Partitioning global patterns of freshwater fish beta diversity reveals contrasting signatures of past climate changes

Here, we employ an additive partitioning framework to disentangle the contribution of spatial turnover and nestedness to beta diversity patterns in the global freshwater fish fauna. We find that spatial turnover and nestedness differ geographically in their contribution to freshwater fish beta diversity, a pattern that results from contrasting influences of Quaternary climate changes. Differences in fish faunas characterized by nestedness are greater in drainage basins that experienced larger amplitudes of Quaternary climate oscillations. Conversely, higher levels of spatial turnover are found in historically unglaciated drainage basins with high topographic relief, these having experienced greater Quaternary climate stability. Such an historical climate signature is not clearly detected when considering the overall level of beta diversity. Quantifying the relative roles of historical and ecological factors in explaining present-day patterns of beta diversity hence requires considering the different processes generating these patterns and not solely the overall level of beta diversity.     

Partitioning the turnover and nestedness components of beta diversity

Aim  Beta diversity (variation of the species composition of assemblages) may reflect two different phenomena, spatial species turnover and nestedness of assemblages, which result from two antithetic processes, namely species replacement and species loss, respectively. The aim of this paper is to provide a unified framework for the assessment of beta diversity, disentangling the contribution of spatial turnover and nestedness to beta-diversity patterns.
Innovation  I derive an additive partitioning of beta diversity that provides the two separate components of spatial turnover and nestedness underlying the total amount of beta diversity. I propose two families of measures of beta diversity for pairwise and multiple-site situations. Each family comprises one measure accounting for all aspects of beta diversity, which is additively decomposed into two measures accounting for the pure spatial turnover and nestedness components, respectively. Finally, I provide a case study using European longhorn beetles to exemplify the relevance of disentangling spatial turnover and nestedness patterns.
Main conclusion  Assigning the different beta-diversity patterns to their respective biological phenomena is essential for analysing the causality of the processes underlying biodiversity. Thus, the differentiation of the spatial turnover and nestedness components of beta diversity is crucial for our understanding of central biogeographic, ecological and conservation issues.     

The role of habitat and daily activity patterns in explaining the diversity of mountain Neotropical dung beetle assemblages

The interaction between land use and climate change is expected to strongly affect species distributions along high elevation landscapes. We aimed to test the effect of climatic variables on community metrics among five types of land use in a high elevation landscape. We described dung beetle spatial and temporal taxonomic and functional diversity patterns, and partitioned β‐diversity into turnover and nestedness components. The interaction between land use and daily period of activity mostly drives abundance, functional richness and functional diversity, but not dung beetle species richness. Unlike Neotropical lowlands, species richness and abundance in open environments are similar to those existing in forests. Temperature is an important predictor of abundance and functional divergence. There is a higher spatial component of the taxonomic β‐diversity, which is highly driven by species turnover. The temporal component of the taxonomic β‐diversity was strongly driven by nestedness, where night assemblages are sub‐sets, although not entirely, of diurnal assemblages. For functional diversity, the temporal β‐diversity was much higher than the spatial β‐diversity, but both were similarly represented by functional group turnover and nestedness. The composition of nocturnal and diurnal assemblages is clearly different, even more than the differences observed between habitats. However, taxonomic turnover is the dominant force between sampling sites while nestedness dominates the daily pattern. This means that forest habitats are unlikely to act as shelters for grassland species under a scenario of rising temperature.     

Contrasting patterns and mechanisms of spatial turnover for native and exotic freshwater fish in Europe

