Influence of urbanization on stream fish assemblages in three microbasins in the Upper Paraná River Basin

The colonization pattern of fish assemblages in streams is often studied in the context of environmental filters. On the other hand, when fish assemblages are subjected to anthropogenic effects, variables associated with environmental quality assume more importance. Therefore, this work evaluated the richness and composition of fish from streams sampled at different urbanization levels, aiming to determine any direct effects on the structure of fish assemblages. To accomplish this, samples were collected from 2003 to 2011 at 31 sites distributed among 3 microbasins in the Rio Ivinhema Basin, Alto Rio Paraná. Based on environmental variables, physicochemical of the water and analysis of the use and occupation of the soil, the microbasins were classified into different urbanization levels (low, medium and high). A total of 4,320 individuals were sampled, out of which 57 fish species were recorded. Sampled sites with medium urbanization level presented higher richness compared to sampled sites with high urbanization level which presented lower richness. Species richness in these sites was explained mainly by water temperature and water velocity. Results confirmed that urbanization does directly affect environmental integrity, which, in turn, can lead to the homogenization of stream assemblages.

ECOLOGIA FILOGENÉTICA DE COMUNIDADES DE PEIXES DE RIACHO NEOTROPICAIS

Neotropical stream fishes exhibit a complex evolutionary history and encompass both old and recent lineages. Patterns of species diversity of stream fishes are relatively well-studied for Neotropical streams, but not for patterns of clade distribution and historical factors that structure these assemblages, which are the main interests of phylogenetic ecology. Understanding the evolutionary context of communities provides important insights into large-scale mechanisms that structure them. This review aims to: (i) discuss the main concepts of phylogenetic ecology and its application to Neotropical stream fishes; and (ii) highlight the main methods applied in this background. The first section presents the main phylogenetic hypothesis of fishes and discusses how their gaps in Neotropical stream fishes hinder phylogenetic ecology. Afterward, we discuss the main concepts of phylogenetic ecology (phylogenetic signal, community phylogenetic structure, and phylogenetic diversity), as well as gaps and potential applications of these concepts and tools to understand Neotropical stream fish assemblages. The second section introduces the main methods to address the phylogenetic ecology, including a standardized procedure to edit fish phylogenetic trees, comparative methods, and indices and analytical tools to understand community structure and conservation importance. Finally, we discuss the perspectives to the next years to better understand the Neotropical stream fish assemblages in the light of past and current historical processes.

Widespread convergence in stream fishes

Convergent evolution, the evolution of similar phenotypes among distantly related lineages, is often attributed to adaptation in response to similar selective pressures. Here, we assess the prevalence and degree of convergence in functional traits of stream fishes at the microhabitat scale in five zoogeographical regions across the world. We categorized species by microhabitat, water velocity and preference for substrate complexity and calculated the prevalence of convergence, degree of convergence and functional diversity for each category. Among species occupying similar microhabitats of small, low-gradient streams, 34% had combinations of convergent traits. Convergence occurred at higher rates than expected by chance alone, implying that adaptation to similar environmental conditions often resulted in similar evolutionary patterns along multiple niche dimensions. Two of the microhabitat groupings had significantly convergent species represented in all zoogeographical regions. Fishes occupying microhabitats with high water velocity and low structural complexity generally occupied a restricted morphospace and exhibited greater prevalence and higher degrees of convergence. This suggests that water velocity and habitat structural complexity interact, selecting a restricted distribution of trait distributions and higher degrees of convergence in stream fish assemblages. Furthermore, these results suggest that microhabitat features in streams select for fish trait distributions in a fairly predictable and deterministic manner worldwide.

Confluences and Land Cover As Agents of Change: Temporal Habitat Variability Modifies the Movement and Assemblage Change of Headwater Fishes

Interspersed inputs of wood and sediment brings about morphological change at confluences and the extent to which these processes are modified by anthropogenic disturbance has ramifications for stream fish assemblages. In this study, we use three functional groups of headwater fishes to assess the influences of confluence size and land cover on habitat stability, distance moved, movement rate, and assemblage change in a Gulf Coastal Plain drainage in the southeastern United States using a 2X2 design. Our results suggest that differences in habitat stability were described by a hydrogeomorphic gradient, and urban reaches characterized by a confluence size > 0.6 displayed the greatest habitat instability. Water-column specialists in urban reaches were more likely to move when habitat change was limited, whereas movement by this functional group in forested reaches was more likely in response to greater habitat instability. Therefore, the distance moved by water-column specialists was related to land cover. Assemblage change also occurred at a more constant rate in urban reaches in response to habitat instability. There was little evidence that confluence size influenced movement or assemblage stability in these headwater assemblages. Our understanding of the extent to which land cover alters the geomorphic and ecological gradients associated with headwater confluences will be critical to ensure the conservation of sensitive species whose fitness is dependent on the integrity of these habitats.

Considerations of variability and power for long-term monitoring of stream fish assemblages

Little attention has been given to optimizing statistical power for monitoring stream fish assemblages. We explored the relationship between temporal variability and statistical power using 34 metrics from fish community data collected annually at six sites over 10 years via electrofishing. Metric variability differed by the life stage and group of species considered, use of abundance or mass data, and data standardization technique. Lower variability was associated with community data, abundance data, and time-based standardizations, while greater variability was associated with young-of-the-year data, mass data, and area-based standardizations. Simulation-based power analysis indicated metric choice, and to a lesser degree, monitoring design (annual, biennial, endpoints, or haphazard sampling) influenced power to detect change. Across a fixed number of surveys (N = 60), endpoints sampling performed best. The N needed to detect change was heavily dependent upon metric choice for all monitoring designs, with the most biologically specific metrics requiring greater N. Large savings in effort and resource expenditure can be obtained utilizing biologically relevant metrics that are robust to temporal noise within an appropriate sampling design.