Species level traits determine positive and negative population impacts of invasive cane toads on native squamates

Abstract

The novel interactions posed by invasive species can have complex effects on ecosystems owing to both their direct and indirect effects on other species. Consequently, the effects of invasive species can be hard to forecast owing to the diversity of interaction-pathways and number of species they can potentially affect. Ultimately, the strength and direction of an invader’s inter-specific effects will be determined by both the traits of the invader and the species they interact with. The cane toad (Rhinella marina) is a highly successful invasive species that poses a serious threat to ecosystem integrity in tropical Australia. Reptilian predators have been particularly affected by the invasion of cane toads because toads possess toxins that are novel to native Australian predators. We used a meta-regression approach to explore how cane toads’ impacts on Australian squamates are modulated by their phylogenetic, behavioural and morphological traits. Species primarily foraging in riparian and terrestrial habitats tended to decline in abundance while population sizes of arboreal squamates might have increased following toad arrival. The negative impact of cane toads on anurophagous squamates scaled with gape size and body mass. Squamate species with smaller heads or body mass tended to increase in abundance while species with larger heads or body mass tended to decline. Our study provides insight into the complexity of impacts that invasive species can have on native species assemblages and highlights how morphological and behavioural factors can mediate the impact of invasive on native species.