Aim We compare the distribution patterns of native and exotic freshwater fish in Europe, and test whether the same mechanisms (environmental filtering and/or dispersal limitation) govern patterns of decrease in similarity of native and exotic species composition over geographical distance (spatial species turnover). Locations Major river basins of Europe. Methods Data related to geography, habitat diversity, regional climate and species composition of native and exotic freshwater fish were collated for 26 major European river basins. We explored the degree of nestedness in native and exotic species composition, and quantified compositional similarity between river basins according to the beta‐sim (independent of richness gradient) and Jaccard (dependent of richness gradient) indices of similarity. Multiple regression on distance matrices and variation‐partitioning approaches were used to quantify the relative roles of environmental filtering and dispersal limitation in shaping patterns of decreasing compositional similarity over geographical distance. Results Native and exotic species exhibited significant nested patterns of species composition, indicating that differences in fish species composition between river basins are primarily the result of species loss, rather than species replacement. Both native and exotic compositional similarity decreased significantly with increasing geographical distance between river basins. However, gradual changes in species composition with geographical distance were found only for exotic species. In addition, exotic species displayed a higher rate of similarity decay (higher species turnover rate) with geographical distance, compared with native species. Lastly, the majority of explained variation in exotic compositional similarity was uniquely related to geography, whereas native compositional similarity was either uniquely explained by geography or jointly explained by environment and geography. Main conclusions Our study suggests that large‐scale patterns of spatial turnover for exotic freshwater fish in Europe are generated by human‐mediated dispersal limitation, whereas patterns of spatial turnover for native fish result from both dispersal limitation relative to historical events (isolation by mountain ranges, glacial history) and environmental filtering.     

A meta‐analysis of nestedness and turnover components of beta diversity across organisms and ecosystems

Aim

The number of studies investigating the nestedness and turnover components of beta diversity has increased substantially, but our general understanding of the drivers of turnover and nestedness remains elusive. Here, we examined the effects of species traits, spatial extent, latitude and ecosystem type on the nestedness and turnover components of beta diversity.

Location

Global.

Time period

1968–2017.

Major taxa studied

From bacteria to mammals.

Methods

From the 99 studies that partition total beta diversity into its turnover and nestedness components, we assembled 269 and 259 data points for the pairwise and multiple site beta‐diversity metrics, respectively. Our data covered a broad variation in species dispersal type, body size and trophic position. The data were from freshwater, marine and terrestrial realms, and encompassed geographical areas from the tropics to near polar regions. We used linear modelling as a meta‐regression tool to analyse the data.

Results

Pairwise turnover, multiple site turnover and total beta diversity all decreased significantly with latitude. In contrast, multiple site nestedness showed a positive relationship with latitude. Beta‐diversity components did not generally differ among the realms. The turnover component and total beta diversity increased with spatial extent, whereas nestedness was scale invariant for pairwise metrics. Multiple site beta‐diversity components did not vary with spatial extent. Surprisingly, passively dispersed organisms had lower turnover and total beta diversity than flying organisms. Body size showed a relatively weak relationship with beta diversity but had important interactions with trophic position, thus also affecting beta diversity via interactive effects. Producers had significantly higher average pairwise turnover and total beta diversity than carnivores.

Main conclusions

The present results provide evidence that species turnover, being consistently the larger component of total beta diversity, and nestedness are related to the latitude of the study area and intrinsic organismal features. We showed that two beta‐diversity components had generally opposing patterns with regard to latitude. We highlight that beta‐diversity partition may give additional insights into the underlying causes of spatial variability in biotic communities compared with total beta diversity alone.     

Beta diversity of stream fish assemblages: partitioning variation between spatial and environmental factors

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Environmental heterogeneity and dispersal limitation explain different aspects of β‐diversity in Neotropical fish assemblages

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Riverine networks constrain β‐diversity patterns among fish assemblages in a large Neotropical river

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Combining projected changes in species richness and composition reveals climate change impacts on coastal Mediterranean fish assemblages

Species Temporal Turnover (STT) is one of the most familiar metrics to assess changes in assemblage composition as a consequence of climate change. However, STT mixes two components in one metric, changes in assemblage composition caused by a process of species loss or gain (i.e. the nestedness component) and changes in assemblage composition caused by a process of species replacement (i.e. the species replacement component). Drawing on previous studies investigating spatial patterns of beta diversity, we propose measures of STT that allow analysing each component (species replacement vs. nestedness), separately. We also present a mapping strategy to simultaneously visualize changes in species richness and assemblage composition. To illustrate our approach, we used the Mediterranean coastal fish fauna as a case study. Using Bioclimatic Envelope Models (BEMs) we first projected the potential future climatic niches of 288 coastal Mediterranean fish species based on a global warming scenario. We then aggregated geographically the species‐level projections to analyse the projected changes in species richness and composition. Our results show that projected changes in assemblage composition are caused by different processes (species replacement vs. nestedness) in several areas of the Mediterranean Sea. In addition, our mapping strategy highlights that the coastal fish fauna in several regions of the Mediterranean Sea could experience a ‘cul‐de‐sac’ effect if exposed to climate warming. Overall, the joint exploration of changes in species richness and composition coupled with the distinction between species replacement and nestedness bears important information for understanding the nature of climate change impacts on biodiversity. These methodological advances should help decision‐makers in prioritizing action in the areas facing the greatest vulnerability to climate.     

