An intensively debated issue in ecology is whether the variations in the biodiversity patterns of different biological groups are congruent in space and time. In addition, ecologists have recognized the necessity of accounting for both taxonomic and functional facets when analysing spatial and temporal congruence patterns. This study aimed to determine how the cross-taxon congruence of taxonomic and functional beta diversity varies across space and time, using data from four floodplains at a continental scale. Our general hypothesis was that the congruence between aquatic biological groups, either taxonomic or functional, would decrease with the “between-group” functional distance. Also, we examined how congruence patterns varied across spatial and temporal scales by focusing on how the cross-taxon relationships differ among Brazilian floodplains and between dry/wet periods. Our study comprised information on eight biological groups from the four largest Brazilian river-floodplain systems, and cross-taxon congruence was assessed using Procrustes analysis. Our results show how detailed analyses can reveal different patterns of cross-taxon congruence, and partially support the hypothesis that the strength of cross-taxon congruence is negatively related to between-group functional distance.
Studies that combine functional and taxonomic beta-diversity are essential for explaining some ecological processes, including the process of species invasion. We evaluated whether environmental factors (such as lake connectivity, subsystem and hydrological period) and biological factors (occurrence and richness of non-native and native fish species) affect beta-diversity components (total, richness and replacement) of fish communities living in the Upper Paraná River floodplain in Brazil. For this, a distance-based redundancy analysis (dbRDA) was performed for both taxonomic (BDtax) and functional (BDfunc) approaches. In order to see which variables influence the local contribution to BDtax and BDfunc (LCBD), mixed effects regression models were fitted. Our results indicated a significant influence of environmental and biological factors on the taxonomic patterns of beta diversity and functional beta-diversity of fish between lakes. Environmental factors influenced the replacement component for both taxonomic and functional diversity, while biotic factors (occurrence and richness of non-native species) influenced the richness component. The richness of native and non-native species, the occurrence of non-native species and hidrological period showed significant influence on LCBD values. Although in our study the occurrence and richness of non-native species are related to beta-diversity, in the long term, these species can cause a decrease in functional and taxonomic beta-diversity, altering the ecological multifunctionality of the environment. Our study emphasizes that both changes in environmental factors and species diversity (such as the introduction of a non-native species) can impact the beta-diversity of Neotropical fish.
Submersed macrophytes have important ecological roles but non-native invasive species may affect biodiversity and water uses. We investigated the native macrophyte Egeria najas and the invasive Hydrilla verticillata and measured their maximum colonization depth and its relationship with Secchi disk depth, their biomass along the depth gradient and their preferred depths of occurrence. The Itaipu Reservoir was monitored for seven years, during which maximum colonization depth and Secchi disk depth were measured. During a separate sampling, plants were collected to determine biomass along the depth gradient. Ancova showed that the maximum colonization depth of both species increased with increasing Secchi disk depth, but the maximum colonization depth of H. verticillata increased faster with increasing water transparency than did that of E. najas. Quadratic regression revealed that the biomass of each species peaks at intermediate depths. Hydrilla verticillata colonizes deeper regions than does E. najas. The patterns found in the present study can be explained by underwater light and, probably, wave disturbances. The preference of H. verticillata for deeper sites indicates that the ecological niches of the two macrophytes differ, and that H. verticillata has great potential to spread and accumulate biomass in reservoirs.
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