Abstract
While the Galápagos Archipelago is known for its endemic flora and fauna, many introduced species have also become naturalised there, especially on the human-inhabited islands. The only amphibian species known to have established on the islands, the Fowler’s snouted treefrog (Scinax quinquefasciatus), is thought to have arrived about two decades ago. Since then, this treefrog has substantially extended its range to the islands of Santa Cruz and Isabela. Our study explores the potential influence of this introduced amphibian on native trophic systems on Santa Cruz and identifies potential antagonists likely to control larval frog populations. To understand the impact of S. quinquefasciatus as a predator of local invertebrate fauna, we performed a stomach-content analysis of 228 preserved adult specimens from seven different localities on Santa Cruz. Of the 11 macroinvertebrate orders recorded, Lepidoptera constituted more than 60% of the contents. We also identified active predators of S. quinquefasciatus tadpoles: larvae of the endemic diving beetle (Thermonectus basillarus galapagoensis). To determine the efficiency of this predator, we conducted predator-prey experiments in ex situ conditions. Tadpole predation was highest after first exposure to the predator and significantly decreased over time. Our experimental results demonstrate that although T. b. galapagoensis larvae are effective tadpole predators, their feeding saturation rates are likely inadequate for frog population control. Our findings provide the first baseline data necessary to make informed ecological impact assessments and monitoring schemes on Santa Cruz for this introduced treefrog.
Highlights
Introduced species, which often transition to invasive species, are considered to be a major threat to global biodiversity (Early et al 2016)
The 54 specimens found in S. quinquefasciatus stomachs consisted mostly of Lepidopterans, followed by Acarina (NP: 44.38%, FO: 5.56%)
This study provides the first record of a S. quinquefasciatus predator in Galápagos: the endemic diving beetle Thermonectus basillarus galapagoensis
Summary
Introduced species, which often transition to invasive species, are considered to be a major threat to global biodiversity (Early et al 2016). The negative impacts of invasive species on native biota are severe in insular ecosystems with high influxes of human trade and travel (Courchamp et al 2003), such as the Hawaiian Archipelago (Beard and Pitt 2006), Guam (Christy et al 2007) and Taiwan (Jang-Liaw and Chou 2015). The Galápagos Archipelago is no exception, with over 1500 established introduced species, many of which are invasive (Toral-Granda et al 2017). Fowler’s snouted treefrog, Scinax quinquefasciatus (Fowler 1913), represents one of these cases. Basic data on this species are still lacking, despite its comparatively long introduction history (Cisneros-Heredia 2018): S. quinquefasciatus is assumed to have been introduced to Galápagos in the late 1990s (Snell et al 1999)
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