Utilization of species checklist data in revealing the spatial distribution of fish diversity

Marine fish species checklists from six Chinese coastal waters were combined for the analysis of taxonomic diversity. The Genus-Family index (G-F index) ranged between 0.39 and 0.84, which generally indicated a decreasing trend with increasing latitude, with the exception of the southernmost area. Average taxonomic distinctness showed a slight increasing trend from northern to central study areas, but whether the taxonomic distinctness indices represent a latitudinal gradient of biodiversity requires further study. The multivariate analysis revealed a distinct latitudinal variation in fish assemblages. These results indicate that species checklist data are helpful in understanding the diversity distribution of fish species in the coastal zone. The potential of a species inventory should be exploited to fully understand biodiversity.     

Measuring ecosystem degradation through half a century of fish species introductions and extirpations in a large isolated lake

The introduction of exotic species and the extirpation of native species that occurred during the past two centuries have strongly modified the structure of most plant and animal assemblages across the globe. Such a biotic change is particularly marked in isolated environments such as islands or isolated lakes. Most studies reported drastic changes between before and after human disturbances, but the dynamics of change in assemblage structure through the invasion and extirpation processes are rarely reported. Here we measured the aquatic ecosystem degradation through exotic species introduction and native species extirpation experienced by Lake Erhai (China) during the last 50 years using structural, functional and taxonomic distinctness biodiversity indices. Structural diversity (species richness) did not varied monotonically along the temporal gradient, due to an opposite trend between exotic species increase and a concomitant decline of native species richness. Functional diversity displayed unclear ascending trends driven by the introduction of exotic species having distinct functional traits than natives. Taxonomic distinctness indices exhibited an increase of the average taxonomic distinctness (Δ⁺), but a decrease of the variation in taxonomic distinctness (Λ⁺) through time. Structural, functional and distinctness indices providing complementary information on ecosystem degradation, we here proposed a new multifaceted degradation index integrating these three facets of biodiversity. Such an index provided an accurate representation of the faunistic changes experienced by Lake Erhai and might constitute a comprehensive way to measure ecosystem degradation through exotic fish species introductions and native fish species extirpations.     

江湖阻隔对长江中下游湖泊鱼类群落分类多样性的影响

基于1950s以来的长江中下游湖泊鱼类调查数据,分析通江湖泊与阻隔湖泊的鱼类分类多样性差异,以及通江和阻隔湖泊鱼类分类多样性的时间序列变化,探讨江湖阻隔对鱼类多样性的影响。结果显示,阻隔湖泊鱼类物种数、平均分类差异指数(Δ⁺)和分类差异变异指数(Λ⁺)平均值分别为48.47±14.64、74.02±3.09和736.89±33.80;通江湖泊为76.22±14.40、78.31±0.98和697.31±25.53。阻隔湖泊物种数和Δ⁺值显著低于通江湖泊(P<0.001),而阻隔湖泊Λ⁺值显著高于通江湖泊(P=0.002),表明阻隔湖泊物种间亲缘关系更近,均匀度下降,即物种分类单元减少,且集中分布于某几个分类阶元,稳定性变差。典型通江与阻隔湖泊鱼类群落分类多样性的时间变化分析发现,两种类型湖泊的鱼类物种数和Δ⁺值均随时间推移整体呈现下降趋势,Λ⁺值整体呈现升高趋势;并且阻隔湖泊的Λ+值随阻隔时间增加而大幅上升,Δ⁺和Λ^+...     

Taxonomic distinctness and species richness as measures of functional structure in bird assemblages

Most traditional "biodiversity" indices have an uncertain ecological interpretation, unfavourable sampling properties, and excessive data requirements. A new index of taxonomic distinctness (the average evolutionary distance between species in an assemblage) has many advantages over traditional measures, but its ecological interpretation remains unclear. We used published behavioural species data in conjunction with bird atlas data to quantify simple functional metrics (the fraction of species engaged in non-competitive interactions, and the average between-species disparity in habitat preferences) for breeding-bird assemblages in Europe and North America. We then analysed correlations of functional metrics with taxonomic distinctness and species richness, respectively. All functional metrics had weak, positive correlations with species richness. In contrast, correlations between functional metrics and taxonomic distinctness ranged from slightly negative to strongly positive, depending on the relative habitat heterogeneity, and on the resource involved in the between-species interaction. Strong positive correlations between taxonomic distinctness and the fraction of interactive species occurred for resources with few producer species per consumer species, and we suggest that taxonomic distinctness is consistently correlated with conservation worth. With its favourable sampling properties and data requirements, this taxonomic distinctness measure is a promising tool for biodiversity research and for environmental monitoring and management.     

