Invasive cane toads are unique in shape but overlap in ecological niche compared to Australian native frogs

• Published in: Ecology and evolution Vol. 7; no. 19; pp. 7609 - 7619
• Main Authors: Vidal‐García, Marta, Keogh, J. Scott
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01.10.2017; John Wiley and Sons Inc
• Subjects: amphibian; Amphibians; biological invasions; body shape; Body size; Competition; Ecological niches; empty niche; Frogs; Hypotheses; Indigenous species; Introduced species; Invasive species; Invasiveness; Morphology; Native species; Niche breadth; Niche overlap; Nonnative species; Original Research; Phenotypic plasticity; Radiation; Success; Toads; Uniqueness; Australia; body shape; morphology; amphibian; biological invasions; empty niche; niche breadth
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.3253

Summary Invasive species are an important issue worldwide but predicting invasiveness, and the underlying mechanisms that cause it, is difficult. There are several primary hypotheses to explain invasion success. Two main hypothesis based on niche spaces stand out as alternative, although not exclusive. The empty niche hypothesis states that invaders occupy a vacant niche space in the recipient community, and the niche competition hypothesis states that invaders overlap with native species in niche space. Studies on trait similarity/dissimilarity between the invader and native species can provide information on their niche overlap. Here, we use the highly invasive and well‐studied cane toad (Rhinella marina) to test these two hypotheses in Australia, and assess its degree of overlap with native species in several niche dimensions. We compare extensive morphological and environmental data of this successful invader to 235 species (97%) of native Australian frogs. Our study is the first to document the significant morphological differences between the invasive cane toad and a continent‐wide frog radiation: despite significant environmental overlap, cane toads were distinct in body size and shape from most Australian frog species, suggesting that in addition to their previously documented phenotypic plasticity and wide environmental and trophic niche breadth, their unique shape also may have contributed to their success as an invasive species in Australia. Thus, the invasive success of cane toads in Australia may be explained through them successfully colonizing an empty niche among Australian anurans. Our results support that the cane toad's distinct morphology may have played a unique role in the invasiveness of this species in Australia, which coupled with a broad environmental niche breadth, would have boosted their ability to expand their distribution across Australia. We also propose RLLR (Relative limb length ratio) as a potentially useful measure of identifying morphological niche uniqueness and a potential measure of invasiveness potential in anuran amphibians. Predicting and explaining invasiveness success of alien species is an enormously important issue worldwide. We test successful invasiveness based on niche opportunities of the highly invasive cane toads in Australia—one of the most successful and best‐known biological invasions—through comparison with all native Australian amphibians. We measured and analyzed body size and shape, as well as environmental variables, of the cane toad in relation to each of the 235 Australian frog species. Cane toads’ body size and shape were strikingly distinct from all frog species; thus, they occupy an empty morphological niche in Australia; while their environmental niche breadth overlapped with most frog species. Their distinct morphology, phenotypic plasticity, and wide environmental niche breadth could have been a crucial factor determining their invasiveness success in Australia.