Different roles for geography, energy and environment in determining three facets of freshwater molluscan beta diversity at broad spatial scales

Effects of environment and metacommunity delineation on multiple dimensions of stream fish beta diversity

Introduction

Beta diversity represents changes in community composition among locations across a landscape. While the effects of human activities on beta diversity are becoming clearer, few studies have considered human effects on the three dimensions of beta diversity: taxonomic, functional, and phylogenetic. Including anthropogenic factors and multiple dimensions of biodiversity may explain additional variation in stream fish beta diversity, providing new insight into how metacommunities are structured within different spatial delineations.

Methods

In this study, we used a 350 site stream fish abundance dataset from South Carolina, United States to quantify beta diversity explainable by spatial, natural environmental, and anthropogenic variables. We investigated three spatial delineations: (1) a single whole-state metacommunity delineated by political boundaries, (2) two metacommunities delineated by a natural geomorphic break separating uplands from lowlands, and (3) four metacommunities delineated by natural watershed boundaries. Within each metacommunity we calculated taxonomic, functional, and phylogenetic beta diversity and used variation partitioning to quantify spatial, natural environmental, and anthropogenic contributions to variations in beta diversity.

Results

We explained 25–81% of the variation in stream fish beta diversity. The importance of these three factors in structuring metacommunities differed among the diversity dimensions, providing complementary perspectives on the processes shaping beta diversity in fish communities. The effect of spatial, natural environmental, and anthropogenic factors varied among the spatial delineations, which indicate conclusions drawn from variation partitioning may depend on the spatial delineation chosen by researchers.

Discussion

Our study highlights the importance of considering human effects on metacommunity structure, quantifying multiple dimensions of beta diversity, and careful consideration of user-defined metacommunity boundaries in beta diversity analyses.

Spatial Factors Outperform Local Environmental and Geo-Climatic Variables in Structuring Multiple Facets of Stream Macroinvertebrates' β-Diversity

Simple Summary

One of the key targets of community ecology and biogeography concerns revealing the variability and underlying drivers of biodiversity. Most current studies understand biodiversity based on taxonomic information alone. Our study was based on macroinvertebrates from 179 stream sampling sites in the Hun-Tai River Basin in Northeastern China. The correlation of different facets of β-diversity was compared while revealing the relative contribution of multiple abiotic factors (i.e., local environmental, geo-climatic, and spatial factors) to shaping β-diversity based on taxonomic, functional, and phylogenetic information. The results showed that functional β-diversity provides important complementary information to taxonomic and phylogenetic β-diversity. Moreover, spatial factors outperform local environmental and geo-climatic variables in structuring multiple facets of stream macroinvertebrates’ β-diversity. Our study provides guidance for future conservation studies of watershed biodiversity, as well as implications for future studies of β-diversity.

Abstract

One of the key targets of community ecology and biogeography concerns revealing the variability and underlying drivers of biodiversity. Most current studies understand biodiversity based on taxonomic information alone, but few studies have shown the relative contributions of multiple abiotic factors in shaping biodiversity based on taxonomic, functional, and phylogenetic information. We collected 179 samples of macroinvertebrates in the Hun-Tai River Basin. We validated the complementarity between the three facets and components of β-diversity using the Mantel test. Distance-based redundancy analysis and variance partitioning were applied to explore the comparative importance of local environmental, geo-climatic, and spatial factors on each facet and component of β-diversity. Our study found that taxonomic and phylogenetic total β-diversity was mainly forced by turnover, while functional total β-diversity was largely contributed by nestedness. There is a strong correlation between taxonomic and phylogenetic β-diversity. However, the correlations of functional with both taxonomic and phylogenetic β-diversity were relatively weak. The findings of variation partitioning suggested that distinct facets and components of macroinvertebrates’ β-diversity were impacted by abiotic factors to varying degrees. The contribution of spatial factors was greater than that of the local environment and geo-climatic factors for taxonomic, functional, and phylogenetic β-diversity. Thus, studying different facets and components of β-diversity allows a clearer comprehension of the influence of abiotic factors on diversity patterns. Therefore, future research should investigate patterns and mechanisms of β-diversity from taxonomic, functional, and phylogenetic perspectives.