Environmental drivers of ant species richness and composition across the Argentine Pampas grassland

Understanding the underlying mechanisms causing diversity patterns is a fundamental objective in ecology and science‐based conservation biology. Energy and environmental‐heterogeneity hypotheses have been suggested to explain spatial changes in ant diversity. However, the relative roles of each one in determining alpha and beta diversity patterns remain elusive. We investigated the main factors driving spatial changes in ant (Hymenoptera, Formicidae) species richness and composition (including turnover and nestedness components) along a 500 km longitudinal gradient in the Pampean region of Argentina. Ants were sampled using pitfall traps in 12 sample sites during the summer. We performed a model selection approach to analyse responses of ant richness and composition dissimilarity to environmental factors. Then, we computed a dissimilarity partitioning of the contributions of spatial turnover and nestedness to total composition dissimilarity. Temporal habitat heterogeneity and temperature were the primary factors explaining spatial patterns of epigean ant species richness across the Pampas. The distance decay in species composition similarity was best accounted by temperature dissimilarity, and turnover had the greatest contribution to the observed beta diversity pattern. Our findings suggest that both energy and environmental‐heterogeneity‐related variables are key factors shaping richness patterns of ants and niche‐based processes instead of neutral processes appear to be regulating species composition of ant assemblages. The major contribution of turnover to the beta diversity pattern indicated that lands for potential reconversion to grassland should represent the complete environmental gradient of the Pampean region, instead of prioritizing a single site with high species richness.     

小兴安岭阔叶红松林地表甲虫Beta多样性

Beta多样性用来衡量集群内物种组成的变异性,可以被分解为空间物种转换和物种集群镶嵌两个组分,是揭示群落构建机制的重要基础。目前开展了较多的地上生态系统beta多样性研究,然而地下生态系统beta多样性进展缓慢。以小兴安岭凉水和丰林自然保护区为研究地区,于2015年8、10月采用陷阱法对阔叶红松林进行调查,揭示地表甲虫(步甲科、隐翅虫科、葬甲科)的beta多样性。结果表明:(1)凉水共发现39种、856只地表甲虫,丰林共发现43种、1182只地表甲虫。8月凉水明显具有较高的全部甲虫(三个科的总和)物种多样性和丰富度,10月正好相反。(2)凉水和丰林之间地表甲虫beta多样性的差异仅发现于8月的步甲科和葬甲科之间。(3)凉水和丰林地表甲虫的beta多样性主要由空间物种转换组成,物种集群镶嵌对beta多样性的贡献很小,说明地表甲虫物种组成变异主要由本地物种之间较高的转换引起。研究表明小兴安岭阔叶红松林地表甲虫的beta多样性主要由空间物种转换组成,在揭示群落构建机制过程中,其内部物种交换和环境调控不容忽视。     

Climate drives temporal replacement and nested‐resultant richness patterns of Scottish coastal vegetation

