Identifying functional species pool of planktonic protozoa for discriminating water quality status in marine ecosystems

It is cost-effective protocol to identify a functional species pool for marine bioassessment by removing redundant species from a raw dataset. The feasibility of functional species pool for discriminating water quality status was studied based on a dataset of 120 samples of ciliated protozoa. From the full 60-species dataset of the whole ciliate communities, a 35-species subset was identified as a functional species pool, the species number, abundance and biodiversity indices of which were significantly correlated with those of the full species dataset. The spatial pattern of the subset was significantly related to the changes in nutrients soluble reactive phosphates (SRP), nitrate/nitrite nitrogen (NO₃-N/NO₂-N) and ammonium nitrogen (NH₄-N). Four indices of the taxonomic diversity (Δ), taxonomic distinctness (Δ*), average in taxonomic distinctness (Δ⁺) and the variation in taxonomic distinctness (Λ⁺) based on this small species pool were significantly correlated with the changes of nutrients NO₃-N and/or (NH₄-N). The paired indices Δ⁺ and Λ⁺ showed a clear decreasing trend of departure from the expected taxonomic pattern. These findings suggest that the 35-species functional species subset may be used as a feasible functional surrogate of ciliated protozoan assemblages for community-based bioassessment in marine ecosystems.     

Seasonal variations in macrobenthic taxonomic diversity and the application of taxonomic distinctness indices in Bohai Bay,northern China

Taxonomic diversity indices have a number of desirable properties as indicators in the assessment of environmental quality, and have become an important measure in biodiversity studies. Macrobenthic taxonomic variations were studied in Bohai Bay, northern China, an area under threat from rapid human development. Four seasonal cruise datasets were collected between 2006 and 2007. Environmental conditions exhibited large fluctuations due to human development; nitrogen and phosphorus were the main environmental stressors. A total of 97 macrofauna taxa were identified belonging to 88 genera, 72 families, 36 orders, 14 classes, and nine phyla. Analysis of similarity indicated that there were significant assemblage differences across sampling stations as well as seasons. Four taxonomic indices, taxonomic diversity (Δ), taxonomic distinctness (Δ*), average taxonomic distinctness (Δ⁺), and variation in taxonomic distinctness (Λ⁺) were calculated using abundance data. Among the stations and seasons, there were greater variations in both Δ and Λ⁺ than in Δ* and Δ⁺. The funnel plot of Δ⁺ could identify disturbed stations to some extent, but was not always a strong indicator of disturbance. The Δ⁺ performance was better in autumn than in spring, but could not identify a disturbed station in autumn due to a low number of species. The efficiency of taxonomic distinctness may depend on taxa or the pollution indicators. Taxonomic distinctness indices can be effective at assessing environmental degradation when correctly applied; however, they are unsuitable for directly assessing environmental quality in a new area prior to efficiency testing.     

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.     

Taxonomic distinctness indices for discriminating patterns in freshwater rotifer assemblages

Taxonomic distinctness indices measure the taxonomic relatedness among species and have been used for environmental assessment to detect disturbed habitats. This is the first application of the Average Taxonomic Distinctness (Δ⁺) and Variance in Taxonomic Distinctness (Λ⁺) indices to the presence/absence data of rotifer communities to examine their sensitiveness in discriminating perturbed environments. The 26 Greek lakes studied spanned a wide range of morphological and physical–chemical characteristics. Δ⁺ was significantly correlated (P < 0.05) with maximum depth, salinity and trophic state, while Λ⁺ was correlated only with salinity. The index Δ⁺ identified lakes characterized by periods of increased salinity. Communities in these lakes were less diverse, consisting of more closely related species as seen by the reduced number of families than other lakes with similar species richness. Lakes identified by Λ⁺ had a higher community distinctness than expected due to the overrepresentation of the family Brachionidae; they were also characterized by periods of water-level fluctuations. Both indices were unaffected by sampling effort in terms of number of species and sampling visits; whereas Shannon diversity index (H′) was correlated to species number. Also, based on the randomization test, the taxonomic distinctness indices differentiated lakes anthropogenically disturbed based on the expected patterns of diversity of the area.

