexed (inP.fllfolensis) andreleased
Africa was since 18,000 years B.P (Pasta 2002). The cli- back in the site of capture. Whereas adult P. fllfolensis
mate is arid, characterised by strong drought periods in could be easily sexed in the field using sexual secondary
summerandby an average annual rainfall lowerthan 300 characters (Corti & Lo Cascio 2002) andhemipenis ever-
mm. The vegetation is mainly dominated by halo-ni- sion, the reduced external differences and the impossibil-
trophile perennial shrubs. The occurrence ofa large colony ity for analysing of internal cloaca did not allow identi-
of gulls causes a strong level of soil eutrophisation and fying the sexes of C. ocellatus in field (see Badir 1959;
&
nutrient imbalances, which allow the expansion ofthe ni- Capula Luiselli 1994).
trophile biannual Malva veneta Soldano, Banfi & Galas-
so, 2005 duringthe late springon the top ofthe islet. Lam- The faecal contents were examinedunderstereoscopicmi-
pione is at present-day uninhabited, but late-Roman ru- croscope (10^10X). Remains were identified to Opera-
ins document an early human presence, though probably tional Taxonomy Units (OTUs) approximated here to the
only seasonal (Pasta & Masseti 2002). The invertebrate order/family level. Item counting was based on cephalic
assemblage ofthe islet reflects several features typical of capsules, wings and legs, following the minimum num-
microinsular and arid environments, namely a low num- bers criterionby sample. Whenpossible, prey lengths were
berofspecies (about 30, excluding flying insects; Lo Cas- obtained measuring the remains with a micrometer eye-
cio 2004, Lo Cascio unpublished), an over-representation piece and calculated by using regression equations (H6-
mm
ofsome groups (e.g., five species ofColeoptera Tenebri- dar 1997) and then assignedto classes of5 in length.
onidae; Canzoneri 1972; Lo Cascio unpublished), some
being found at extremely high densities.
Bonn zoological Bulletin 57 (2): 111-118 ©ZFMK
Diet ofLampione lizards 113
Statistical methods phism favourable to males (ANOVA F = 267.58, P <
2 128
10"6 Scheffe tests C. ocellatus-P. filfolensis males
,
Three diet descriptors were used: the percentage ofpel- P< 10-6, C. ocellatus-P.filfolensis females P< 10 6, P.fil-
lets containing an OTU (%P), the percentage ofnumeric folensis males-females P = 0.05).
abundance of each OTU (%N), and the use index (IU)
%N
(Jover 1989); the latter is preferredbecause combines The number ofprey items by pellet (Table 1) was simi-
and %P; the importance ofa certain OTU in the diet be- larbetween both species andbetween male and femaleP.
ingestimatedbycalculation ofthe homogeneity ofits con- filfolensis (ANOVAF2i]28= °-45> p= °-64)- However, the
sumption throughout all the individual contents (Carretero taxonomic composition ofthe diet (Table 1) showed sub-
2004). Brillouin's index was used to estimate the diet di- stantial interspecific differences, whereas intersexual dif-
versity according to Magurran (2004). For a given sam- ferences withinP.filfolensis were minor. Both species con-
ple, the average individual diversity (Hi) was obtainedby sumed important amounts ofplant matter (IU = 41.61%
averaging the diversity values ofeach pellet whereas the in C. ocellatus and IU = 18.37% in P.filfolensis). With-
(asymptotic) population diversity (Hp) was estimated in P.filfolensis, males (IU = 22.55%) used this resource
through jack-knife resampling (Jover 1989, Magurran, more than females (IU = 9.69%). Moreover, C. ocellatus
2004), that is, recalculatingthe total diversity missing out also consumed seeds and fruits (IU = 18.31%) but P.fil-
each sample in turn and generating pseudovalues, which folensis almost did not (IU = 1.24%).
