Prey Availability or Electivity in the Diet of some Amphibians from Olinlin-Uzea, Esan North East, Edo State, Nigeria (original) (raw)

The diet of four species of frogs, Hoplobatrachus occipitalis, Ptychadena bibroni, Amietophrynus maculatus and Leptopelis sp. from Olinlin-Uzea, Esan North East Local Government Area in Edo State, Nigeria was studied between July and November 2014. Specimens were stomach-flushed and a total of 166 prey items from 13 prey categories recorded. Hoplobatrachus occipitalis had the highest niche breadth (6.04) indicating a rich diversity of prey while Leptopelis sp. an arboreal frog had the least (2.67). Hoplobatrachus occipitalis and P. bibroni had a niche overlap of 0.79 indicating a common use of the microhabitat while no overlap was recorded between Leptopelis sp. and Amietophrynus maculatus and P. bibroni. The low electivity indices observed in Hoplobatrachus occipitalis, Ptychadena bibroni, and Amietophrynus maculatus is an indication that feeding was based more on the availability of prey rather than preference. Although a high electivity index was recorded for Leptopelis sp, it is most likely due to its restricted microhabitat and the corresponding available prey. Caution should, however, be employed with electivity indices as results could be affected by inadequate sampling. 1.0. Introduction Amphibians have often been thought of as generalist or opportunistic feeders, feeding mainly on insects. Although diet studies in amphibians date as far back as Toft (1980) few studies have however been done to determine if the diet was based on prey availability or electivity. In one of such works, Junca and Eterovick (2007) suggested stability either in prey availability or food selection in Anomaloglossus stepheni due to the similar diet composition between populations in different time zones. In a similar work, although electivity index showed Hypsiboas punctatus to forage more on dipterans slightly above the environmental abundance which would have placed it as a specialist feeder, resource availability data however placed it as a generalist feeder feeding more on the main food item and other secondary prey based on their resource availability (Lopez et al., 2009). It is thus important to have an idea of the resource availability when making interpretations from diet analysis. Thus, a knowledge of amphibian species diet and deductions from its interwoven nature and relationships is needed more than ever before in ecological studies for a better understanding of their feeding ecology. More recent works on prey electivity by Costa et al. (2014) showed contradictory results in prey ingested based on the method of analysis with stomach flushing method more preferred to faecal analysis method as most soft-bodied prey get digested in the stomach without traces of it in the faecal content giving a false information on prey selectivity. Electivity values should, however, be used with care as it has been shown that inadequate sampling of the environment for prey could lead to high electivity values which do not give a true picture of the diet preferences of the particular species being studied. Flowers and Graves (1995), Caldert et al. (2012). This work was undertaken to determine if the diet of the four anurans under study is based on prey availability or electivity.