     

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.     

Application of biotic and taxonomic distinctness indices in assessing the Ecological Quality Status of two coastal lakes: Caprolace and Fogliano lakes (Central Italy)

Marine biotic indices (AMBI, BENTIX) and the statistical tool M-AMBI (Multivariate AMBI) were applied as a comparative approach in assessing the Ecological Quality Status (EcoQS) of two Mediterranean coastal lakes (Caprolace and Fogliano lakes) situated in the Circeo National Park (Central Italy). The macrobenthic community was analysed using univariate indices (community structure), correspondence analysis (CA) and taxonomic distinctness indices (Δ⁺ and Λ⁺). The community composition showed a dominance of lagoonal species in both coastal lakes, while in Caprolace lake marine taxa were also found. Diversity index (H′) complies to ranges found in Mediterranean lagoons and taxonomic distinctness indices demonstrated that taxonomy structure is in accordance with natural variability ranges. Principal component analysis (PCA) on chemical parameters of water and sediment showed that both coastal lakes differ mainly in their organic matter composition. In fact, the protein fraction of bio-polymeric carbon prevails in Fogliano lake, while the ‘refractory’ component represented by carbohydrate fraction is predominant in Caprolace lake. The difference between the two coastal lakes was also demonstrated by co-inertia analysis (COIA) performed using abundance of species and concentrations of chemical parameters. The results from the application of the three biotic indices do not highlight a clear distinction between the two lagoons. However, the AMBI index provided a more suitable evaluation of EcoQS corresponding to ‘slightly polluted’ lagoons while M-AMBI and moreover BENTIX indices indicated a worsening situation. The biotic indices are widely used in assessing the EcoQS in marine environments, but their proper application in transitional waters would depend on a resettlement; thresholds established in the biotic index scale values need to be modified according to natural variability of transitional waters referring to abiotic conditions and abundance of tolerant species.     

The use of taxonomic distinctness to assess environmental disturbance of insect communities from running water

1. Taxonomic distinctness (or average taxonomic breadth) of a sample is a measure of diversity that has the great advantage of not being sensitive to variations in sampling effort, unlike measures of species richness. It can also be tested for departures from expectation and can thus be used to determine whether a site has suffered from a genuine loss of diversity. 2. Taxonomic distinctness or delta⁺ was measured using all insect species from three datasets obtained from running water habitats: reference or least disturbed sites from channel and bank habitats on rivers from the Australian state of Victoria; test sites distributed along a water quality gradient in Victoria and sites immediately below a series of dams in Victoria and New South Wales. The last two datasets comprised sites subject to a range of obvious disturbances. 3. At reference sites delta⁺ was generally within the range of expected values (95% confidence limits) for both habitats as would be anticipated for these essentially undisturbed sites. However, 13–14% of sites fell below the lower confidence limits. Sites in river basins with less cover of natural habitat had slightly but significantly lower delta⁺ values than those with more cover and these sites contributed to this anomaly. 4. Delta⁺ was inversely correlated with water quality (r = −0.54, P = 0.002) as measured by the first axis of a PCA of water quality variables. It was also inversely correlated with individual variables, such as turbidity and total phosphorous. 5. Delta⁺ was below expectation for 18 of the 19 dam sites and at 13 of these sites delta⁺ values were below the lower confidence limit. 6. Delta⁺ was a sensitive index of diversity that generally distinguished sites suffering from environmental disturbance. Only a few previous studies of river ecosystems have used delta⁺, which did not respond consistently to disturbance because either too few taxa at species or higher taxonomic levels were available or because longitudinal changes in species composition swamped the signal from delta⁺. Neither of these problems occurred with the current datasets. 7. Delta⁺ responded more readily to disturbance than number of species, perhaps because taxonomic distinctness reflects some of the multivariate nature of community samples, whereas number of species is blind to this aspect.     

