Tenerife lizards as seed predators

During a fieldwork campaign in late June 2025 at El Teide National Park (Tenerife, Canary Islands) we discovered an unexpected behavior in the Tenerife lizard (Gallotia galloti), a species primarily recognized as a key seed disperser on the island (Mendes et al., 2025). While monitoring seed depots to assess post‐dispersal seed predation by rodents, our camera trap and subsequent direct observations revealed that Tenerife lizards actively prey upon the seeds of Rhamnus integrifolia, a native fleshy‐fruited species (Figure 1). As shown in Figure 1 and the accompanying media (Video S1), adult lizards use their jaws to crush the seeds, consuming the nutrient‐rich embryos. Although this lizard is a legitimate seed disperser for many plant species, including R. integrifolia and other congeners (Mendes et al., 2025; Nogales et al., 2025; Rodríguez et al., 2008), our observations confirm that it can play a dual role as both seed disperser and seed predator.

FIGURE 1.

Pictures showing the seed‐predation behavior of Tenerife lizards (Gallotia galloti, Lacertidae) at “El Portillo Botanic Garden” (El Teide National Park, Tenerife, Canary Islands) in late June 2025. (a) Female Tenerife lizard preying upon a Rhamnus integrifolia (Rhamnaceae) seed. (b) Male Tenerife lizard crushing a R. integrifolia seed with its teeth. White arrows indicate seeds within the lizards' mouths for easier visualization. The white‐dashed circle in panel b indicates a seed offering on the rocks. Photo credits: Juan P. González‐Varo.

El Teide National Park is characterized by an arid climate, with hot and dry summers, and a mean annual rainfall of 350 mm (Martín‐Esquivel et al., 2020). It encompasses a high‐mountain vegetation belt dominated by shrubby plants and extending approximately between 2000 and 3000 m above sea level (asl) (del Arco‐Aguilar & Rodríguez‐Delgado, 2018). Within this ecosystem, six plant species have fleshy fruits (either true fruits or fleshy gymnosperm cones): Bencomia exstipulata (Rosaceae), Ephedra nebrodensis (Ephedraceae), Juniperus cedrus (Cupressaceae), R. integrifolia (Rhamnaceae), Rosa cannadas‐teydensis (Rosaceae), and Aria edulis (Rosaceae). Five of them (all but A. edulis) are known to be dispersed by Tenerife lizards in the National Park (Nogales et al., 2025), mainly during spring and summer when they are more active in response to the higher temperatures (Rumeu et al., 2011). Consequently, our observations of seed‐predation behavior coincided with a period of peak lizard activity.

Island biota is characterized by niche shifts in response to their particular environments (MacArthur & Wilson, 1967). Accordingly, insular species often exhibit wider trophic niches due to ecological release, that is, reduced interspecific competition that allows them to exploit new resources (e.g., Diamond, 1970). A well‐known example of this niche expansion involves insular lizards, which often shift from a mainly carnivorous diet on the mainland to a high degree of herbivory and frugivory on islands (Cooper & Vitt, 2002; Olesen & Valido, 2003). Food scarcity on islands is considered a key driver for lizards to expand their dietary niches towards plant matter (Olesen & Valido, 2003; Valido & Olesen, 2019). However, while true herbivory (> 90% of plant volume in diet) can occur (Cooper & Vitt, 2002), consumption of more digestible plant organs or products—such as nectar, flowers, and fruit pulp—is more frequent (Valido & Olesen, 2019). Consequently, the role of lizards as pollinators and seed dispersers is primarily recognized as an insular phenomenon (Olesen & Valido, 2003; Valido & Olesen, 2019). In contrast, direct seed predation (granivory) is very scarcely and sparsely reported in the literature, the most explicit case being seed consumption by the shovel‐snouted sand dune lizard (Meroles anchietae, Lacertidae) in the Namib Desert (Murray & Schramm, 1987; Nagy & Shemanski, 2009). Nevertheless, the seed‐eating behavior of M. anchietae might be better described as herbivory than as granivory, as most of the “seed” remains recovered from stomachs and pellets appear to be green and immature, and could be the result of direct consumption of flowers (Nagy & Shemanski, 2009).

The genus Gallotia (Lacertidae), endemic to the Canary Islands, represents a notable oceanic radiation comprising seven extant species distributed across the archipelago (Arnold et al., 2007). The Tenerife lizard (G. galloti) is a common medium‐sized species (snout‐vent length: 135–145 mm) inhabiting Tenerife and La Palma (Molina‐Borja & Bohórquez‐Alonso, 2023). All Gallotia species are omnivorous, and their key role as legitimate seed dispersers in different habitats of the archipelago is well documented (e.g., Mendes et al., 2025; Rodríguez et al., 2008; Rumeu et al., 2011; Valido, 1999; Valido et al., 2003). However, seed predation (i.e., granivory) by this genus has not yet been described.