Beta diversity quantifies spatial and/or temporal variation in species composition. It is comprised of two distinct components, species replacement and nestedness, which derive from opposing ecological processes. Using Scotland as a case study and a β‐diversity partitioning framework, we investigate temporal replacement and nestedness patterns of coastal grassland species over a 34‐yr time period. We aim to 1) understand the influence of two potentially pivotal processes (climate and land‐use changes) on landscape‐scale (5 × 5 km) temporal replacement and nestedness patterns, and 2) investigate whether patterns from one β‐diversity component can mask observable patterns in the other. We summarised key aspects of climate driven macro‐ecological variation as measures of variance, long‐term trends, between‐year similarity and extremes, for three important climatic predictors (minimum temperature, water‐balance and growing degree‐days). Shifts in landscape‐scale heterogeneity, a proxy of land‐use change, was summarised as a spatial multiple‐site dissimilarity measure. Together, these climatic and spatial predictors were used in a multi‐model inference framework to gauge the relative contribution of each on temporal replacement and nestedness patterns. Temporal β‐diversity patterns were reasonably well explained by climate change but weakly explained by changes in landscape‐scale heterogeneity. Climate was shown to have a greater influence on temporal nestedness than replacement patterns over our study period, linking nestedness patterns, as a result of imbalanced gains and losses, to climatic warming and extremes respectively. Important climatic predictors (i.e. growing degree‐days) of temporal β‐diversity were also identified, and contrasting patterns between the two β‐diversity components revealed. Results suggest climate influences plant species recruitment and establishment processes of Scotland's coastal grasslands, and while species extinctions take time, they are likely to be facilitated by climatic perturbations. Our findings also highlight the importance of distinguishing between different components of β‐diversity, disentangling contrasting patterns than can mask one another.     

Effects of dispersal mode on the environmental and spatial correlates of nestedness and species turnover in pond communities

Advances in metacommunity theory have made a significant contribution to understanding the drivers of variation in biological communities. However, there has been limited empirical research exploring the expression of metacommunity theory for two fundamental components of beta diversity: nestedness and species turnover. In this paper, we examine the influence of local environmental and a range of spatial variables (hydrological connectivity, proximity and overall spatial structure) on total beta diversity and the nestedness and turnover components of beta diversity for the entire macroinvertebrate community and active and passively dispersing taxa within pond habitats. High beta diversity almost entirely reflects patterns of species turnover (replacement) rather than nestedness (differences in species richness) in our dataset. Local environmental variables were the main drivers of total beta diversity, nestedness and turnover when the entire community was considered and for both active and passively dispersing taxa. The influence of spatial processes on passively dispersing taxa, total beta diversity and nestedness was significantly greater than for actively dispersing taxa. Our results suggest that species sorting (local environmental variables) operating through niche processes was the primary mechanism driving total beta diversity, nestedness and turnover for the entire community and active and passively dispersing taxa. In contrast, spatial factors (hydrological connectivity, proximity and spatial eigenvectors) only exerted a secondary influence on the nestedness and turnover components of beta diversity.     

Temporal changes in fish diversity in lotic and lentic environments along a reservoir cascade

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Contrasted impacts of climate change on stream fish assemblages along an environmental gradient

Aim To investigate the potential impacts of climate change on stream fish assemblages in terms of species and biological trait diversity, composition and similarity. Location One‐thousand one‐hundred and ten stream sections in France. Methods We predicted the future potential distribution of 35 common stream fish species facing changes in temperature and precipitation regime. Seven different species distribution models were applied and a consensus forecast was produced to limit uncertainty between single‐models. The potential impacts of climate change on fish assemblages were assessed using both species and biological trait approaches. We then addressed the spatial distribution of potential impacts along the upstream–downstream gradient. Results Overall, climate change was predicted to result in an increase in species and trait diversity. Species and trait composition of the fish assemblages were also projected to be highly modified. Changes in assemblages’ diversity and composition differed strongly along the upstream–downstream gradient, with upstream and midstream assemblages more modified than downstream assemblages. We also predicted a global increase in species and trait similarity between pairwise assemblages indicating a future species and trait homogenization of fish assemblages. Nevertheless, we found that upstream assemblages would differentiate, whereas midstream and downstream assemblages would homogenize. Our results suggested that colonization could be the main driver of the predicted homogenization, while local extinctions could result in assemblage differentiation. Main conclusions This study demonstrated that climate change could lead to contrasted impacts on fish assemblage structure and diversity depending on the position along the upstream–downstream gradient. These results could have important implications in terms of ecosystem monitoring as they could be useful in establishing areas that would need conservation prioritization.     