Relationships between taxonomic and functional components of diversity: implications for conservation of tropical freshwater fishes

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鄱阳湖鱼类多样性的时空变化特征研究

研究基于2010年4月、7月和2018年8月、2019年5月在鄱阳湖9个区域的鱼类多样性调查数据,分析鱼类物种多样性、功能多样性和分类差异指数的时空变化以及其与环境之间的关系,了解鄱阳湖近十年来鱼类群落多样性的时空变化特征。结果显示, 2010年和2018—2019年分别调查到鱼类74种和93种,群落结构差异显著(P<0.05),差异贡献率最高的物种为短颌鲚、似鳊、鲫、光泽黄颡鱼和鲤;水温、总悬浮物和叶绿素等环境因素具有显著的年际和季节差异(P<0.05)。与2010年相比, 2018—2019年鱼类物种多样性和功能多样性指数有一定增加,分类差异指数没有显著变化。分类差异指数的随机检验显示(Randomization test),与2010年相比, 2018—2019年位于95%概率置信范围下方的区域增加。水温、总悬浮物和叶绿素等环境因素对物种多样性、功能多样性和分类差异指数有显著的影响(P<0.05)。结果表明,近十年来,鄱阳湖鱼类群落结构发生明显改变,但是小型鱼类依旧是优势种,鱼类群落小型化明显,主要原因可能是过度捕捞的影响。同时,鄱阳湖的人类活动干扰增大,鄱阳县...     

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.     

Death assemblages of molluscs on St Martin's Flats, Isles of Scilly: a surrogate for regional biodiversity?

We test the hypothesis that the biodiversity of the death assemblage of shelled molluscs (gastropods and bivalves) on a single sandflat is representative of the biodiversity of the regional living fauna from the complete spectrum of habitat types, and can therefore be used as a surrogate for the purposes of rapid biodiversity assessment. Two biodiversity indices considered appropriate for such an assessment are average taxonomic distinctness (⁺) and the variation in taxonomic distinctness (⁺), which are, respectively, measures of the degree to which the species are taxonomically related to each other (i.e. the average taxonomic spread), and the degree to which taxa are over or under represented (i.e. the evenness of the distribution across the taxonomic tree). In each case, measured values were compared with the regional living species pool using a randomisation test. Collections and identifications of shells were made by both a non-expert in mollusc taxonomy and by taxonomic experts, the latter using microscopic examination of sediment samples as well as simple surface searches for macro-species. In all studies, ⁺ for the gastropods in the death assemblage was fully representative of the regional living fauna, but for bivalves it was significantly lower. This is because most of the bivalves were characteristic of the sandflat habitat, which introduced a bias, whereas post-mortem transport of gastropods, characterising exotic habitats, is more random. For gastropods, in all studies but one, ⁺ was significantly higher than expected from a random sample of the regional species pool, and for bivalves this was the case for all studies, suggesting the over-representation of some taxa and the under-representation of others. For the total shelled molluscan fauna (gastropods + bivalves) all ⁺ values were below, and all ⁺ values above, expectation. Results obtained by experts and a non-expert in mollusc taxonomy did not differ. In general, death assemblages at a single location are only likely to be representative of a wider region if there is randomisation as a result of post-mortem transport processes.     

The composition and structure of the benthic diatom taxocene (Bacillariophyta) near Cape Fiolent (the Crimea,the Black Sea)

For the first time in the waters of the Cape Fiolent Reserve, a high species richness of benthic diatoms was revealed on natural substrates, 290 species and infraspecific taxa (IT), belonging to 281 species, 68 genera, 32 families, 19 orders, and 3 classes. A total of 68 species and 3 genera were previously registered as new for the flora of the Black Sea; 3 species and 1 taxonomic combination were previously described as new to science, as well as 4 species that did not occur in the Black sea in the past 50 and 100 years of research. Navicula (41 species and IT), Amphora (30), Nitzschia (29), Fallacia (20), Cocconeis (17) and Diploneis (16) were the most represented genera. Only one representative was identified in each of the orders Anaulales, Ardissoneales, Thalassionematales, Rhaphoneidales, and Rhopalodiales. The diversity assessment that was carried out using taxonomic distinctness indices, TaxDI, revealed that the structure of the phylogenetic diatom tree was formed by branches with various species saturation levels and different hierarchical subordination, but with the predominance of polyspecific taxa up to at genera level. The TaxDI values (Δ⁺ = 76.71; Λ⁺ = 361.52) indicate the low evenness and high variability of the structure of the benthic diatom taxocene near Cape Fiolent.     

