Abundância e estrutura de tamanho das comunidades de protozoários planctônicos em uma planície de inundação neotropical : efeitos dos mecanismos de controle ascendente e descendente.

Abstract

The understanding of ecosystem functioning occurs, in large part, through knowledge of their interactions within food webs, in which occurs the flow of matter and energy. Studies of interactions between its components are fundamental to the understanding of food chains, given its importance to nutrient cycling, accumulation of biomass and carbon flux. These organisms can be strongly affected by the availability of resources and the effect of predation on aquatic environments. We evaluated the influence of bottom-up and top-down control mechanisms on the abundance and size structure of planktonic protists (flagellates and ciliates), and hypothesized that bottom-up would control the abundance while top-down would affect the size of those organisms. As predicted, resources were the most important variables determining the abundance of protists, mostly by picophytoplankton and bacteria. The size structure was influenced by both resources and predation. Besides, resource contribution to protist biomass was mainly through herbivory in all phytoplankton sizes, both at the surface and the bottom of the environments.