Hábito alimentar da rã invasora Lithobates catesbeianus (Shaw, 1802) e sua relação com anuros nativos na Zona da Mata de Minas Gerais, Brasil / Feeding habits of the invasive frog Lithobates catesbeianus (Shaw, 1802) and its relationship with native anurans in the Zona da Mata of Minas Gerais state, Brazil

Emanuel Teixeira da Silva

The American Bullfrog (Lithobates catesbeianus) was introduced into several countries for commercial breeding, settling invasive populations during this process. In Brazil the beginning of its farming occurred on the 1930 s, and currently invasive populations can be found in the South, Southeast and Central-West regions. It has a generalist feeding habit, and due to the large size reached by adults it is known as a predator of small vertebrates, among these other anuran species. The establishment of the Bullfrog in areas where it is not native is considered one motive of anuran population declines, due to predation, interspecific competition and possible pathogen transmission. The feeding habits of this species were studied in four sites located at the Universidade Federal de Viçosa campus, in Viçosa, and in two farms in Vieiras, municipalities of the region Zona da Mata, Minas Gerais state, in order to access data on its relationship with native anurans. Data collection in Viçosa was between August 2005 and March 2007, and in Vieiras from September 2008 to April 2009 and September to November 2009, through nocturnal field surveys and stomach content analyses. In the first article of this work the feeding habits and spatial distribution of this invasive species were compared to those of the native "Common Thin-toed Frog" (Leptodactylus ocellatus) in Vieiras, relating the feeding ecology to the coexistence between these species. Juveniles of both species had similar body sizes, whereas native adults were smaller than the invasive adults. Insects in general and spiders dominated the diets of juveniles of both species, as well as of Le. ocellatus adults, whereas anurans and water-bugs stuck out in adult Bullfrog diet. The native frog ate more prey in average than the invasive, although its preys were smaller in volume. The invasive frog proved to be more aquatic than the native, so that aquatic and amphibious preys were more common in its diet. The feeding niche overlap was higher between conspecific pairs, and varied from low to intermediate between species, according to the age group compared. The differences in diet and spatial distribution may be promoting the coexistence between these frogs in the studied region. In the second article the predation on native anurans by invasive Bullfrogs was analyzed in both localities, regarding the spatial variation and influences of seasonality and microhabitat use by native species. Anurans of the families Bufonidae, Hylidae, Leiuperidae and Microhylidae were found among Bullfrog preys, and had intermediate to high similarity in microhabitat use with Bullfrogs. Predation was more frequent in the site of Viçosa where the natural vegetation is preserved. The number of anurans preyed was higher during the first months of the raining season, which is the reproductive period of the most of native species. Thus, the possible negative impact of the Bullfrog on Brazilian anurans may be more significant among species which are similar to the invasive in relation to microhabitat use, and during their reproductive season. The effect of predation also may be higher in preserved sites, such as forest fragments of conservation units, increasing the importance of monitoring the spread of this invasive frog throughout natural areas, as well as starting control programs.

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