On 25 June 2025, as part of a research project assessing ecological filters for the recruitment of fleshy‐fruited species in El Teide National Park, we conducted a pilot seed‐predation experiment using seeds of R. integrifolia and J. cedrus. R. integrifolia seeds are smaller and, on average, four times lighter (mean mass = 14.2 mg) than those of J. cedrus (mean mass = 53.2 mg; Rumeu et al., 2009) (Figure 2). Furthermore, R. integrifolia seeds have an elaiosome along a longitudinal groove, which suggests an adaptation to myrmecochory (see Bas et al., 2009). We assessed seed fate in an area of the park known as Siete Cañadas, at two microhabitats where birds and lizards typically disperse seeds: (1) “under shrub” canopies and (2) “among rocks.” We placed eight seed depots (four per plant species and microhabitat), each consisting of 10 seeds firmly glued to a 10 cm × 10 cm plastic mesh (1 mm pore size) and nailed to the ground to prevent displacement by wind or animals (González‐Varo et al., 2019). We monitored the depots after 24 and 48 h and classified seeds as either intact or preyed upon (if the seeds were absent or broken/gnawed). Additionally, we deployed a camera trap (Browning Spec Ops Elite HP5) at one “under‐shrub” depot to identify potential vertebrate species acting as seed predators. We found high seed‐predation rates for R. integrifolia in both microhabitats (80%–100% per depot; Appendix S1: Tables S1 and S2). In contrast, all J. cedrus seeds remained intact. Unexpectedly, the camera trap revealed that the R. integrifolia seeds were consumed by Tenerife lizards. The absence of rodent‐specific tooth marks on the remaining depots suggested that seed predation could be attributable to lizards in all cases.

FIGURE 2.

Seeds of the four fleshy‐fruited species offered to Tenerife lizards (Gallotia galloti, Lacertidae) between June 25 and July 1, 2025, on the island of Tenerife. The top row shows smaller seeded species for which seed predation by Tenerife lizards was observed, whereas the bottom row shows large‐seeded species ignored by the lizards. (a) Rhamnus integrifolia, with a mean size of 6.0 × 2.7 mm (length × width), and mean mass 14.2 mg (this study). (b) Rhamnus crenulata, with a mean size of 4.2 × 2.7 mm and a mean mass of 7.0 mg (this study). (c) Juniperus cedrus, with a mean seed size of 6.5 × 4.5 mm and mean mass 53.2 mg (Rumeu et al., 2009); (d) Rhamnus glandulosa, with a mean size 6.9 × 4.4 mm and mean mass 28.0 mg (this study). Note that R. glandulosa (d) retains the endocarp after dispersal, whereas in R. integrifolia and R. crenulata (top row), the endocarp naturally detaches and reveals a central groove where the elaiosome is located. Photo credits: Beatriz Rumeu.

Following this finding, on 27 and 28 June 2025, we conducted further seed‐offering trials at El Portillo Botanic Garden, a site located 4.5 km away from Siete Cañadas but within the same vegetation belt and elevation (~2050 m asl). This site supports a high lizard density and is adjacent to a Visitor Center of the National Park. We performed 10 trials in which we simply offered depots of R. integrifolia seeds (on average approximately 5 seeds; see Appendix S1: Table S2) placed over a rock and monitored lizards' behavior during approximately 5‐min periods. Given the tame behavior of lizards at this location, we were able to observe and video‐record high seed‐predation rates by adult male and female lizards (80%–100% across offerings; see Figure 1 and Video S1); juveniles did not exhibit this behavior (Appendix S1: Tables S1 and S2). The lizards detected and consumed the seeds very quickly, with a mean detection time of 1 min (range: 0.5–2.5 min), and an average consumption time of approximately 0.4 min per seed (Appendix S1: Tables S1 and S2). We then offered elaiosomes detached from R. integrifolia seeds with fine‐tipped tweezers (~5–10 per trial) to assess the lizards' response to this specific tissue. All elaiosomes were detected and consumed in three out of four trials (see Appendix S1: Table S3), indicating that R. integrifolia elaiosomes also attract lizards for consumption.

Arthropod shortages in extreme environments, such as deserts, can be significant drivers of diet shifts towards plant‐based diets (Valido & Olesen, 2019). Thus, we wondered to what extent the seed‐eating behavior we observed was a high‐altitude phenomenon. Do Tenerife lizards exhibit this seed‐predation behavior at lower elevations with milder climatic conditions? To answer this question, on 1 July 2025, we conducted additional trials at El Sauzal (456 masl), a site located at the interface of thermophilous woodland and laurel forest (del Arco‐Aguilar & Rodríguez‐Delgado, 2018). In these formations, two other Rhamnus species occur: the smaller seeded R. crenulata and the larger seeded R. glandulosa (mean seed mass = 7.0 and 28.0 mg, respectively). Notably, the endocarp of R. glandulosa remains attached after dispersal, unlike in R. integrifolia or R. crenulata (Figure 2). We performed eight offerings (four per species) following the same procedure described above for El Portillo Botanic Garden. We confirmed seed predation by Tenerife lizards at this lower elevation site, where lizards exclusively preyed upon the smaller seeds of R. crenulata (predation rates = 17%–100%), while larger R. glandulosa seeds remained intact (Appendix S1: Tables S1 and S2). Because of the lizards' shy behavior at this site, video recording and sex identification were achieved only once; this footage revealed a female lizard that ignored R. glandulosa seeds in favor of R. crenulata ones (Appendix S1: Tables S1 and S2).