Spatial variation in taxonomic distinctness of ciliated protozoan communities at genus-level resolution and relationships to marine water quality in Jiaozhou Bay,northern China

Taxonomic distinctness of ciliated protozoan communities at genus-level resolution was studied over a 12-month period (June 2007–May 2008) in Jiaozhou Bay, northern China. Samples were collected biweekly from three different depths at each of five sites. A range of physico-chemical parameters were also measured in order to determine water quality. Multivariate and univariate analyses showed that (1) spatial patterns of ciliated protozoan communities were significantly different among the five sampling sites (P < 0.05); (2) there were no significant differences among the three depths at each site (P > 0.05); (3) the taxonomic patterns of ciliate communities at genus-level resolution were significantly correlated with the spatial variation of environmental variables, in particular nitrate nitrogen (NO₃-N), sum of NO₃-N and nitrite nitrogen (NO _n -N), and soluble reactive phosphate (SRP); (4) the Margalef’s index did not show a significant correlation with chemical parameters although it was higher for the less eutrophic than the more eutrophic sites (P > 0.05); (5) the average taxonomic distinctness (Δ⁺) and variation in taxonomic distinctness (Λ⁺) of the ciliate communities at genus-level resolution were significantly negatively correlated with the combination of NO _n -N and SRP; (6) the paired taxonomic biodiversity indices (Δ⁺ and Λ⁺) showed a clear decreasing trend of departure from the expected taxonomic breadth in response to water quality. These results suggest that spatial patterns and taxonomic distinctness (especially the paired Δ⁺ and Λ⁺) of ciliated protozoan communities at genus-level resolution can be used as potential indicators for assessing marine water quality while minimizing costs in terms of the time and resources needed for sample analysis.     

Mangrove and coral reef sponge faunas: untold stories about shallow water Porifera in the Caribbean

Sponge faunas from coral reefs and mangrove ecosystems in the Caribbean have mostly been studied from an ecological perspective, with researchers considering the effects of physical and biological factors on their species distribution. To discern evolutionary patterns, this study analyzed the systematic composition, taxonomic diversity, and ecological properties (reproductive strategies, size, shape, endosymbiosis) of mangrove and reef sponge assemblages from seven distant Caribbean localities. Species composition was compared by use of cluster analysis (Sørensen’s), and taxonomic diversity by use of the biodiversity index average taxonomic distinctness (AvTD). Mangrove and reef-associated sponge faunas were found to be statistically dissimilar, with the AvTD values suggesting stronger taxonomic bias toward specific groups in mangroves, irrespective of geographic distance. Most Demospongiae orders have 30–50% more species in coral reefs than in mangroves. The richest reef genera (Agelas, Aplysina, Callyspongia, Petrosia, and Xestospongia) rarely colonize contiguous mangrove formations. The distribution and diversity of suprageneric taxa suggest that coral reef sponge assemblages might represent an older fauna. This historical interpretation would place mangrove subtidal habitats as the youngest marine ecosystem, rather than a below-optimum ecosystem. Life history traits support a biological split discussed here from the perspective of distinct evolutionary histories and different environmental conditions.     

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.     

Dung beetle persistence in human-modified landscapes: Combining indicator species with anthropogenic land use and fragmentation-related effects