are normally distributed. Whereas Hi and Hp have stan-
dard errors and allow statistical inference, the total accu- Regarding the prey ofanimal origin (Table 1), the diet of
mulated diversity (Hz) ofall pellets is a fixed value only C. ocellatus was strongly biased towards Coleoptera (IU
provided forcomparingwith the literature (Ruiz andJover = 24.95%) and only secondarily to insect larvae (IU =
1981). 7.79%). In contrast, the animal prey consumed by P.fil-
folensis were more evenly distributed between Formici-
Overlap between diets was evaluatedby means ofthe Pi- dae (IU = 26.73%), Coleoptera (IU = 15.08%) and insect
anka's index (Pianka 1973) applied on the IU values of larvae (IU = 14.27%) with minimal differences between
OTUs and size classes (Carretero et al. 2006) using the sexes. Interestingly, the diet ofthe Maltese wall lizard in-
Ecosym software (Gotelli & Entsminger 2004). Hypoth- cluded some minor prey (Araneae, Pseudoscorpiones,
&
esis ofnon-random similarity(Gotelli Graves 1996) was Acarina, Homoptera, Malophaga) that were completely
tested using the RA2 (niche breadth relaxed / zero states absent from the diet ofthe Ocellated skink. Overall, ani-
retained) and RA3 (niche breadth retained / zero states mal diet was very similarbetween male and femaleP.fil-
reshuffled) Monte Carlo randomisation algorithms (Wine- folensis, the latter consuming more Araneae and Het-
&
miller Pianka 1990) generating 1000 pseudomatrices eroptera (Table 1). It is worth noting that tails ofjuvenile
considering each OTU equiprobable. P. filfolensis were found in adult conspecifics (two in
males and two in females) and also in C. ocellatus (also
Normality (Lilliefors test) and homoscedasticity (Fisher two).
test) were assured prior to the application ofparametric
tests. Individual diversity and number ofprey per pellet Consequently, diet diversity (Table 2) was lower in C.
were comparedusing one-wayANOVA. Populationdiver- ocellatus than inP.filfolensis, withno differencesbetween
sity estimations obtained throughjack-knife could notbe males andfemales. This was truewhen considering either
comparedusingANOVAs since the software provides on- individuals (ANOVAF2128 = 9.93, P< 10"4; Scheffe tests
ly mean±SE and diversity is non-additive (Carretero & C. ocellatus - P.filfolensis males P = 0.0003, C. ocella-
Llorente 1993). Instead, t-tests correctedformultiple tests tus -P.filfolensis femalesP= 0.0005, P.filfolensis males
(usingFalse DiscoveryRate, FDR, Benjamini & Hochberg - P.filfolensis females P = 0.99) or populations (C. ocel-
1995) were applied. latus - P. filfolensis males T101 = 4.67, P = 5*10"6, PFDR
<10-4; C. ocellatus - P. filfolensis females T71 = 4.82, P
= 4*10-6, PFDR < 10-4; P.filfolensis males - P.filfolensis
RESULTS females T84 = 1.59, P = 0.06, PFDR = 0.06).
Pellets were obtained from 45 C. ocellatus and 86 P.fil- As to the size ofthe items consumed (Table 3), C. ocel-
folensis (58 males and 28 females). The SVLs in mm, latus ate bigger prey than P.filfolensis but males and fe-
mean±SE (range) of such specimens were 104.02±2.26 males ofthe latter species did not differ (ANOVA F
2 178
(62.0-140.0) for C. ocellatus, 65.45±0.56 (54.0-72.0) for = 20.81, P < 10-6 Scheffe tests C. ocellatus-P.filfolensis
,
maleP.filfolensis, and 60.00±0.53 (44.5-67.0) forfemale males P < 10 6 C. ocellatus-P. filfolensis females
,
P.filfolensis, The skinks were, in fact, much bigger than P = 5*10-5, P. filfolensis males-females P = 0.94). The
mm
the wall lizards which displayed slight sexual size dimor- modal size class of C. ocellatus was 5-10 whereas
Bonn zoological Bulletin 57 (2): 111-118 ©ZFMK
114 Miguel A. Carretero et al.
mm
P. filfolensis was shifted to the 1-5 class. In fact, ex- Coleoptera (Carretero et al. 2006) andthere is experimen-
cept in two females, pellets ofP. filfolensis did not con- tal evidence for inter- and intraspecific differences in bite
tain items larger than 10 mm. No significant correlation force for prey crashing associated with the jaw muscle
between prey and predator sizes was detectedwithin each mass (Herrel etal. 1999, 2001). Nonetheless, sexuallydi-
group although those P. filfolensis females eating the morphic lacertid heads, as intersexual differences in bite
10-15 mm prey were bigger than the rest (ANOVA F235 force, primarily derive from sexual selection (Herrel et al.
