Invasive bullfrogs as predators in a Neotropical assemblage: What frog species do they eat?

Abstract

Anurans are important prey for the American buUfrog Lithobates catesbeianus, but field assessments of its diet in the context of a local prey assemblage are lacking. We aimed to identify the frog species consumed by an invasive bullfrog population in subtropical South America, and to assess their relative importance among other types of prey. Characterization of the frog assemblage in the study area also allowed us to calculate the degree of electivity of the recorded anuran prey, in order to gain insight regarding bullfrog feeding preferences and to test if the bullfrog prey composition differed from a random sample of the assemblage. A total of 32.6% of the bullfrogs had at least one anuran in the stomach contents, and post-metamorphic anurans represented 49.1% of the relative prey importance for adult bullfrogs. Anurans were preyed on by all size classes, and constituted the volumetrically most important prey category in the diet of individuals heavier than 100 g. Cycloramphidae, HyMdae and Leiuperidae were positively selected, and Hypsiboas pulchellus and Physalaemus cuvieri were the species most often taken. We found a low occurrence of cannibalism, despite the high density of bullfrogs at the study site. Our results showed that the degree of electivity differed among bullfrog prey types, suggesting that some frog species may be preyed on in a higher proportion than their relative abundance in the assemblage. Testing the clues provided by this assemblage-level approach may lead to a better assessment of the interactions between buUfrogs and the native frog fauna.

More invaders do not result in heavier impacts: The effects of non‐native bullfrogs on native anurans are mitigated by high densities of non‐native crayfish

“…Compared with a large body of literature reporting bullfrog predation on adult native frogs (e.g. Boelter, Kaefer, Both, & Cechin, 2012;Jancowski & Orchard, 2013;Liu et al, 2015), mesocosm and laboratory experiments have found that the crayfish P. clarkii mainly feeds on amphibian embryos and swimming larvae in North America (Gamradt & Kats, 1996), Europe (Cruz & Rebelo, 2005;Cruz, Pascoal, Tejedo, & Rebelo, 2006;Cruz, Rebelo, & Crespo, 2006;Renai & Gherardi, 2004) and Asia (e.g. F. limnocharis here, Wu et al, 2008), but such results are not surprising considering that P. clarkii is an opportunistic omnivorous predator that consumes diverse aquatic algal and animal foods (Geiger, Alcorlo, Baltanas, & Montes, 2005).…”

Reproductive phenology of the American Bullfrog in subtropical Brazil: photoperiod as a main determinant of seasonal activity

“…However, in Brazil there are no records of predators of adult bullfrogs, while predators of juveniles exist Filho 2009, Medeiros et al 2012). However, the microhabitat segregation could also be related to the avoidance of cannibalism, which is common in this species (Boelter et al 2012). Juveniles were observed to avoid areas close to adult males in both ponds (Medeiros, C. pers.…”

“…A series of studies on bullfrog biology conducted in Brazil indicate that this species has adapted to climatic conditions and can survive and reproduce in invaded areas , Kaefer et al 2007, Alves et al 2008, Afonso et al 2010, Leivas et al 2012, Boelter et al 2012. It has been suggested that bullfrogs might negatively affect various native species in Brazil, however there is a lack of evidence supporting such impacts (see Both et al 2014).…”

Responses in the diet composition of the Common frog (Rana temporaria) to the stochastic gradation of Autumnal moth (Epirrita autumnata) larvae

“…Mite eating is also known in specialized foreger salamander Salamandrina perspicillata (Costa et al 2015). Boelter et al (2012) proved that invasive Lithobates catesbeianus consume other frog species selectively and in high volume. In a study on a Hungarian frog assemblage Kovács (2003) found that Bombina bombina tend to eat a vast amount of collembolas from the water surface while adult Bufo bufo tend to prey on ants primarily in the same location.…”