Native predators living in invaded areas: responses of terrestrial amphibian species to an Argentine ant invasion

Abstract

Predator-prey interactions play a key role in the success and impacts of invasive species. However, the effects of invasive preys on native predators have been poorly studied. Here, we first reviewed hypotheses describing potential relationships between native predators and invasive preys. Second, we examined how an invasive prey, the Argentine ant (Linepithema humile), affected a native terrestrial amphibian community. In the field, we looked at the structure of the amphibian community in invaded versus uninvaded areas and characterized amphibian trophic ecology. The amphibian community sampled seemed to show a species-dependent response in abundance to invasion: adults of the natterjack toad (Bufo calamita), the species demonstrating the highest degree of ant specialization, were less abundant in invaded areas. Although available ant biomass was significantly greater in invaded than in uninvaded areas (only Argentine ants occurred in the former), amphibians consumed relatively fewer ants in invaded areas. In the lab, we quantified amphibian consumption of Argentine ants versus native ants and assessed whether consumption patterns could have been influenced by prior exposure to the invader. The lab experiments corroborated the field results: amphibians preferred native ants over Argentine ants, and prior exposure did not influence consumption. Differences in preference explained why amphibians consumed fewer Argentine ants in spite of their greater relative availability; they might also explain why the most ant-specialized amphibians seemed to avoid invaded areas. Our results suggest the importance to account for predator feeding capacities and dietary ranges to understand the effects of invasive species at higher trophic levels.

Effects of the Argentine ant venom on terrestrial amphibians

“…2011; Alvarez‐Blanco et al. 2017). Consequently, emerging E. calamita have little chance of surviving in ant‐invaded areas.…”

“…nigerrimum. Besides its greater toxicity, the augmented threat from L. humile arises from its high abundance and monopolization of invaded areas (e.g., around ponds) (Angulo et al 2011;Alvarez-Blanco et al 2017). Consequently, emerging E. calamita have little chance of surviving in ant-invaded areas.…”

“…2010; Alvarez‐Blanco et al. 2017). We collected individuals of the 3 most abundant amphibian species: natterjack toads ( Epidalea calamita ), Mediterranean treefrogs ( Hyla meridionalis ), and western spadefoot toads ( Pelobates cultripes ) (detailed methods in Supporting Information).…”

“…The Doñana Biological Reserve (RBD) (Spain, 36°59. 491'N, 6°26.999'W) hosts both terrestrial amphibians and the invasive L. humile (Díaz-Paniagua et al 2010;Alvarez-Blanco et al 2017). We collected individuals of the 3 most abundant amphibian species: natterjack toads (Epidalea calamita), Mediterranean treefrogs (Hyla meridionalis), and western spadefoot toads (Pelobates cultripes) (detailed methods in Supporting Information).…”

“…Welzel et al (2018) established that it deploys its defensive compounds against native ants. Although indirect effects on vertebrates are also known, such as contributing to the decline of the horned lizard (Phrynosoma coronatum) and the spatial shift in habitat use of amphibians (Alvarez-Blanco et al 2017), direct effects (i.e., capacity to subdue vertebrates), which could explain some of the reported indirect effects, have not been demonstrated.…”