= 5.35, P = 0.009; Scheffe tets: 1-5 mm - 5-10 mm P= 1999; Kaliontzopoulou et al. 2007), and dietary shifts
0.86, 1-5 mm - 10-15 mm P = 0.01, 5-10 mm - 10-15 (minimal in P.filfolensis) should be interpreted as a by-
mm P = 0.01). product.
Finally, diet overlaps (Table 4) calculated from both tax- While divergent anatomy, foraging tactics and habitatuse
onomical and size classification ofprey were very simi- between both species accounted for a substantial part of
lar, attaining moderate values between species but high the interspecific variation found, comparison with other
valuesbetween male and femaleP. filfolensis. Pseudocom- populations indicates that other factors modified the tax-
munity analysis at species level revealed that taxonomi- onomic composition oftheir diets. As other insular lacer-
cal overlap was higher than simulated in the RA3 matrix tids in the Mediterranean (Perez-Mellado & Corti 1993;
(niche breadth retained, P= 0.02) but similar to the RA2 Carretero et al. 2001; Corti et al. 2008), P.filfolensis con-
matrix (zero states retained, P= 0.50). When considering sumed great amounts ofantsnot only in Lampione butal-
thethree classes (C. ocellatus, male and femaleP. filfolen- so in Linosa (Sorci 1990; Bombi et al. 2005) and Lampe-
&
sis) none ofthe two algorithms indicated significant de- dusa (Lo Cascio Corti 2008). Since onlyPodarcis pop-
viations from random. No significant differences were ei- ulations inhabiting ancient Mediterranean islands (i.e.
ther detected for the size overlap. Balearics, Mylos) are myrmecophagous, this hasbeen in-
terpreted as a result of long term evolution in insularity
(Perez-Mellado & Corti 1993; Carretero 2004). The de-
DISCUSSION crease inpredation pressure, the scarcityofalternativere-
sources, together with the gregarious behaviour and sea-
Differences in lizard diet arise from multiple factors in- sonal stability of this prey may compensate for its low
cluding anatomy, sex, reproductive state, body condition, profitability andnoxiousness (Carretero 2004). Apparent-
experience, prey availability, predation pressure, compe- ly, C. ocellatus has notbeen able to follow a similarstrat-
tition and evolutionary history (Schoener 1974; Dunham egy since neither continental nor insular populations are
& &
1980; Pianka 1986; Losos 1992; Vitt Zani 1998; Vitt myrmecophagous (Capula Luiselli 1994; Kalbousssi
etal. 1999; Perry& Pianka 1999; Pitt& Ritchie 2002; Car- 2004; Lo Cascio & Corti 2008). Whether this is due to
retero 2004). In Lampione, the manifest size differences evolutionary constraints orto recent colonisation ofLam-
between both species constitute the most obvious con- pione currently remains under debate.
straint for the prey they consume. Within species, prey
sizes tend to follow a logarithmic distribution, small in- Cannibalism and, in general, saurophagy seem also to in-
dividuals simply not been able to consume the biggest crease ininsularconditions due tothe scarce resources and
&
items of the prey spectrum of the large individuals (Pi- high lizard densities (Perez-Mellado Corti 1993; Car-
anka 1986). However, between species this pattern can be retero etal. 2001) as is the caseofP.filfolensis and C. ocel-
altered ifdrastic divergence in anatomy or foraging tac- latus (Scalera et al. 2004; Lo Cascio et al. 2006). How-
tics occurs (Carretero 2004). This seems to be the case, ever, the predation ofP.filfolensis by C. ocellatus consti-
since C. ocellatus not only consumed large prey inacces- tutes not only an additional food source but also an in-
sible forP.filfolensis as expected, but also kept the same stance of direct, asymmetric interaction between both
number ofprey items but biased to medium sizes. This species (Chase et al. 2002).
