Symmetries and asymmetries in the topological roles of piscivorous fishes between occurrence networks and food webs

Abstract

1. Ecological networks represent the architecture over which diversity is assembled. The compartmentalization of trophic links and the spatial aggregation of

Food web structure mediate positive and negative effects of diversity on ecosystem functioning in a large floodplain river

“…Our results confirm the dominance of weak interactions in the food webs of the Paraná River, but also highlight that the biases toward weak interactions is tightly associated with community richness. In addition, the presence of inter-modular connections by species feeding in alternative compartments of food webs, which is theoretically supported as a stabilizing property and has been progressively reported in different ecosystems (McCann 2011;McMeans et al 2016, Borzone Mas et al 2022, was found to significantly increase with diversity in our study. This relationship could arise as a byproduct of the increase in modularity, which makes it more likely for predators to capture prey from different modules.…”

“…In its middle reach, the Paraná River has an extensive floodplain with a high diversity of microhabitats and a vast fish species richness (Marchetti et al 2013; Scarabotti et al, 2017). The marked thermal seasonality and hydrological variability of the Parana River deeply modify the environmental heterogeneity, the riverscape connectivity, the composition of the communities and the interaction networks (Scarabotti et al 2017; Borzone Mas et al 2022). This combination of biodiversity, spatial heterogeneity, and temporal variability makes the Middle Paraná River an interesting model to test hypotheses about the relationship among diversity, food web structure, and ecosystem functioning (Figure 1).…”

“…Fishes were sampled from 27 water bodies grouped into four habitat types according to their flow, size and connectivity: major rivers; secondary channels, connected lakes and isolated lakes (see details in Borzone Mas et al 2022). Sampling surveys were carried out at one of four different hydro-climatic conditions that resulted from the combination of hydrometric level and temperature seasonality in high waters cold season, high waters warm season, low waters cold season and low waters warm season.…”

“…Mechanisms based on the horizontal dimension investigate how species belonging to the same trophic level allocate and compete for resources (Duffy et al 2007, Carroll et al 2011; Schneider et al 2016). Communities where complementarity effects prevail, tend to exhibit high network modularity, which results from the compartmentalization of trophic interactions and spatial distributions (Rezende et al 2009, Pinheiro et al 2019, Borzone Mas et al 2022), being food web modularity the multifunctional equivalent of trophic complementarity (Montoya et al 2015). Similarly, communities where selection effects promote biomass tend to produce nested networks.…”

“…A high intermodular connection by predators is expected to result in greater coupling of energy channels (Gauzens et al 2015). Moreover, the role of intermodular connection is positively related to predator body size (McCann et al 2005; Rooney et al 2008; Arim et al 2010; Pintho-Cohelo et al 2021, Borzone Mas et al 2022). In this sense, a greater coupling between energy channels can promote an increase in community biomass due to the constant supply of energy and/or the increase in the populations of large predators (Arim et al 2010, Maureaud et al 2019, Borzone Mas et al 2022).…”