Patterns in freshwater diatom taxonomic distinctness along an eutrophication gradient

1. A variety of species richness measures have been used to assess the effects of environmental degradation on biodiversity. Such measures can be highly influenced by sample size, sampling effort, habitat type or complexity, however, and typically do not show monotonic responses to human impact. In addition to being independent of the degree of sampling effort involved in data acquisition, effective measures of biodiversity should reflect the degree of taxonomical relatedness among species within ecological assemblages and provide a basis for understanding observed diversity for a particular habitat type. Taxonomic diversity or distinctness indices emphasize the average taxonomic relatedness (i.e. degree of taxonomical closeness) between species in a community. 2. Eutrophication of freshwater ecosystems, mainly due to the increased availability of nutrients, notably phosphorus, has become a major environmental problem. Two measures of taxonomic distinctness (Average Taxonomic Distinctness and Variation in Taxonomic Distinctness) were applied to surface sediment diatoms from 45 lakes across the island of Ireland to examine whether taxonomic distinctness and nutrient enrichment were significantly related at a regional scale. The lakes span a range of concentrations of epilimnic total phosphorus (TP) and were grouped into six different types, based on depth and alkalinity levels, and three different categories according to trophic state (ultra‐oligotrophic and oligotrophic; mesotrophic; and eutrophic and hyper‐eutrophic). 3. The taxonomic distinctness measures revealed significant differences among lakes in the three different classes of trophic state, with nutrient‐rich lakes generally more taxonomically diverse than nutrient‐poor lakes. This implies that enrichment of oligotrophic lakes does not necessarily lead to a reduction in taxonomic diversity, at least as expressed by the indices used here. Furthermore, taxonomic distinctness was highly variable across the six different lake types regardless of nutrient level. 4. Results indicate that habitat availability and physical structure within the study lakes also exert a strong influence on the pattern of taxonomic diversity. Overall the results highlight problems with the use of taxonomic diversity measures for detecting impacts of freshwater eutrophication based on diatom assemblages.     

Can taxonomic distinctness assess anthropogenic impacts in inland waters? A case study from a Mediterranean river basin

1. It is increasingly recognised that adequate measures of biodiversity should include information on the ‘relatedness’ of species within ecological assemblages, or the phylogenetic levels at which diversity is expressed. Taxonomic distinctness measures provide a series of indices to achieve this, which are independent of sample size. Taxonomic distinctness has been employed widely in marine systems, where it has been suggested that this index can provide a reliable measure of anthropogenic impact. 2. We tested the behaviour of three related taxonomic distinctiveness indices (Average Taxonomic Distinctness, Δ⁺; Variation in Taxonomic Distinctness, Λ⁺; and Total Taxonomic Distinctness, sΔ⁺) in relation to putative levels of anthropogenic impact in inland waters and their potential utility in environmental monitoring, using an extensive data set for aquatic beetles from the south‐east of the Iberian Peninsula. 3. Taxonomic distinctness measures were not able to identify human disturbance effects and there were no clear relationships between these new biodiversity measures and the disturbance level recorded at individual localities. Furthermore, the taxonomic distinctness measures used were apparently less sensitive to the effects of anthropogenic impact than other diversity metrics, such as species richness and rarity. 4. We conclude that taxonomic distinctness indices may not always perform as well as other metrics in the assessment of environmental quality. In addition, taxonomic distinctness measure should be interpreted with caution, as their performance and ability to detect anthropogenic disturbance may depend on the phylogenetic structure of sampled taxa within a region, and their evolutionary and ecological history.     