Evaluating macroinvertebrate metrics for ecological assessment of large saline rivers (Argentina)

Benthic macroinvertebrates have been used around the world as indicators of the biological quality of freshwater habitats. Because of the intensive deterioration of waterbodies as a result of different land uses, indicators are used for environmental monitoring, control and remediation. The aim of this study was to assess (1) the sensitivity of taxonomical metrics and (2) functional traits to select the most appropriate for evaluating environmental impacts on rivers with high salinity and (3) to propose a multimetric index based on the selected metrics. Information from a preexisting database on twenty-eight sites in the Salado River basin (Argentina) was used. One hundred and twenty-three metrics were calculated to assess sensitivity to different land uses along the gradient of habitat condition, from low-disturbed (reference), to medium-disturbed (agricultural and industrial) and high-disturbed (agricultural, industrial and urban). This gradient was defined by available information in original articles and by quantifying the percentage of the different land uses. Filtering collectors (%), Gathering collectors (%), Ostracoda density, Limnodrilus hoffmeisteri/Total density, Naididae (%), Tubifex/Total density and Pristina/Total density were the metrics that distinguished the different land uses along the gradient of habitat condition. These metrics were used to propose a macroinvertebrate multimetric index in saline rivers: Index of Benthic Invertebrates in Saline Rivers (IBIS). Thus, this study provides a useful tool for management and monitoring of saline rivers and diagnoses of salinized environments.

Damming affects riverine macroinvertebrate metacommunity dynamics: Insights from taxonomic and functional beta diversity

Understanding ecological processes that drive metacommunity dynamics is essential for elucidating the mechanisms of community assembly and for guiding biodiversity conservation. This is especially important in dammed rivers. Here, we examined the taxonomic and functional beta diversity of macroinvertebrates and their underlying drivers in a dammed tropical river and compared the patterns with those in an adjacent undammed river. We found that both taxonomic and functional beta diversities were higher in the dammed river than in the undammed river across wet and dry seasons. The replacement component contributed most to the overall beta diversity for both taxonomic and functional facets, and this component was higher in the dammed river than in the undammed river. In addition, the taxonomic richness difference component was significantly higher in the dammed river in the dry season, but the functional richness difference component showed no difference between the two rivers and between the two seasons. Environmental filtering was the primary driver of total beta diversity and its replacement component, whereas the richness difference component was mainly explained by spatial factors, but these drivers varied in the dammed river in different seasons. Overall, our results indicated that damming induced changes in physiochemical variables (e.g., temperature, conductivity, and nutrients), accompanied by alterations in flow regime and longitudinal connectivity, increased replacement and loss of taxa or traits. These changes have consequently led to alteration of macroinvertebrate taxonomic and functional community dissimilarity and affected the relative effects of environmental and spatial factors on beta diversity and its components. Our study helps understand the ecological processes associated with dam impacts on macroinvertebrate biodiversity and the conservation potential of undammed rivers. In addition, our results showed that taxonomic and functional beta diversities can provide complementary information about dam impacts on riverine biodiversity.

Ecoregions, climate, topography, physicochemical, or a combination of all: Which criteria are the best to define river types based on abiotic variables and macroinvertebrates in neotropical rivers?

The baseline conditions for a particular river or stream type are essential to classify aquatic ecosystems based on physical and biological characteristics. In this study, we proposed a river typology for different ecoregions, climate and topography of northwestern Argentina using parameters, and combined key variables to establish reference conditions. A set of geographical, hydro-morphological, hydrological, geological (pedology and sedimentology) and physicochemical variables were measured from different rivers and analyzed with clustering and ordination techniques to develop a typology. We analyzed the correspondence of the physical river conditions and benthic macroinvertebrate assemblages using non-metric multidimensional scaling analysis, dissimilarity among assemblages, ANOSIM approach and envfit analysis in order to make an ecological validation of the classification. Our results allowed us to classify the neotropical rivers studied, according to typological systems adapted from the European Water Framework Directive. The combination of ecoregions and topography along with other variables associated (system B), was better corresponded with biological arrangements. Hence, ecoregions and topography combined turned out to be more precise as a criterion to define river types and their local abiotic and biotic reference conditions. Macroinvertebrate distribution corresponded with the classifications proposed and was related with abiotic features of the rivers. The physical variables as altitude, grain size, water temperature and turbidity were key parameters to develop a schematic model to define river types that could be implemented and tested in other countries of the region. Five river types have been identified, characterized, and included in three large groups: Mountains, Foothills, and Lowlands (Plains). Our results showed that topography and climate are two aspects that strongly influence South American freshwater biota. We propose the schematic model developed in our study as a baseline to define freshwater biomes based on altitude (topography), ecoregions (climate) and biological functional traits at a broad spatial scale (continental or global).

