ABSTRACT
Prey size is an important factor in food consumption. In studies of feeding ecology, prey items are usually measured individually using calipers or ocular micrometers. Among amphibians and reptiles, there are species that feed on large numbers of small prey items (e.g. ants, termites). This high intake makes it difficult to estimate prey size consumed by these animals. We addressed this problem by developing and evaluating a procedure for subsampling the stomach contents of such predators in order to estimate prey size. Specifically, we developed a protocol based on a bootstrap procedure to obtain a subsample with a precision error of at the most 5 percent, with a confidence level of at least 95 percent. This guideline should reduce the sampling effort and facilitate future studies on the feeding habits of amphibians and reptiles, and also provide a means of obtaining precise estimates of prey size.
O tamanho das presas é uma importante dimensão do nicho trófico. Em estudos de ecologia alimentar, os itens alimentares são geralmente medidos individualmente com o uso de paquímetro ou ocular micrométrica. Entre os anfíbios e répteis, há espécies que consomem grande número de itens alimentares pequenos (e.g. formigas, cupins). Esse grande número, por sua vez, torna a estimativa do tamanho das presas consumidas uma tarefa difícil. Desenvolvemos um método para colher subamostras dos conteúdos estomacais desses animais com o objetivo de obter estimativas de tamanho das presas. Especificamente, desenvolvemos um protocolo baseado em uma rotina de bootstrap que permite a obtenção de subamostras com erro de precisão de no máximo 5 por cento e confiança de 95 por cento. Esse método deve diminuir o esforço amostral e facilitar estudos futuros sobre os hábitos alimentares de anfíbios e répteis, além de fornecer um meio de obter estimativas precisas de tamanho de presas.
Subject(s)
Animals , Anura/physiology , Body Size , Food Chain , Feeding Behavior/physiology , Predatory Behavior/physiology , Algorithms , Data Interpretation, Statistical , Gastrointestinal ContentsABSTRACT
This study reports on 156 specimens of the amphibian Eupemphix nattereri, a widely distributed leiuperid, obtained from 11 municipalities of central Brazil. The extent of genetic variation was quantified by determining the mean number of alleles per locus and the proportion of polymorphic loci. An analysis of molecular variance (AMOVA) was performed on the random amplified polymorphic DNA (RAPD) haplotypes. The genetic distances obtained by calculating pairwise phist among local samples were used to determine population relationships using the unweighted pair-group method (UPGMA) and non-metric multidimensional scaling (NMDS). The cophenetic correlation was calculated to confirm agreement between the genetic matrix and the unweighted pair group method with averages (UPGMA) dendrogram. To determine if genetic distances were correlated to geographical distances we constructed pairwise genetic distance and geographical distance matrices and compared them using the Mantel test. The AMOVA results indicated significant genetic differences (p < 0.001) between E. nattereri populations, representing 69.5 percent of the within population genetic diversity. The Mantel test showed no significant correlation (r = 0.03; p = 0.45) between the genetic and geographical distance matrices. Our findings indicate that the genetic variation of E. nattereri populations was randomly distributed in geographic space and that gene flow for this species is probably structured at spatial scales smaller than those between our samples.