Linking ecology with parasite diversity in Neotropical fishes

A comparative analysis was performed to seek large-scale patterns in the relationships between a set of fish species traits (body size, type of environment, trophic level, schooling behaviour, depth range, mean habitat temperature, geographical range, ability to enter brackish waters and capability of migration) and the diversity of their metazoan parasite assemblages among 651 Neotropical fish species. Two measurements of parasite diversity are used: the species richness and the taxonomic distinctness of a fish's parasite assemblage, including all metazoan parasites, ectoparasites only, or endoparasites only. The results showed that, on this scale, the average taxonomic distinctness of parasite assemblages was clearly more sensitive to the influence of host traits than parasite species richness. Differences in the taxonomic diversification of the parasite assemblages of different fish species were mainly related to the fish's environment (higher values in benthic–demersal species), trophic level (positive correlation with increasing level), temperature (positive correlation with temperature in marine ectoparasites, negative in endoparasites; positive for all groups of parasites in freshwater fishes) and oceanic distribution (higher values in fish species from the Pacific Ocean than those of the Atlantic). The results suggest that, among Neotropical fish species, only certain key host traits have influenced the processes causing the taxonomic diversification of parasite assemblages.     

Patterns in species richness and endemism of European freshwater fish

Aim  To analyse the patterns in species richness and endemism of the native European riverine fish fauna, in the light of the Messinian salinity crisis and the Last Glacial Maximum (LGM).
Location  European continent.
Methods  After gathering native fish faunistic lists of 406 hydrographical networks, we defined large biogeographical regions with homogenous fish fauna, based on a hierarchical cluster analysis. Then we analysed and compared the patterns in species richness and endemism among these regions, as well as species–area relationships.
Results  Among the 233 native species present in the data set, the Cyprinidae family was strongly dominant (> 50% of the total number of species). Seven biogeographical regions were defined: Western Peri-Mediterranea, Central Peri-Mediterranea, Eastern Peri-Mediterranea, Ponto-Caspian Europe, Northern Europe, Central Europe and Western Europe. The highest regional species richness was observed for Central Peri-Mediterranea and Ponto-Caspian Europe. The highest endemic richness was found in Central Peri-Mediterranea. Species–area relationships were characterized by high slope values for Peri-Mediterranean Europe and low values for Central and Western Europe.
Main conclusions  The results were in agreement with the 'Lago Mare' hypothesis explaining the specificity of Peri-Mediterranean fish fauna, as well as with the history of recolonization of Central and Western Europe from Ponto-Caspian Europe following the LGM. The results also agreed with the mechanisms of speciation and extinction influencing fish diversity in hydrographical networks. We advise the use of the seven biogeographical regions for further studies, and suggest considering Peri-Mediterranean Europe and Ponto-Caspian Europe as 'biodiversity hotspots' for European riverine fish.     

Intensive agriculture reduces soil biodiversity across Europe

Soil biodiversity plays a key role in regulating the processes that underpin the delivery of ecosystem goods and services in terrestrial ecosystems. Agricultural intensification is known to change the diversity of individual groups of soil biota, but less is known about how intensification affects biodiversity of the soil food web as a whole, and whether or not these effects may be generalized across regions. We examined biodiversity in soil food webs from grasslands, extensive, and intensive rotations in four agricultural regions across Europe: in Sweden, the UK, the Czech Republic and Greece. Effects of land‐use intensity were quantified based on structure and diversity among functional groups in the soil food web, as well as on community‐weighted mean body mass of soil fauna. We also elucidate land‐use intensity effects on diversity of taxonomic units within taxonomic groups of soil fauna. We found that between regions soil food web diversity measures were variable, but that increasing land‐use intensity caused highly consistent responses. In particular, land‐use intensification reduced the complexity in the soil food webs, as well as the community‐weighted mean body mass of soil fauna. In all regions across Europe, species richness of earthworms, Collembolans, and oribatid mites was negatively affected by increased land‐use intensity. The taxonomic distinctness, which is a measure of taxonomic relatedness of species in a community that is independent of species richness, was also reduced by land‐use intensification. We conclude that intensive agriculture reduces soil biodiversity, making soil food webs less diverse and composed of smaller bodied organisms. Land‐use intensification results in fewer functional groups of soil biota with fewer and taxonomically more closely related species. We discuss how these changes in soil biodiversity due to land‐use intensification may threaten the functioning of soil in agricultural production systems.     

