Do metacommunity theories explain spatial variation in fish assemblage structure in a pristine tropical river?

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Distribution of fishes in the Río Guayalejo-Río Tamesí system and relationships with environmental factors in northeastern Mexico

A priority issue in ecology and biogeography is understanding the patterns in species diversity and the causal factors of their distribution, which allows the generation of information for conservation strategies. The longitudinal distribution of fishes and their relationships with environmental variables were studied in the Guayalejo-Río Tamesí system (northeastern Mexico) from February 2000 to July 2001. A total of 5918 fish were caught in 27 collections along an altitudinal gradient in the main river course, from high mountain (1500 masl) to coastal plain near Tampico. Forty-three native and five exotic species, belonging to 35 genera in 23 families, were identified. Cluster analyses identified four major fish habitats in the river system. A distinctive euryhaline marine fish habitat (1) occurs near the mouth with native and two exotic species. Two other habitats consist essentially of freshwater fish species that are distributed along the longitudinal gradient. One of these habitats (habitat 4) shows greater diversity, as per the Shannon index value, and also includes amphidromous fish, in addition to two exotic freshwater fish; the other (habitat 2) includes freshwater, euryhaline and three exotic species. The changes in the frequency of occurrence and the abundance of Gambusia vittata, Astyanax mexicanus, and Xiphophorus variatus contribute to explaining differences between these habitats. Another habitat (3) is represented by two sampling sites located near the mouth and consist of freshwater and euryhaline fish and three exotic cyprinids with broad salinity tolerance. The low abundance and richness of exotic species suggest little impact on native fish fauna in this river. The fish assemblage of the Guayalejo-Tamesí river system species changes along a longitudinal gradient with the addition, replacement and presence of indicator species. Upstream fish fauna is mostly composed of freshwater species, some of them generalists that inhabit the entire longitudinal gradient, others that are restricted to certain sites, and the remainder of species is an assemblage composed of a mixture of euryhaline freshwater and marine species near the mouth.     

Patterns in the distribution of fish assemblages in Río Amacuzac,Mexico: influence of abiotic factors and biotic factors

Patterns in spatial and seasonal distribution of fish communities were analyzed in the Río Amacuzac, Mexico, and their relationship to environmental variables and habitat characteristics. The PCA biplot of the study sites and environmental factors showed the first two axes accounting for 52.93% of the variance. The diagram showed the study sites ordination in environmental gradients. The first axis explained variables related to habitat characteristics and temperature (36.30%) and second axis arranged the sites in physicochemical and water quality environmental gradients (conductivity, dissolved oxygen, orthophosphates, ammonium, pH) displaying seasonal variation. Fifteen species were recorded, eight of them are exotic. One new record appeared for the Río Amacuzac: Pterygoplichthys disjunctivus is exotic. Study sites with highest species richness were: 5, 7 and 9 (twelve species each one); while the study sites with low species richness were 1, 2, 3 and 6 (eight species each one). Six of the species were distributed throughout the whole river. Based on the composition of the fish fauna, the study sites form two groups and the analysis of fish species displays three groups according to the Bray–Curtis index. The diagram of the canonical correspondence analysis relates environmental parameters to the abundance of fish species and showed that the first two axes exhibit 78.31% of the explained variance. Species richness had a spatial pattern associated to the introduction of exotic species for ornamental uses. According to the results of the importance value index (IVI), the dominant species were the poecilids Poeciliopsis gracilis and Heterandria bimaculata, small fishes that were introduced in the river. Río Amacuzac has a biotic alteration in the structure of fish communities due to the invasion of exotic species, representing risks to the integrity of the native fish fauna.     

Ecohydrological characterization of a groundwater-fed alluvial floodplain mire

Abstract. In a small alluvial floodplain depression (21 ha) of the river Dijle, a selection of 56 characteristic, mainly groundwater-depending plant species was mapped using a regular 20 by 20 m square cell mapping grid. In order to understand the spatial distribution of the plant species and their vegetation types, several environmental variables, including groundwater regime, groundwater chemistry, soil texture, soil chemical composition and management type were measured in detail. Using Detrended Correspondence Analysis and Canonical Detrended Correspondence Analysis, the relation between these environmental variables and the plant species and vegetation types, respectively, is described in detail. Management type and groundwater fluctuations are recognized as the two main sets of environmental variables causing the specific spatial distribution of plant species and vegetation types for the mire-ecosystem of the silty alluvial floodplain.     

