Diet of Bullfrog Tadpoles Lithobates catesbeianus, Shaw 1802, an Invasive Species from Monte Desert
The competitive effects among tadpoles make the bullfrog a possible agent of native amphibian population declines at its introduction sites. Our aim was to analyze the dietary composition of an invasive population of Lithobates catesbeianus tadpoles and to evaluate the degree of dietary changes among activity months. We hypothesized that bullfrog tadpoles would exhibit temporal changes in diet, consistent with the variation of tadpole size and availability of resources. We collected 94 bullfrog tadpoles and identified 50 taxa in their digestive tracts. The items most frequently consumed were microalgae of the genera Navicula (frequency of occurrence [Fo] = 19) and Cymbella (Fo = 17). The trophic niche breadth was 8.13, which is considered moderate-high. The trophic habits of L. catesbeianus larvae changed seasonally, with the diets during October and December being numerically similar (Morisita's quantitative index = 0.86). The composition of the diet had a similarity of 63% (Jaccard's qualitative index) between August and October. The larvae of L. catesbeianus collected during the different months showed significant differences in their stages of development and body mass. On average, individuals were larger and more developed in the month of December, which was to be expected given that the abundance of prey items is greatest during the summer season. Our results show that L. catesbeianus tadpoles have a wide trophic niche with a diet that is not strongly selective; thus, the aquatic life-history stages play an important role in the structuring of invaded anuran larval communities.ABSTRACT
(A) Locations of studied invasive population of Lithobates catesbeianus from San Juan (yellow star). (B) Bullfrog tadpole from (C) Castaño Viejo River, Calingasta, San Juan.
Quantitative variation (Morisita similarity index) in the diet of bullfrog tadpoles during the different months of study. The diet during the months of October and December are 86% similar compared with August.
Qualitative variation (Jaccard index) in the diet of bullfrog tadpoles during the different months of study. The diet during the months of August and October share 63% of food items compared with December.
Relationship between the richness of items (number of taxa) in the diet of bullfrog tadpoles and body size (body mass) from Castaño Viejo River, San Juan, Argentina.
Variation in the developmental stage (Gosner, 1960; ANOVA F2.91 = 27.9, P < 0.001, horizontal bars) and body masses of Lithobates catesbeianus tadpoles in the sampling months (ANOVA F2.91 = 3.39, P < 0.03, vertical bars) from Castaño Viejo River, San Juan, Argentina.
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