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Gallotia caesaris (Caesar’s Lizard): Nectarivory

Authors:
  • Grupo de Ornitología e Historia Natural de las islas Canarias
Herpetological
Review
GALLOTIA CAESARIS (Caesar’s Lizard). NECTARIVORY
felipe SiveRiO (e-mail: felipe.siverio@telefonica.net), Alas Cinemato-
grafía S.L., Los Aigidos 43, 38410 Los Realejos, Tenerife, Canary Islands,
Spain; mARÍA c. ROdRÍGueZ-ROdRÍGueZ, Integrative Ecology Group,
Estación Biológica de Doñana (CSIC), Avda. Américo Vespucio s/n, 41013
Sevilla, Spain.
Herpetological Review 42(4), 2011
602 nAtuRAl hiStORy nOteS
GALLOTIA CAESARIS (Caesar’s Lizard). NECTARIVORY. Plant-
lizard mutualistic interactions (pollination and seed dispersal)
have been considered a phenomenon more frequently detected
on islands due to the high densities commonly seen in insular
lizards (Olesen and Valido 2003. Trends Ecol. Evol. 18:177–181).
Lizards experience stronger intraspecific competition, favored
by a lower predation risk and arthropod food supply compared
to mainland taxa, expanding their diet to incorporate novel food
resources (e.g., fruit pulp and floral rewards; Olesen and Valido,
op. cit.). This appears to be the case observed in endemic Ca-
narian lizards, Gallotia spp., which include a signiλcant amount
of plant matter in their diets, whereas their closest continental
relatives are mainly insectivorous (Carretero et al. 2006. Rev. Esp.
Herpetol. 20:105–117; Martín et al. 2005. Zoology 108:121–130;
Valido and Nogales 2003. Amphibia-Reptilia 24:331–344; Van
Damme 1999. J. Herpetol. 33:663–674). The role of Gallotia spp.
as seed dispersers of Canarian flora has been well established,
with fleshy fruit as the most significant component of their
Herpetological Review 42(4), 2011
nAtuRAl hiStORy nOteS 603
diet year round (e.g., G. galloti; Valido and Nogales 1994. Oikos
70:403–411). However, their role as pollinators has received less
attention despite nectar-feeding field observations on native
and exotic flora (Font and Ferrer 1995. Herpetol. Rev. 26:35–36;
Valido et al. 2002. Acta Oecol. 23:413–419; Valido et al. 2004. J.
Biogeogr. 31:1945–1953). Most of these observations refer to the
Canary Lizard (G. galloti) from Tenerife, with the unique excep-
tion of G. caesaris from El Hierro observed visiting Euphorbia
lamarckii flowers (Speer 1994. Salamandra 30:48–54). Here, we
report a new account of nectarivory and presumptive pollinating
behavior by G. c. caesaris on flowers of Echium hierrense (Bor-
aginaceae); both are endemic taxa from El Hierro (27.733333°N,
18.05°W), the smallest and the westernmost island of the Canar-
ian archipelago. Observations were made in the south of the is-
land, at a xeric scrubland area known as El Lajial (255 m elev.).
From 20 to 22 April 2007, we performed daily 2-h monitoring
(approximately 1000–1200 h), during which we observed G. cae-
saris visiting flowers of E. hierrense. In each of these periods, one
male individual climbed the same plant three to four times, visit-
ing different flowers from the same inflorescence (Fig. 1). Occa-
sionally, we also saw the aforementioned lizard accompanied by
a conspecific crawling up other inflorescences of the same plant.
In both cases, lizards visited flowers legitimately (i.e., the snout
brushed against the anthers and stigma of the flowers as they
clearly licked nectar from them). We never detected agonistic in-
teractions between lizards, nor did we observe lizards trying to
capture pollinating insects (mainly Hymenoptera) while in the
inflorescences.
Lizards are not the only flower visitor of E. hierrense. In the
Canary Islands, Echium species are considered to be mainly bee-
pollinated (Dupont and Skov 2004. Int. J. Plant Sci. 165:377–386).
However, the endemic E. wildpretii, distributed in the arid high-
altitude sub-alpine vegetation zone, is also visited by Gallotia
lizards (Valido et al. 2002, op. cit.). Our observations suggest the
possibility of more Gallotia-Echium interactions in the Canar-
ian archipelago. This raises the question of what intrinsic (e.g.,
floral rewards) and extrinsic (e.g., water scarcity) plant factors
promote interactions and how these interactions impact Echium
reproductive success.
The observations described here were made as part of work
for a documentary film series (Canarias, reductos de biodiver-
sidad) on Canarian biodiversity conducted by Alas Cinemato-
grafía S.L. We thank Pedro Felipe and José J. Hernández for their
invaluable help in the field, as well as Alfredo Valido, Rubén
Barone, and Kimberly Holbrook for reviewing an early draft of
the manuscript.
felipe SiveRiO (e-mail: felipe.siverio@telefonica.net), Alas Cinemato-
grafía S.L., Los Aigidos 43, 38410 Los Realejos, Tenerife, Canary Islands,
Spain; mARÍA c. ROdRÍGueZ-ROdRÍGueZ, Integrative Ecology Group,
Estación Biológica de Doñana (CSIC), Avda. Américo Vespucio s/n, 41013
Sevilla, Spain.
Fig. 1. Gallotia caesaris visiting Echium hierrense (Boraginaceae) in-
florescences from El Hierro, Canary Islands. The tail seems to play
an important role as a prehensile appendix as the lizard climbs to
higher flowers.
PHOTO BY PEDRO FELIPE
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Article
Islands harbor a considerable portion of global biodiversity and endemic biota, and also are the recipients of the largest proportional numbers of alien invaders. Such invaders may jeopardize the performance of native species, through either their direct or indirect effects. In this study, we investigated the reproductive ecology of the endemic scrambling perennial herb Canarina canariensis in remnants of the former thermosclerophyllous woodland of Tenerife (Canary Islands), assessing how two widespread alien invasive species, the honeybee (Apis mellifera) and the black rat (Rattus rattus), affect its reproductive success. Apis mellifera visits its flowers whereas the black rat consumes both its flowers and fruits. Here, we compared the pollination effectiveness of different animal guilds (vertebrates vs insects) by means of selective exclosures and determined the level of floral herbivory. Three bird species (Phylloscopus canariensis, Cyanistes teneriffae and Sylvia melanocephala), a lizard (Gallotia galloti) and two insects (A. mellifera and the butterfly Gonepteryx cleobule) were the main flower visitors. Phylloscopus canariensis was the most frequent visitor in the early flowering season whereas A. mellifera predominated in the flowers during mid and late flowering periods. Birds increased fruit set, whilst lizards and insects had a negligible effect. Rats consumed about 10% of the flowers and reduced fruit set to one third. Besides contributing little to plant reproduction, A. mellifera might interfere with bird pollination by depleting flowers of nectar. We conclude that both alien species can threaten C. canariensis reproduction and hence population sustainability in the thermosclerophyllous vegetation. Apis mellifera, in particular, may become especially detrimental if apiculture keeps expanding, or if this bee becomes active earlier in the season due to global warming.
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