Diet composition of an invasive population ofLithobates catesbeianus(American Bullfrog) from Argentina

Abstract

The American bullfrog Lithobates catesbeianus has been introduced around the world, with invasive populations reported from almost all South American countries. A population of this species was introduced in the Calingasta department of San Juan province, which is an arid environment in western Argentina. This work provides information on the dietary composition of an invasive population of L. catesbeianus, and compares the degree of dietary overlap between adults and juveniles. Stomach contents of 169 bullfrogs (82 adults and 87 juveniles) were analysed. Adults consumed 40 prey taxa and Hymenoptera (Insecta) was the most numerous prey item (41.8%), followed by Araneae (13.6%) and Aeglidae (13.4%). Juveniles consumed 29 prey taxa and Hymenoptera constituted the highest percentage in prey number (77.2%). The trophic overlap niche index at the same level shows a value of 0.64 overlap in dietary community between adults and juveniles of this bullfrog. Aeglidae was volumetrically the most important trophic item (25.4%), followed by Anura (25.02%). Our results showed that cannibalism in bullfrogs is more common than the consumption of native anurans, coinciding with that reported in other populations of introduced bullfrogs. The high similarity in the diets of both size classes and the association between the size of the predator and prey suggest that the impact caused by bullfrogs throughout their ontogeny is high and probably has an impact on their prey. Freshwater crabs are the main items in the diet of Lithobates catesbeianus in other introduced populations and are usually the most conspicuous at our study site. The crabs in freshwater ecosystems are part of the lowest trophic level in the food chain. The major threats to the southern region's freshwater crabs include deforestation, farming and exotic species. Lithobates catesbeianus has a generalist diet and high overlap between adults and juveniles.

Introduced American Bullfrog Distribution and Diets in Grand Teton National Park

“…In fact, PSAi and Oi were ~ 100% for all three sampling periods (Figure 3), which indicates that this was an energetically important and common resource that larger individuals specialized on. This contrasts with previous research that showed large prey items (such as mice) to have lower occurrence than small prey items (such as invertebrates) (e.g., Bury and Whelan 1984, Hirai 2004, Jancowski and Orchard 2013, Quiroga et al 2015. For sit-and-wait predators like large bullfrogs, consumption of prey that are large relative to the predator is predicted to maximize energetic potential.…”

“…Non-native prey included one putative bullfrog larva, several tadpole madtom and swordtail fishes, and multiple redrimmed melania snails. Cannibalism is frequent in other introduced, abundant bullfrog populations (Wu et al 2005, Quiroga et al 2015, so the single observation of a putative bullfrog larva was unexpected given that we captured at least 225 postmetamorphic bullfrogs and more than 900 larvae during the 2015 sampling season (unpublished data). Future studies of native and non-native prey abundance in the KWS/SD complex may help to contextualize these unexpected results.…”

Disentangling the trophic interactions between American bullfrogs and native anurans: Complications resulting from post‐metamorphic ontogenetic niche shifts

“…Adults, in fact, were mostly collected in aquatic habitats and, consequently, relied more heavily on aquatic prey, whereas juveniles were captured mostly on banks or in shallow waters near the shore, and primarily consumed prey of terrestrial origin. Juveniles may also remain close to terrestrial habitats in order to facilitate their antipredator response, especially towards conspecific adults (Quiroga et al, ). The cannibalism of immature bullfrogs by adults is well documented (Bury & Whelan, ; Govindarajulu et al, ), and may provide more than 80% by volume of the total adult food content (Stuart & Painter, ); however, there were no observations of juvenile cannibalism by adult American bullfrogs during the present study.…”

Centrorhynchus spp. (Acanthocephala) in South America: new anuran record and checklist of vertebrate hosts

“…We examined host gender during necropsies, observing the gonads and considering external sexual dimorphism. Hosts stage of maturation (juveniles or adults) were defined according to Quiroga et al (2015) .…”