Contrasting metacommunity structure and beta diversity in an aquatic‐floodplain system

Habitat connectivity and dispersal interact to structure metacommunities, but few studies have examined these patterns jointly for organisms across the aquatic–terrestrial ecotone. We assessed metacommunity structure and beta diversity patterns of instream benthic invertebrates, riparian carabid beetles (Order: Coleoptera; Family: Carabidae) and riparian spiders (Order: Araneae) at fifteen sites in a river‐floodplain system. Sampling took place over a three‐year period (2010–2012) in the Rhine‐Main‐Observatory LTER site on the Kinzig River, central Germany. This allowed disentangling the combined influence, and temporal variability, of habitat connectivity (i.e. between aquatic and terrestrial) and dispersal ability (i.e. between spiders and beetles, and aerial and aquatic dispersing invertebrates) on the dominant paradigms structuring these metacommunities. We found mostly consistent differences in the manner that metacommunities were structured between groups, with lower levels of variability explained for beetles compared to the other groups. Beetles were consistently structured more by turnover than nestedness components, with greater beta diversity than expected by chance and a minor spatial compared to environmental signal emerging with variance partitioning. Conversely, spiders and benthic invertebrates had lower beta diversity and greater nestedness than null expectation, and a clearer spatial signal controlling metacommunity structure. Our results suggest varying levels of mass effects and species sorting shape river‐floodplain metacommunities, depending on habitat connectivity and dispersal ability. That is, greater connectivity and lower fragmentation along the river compared to the terrestrial zone promoted mass effects, and differences in overall dispersal ability and mode (i.e. active and passive) for instream and riparian communities shifted paradigms between mass effects and species sorting.     

Biodiversity pattern of fish assemblages in Poyang Lake Basin: Threat and conservation

Poyang Lake Basin is of great importance to maintain regional ecological balance. However, fish biodiversity in this basin has rapidly declined as the result of anthropogenic habitat alteration, such as dam construction, sand mining, and water pollution. Here, we aimed to analyze the temporal and spatial changes in biodiversity patterns of fish in Poyang Lake Basin over the last 37 years. The number of fish species underwent a significant decrease in the current period. In particular, 36.7% of the migration of fish was extirpated. Twenty‐seven fish species have been formally assessed using the Chinese Red List were currently listed as Critically Endangered (9), Endangered (3), Vulnerable (10), and Near Threatened (5). Alpha and gamma diversity revealed that fish diversity had also decreased, and beta diversity showed significant composition dissimilarity in two periods. PCoA showed that the historical fish composition dissimilarity was significantly different from that of the current period. We found a significant effect of the geographical distance on the spatial turnover component for the historical and current periods. In addition, the nestedness component was the main contributor to beta diversity, which indicated one large protected area should be established in Poyang Lake and the Ganjiang River Basin with higher species richness. These results indicated that fish biodiversity declined in the current period likely caused by anthropogenic habitat alteration and other threatened factors. Therefore, we suggest that the habitat reconstruction and biodiversity conservation for fish have become imperative in this basin, and a complete management plan should be carried out.     

Temporal variation in phytoplankton beta diversity patterns and metacommunity structures across subtropical reservoirs

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A macroecological perspective of diversity patterns in the freshwater realm

