Lntraspecific Dietary Breadth, Overlap Indices and Feeding Strategies of Puntius gonionotus Bleeker and Oreochromis spp. in a shallow pond from Bangladesh

Abstract

Intraspecific virtual dietary breadth, degree of diet similarity, dietary overlap and feeding strategies of the silver barb Puntius gonionotus and the tilapia Oreochromis spp. were estimated in a pond from Bangladesh and compared using various niche indices. Appropri­ateness, ease of interpretation and explanation of different indices were evaluated. Dietary breadths were relatively higher in small sizes of P. gonionotus than large ones, though neither size class could be considered as a generalist feeder. There was a significant di­etary overlap between large and small barbs. Niche breadths were similar for both sizes of Oreochromis spp., a little higher for the small sizes, although as with the barbs, neither size class could be considered as a generalistic feeder. Dietary overlap of large tilapia on small ones was much greater but significant in both ways. Czekanowskis' Proportional Similarity (PS) index reveals a much broader aspect of the ecological determinants of niche breadth as it incorporates resource availability and resource use and has got the ease of biological interpretation. Similarly, Levins' dietary overlap indices reveal clearly both the significance, strength and direction of dietary overlap between competitors. According to the PS index, both species are opportunistic feeders, although tilapias are relatively more generalist than the silver barbs. Evidence of significant dietary overlap between the large and small sizes of both species reflects strong competition and indicates caution for mixed-­size stocking of tilapia in pond polyculture. Feeding pattern of silver barb reflected a mixed strategy with a combination of both high between- and within-phenotype contributions to the niche width, but with the between-phenotype contribution as the largest. While tila­pias reflected high within-phenotype contributions to the niche width, a generalized feed­ing strategy showed a trend of specialization of a population for periphytic food.