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.
Highlights
This study aimed to provide a quantitative assessment of the occurrence of amphibians in the diet of invasive marsh frogs in their invaded range (Larzac) in a replicated design across space and time
The present study provides a quantitative assessment of the consumption of native amphibians by invasive marsh frogs in ponds and highlights the predation pressure on both Mediterranean tree frogs and newts
The present study did not measure native amphibian population dynamics and potential decline patterns, the results show that metamorphosed native amphibians, especially Mediterranean tree frogs and palmate newts, were preyed upon by invasive marsh frogs in several surveys and ponds
Summary
Freshwater habitats often have to cope with invasive alien species [1]. The introduction of novel predators induces additional predation pressure to which native organisms may not respond effectively [5]. Invasive alien predators may reach high densities because of their life-history traits (e.g., high reproduction rates), various associations with humans, or through the absence of natural predators and parasites [6]. Native species may suffer from excessive predation pressure, which influences the dynamics of their populations [7]. Predation by invasive alien species is an often-reported cause of native species decline [3], especially in fully or partially aquatic species [8,9]
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