Collapse of the endemic lizard Podarcis pityusensis on the island of Ibiza mediated by an invasive snake

Abstract

The invasive snake Hemorrhois hippocrepis colonized the island of Ibiza (Balearic Islands) in 2003 as stowaways inside trunks of olive trees imported for gardening. It has quickly spread since 2010, posing a threat to the island’s only remaining endemic vertebrate, the Ibiza wall lizard Podarcis pityusensis. We map the yearly expansion rate of the snake and estimate via transect surveys how severely it affects the distribution and abundance of the endemic lizard. As well, we surveyed nine of 30 small lizard populations on islets surrounding Ibiza that have been isolated since the Last Glacial Maximum. Snakes had invaded 49% of Ibiza’s land area by 2018, and censuses show a critical contrast in lizard abundance between areas with and without snakes; almost all censuses in areas without snakes show lizard presence whereas nearly all censuses in areas with H. hippocrepis lack lizard sightings. Moreover, at least one subspecies previously thriving on one of the offshore islets has become extinct, and there have been several snakes recorded swimming between Ibiza and the surrounding islets. Therefore, lizard populations have been dramatically reduced or have vanished within the range of the snake, and our results quantitatively support upgrading this species’ threat level for extinction. This study can inform to programs to manage invasive snake populations and to conservation actions to recover the endemic lizard.

Invasive snake causes massive reduction of all endemic herpetofauna on Gran Canaria

“…Additionally, native reptiles became one of the most frequent prey of B. irregularis in Guam once native birds had been extirpated [5,7], which altered skink and gecko assemblages [8]. Similarly, the invasive horseshoe snake, Hemorrhois hippocrepis, affects native reptiles in the Balearic Islands [9,10], the common wolf snake, Lycodon capucinus, is presumed to be primarily responsible for the demise of endemic reptiles on Christmas Island [11], and the Indian wolf snake, L. aulicus, feeds on the endemic herpetofauna of La Réunion [12], though impacts per se have not yet been demonstrated, only presumed. These cases indicate that invasive snakes can potentially impact insular herpetofauna around the globe, even though such impacts remain unnoticed in most cases (see [1,2]).…”

Far from home: tracing the origin of non-native water frogs (genus Pelophylax) in Malta by molecular markers

“…On the other hand, populations of these rare species having limited distributions can hold an invasive potential in an introduced environment. These cases are well-documented in lizards (Pupins et al 2023), snakes (Montes et al 2022) or amphibians (Holsbeek et al 2008;Domeneghetti et al 2013). In this paper, we bring evidence for the geographical origin of non-native water frogs in Malta, which, in their native range, represent a unique evolutionary lineage with limited distribution.…”

Far from Home: Tracing the non-native origin of water frogs (genus Pelophylax) in Malta by molecular markers

“…On the other hand, populations of these rare species having limited distributions can hold an invasive potential in an introduced environment. These cases are welldocumented in lizards (Pupins et al 2023), snakes (Montes et al 2022) or amphibians (e. g. Holsbeek et al 2008, Domeneghetti et al 2013. In this paper, we bring evidence for the geographical origin of nonnative water frogs in Malta, which, in their native range, represent a unique evolutionary lineage with limited distribution.…”