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Trophic interactions have been a long-standing field of interest in ecology, helping to understand the relationships between organisms and how ecosystems function. In this study, we describe the trophic relationships of fish from karst environments in headwater streams of the upper Paraguai River basin. We analyzed the stomach contents of 81 fish species from the Serra da Bodoquena, calculated the metrics associated with the trophic network, incorporating the body size component in the analyses, and evaluated the participation of each species in network/module connectivity. The analyzed community trophic organization was based mainly on autochthonous items which were the most consumed items for about 30% of fish species. The trophic network showed a modular pattern without nestedness or specialization. However, nestedness was significant within each module, demonstrating a hierarchical compound topology (i.e., species with few connections interacted with subsets of the pairs of more connected species within each module). We also found a relationship between network connectivity and fish body size, in which small species tend to connect modules through generalist feeding strategies. Thus, we demonstrated a still little-known role of small species in fish trophic networks, and how trophic segregation occurs in a highly diverse community from Pantanal headwater streams. [ABSTRACT FROM AUTHOR]

Data obtained by direct observation of organisms in their natural habitats can provide valuable contributions regarding intra- and inter-specific interactions, as well as spatial distribution and trophic relationships. However, relatively few such data are available for the Neotropical ichthyofauna relative to the great species diversity of this region. We present data on the ichthyofauna in karst environments of the Serra da Bodoquena, Upper Paraguay River basin regarding their categorization into functional trophic groups. We used direct observations that focused on the most frequent feeding tactics and their spatial (vertical and horizontal) distribution in the channel. We observed 83 fish species in 17 functional trophic groups. The greatest species richness was concentrated in the Characidae and Loricariidae in the categories Diurnal Backwater Drift Feeders and Grazers, respectively. Regarding horizontal depth stratification, we found a positive relationship between the association of small fish with the shallow marginal habitats. This work represents a contribution to a region known for its high tourist potential and to the important diversity of the entire ichthyofauna of the Upper Paraguay basin region that requires proper conservation strategies for sustaining these species. [ABSTRACT FROM AUTHOR]