Abstract
Lithobates catesbeianus (Shaw, 1802) is an invasive anuran introduced in Brazil that is associated with the displacement and the decline of populations of native species worldwide. There is evidence that biological invasions are facilitated by certain attributes of the invading species, for instance niche breath, and that invasive species have a broader ecological niche with respect to native ones. We designed a study to ascertain the temporal, ontogenetic, and sex differences in the niche dynamics of the American bullfrog. We sampled monthly from June 2008 to May 2009 in the state of Paraná, southern Brazil. For each individual, we gathered biometric and stomach content data. We then estimated the niche breath of the juveniles and adults, and compared it between the sexes. A total of 104 females and 77 males were sampled. Lithobates catesbeianus has a generalist diet, preying upon invertebrates and vertebrates. Even though the diet of the studied population varied seasonally, it did not differ between the sexes nor did it respond to biometric variables. Niche breadth was more restricted in the winter than in the autumn. The trophic niche of juveniles and adults did not overlap much when compared with the trophic niche overlap between males and females. Adult males and females had a considerable niche overlap, but females had a broader trophic niche than males in the winter and in the spring. These niche characteristics point to an opportunistic predation strategy that may have facilitated the process of invasion and establishment of this species in the study area.
Highlights
Biological invasions are recognized worldwide as one of the most complex social and environmental problems because they have negative impacts on the economy and biodiversity of various countries (VILÀ et al 2010)
Given the background presented above, and considering that there is evidence that L. catesbeianus has a negative effect on other species of frogs, which is mediated by predation, and the possible relationship between niche breadth and dominance by L. catesbeianus in the system, this study aimed to determine the overall trophic niche breadth of the American Bullfrog in a natural environment
Among the biological factors implicated in biological invasions, the amplitude of the trophic niche can act as a facilitator
Summary
Biological invasions are recognized worldwide as one of the most complex social and environmental problems because they have negative impacts on the economy and biodiversity of various countries (VILÀ et al 2010). The negative impacts of invasive species on native ones and which affect local biodiversity can be direct (for instance predation and competition) (ALTIERI et al 2010, SIH et al 2010) and indirect (such as transmission of pathogens) (SCHLOEGEL et al 2009). There is evidence that they depend on the characteristics of 1) the environment; 2) the native community (presence of predators and availability of resources) (KEANE & CRAWLEY 2002, ALTIERI et al 2010); and 3) the biological attributes of the invading organism (VÁZQUEZ 2006). A broader niche guarantees a constant input of energy for the basic biological processes (e.g., reproductive events), and has a positive impact on the population dynamics and dispersal of invasive species (KOLAR & LODGE 2001, VÁZQUEZ 2006)
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