Matheus Tenório Baumgartner

Extreme drought events can promote homogenization of benthic macroinvertebrate assemblages in a floodplain pond in Brazil

Extreme weathers tend to become frequent following global warming and may promote important changes in species composition. We used benthic macroinvertebrates to test the hypothesis that extreme drought events could lead to local biotic homogenization in a floodplain pond. We took sediment samples in three sampling areas of a floodplain pond during a period of the usual hydrological cycle and during an extreme weather event that caused an atypical hydrological cycle with prolonged drought period. We found that community composition significantly differs between usual hydrological cycle and extreme drought periods, in which only species adapted to unfavorable environmental conditions remained. The spatial beta diversity decreased during the extreme drought periods, presenting lower variability compared to the usual hydrological cycle. However, species density, richness, and diversity increased during the droughts. We expect that, in scenarios of climate change with frequent extreme weathers, droughts may cause permanent negative impacts on aquatic communities, leading to biotic homogenization. Moreover, our findings indicate that prolonged droughts could increase the time needed to community recovery, suggesting lower community resilience to environmental stressors. Therefore, increasing frequency of extreme drought events may result in an alternative community structure.

Correction to: Extreme drought events can promote homogenization of benthic macroinvertebrate assemblages in a floodplain pond in Brazil

Due to an unfortunate turn of events, the surname of the first author appeared incorrectly in the original publication as it should have read A. P. S. Bertoncin. The original article has been corrected and the proper representation of the authors’ names and their affiliation is also listed here. We apologize to the authors and readers for the inconvenience.

Is coexistence between non-native and native Erythrinidae species mediated by niche differentiation or environmental filtering? A case study in the upper Paraná River floodplain

The limiting similarity theory predicts that divergence in the functional traits of native and introduced species is an essential component in species establishment, as introduced species must occupy a niche that is unoccupied by resident species. On the other hand, the environmental filtering hypothesis predicts convergence between introduced and native species, as both possess traits that make them adapted to the local abiotic environment. Morphology, spatial co-occurrence, diet, feeding selectivity, and niche breadth and overlap of Erythrinidae were evaluated to detect possible mechanisms acting in the coexistence between non-native and native species. Native (Hoplias sp. B and Hoplias cf. malabaricus) and nonnative (Hoplerythrinus unitaeniatus and Hoplias mbigua) species presented differences in morphological traits, spatial cooccurrence, diet, selectivity, and niche breadth and overlap. The mechanisms mediating species coexistence seem to vary according to species. The absence of spatial and feeding overlap suggests that non-native species H. unitaeniatus occupy a different niche than native species, supporting its successful establishment without eliminating the native species. However, low feeding overlap and similar morphologies between non-native and native species of Hoplias point to environmental filters; in this case, the non-native H. mbigua is able to establish due to similarities in functional traits.

Spatial and temporal variations in fish assemblage: testing the zonation concept in small reservoirs

Large reservoirs usually present spatial gradients in fish assemblage, distinguishing three strata (littoral, pelagic, and bathypelagic) along the vertical and horizontal axes, and three zones (fluvial, transitional, and lacustrine) along the longitudinal axis. The main objective of this study was to assess if small reservoirs also present the spatial gradients in fish assemblage attributes and structure as already observed in large reservoirs. Fish surveys were conducted quarterly, from 2003 to 2008, in the Mourão Reservoir (Mourão River, Paraná, Brazil), using gillnets with different mesh sizes, arranged in all strata of all three zones. Community attributes (species richness and evenness) were calculated for each sample, and differences were tested using three-way ANOVA (factors: zone, strata, year). Community composition was summarized using Correspondence Analysis (CA) and differences were tested with three-way ANOVA for each axis, controlling the same three factors. Because of the high variability in reservoir water level through time, all analyses were made considering temporal variations. Species richness presented a decreasing trend from fluvial to lacustrine zones, and higher values in littoral strata, possibly because upper reaches and littoral regions provide better conditions for fish to feed and to reproduce. Evenness was considerably low, presenting high variability, and no evident pattern. The expected longitudinal gradient was not found in this study indicating longitudinal similarity, contrary to observed in large reservoirs. Vertical and horizontal gradients were observed in all sampling stations, indicating that abiotic and biotic conditions are influencing fish distributions within the reservoir.