result suggests that both species may follow different for-
aging strategies (Perry & Pianka 1999). In fact, C. ocel- As in the case ofthe ants, plants are also low profitable
latus is described a semi-fossorial, sit-and-wait forager in matterandtheirconsumption seems to be restrictedto old
&
plant litterorunderstones (Arnold 1984; Capula Luisel- insularlacertid lineages which have developedbehaviour-
&
li 1994; Kalboussi Nouira2004; Lo Cascio et al. 2008) al and anatomical adaptations for herbivory (Perez-Mel-
&
whereasP.filfolensis as most lacertids actively forages on lado Corti 1993; Carretero 2004). BothP.filfolensis and
&
the surface (Corti Lo Cascio 2002; Bombi et al. 2005; C. ocellatus were partially herbivorous in Lampione.
Lo Cascio etal. 2006). Nevertheless, there is also evidence However, other populations ofP.filfolensis studied also
for anatomical constraints, since ocellated skinks con- consumed substantial amounts ofseeds, fruits and other
sumed more hard prey (Coleoptera) than the wall lizards. plant remains (Sorci 1990; Bombi et al. 2005; Lo Cascio
In lacertids, large species tend to consume more & Corti 2008) and even seed dispersal for some plant
Bonn zoological Bulletin 57 (2): 111-118 ©ZFMK
Diet ofLampione lizards 115
& several visits at Lampione. We are also sincerely grateful to
species has been described in Linosa (Fici Lo Valvo Damiano Sferlazzo, who help us significantly during the field
2004). This suggests niche conservatism for herbivory in work. The analysis ofthe collected samples has been done in
this species. In contrast, herbivory seems to be rare in C. the framework ofthe scientific research projects ofthe Associ-
ocellatus. Only two other microinsular populations, on azione Nesos (Lipari). Analytical work was funded by the proj-
Lampedusa andthe Conigli islet(Lo Cascio & Corti 2008; ect PTDC/BIA-BDE/67678/2006 and PTDC/BIA-
Lo Cascio et al. 2008), werepartially herbivorous, where- BnoElCo/gi1a0,1F25C6T/2(0P0o8rt(utgoalM)A.CW)eoafrFeutnhdaanckafoulpatroataheCiIetnacliiaaneMainTiesc--
as, no or almost no plant remains were found in the pop- terodelFAmbienteedellaTuteladelTerritorio forhavingissued
&
ulations from Sardinia (Capula Luiselli 1994) and the permits to study these lizard populations (Prot.DPN-
&
Tunisia (Kalboussi Nouira 2004). Nevertheless, even /20/2004/17301).
continental ocellated skinks accept fruits in captivity
(Schleich etal. 1996) suggestingcertain exaptation forher-
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Appendix
Table 1. Descriptors ofthe taxonomic composition ofthe diet for Chalcides ocellatus andPodareisfilfolensis from Lampione is-
land. OTU: Operational taxonomical unit, %P: percentage ofpresence; %N: percentage ofnumerical abundance; IU: Resourceuse
index: - not consumed; 0.00: consumed but index value next to zero.
