Predation Pressure of Invasive Marsh Frogs: A Threat to Native Amphibians?

Abstract

Anurans have been introduced in many parts of the world and have often become invasive over large geographic areas. Although predation is involved in the declines of invaded amphibian populations, there is a lack of quantitative assessments evaluating the potential risk posed to native species. This is particularly true for Pelophylax water frogs, which have invaded large parts of western Europe, but no studies to date have examined their predation on other amphibians in their invaded range. Predation of native amphibians by marsh frogs (Pelophylax ridibundus) was assessed by stomach flushing once a month over four months in 21 ponds in southern France. Nine percent of stomachs contained amphibians. Seasonality was a major determinant of amphibian consumption. This effect was mediated by body size, with the largest invaders ingesting bigger natives, such as tree frogs. These results show that invasive marsh frogs represent a threat through their ability to forage on natives, particularly at the adult stage. The results also indicate that large numbers of native amphibians are predated. More broadly, the fact that predation was site- and time-specific highlights the need for repeated samplings across habitats and key periods for a clear understanding of the impact of invaders.

Efficiency of aquatic PIT-tag telemetry, a powerful tool to improve monitoring and detection of marked individuals in pond environments

“…All studied ponds were colonized by marsh frogs (Pelophylax ridibundus) which are invasive in the area historically devoid of native Pelophylax species. The taxonomic status of marsh frogs in the studied sites was confirmed by molecular markers (Dufresnes et al, 2017;Pille et al, 2021). Larzac is a traditionally managed agricultural area where ponds are primarily used to water cattle (Durand-Tullou, 1959).…”

High habitat invasibility unveils the invasiveness potential of water frogs

“…Frog removal in target habitats may help locally native species but is likely difficult given the high number of invaded ponds. The difficulties of management along with the broad-scale invasion and the identified predatory pressure on native amphibians (Pille et al 2021) are therefore particularly alarming. Future research should encompass the long-term impacts of these invaders on native communities, how the spatial niche of invaders and native species overlap at local and landscape scales and what solutions could benefit native species.…”

“…Pelophylax water frogs are cryptic invaders in many European countries (Dufresnes et al 2017). The most widespread taxon, the marsh frog (Pelophylax ridibundus), native to Central and Eastern Europe, was introduced multiple times in Western Europe for ornamental and culinary reasons where it is currently spreading broadly (Dufresnes et al 2018), and recognized as harmful invaders of aquatic ecosystems in many countries (Holsbeek et al 2008;Dubey et al 2014;Pagano et al 2001;Pille et al 2021). Invasive water frogs can eliminate the genome of native Pelophylax species through hybridogenesis, raising concerns about the preservation of the genetic integrity of native taxa (Dufresnes and Mazepa 2020).…”

“…comm.). P. ridibundus was introduced at the end of the twentieth century in Larzac and has since expanded across the whole landscape (Dufresnes et al 2017;Duret et al 2022), where it preys on multiple native species (Pille et al 2021). Specifically, we aimed to (A) determine the level of invasion in the area (i.e.…”

Bending the curve: Simple but massive conservation action leads to landscape-scale recovery of amphibians

“…S5); hence, it was also a beneficiary of pond construction. Similar to American bullfrogs (45), this large frog has negative impacts on native amphibians through predation or competition (46,47). Nonetheless, most native species showed increased metapopulation sizes in response to pond construction, but the increase might have been even stronger in the absence of invasive species.…”