The Evolution of Taxonomic Diversity in Helminth Assemblages of Mammalian Hosts

Several studies have searched for the key forces behind the diversification of parasite assemblages over evolutionary time. All of these studies have used parasite species richness as their measure of diversity, thus ignoring the relatedness among parasite species and the taxonomic structure of the assemblages. This information is essential, however, if we want to elucidate which processes have caused an assemblage of parasites to acquire new species. Here, we performed a comparative analysis across 110 species of mammalian hosts in which we evaluated the effects of four host traits (body mass, population density, geographic range, and basal metabolic rate) on the diversity of their assemblages of helminth endoparasites. As measures of diversity, we used parasite species richness, as well as the average taxonomic distinctness of the assemblage and its variance; the latter measures are based on the taxonomic distance between two parasite species, computed across all possible species pairs in an assemblage. Unlike parasite species richness, both the average taxonomic distinctness and its variance were unaffected by the number of hosts examined. These two measures of parasite diversity also proved highly repeatable among host populations of the same mammalian species; in contrast, parasite species richness was unreliable as a species character, as it varied as much within a host species than among different host species. Using phylogenetically independent contrasts, and correcting for potential confounding variables, we found that host population density correlated positively with parasite species richness. There were, however, no other relationships between any of the four host traits investigated and either of our measures of parasite diversity. The processes facilitating the taxonomic diversification of parasite assemblages thus remain unclear, but their elucidation will be necessary if we are to fully understand parasite evolution.     

Interdecadal changes in ichthyofauna in a tropical bay with high anthropogenic influences: functional stability despite turnover predominance

Functional characteristics of species are of great importance for understanding their roles in ecosystems and can be used to detect long-term chances in the environment. We evaluated temporal changes (1983–1985 and 2017–2019) in taxonomic and functional indices of the fish fauna in shallow areas of a tropical bay heavily impacted by anthropogenic activities in recent decades. The hypothesis that functional indices change over time as a result of environmental degradation was tested. Our results showed a significant decrease in species richness and abundance over time, and in functional richness, while others functional diversity indices (divergency, evenness, and originality) remained stable. Thirteen functional groups were detected, some of which contained only one species, raising concerns about the loss of ecosystem functions due to ongoing changes. We also observed an increase in beta diversity over time, which may be the result of a decrease in local richness without leading to regional extinctions. Turnover was the most important process in structuring the fish fauna at the evaluated time scale. The relative stability of the functional structure and the higher levels of turnover seem to be related to the dominance of functional groups, within which species replace each other according to their responses to environmental filters that select for specific functional traits. Incorporating functional diversity indices and beta diversity variations in the fish community helped to enhance the existing information about this coastal system by offering improved estimates of biological diversity through diverse approaches. The predominance of turnover identified in the preset study suggests a dynamic and fluctuating species composition within the habitat. In this sense, habitat preservation should prioritize the protection of diverse habitats to accommodate a broad spectrum of species.     

Concordant Biogeographic Patterns among Multiple Taxonomic Groups in the Mexican Freshwater Biota

In this paper we analyse the degree of concordance in species richness and taxonomic distinctness (diversity) patterns among different freshwater taxonomic groups in order to test three long held patterns described in Mexican freshwater biogeography: 1. The aquatic biota of Mexico includes two distinct faunas, a rich Neotropical component in the south and a south-eastern region and a less rich Nearctic component towards central and northern latitudes of the country. 2. A hotspot of species richness and diversity has been recorded in the Usumacinta, including the Yucatan Peninsula. 3. The presence of two distinct biotas in Mexico, an eastern one distributed along the Gulf of Mexico slope, and a western one associated to the Pacific versant. We use species richness and taxonomic distinctness to explore patterns of diversity and how these patterns change between zoogeographical regions. This paper points out a clear separation between Neotropical and Nearctic drainage basins but also between eastern (Gulf of Mexico) and western (Pacific) drainage basins. Present data gives additional empirical support from freshwater biota for three long held beliefs regarding distributional patterns of the Mexican biota. The neotropical basins of Mexico are generally host to a richest and more diversified fauna, that includes more families, genera and species, compared to the less rich and less diverse fauna in the nearctic basins.     