Untangling the assembly of macrophyte metacommunities by means of taxonomic, functional and phylogenetic beta diversity patterns

Metacommunity ecology has broadened considerably with the recognition that measuring beta diversity beyond the purely taxonomic viewpoint may improve our understanding of the dispersal- and niche-based mechanisms across biological communities. In that perspective, we applied a novel multidimensional approach including taxonomic, functional and phylogenetic data to enhance our basic understanding of macrophyte metacommunity dynamics. For each beta diversity metric, we calculated the mean overall value and tested whether the mean value was different from that expected by chance using null models. We also employed evolutionary and spatially constrained models to first identify the degree to which the studied functional traits showed a phylogenetic signal, and then to estimate the relative importance of spatial and environmental effects on metacommunity structure. We first found that most individual ponds were inhabited by species that were merely random draws from the taxonomic and phylogenetic species pool available in the study region. Contrary to our expectations, not all measured traits were conserved along the phylogeny. We also showed that trait and phylogenetic dimensions strongly increased the amount of variation in beta diversity that can be explained by degree of environmental filtering and dispersal limitation. This suggests that accounting for functional traits and phylogeny in metacommunity ecology helps to explain idiosyncratic patterns of variation in macrophyte species distribution. Importantly, phylogenetic and functional analyses identified the influence of underlying mechanisms that would otherwise be missed in an analysis of taxonomic turnover. Together, these results let us conclude that macrophyte species have labile functional traits adapted to dispersal-based processes and some evolutionary trade-offs that drive community assembly via species sorting. Overall, our exploration of different facets of beta diversity showed how functional and phylogenetic information may be used with species-level data to test community assembly hypotheses that are more ecologically meaningful than assessments of environmental patterns based on the purely taxonomic viewpoint.

Ecological drivers of alpha and beta diversity of freshwater invertebrates in arid and semiarid Patagonia (Argentina)

Freshwater biodiversity is showing a global decline in relation to environmental change and there is an urgent need to quantify different facets of biodiversity to assess the conservation value of freshwater ecosystems. Identifying the ecological drivers of arid and semiarid Patagonian waterbodies is a critical requirement for planning action to conserve these still poorly understood habitats. We tested the responses of alpha and beta diversity of invertebrates (presence-absence, abundance, and biomass) to local, landscape, and climatic features, in 45 Patagonian freshwater bodies classified in three groups: isolated ponds, connected ponds, and lotic systems. We first compared the invertebrate community compositions of the different waterbodies. Secondly, using a co-inertia analysis we assessed the relative roles of local, landscape and climatic factors in driving variation in assemblage composition. Finally, we compared different facets of beta diversity and modelled their responses to environmental variables (predictors), by generalized dissimilarity modelling (GDM). Unexpectedly, lotic systems with a total of 109 taxa, were richer than lentic ones, but isolated ponds contributed most to beta diversity and supported more unique and proportionally more endemic species. Alpha and beta diversity were mainly driven by local features and secondly by climatic descriptors. However, these patterns shifted according to different community composition measures. Collectively, our results suggest that isolated ponds have a higher biodiversity value and would be more vulnerable than connected ponds and lotic systems to environmental changes. However, all waterbody types contributed to gamma biodiversity, reinforcing the importance of conserving a diversity of freshwater ecosystems in any landscape and particularly in arid and semiarid Patagonia. Our findings are a first step to resolving and quantifying the amount of changes occurring in Patagonian waterbodies, and are a prerequisite for predicting changes in species distributions in the face of global change.