Identifying and making use of ecological indicators becomes an essential task in the conservation of tropical systems, mainly in fragmented landscapes where land use intensification and habitat loss are confounding factors in the detection of species’ responses to human-caused disturbance. We aimed to analyze the importance of anthropogenic land use and fragmentation-related effects on dung beetle (Coleoptera: Scarabaeinae) persistence according to the interior–exterior non-linear gradient (forest + matrix) in a fragmented Atlantic Forest landscape used to sugar cane production and cattle ranching/farming. We offer scores for a comprehensive set of community-level attributes, from beetle abundance to taxonomic and ecological composition (i.e. species body size), including a list of indicator species of different forest habitats and adjacent matrix. Dung beetles were surveyed by traps across forest interiors (i.e. core forest areas) and edges of a primary forest, small fragments, sugar cane fields and pastures in a total of 60 sites. Indicator analyses were conducted across the landscape, using two well-established methods (IndVal and SIMPER). Our results suggest that (1) cross-habitat taxonomic distinctness is associated with the presence of indicator species, (2) some species benefit or are dependent of open habitats created by human-disturbances, such as forest edges (e.g. Canthon nigripennis) and matrices (e.g. Canthon aff. piluliformis, Dichotomius nisus and Trichilum externepunctatum), (3) although landscape habitats exhibit reduced beta diversity, dung beetle assemblages are spatially organized in response to the presence of both forest habitats and matrix and fragment area, (4) forest interior supports beetle assemblages biased toward large-bodied species, (5) accordingly forest interior, forest edges and matrix support taxonomically distinct assemblages, both contributing to the bulk of species richness at landscape level, (6) the response of dung beetles to the interior–exterior non-linear gradient (i.e. forest edge + matrix) reveals a similar pattern regardless of the nature of the matrix, and (7) there is no within-habitat variation in beetle abundance and species richness associated with distance from forest edge. Given that there is a high number of forest-dependent or forest-interior specialist species (e.g. Aphengium aff. sordidum, Ateuchus aff. alipioi, Dichotomius mormon, Ontherus aff. erosus and Onthophagus aff. clypeatus) dung beetle persistence in human-modified landscape is highly dependent on the presence of core areas, although edge-affected and matrix habitats may be complementary. This information is essential to permit a better prospect for dung beetle persistence in human-modified landscapes as they continue to move toward edge-dominated landscapes with intensively managed matrices.     

河流鱼类分类群和功能群的纵向梯度格局——以新安江流域为例

确定鱼类群落的空间格局是保护和管理河流鱼类多样性的基础。尽管河流鱼类分类群（基于物种组成）的纵向梯度格局已得到大量报道,但其功能群（基于功能特征）的空间格局研究较少。以皖南山区新安江为研究流域,沿其"正源-下游"梯度共设置27个调查样点,分别于2017年5月和10月完成2次调查取样,着重研究了鱼类分类群和功能群结构的纵向梯度格局及其形成机制。共采集鱼类44种,可分为5个运动功能群和4个营养功能群,构成14个"营养-运动"复合功能群。双因素交互相似性分析结果显示,鱼类分类群和功能群均随河流级别显著变化,但两者均无显著的季节变化;根据相似性百分比分析,由1级至3级河流,数量优势物种和功能群的空间变化主要呈嵌套格局,而由3级至5级河流其变化主要呈周转格局。方差分解结果显示,局域栖息地、陆地景观和支流空间位置3类解释变量对分类群和功能群空间变化的解释率分别为33.6%和38.5%,其中,分类群受局域栖息地和支流空间位置变量的显著影响,而功能群受局域栖息地和陆地景观变量的显著影响。研究表明,沿着新安江的"上游-下游"纵向梯度,鱼类分类群和功能群的空间格局基本一致,但两者的形成机制不同：分类群的纵向梯度变化受环境过滤和扩散过程的联合影响,而功能群则主要受环境过滤影响。     

Taxonomic distinctness in a linear system: a test using a tropical freshwater fish assemblage

Taxonomic distinctness, a measure of diversity that captures the phylogenetic relatedness of an assemblage, has been successfully applied in several marine communities and appears to have considerable potential for environmental assessment and conservation. This approach has, however, not hitherto been used in structured freshwater systems. We evaluated this technique in the context of vulnerable tropical river drainages in India. We found that the inherent physical structure of river systems and longitudinal gradients in habitat characteristics influenced the pattern of taxonomic distinctness. Downstream locations were in general more taxonomically diverse than upstream ones. This in turn means that highly perturbed sites in the lower reaches of rivers would not display a reduction in taxonomic distinctness relative to a random expectation. The utility of the approach for detecting habitat and other disturbances on stream fish communities is thus limited. Implications of these unique properties of river ecosystems and their communities to conservation are discussed.     

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.