Global patterns of amphibian phylogenetic diversity

Aim Phylogenetic diversity can provide insight into how evolutionary processes may have shaped contemporary patterns of species richness. Here, we aim to test for the influence of phylogenetic history on global patterns of amphibian species richness, and to identify areas where macroevolutionary processes such as diversification and dispersal have left strong signatures on contemporary species richness. Location Global; equal‐area grid cells of approximately 10,000 km². Methods We generated an amphibian global supertree (6111 species) and repeated analyses with the largest available molecular phylogeny (2792 species). We combined each tree with global species distributions to map four indices of phylogenetic diversity. To investigate congruence between global spatial patterns of amphibian species richness and phylogenetic diversity, we selected Faith’s phylogenetic diversity (PD) index and the total taxonomic distinctness (TTD) index, because we found that the variance of the other two indices we examined (average taxonomic distinctness and mean root distance) strongly depended on species richness. We then identified regions with unusually high or low phylogenetic diversity given the underlying level of species richness by using the residuals from the global relationship of species richness and phylogenetic diversity. Results Phylogenetic diversity as measured by either Faith’s PD or TTD was strongly correlated with species richness globally, while the other two indices showed very different patterns. When either Faith’s PD or TTD was tested against species richness, residuals were strongly spatially structured. Areas with unusually low phylogenetic diversity for their associated species richness were mostly on islands, indicating large radiations of few lineages that have successfully colonized these archipelagos. Areas with unusually high phylogenetic diversity were located around biogeographic contact zones in Central America and southern China, and seem to have experienced high immigration or in situ diversification rates, combined with local persistence of old lineages. Main conclusions We show spatial structure in the residuals of the relationship between species richness and phylogenetic diversity, which together with the positive relationship itself indicates strong signatures of evolutionary history on contemporary global patterns of amphibian species richness. Areas with unusually low and high phylogenetic diversity for their associated richness demonstrate the importance of biogeographic barriers to dispersal, colonization and diversification processes.     

Increasing variation in taxonomic distinctness reveals clusters of specialists in the deep sea

Changes in biodiversity with latitude or along a given environmental gradient have been described in many studies, including for marine ecosystems. Currently there is no scientific consensus, however, regarding macroecological patterns of diversity vs depth. Here, we describe variation in the biodiversity of fishes along a depth gradient from 0 to 2000 m in the region of the Norfolk Ridge and Lord Howe Rise (Western Pacific), using data obtained during the NORFANZ voyage. We modelled α diversity (richness), β diversity (using Jaccard's coefficient), evenness, taxonomic distinctness and taxonomic resemblances among fish communities. Although α diversity did not change appreciably with depth, β diversity decreased significantly in deeper strata. Both taxonomic resemblances and Jaccard similarities diminished with depth, indicating convergence in community structure. In addition, average taxonomic distinctness showed no clear pattern with depth, but taxonomic trees constructed among species within deeper samples had more variable path‐lengths than those in shallower samples. The presence of taxonomically distinct clusters of highly related species at depth indicates specialised niches that have developed in a relatively extreme (dark, pressurized) yet stable environment. We propose that reduced β diversity and increased variation in taxonomic distinctness might serve as indicators of ecological communities living in harsh environments – a hypothesis that should be tested in other systems, such as deserts, high altitudes or latitudes.     

A test of traditional diversity measures and taxonomic distinctness indices on benthic diatoms of soda pans in the Carpathian basin

Saline lakes are threatened all over the world and their conservation has been a key issue. Various diversity indices are available for ecological status assessments, however, with poorly explored relevance and applicability in saline, alkaline pans. Therefore, traditional diversity measures (species richness and Shannon diversity) and taxonomic distinctness indices (Average [AvTD] and Variance of Taxonomic Distinctness [VarTD]) were tested in more than 100 sampling sites of 39 soda pans in Central-Europe to find sufficient indicators of the ecological condition and simultaneously to facilitate their preservation according to the modern conservation practices. Results of the analyses showed that healthy soda pan ecosystems with high level of natural stress and reduced habitat heterogeneity are characterized by low diversity diatom assemblages. In soda pans where the stress can be extremely high from natural reasons, oligopoly of closely related species can develop: the average taxonomic distinctness appeared between genus and family level. The non-DNA-sequence based phylogenetic diversity measures (AvTD and VarTD), were generally sensitive to the trophic state of the lakes, in contrast to traditional diversity metrics, which were unequivocally indicative for the special physical and chemical parameters (e.g. conductivity, pH) of the soda pans. In some cases, when the response of the diversity measures for a given environmental variable (pH, temperature) overlapped, the AvTD was found to be a more precise indicator of the environmental changes (pH) than traditional ones. The decreasing tendency of the AvTD along the intensified natural impact may be explained by the long available time for the species to adapt to these special environments.     