1. The aim of this paper is to review literature on species diversity patterns of freshwater organisms and underlying mechanisms at large spatial scales. 2. Some freshwater taxa (e.g. dragonflies, fish and frogs) follow the classical latitudinal decline in regional species richness (RSR), supporting the patterns found for major terrestrial and marine organism groups. However, the mechanisms causing this cline in most freshwater taxa are inadequately understood, although research on fish suggests that energy and history are major factors underlying the patterns in total species and endemic species richness. Recent research also suggests that not all freshwater taxa comply with the decline of species richness with latitude (e.g. stoneflies, caddisflies and salamanders), but many taxa show more complex geographical patterns in across‐regions analyses. These complexities are even more profound when studies of global, continental and regional extents are compared. For example, clear latitudinal gradients may be present in regional studies but absent in global studies (e.g. macrophytes). 3. Latitudinal gradients are often especially weak in the across‐ecosystems analyses, which may be attributed to local factors overriding the effects of large‐scale factors on local communities. Nevertheless, local species richness (LSR) is typically linearly related to RSR (suggesting regional effects on local diversity), although saturating relationships have also been found in some occasions (suggesting strong local effects on diversity). Nestedness has often been found to be significant in freshwater studies, yet this pattern is highly variable and generally weak, suggesting also a strong beta diversity component in freshwater systems. 4. Both geographical location and local environmental factors contribute to variation in alpha diversity, nestedness and beta diversity in the freshwater realm, although the relative importance of these two groups of explanatory variables may be contingent on the spatial extent of the study. The mechanisms associated with spatial and environmental control of community structure have also been inferred in a number of studies, and most support has been found for species sorting (possibly because many freshwater studies have species sorting as their starting point), although also dispersal limitation and mass effects may be contributing to the patterns found. 5. The lack of latitudinal gradients in some freshwater taxa begs for further explanations. Such explanations may not be gained for most freshwater taxa in the near future, however, because we lack species‐level information, floristic and faunistic knowledge, and standardised surveys along extensive latitudinal gradients. A challenge for macroecology is thus to use the best possible species‐level information on well‐understood groups (e.g. fish) or use surrogates for species‐level patterns (e.g. families) and then develop hypotheses for further testing in the freshwater realm. An additional research challenge concerns understanding patterns and mechanisms associated with the relationships between alpha, beta and gamma components of species diversity. 6. Understanding the mechanistic basis of species diversity patterns should preferably be based on a combination of large‐scale macroecological and landscape‐scale metacommunity research. Such a research approach will help in elucidating patterns of species diversity across regional and local scales in the freshwater realm.     

Cross-Scale Responses of Biodiversity to Hurricane and Anthropogenic Disturbance in a Tropical Forest

Abstract In studies of biodiversity, considerations of scale—the spatial or temporal domain to which data provide inference—are important because of the non-arithmetic manner in which species richness increases with area (and total abundance) and because fine-scale mechanisms (for example, recruitment, growth, and mortality of species) can interact with broad scale patterns (for example, habitat patch configuration) to influence dynamics in space and time. The key to understanding these dynamics is to consider patterns of environmental heterogeneity, including patterns produced by natural and anthropogenic disturbance. We studied how spatial variation in three aspects of biodiversity of terrestrial gastropods (species richness, species diversity, and nestedness) on the 16-ha Luquillo Forest Dynamics Plot (LFDP) in a tropical forest of Puerto Rico was affected by disturbance caused by Hurricanes Hugo and Georges, as well as by patterns of historic land use. Hurricane-induced changes in spatial organization of species richness differed from those for species diversity. The gamma components of species richness changed after the hurricanes and were significantly different between Hurricanes Hugo and Georges. Alpha and two beta components of species richness, one related to turnover among sites within areas of similar land use and one related to variation among areas of different land use, varied randomly over time after both hurricanes. In contrast, gamma components of species diversity decreased in indistinguishable manners after both hurricanes, whereas the rates of change in the alpha component of species diversity differed between hurricanes. Beta components of diversity related to turnover among sites declined after both hurricanes in a consistent fashion. Those related to turnover among areas with different historic land uses varied stochastically. The immediate effect of hurricanes was to reduce nestedness of gastropod assemblages. Thereafter, nestedness increased during post-hurricane secondary succession, and did so in the same way, regardless of patterns of historic land use. The rates of change in degree of nestedness during secondary succession were different after each hurricane as a result of differences in the severity and extent of the hurricane-induced damage. Our analyses quantified temporal changes in the spatial organization of biodiversity of gastropod assemblages during forest recovery from hurricane-induced damage in areas that had experienced different patterns of historic human land use, and documented the dependence of biodiversity on spatial scale. We hypothesize that cross-scale interactions, likely those between the local demographics of species at the fine scale and the landscape configuration of patches at the broad scale, play a dominant role in affecting critical transfer processes, such as dispersal, and its interrelationship with aspects of biodiversity. Cross-scale interactions have significant implications for the conservation of biodiversity, as the greatest threats to biodiversity arise from habitat modification and fragmentation associated with disturbance arising from human activities.