A piscivoria controlando a produtividade em reservatórios: explorando o mecanismo top down

Abstract

In many tropical ecosystems, predation is assumed to be the main factor determining fish biomass, individuals number and community composition. In Paraná state and limitrophe watershed, many reservoirs show different values of piscivores species richness, abundance and standing stock. To test the hypothesis that piscivory is the main factor controlling overall fish biomass, samples were taken in 31 reservoirs in 2001. A positive relation was found between richness/biomass of piscivore species and richness/biomass of prey species. It is possible that high values of species richness and biomass in some reservoirs are able to maintain more piscivores. There was no relation between prey biomass and piscivores species richness. However, when relative piscivore biomass was considered, a negative relation was noticed. It is necessary discern if this relation is a result from (i) a top down mechanism controlling fish biomass in these reservoirs, or (ii) if some reservoirs are characterized naturally by low prey biomass, maintaining piscivores by the high individuals/biomass turnover of small species.