Land‐use effects on the functional distinctness of arthropod communities

Land‐use change is a major driver of the global loss of biodiversity, but it is unclear to what extent this also results in a loss of ecological traits. Therefore, a better understanding of how land‐use change affects ecological traits is crucial for efforts to sustain functional diversity. To this end we tested whether higher species richness or taxonomic distinctness generally leads to increased functional distinctness and whether intensive land use leads to functionally more narrow arthropod communities. We compiled species composition and trait data for 350 species of terrestrial arthropods (Araneae, Carabidae and Heteroptera) in different land‐use types (forests, grasslands and arable fields) of low and high land‐use intensity. We calculated the average functional and taxonomic distinctness and the rarified trait richness for each community. These measures reflect the range of traits, taxonomic relatedness and number of traits that are observed in local communities. Average functional distinctness only increased significantly with species richness in Carabidae communities. Functional distinctness increased significantly with taxonomic distinctness in communities of all analyzed taxa suggesting a high functional redundancy of taxonomically closely related species. Araneae and Heteroptera communities had the expected lower functional distinctness at sites with higher land‐use intensity. More frequently disturbed land‐use types such as managed grasslands or arable fields were characterized by species with smaller body sizes and higher dispersal abilities and communities with lower functional distinctness or trait richness. Simple recommendations about the conservation of functional distinctness of arthropod communities in the face of future land‐use intensification and species loss are not possible. Our study shows that these relationships depend on the studied taxa and land‐use type. However, for some arthropod groups functional distinctness is threatened by intensification and conversion from less to more frequently disturbed land‐uses.     

Multiple facets of stream macroinvertebrate alpha diversity are driven by different ecological factors across an extensive altitudinal gradient

Environmental filtering and spatial structuring are important ecological processes for the generation and maintenance of biodiversity. However, the relative importance of these ecological drivers for multiple facets of diversity is still poorly understood in highland streams. Here, we examined the responses of three facets of stream macroinvertebrate alpha diversity to local environmental, landscape‐climate and spatial factors in a near‐pristine highland riverine ecosystem. Taxonomic (species richness, Shannon diversity, and evenness), functional (functional richness, evenness, divergence, and Rao's Quadratic entropy), and a proxy of phylogenetic alpha diversity (taxonomic distinctness and variation in taxonomic distinctness) were calculated for macroinvertebrate assemblages in 55 stream sites. Then Pearson correlation coefficient was used to explore congruence of indices within and across the three diversity facets. Finally, multiple linear regression models and variation partitioning were employed to identify the relative importance of different ecological drivers of biodiversity. We found most correlations between the diversity indices within the same facet, and between functional richness and species richness were relatively strong. The two phylogenetic diversity indices were quite independent from taxonomic diversity but correlated with functional diversity indices to some extent. Taxonomic and functional diversity were more strongly determined by environmental variables, while phylogenetic diversity was better explained by spatial factors. In terms of environmental variables, habitat‐scale variables describing habitat complexity and water physical features played the primary role in determining the diversity patterns of all three facets, whereas landscape factors appeared less influential. Our findings indicated that both environmental and spatial factors are important ecological drivers for biodiversity patterns of macroinvertebrates in Tibetan streams, although their relative importance was contingent on different facets of diversity. Such findings verified the complementary roles of taxonomic, functional and phylogenetic diversity, and highlighted the importance of comprehensively considering multiple ecological drivers for different facets of diversity in biodiversity assessment.     