Our results provide unequivocal evidence of direct seed predation by Tenerife lizards. While diet shifts towards the inclusion of plant matter are well documented in island lizards (Cooper & Vitt, 2002; Olesen & Valido, 2003; Valido & Olesen, 2019), their role as seed predators remains largely unstudied. Our pilot experiment and observations demonstrate that seed predation by Tenerife lizards is consistently high for the smaller seeds but absent for the larger seeds at different vegetation belts (Figure 2). Seed traits—specifically size and endocarp thickness—are likely key drivers of seed predation. The avoidance of larger J. cedrus and R. glandulosa seeds (Figure 2) suggests a mechanical threshold related to jaw strength and handling time (Dylewski et al., 2020; Zhang & Zhang, 2008). This may also explain the age‐dependent nature of the behavior, as only adults seem to be capable of seed consumption. Furthermore, although still unclear, the attraction to Rhamnus seeds could be reinforced by the elaiosome, which is exposed in R. integrifolia and R. crenulata but remains enclosed within the endocarp in R. glandulosa (Figure 2).

Given the high abundance of Tenerife lizards across the diverse habitats of Tenerife and La Palma (Bohórquez‐Alonso et al., 2011), this seed‐predation behavior could have widespread ecological implications. Notably, our findings reveal that Tenerife lizards occupy a complex position on a mutualism‐antagonism continuum, acting as both mutualists (dispersing viable seeds) and antagonists (preying upon dispersed seeds). This dual role—which will probably be more pronounced for plant species with small seed size and light coats—adds a significant layer of complexity to the local plant–frugivore networks that was not previously accounted for (e.g., Mendes et al., 2025; Nogales et al., 2025). In El Teide National Park, determining whether Tenerife lizards also act as seed predators for the other three fleshy‐fruited species they disperse (B. exstipulata, E. nebrodensis and R. cannadas‐teydensis) is crucial. If so, such antagonism, along with a historically defaunated assemblage of seed dispersers (Nogales et al., 2025), could hamper to some extent the recruitment of these endemic and threatened plant species. Future studies should therefore compare seedling establishment rates along gradients of seed‐predation intensity to quantify this demographic impact. While similar dual roles are known in synzoochorous species (Gómez et al., 2019), as far as we know, there is no previous evidence of a dual mutualistic–antagonistic role in lizard–plant dispersal systems.

It is noteworthy that the seed‐eating behavior of the Tenerife lizard has largely gone unnoticed despite the abundant literature documenting its importance as a seed disperser. We suggest that this oversight may be due to seed dispersal being easily detected via fecal analysis, whereas seed predation requires direct observation. Indeed, the presence of damaged seeds of at least eight other fleshy‐fruited species (lacking an elaiosome) in fecal samples of Tenerife lizards (González‐Castro et al., 2015) may suggest active granivory rather than incidental damage previously interpreted as occurring during frugivory. This reinterpretation implies that the seed‐eating behavior might be a widespread ecological phenomenon among Tenerife lizards.

Our observations open a new avenue in the ecology and behavior of island lizards, as well as on the demographic consequences for the eaten seed species. At the regional scale, it is essential to determine whether seed predation by lizards is widespread across other lizard and plant species within the Canary archipelago. Future research should prioritize larger sample sizes to establish the specific relationship between lizard body size and the seed‐coat hardness thresholds that constrain predation. On a global scale, these findings serve as a catalyst to investigate whether this mutualistic–antagonistic duality is a more prevalent phenomenon in insular ecosystems than currently acknowledged.

AUTHOR CONTRIBUTIONS

Beatriz Rumeu and Juan P. González‐Varo conceptualized the study and provided images. Beatriz Rumeu, Tamara Burgos, Ana Otero‐Ruiz, and Juan P. González‐Varo carried out the fieldwork experiments. Beatriz Rumeu wrote the original draft; all authors contributed to review and edit the revised manuscript and approved the final submission.

CONFLICT OF INTEREST STATEMENT

The authors declare no conflicts of interest.

Supporting information

Appendix S1.

Video_S1_Metadata.

Video S1.

Rumeu, Beatriz , Burgos Tamara, Otero‐Ruiz Ana, and González‐Varo Juan P.. 2026. “Tenerife Lizards as Seed Predators.” Ecology 107(7): e70464. 10.1002/ecy.70464