Chalcides ocellatus Podareisfilfolensis Podareisfilfolensis Podareisfilfolensis
total total males females
OTU %P %N IU %P %N IU %P %N IU %P %N IU
Gastropoda 9.09 1.28 0.65 2.33 0.39 0.09 7.14 1.16 0.42
Isopoda 9.09 1.28 0.65 11.63 1.94 1.47 10.34 1.74 1.13 14.29 2.33 1.70
Araneae 12.79 2.13 1.68 5.17 0.87 0.35 28.57 4.65 5.10
Pseudoscorpiones 12.79 2.71 2.04 15.52 2.91 2.24 7.14 2.33 0.85
Acarina 2.33 0.39 0.09 3.45 0.58 0.15
Diptera 15.15 2.55 1.79 24.42 6.01 5.66 27.59 6.98 6.51 17.86 4.07 3.20
Coleoptera 66.67 18.30 24.95 55.81 12.40 15.08 56.90 12.21 14.98 53.57 12.79 16.48
Hymenoptera 25.58 7.56 6.95 27.59 7.27 6.41 21.43 8.14 7.04
Formicidae 18.18 4.26 3.19 60.47 23.45 26.73 58.62 22.38 25.18 64.29 25.58 31.15
Homoptera 6.98 1.74 0.97 10.34 2.62 1.60
Heteroptera 6.06 0.85 0.27 17.44 3.49 2.90 13.79 2.33 1.75 25.00 5.81 5.25
Mallophaga 9.30 1.55 1.06 10.34 1.74 1.13 7.14 1.16 0.42
insect larvae 30.30 8.51 7.79 37.21 14.15 14.27 34.48 15.70 14.93 42.86 11.05 13.26
Arm ind. 9.09 1.70 0.78 9.30 1.55 1.06 5.17 0.87 0.35 17.86 2.91 2.47
Squamata 3.03 0.43 0.00 4.65 0.78 0.35 3.45 0.58 0.15 7.14 1.16 0.42
seeds, fruits 21.21 25.53 18.31 6.98 3.10 1.24 6.90 1.16 0.59 7.14 6.98 2.55
other plant matter 54.55 35.32 41.61 45.35 16.67 18.37 53.45 20.06 22.55 28.57 9.88 9.69
Total (mean±SE) 45 pellets, 235 items 86 pellets, 516 items 58 pellets, 344 items 28 pellets, 178 items
5.91±0.83 items/pellet 5.19±0.34 items/pellet 5.16±0.38 items/pellet 5.25±0.70 items/pellet
Bonn zoological Bulletin 57 (2): 111-118 ©ZFMK
118 Miguel A. Carretero et al.
Table 2. Diet diversities ofChalcides ocellatus and Podarcisfilfolensis from Lampione island. Numbers indicate mean±SE. Hi:
individual diversity; Hp: population diversity; Hz: total accumulated diversity; all using Brillouin's index.
Species (class) N Hi Hp Hz
Chalcides ocellatus (total) 45 0.61±0.03 2.57±0.11 2.44
Podarcisfilfolensis (total) 86 0.98±0.02 3.33±0.08 3.22
Podarcis filfolensis (males) 58 0.98±0.03 3.19±0.08 3.05
Podarcisfilfolensis (females) 28 0.98±0.06 3.43±0.14 3.17
Table 3. Descriptors ofthe prey size composition ofthe diet for Chalcides ocellatus and Podarcis filfolensis from Lampione is-
land. OTU: Operational taxonomical unit, %P: percentage ofpresence; %N: percentageofnumerical abundance; IU: Resource use
index: - not consumed; 0.00: consumed but index value next to zero.
Chalcides ocellatus Podarcisfilfolensis Podarcisfilfolensis Podarcisfilfolensis
total total males females
OTU %P %N IU %P %N IU %P %N IU %P %N IU
mm
0-5 32.14 24.62 19.09 80.00 67.24 68.92 73.68 64.10 64.41 100.00 73.68 78.66
mm
5-10 85.71 58.46 69.63 84.00 31.03 31.08 84.21 35.90 35.59 83.33 21.05 21.34
mm
10-15 17.86 7.69 5.31 4.00 1.72 0.00 16.67 5.26 0.00
> 15 mm 17.86 9.23 5.96
Total (mean±SE) 65 (of235) items measured 116 (of516) items measured 78 (of344) items measured 38 (of 178) items measured
mm mm mm mm
7.42±0.51 4.22±0.24 4.29±0.27 4.08±0.47
Table 4. Diet overlaps (Pianka's index) between the lizard species and classes from Lampione island considering the taxonomi-
cal and size composition ofthe prey consumed.
taxonomical overlap size overlap
C. ocellatus (total) -P. filfolensis (total) 0.54 0.63
C. ocellatus (total) -P.filfolensis (males) 0.54 0.64
—
C. ocellatus (total) P.filfolensis (females) 0.53 0.50
P.filfolensis (males) - P.filfolensis (females) 0.97 0.97
Bonn zoological Bulletin 57 (2): 111-118 ©ZFMK