Effect of non-native species on taxonomic and functional diversity of fish communities in different river types

Recent researches suggest that functional diversity represents the response of communities to environmental alterations better than taxonomic diversity. However, there is scarce information about how the functional diversity of freshwater fishes is affected by habitat type and the dominance of non-native species. To address this question, we analysed a large database containing 15 morpho-functional traits of 61 fish species from the Pannon Biogeographic region (Hungary). Based on a fish faunistic list and relative abundance of taxa, we quantified the taxonomic and functional diversity of riverine communities for?>?700 sites of six habitat types. We asked how non-native fishes affected the taxonomic and functional diversity in different river types and at the local scale (i.e. at the site level), and how the diversity measures of native fauna elements changes along the invasion gradient. Our results showed that both functional and taxonomic richness increases with habitat complexity, from small headwater streams to large rivers. Therefore taxonomic diversity served as a good proxy for functional diversity along the environmental gradient of river types. Non-natives showed considerable functional diversity relative to their species number in each habitat type. Diversity values of native fauna elements initially increased, and then showed a major decrease along the invasion gradient. River type-specific evaluations highlighted the importance of considering the proliferation of invasive species based on both taxonomic and functional diversity indices. We argue that type-specific action plans are needed in conservation management to preserve the taxonomic and functional diversity of native fishes in Hungary, but also elsewhere.

     

Responses of taxonomic distinctness and species diversity indices to anthropogenic impacts and natural environmental gradients in stream macroinvertebrates

1. Many studies have shown traditional species diversity indices to perform poorly in discriminating anthropogenic influences on biodiversity. By contrast, in marine systems, taxonomic distinctness indices that take into account the taxonomic relatedness of species have been shown to discriminate anthropogenic effects. However, few studies have examined the performance of taxonomic distinctness indices in freshwater systems. 2. We studied the performance of four species diversity indices and four taxonomic distinctness indices for detecting anthropogenic effects on stream macroinvertebrate assemblages. Further, we examined the effects of catchment type and area, as well as two variables (pH and total phosphorus) potentially describing anthropogenic perturbation on biodiversity. 3. We found no indications of degraded biodiversity at the putatively disturbed sites. However, species density, rarefied species richness, Shannon's diversity and taxonomic diversity showed higher index values in streams draining mineral as opposed to peatland catchments. 4. Of the major environmental gradients analysed, biodiversity indices showed the strongest relationships with catchment area, lending further support to the importance of stream size for macroinvertebrate biodiversity. Some of the indices also showed weak linear and quadratic relationships to pH and total phosphorus, and residuals from the biodiversity index‐catchment area regressions (i.e. area effect standardized) were more weakly related to pH and total phosphorus than the original index values. 5. There are a number of reasons why the biodiversity indices did not respond to anthropogenic perturbation. First, some natural environmental gradients may mask the effects of perturbation on biodiversity. Secondly, perturbations of riverine ecosystems in our study area may not be strong enough to cause drastic changes in biodiversity. Thirdly, multiple anthropogenic stressors may either increase or decrease biodiversity, and thus the coarse division of sites into reference and altered streams may be an oversimplification. 6. Although neither species diversity nor taxonomic distinctness indices revealed anthropogenic degradation of macroinvertebrate assemblages in this study, the traditional species diversity and taxonomic distinctness indices were very weakly correlated. Therefore, we urge that biodiversity assessment and conservation planning should utilize a number of different indices, as they may provide complementary information about biotic assemblages.     

Influence of sampling effort on metrics of fish-based indices for the assessment of estuarine ecological quality

Multimetric fish-based indices have been increasingly gaining importance in Europe, as the Water Framework Directive (WFD) requires fish fauna, and particularly its composition and abundance, to be taken into account in the assessment of the ecological quality of continental surface waters, including transitional waters. These indices are composed of several metrics, mostly related with structural and functional characteristics of fish communities, such as species richness, the role of nursery areas, or trophic web structure. Therefore, ecological quality assessments should ensure that these structural and functional characteristics of fish communities were covered by the sampling methods used. In the present work, the influence of sampling effort on several metrics of the Estuarine Fish Assessment Index (EFAI) was studied. Pseudo-random samples were generated from data of four Portuguese estuaries and bootstrap cycles were performed, in order to obtain metrics’ means and standard deviations per number of hauls analysed. The number of hauls necessary for the means to level off differed with the metrics considered. Generally, for metrics on percentages (percentage of marine migrants, percentage of estuarine residents and percentage of piscivores) the curve levelled off with less than 20 hauls, both for the estuary as a whole and for different estuarine salinity zones. On the other hand, metrics on species richness required much larger samples. In order to decrease to −5% the current estimated bias of metrics, the WFD sampling costs would have to be more than 3 times higher than they currently are. The findings in the present study are of great importance for an effective assessment of estuarine ecological quality and particularly in the context of the WFD, as the metrics studied are common to other Member State indices.