Day-night behavior in river entry of kutum and its relation to melatonin

Reproduction in most fish species is a scheduled phenomenon and spawning occurs at a precise time ensuring maximum survival of offspring. During the spawning season, reproductive activities of fish species and their daily entry to rivers are influenced by environment. Number of Rutilus frisii kutum entered a river discharging to Caspian Sea was analyzed to investigate the association between timing of river entry and day–night changes in environmental variables. Four thousand five hundred and sixty seven ascending adult kutum were collected in Khoshkrood River between March and May 2012. Physicochemical parameters were recorded and Melatonin levels were measured in a hundred migratory kutum over day and night during the spawning period. A significant effect of daytime on river entry was observed, as more fish entered the river at night. Melatonin levels decreased to the minimum level during peak days of migration, suggesting variations in melatonin levels can help to harmonize the daily rhythm in kutum migration.     

Distribution Patterns of Indigenous Freshwater Fishes in the Tagus River Basin, Spain

Classification and ordination methods used to examine the internal complexity of the Mediterranean Tagus River catchment based on fish distribution revealed that it is not a homogeneous biogeographical unit. The indigenous fishes analyzed in this study are distributed through the basin forming geographical communities (chorotypes), some of which are associated with environmental factors like river morphology, water quality or geographical location. Nevertheless, 40% of the variation in species occurrence remains unexplained by either environmental or geographical variables, suggesting that historical factors may influence the freshwater fish distribution patterns. Three main biogeographical areas, delimited by significant boundaries, were identified. Two of them are identified as the upper and the middle-lower basins of the Tagus River catchment; the third corresponds to the Alagón River and seems to be linked to historical factors of the catchment.     

Relationships between fish assemblages, macrophytes and environmental gradients in the Amazon River floodplain

During the flood season of 1992–1993, 139 species of fishes were collected from a floodplain lake system in the central Amazon Basin. Fish species distribution was examined relative to abiotic variables in seven vegetation strata on Marchantaria Island, Solimões River. Both environmental variables and species distributions were influenced by a river channel to floodplain-interior gradient. Species diversity was significantly higher in vegetated areas than in unvegetated areas, with deeper water Paspalum repens stands harbouring the highest diversity. As a result, species richness and catches were positively related to habitat complexity, while catch was also negatively related to dissolved oxygen (DO) and water depth. Low DO and shallow waters appeared to act as a refuge from predation. Fish assemblages were related to water chemistry, but species richness was not. Canonical correspondence analysis provided evidence that floodplain fish assemblages formed by the 76 most common species were influenced by physical variables, macrophyte coverage and habitat complexity, which jointly accounted for 67% of the variance of fish species assemblages. Omnivores showed no pattern relative to the river channel to floodplain-interior gradient while detritivores were more likely to be found at interior floodplain sites and piscivores closer to the river. Piscivores could be further separated into three groups, one with seven species associated with free-floating macrophytes in deep water, a second with five species found in shallow waters with rooted grasses and a third with six open water orientated species. The results suggest that fish assemblages in the Amazon floodplain are not random associations of species.     

River flow,zooplankton and dominant zooplanktivorous fish dynamics in a warm‐temperate South African estuary

The possible links between river flow, zooplankton abundance and the responses of zooplanktivorous fishes to physico‐chemical and food resource changes are assessed. To this end, the seasonal abundance, distribution and diet of the estuarine round‐herring Gilchristella aestuaria and Cape silverside Atherina breviceps were studied in the Kariega Estuary. Spatio‐temporal differences were determined for selected physico‐chemical variables, zooplankton abundance and zooplanktivorous fish abundance and distribution. Results indicated that, following a river flood event in winter (>30 m³ s^?1), altered physico‐chemical conditions occurred throughout the estuary and depressed zooplankton stocks. Abundance of G. aestuaria was highest in spring, with this species dominant in the upper and middle zones of the estuary, while A. breviceps was dominant in summer and preferred the middle and lower zones. The catch per unit of effort of both zooplanktivores also declined significantly following the flooding, thus suggesting that these fishes are reliant on zooplankton as a primary food source for healthy populations. Copepods dominated the stomach contents of both fish species, indicating a potential for strong interspecific competition for food, particularly in the middle reaches. Temporal differences were evident in dietary overlap between the two zooplanktivorous fish species and were correlated with river flow, zooplankton availability and fish distribution. The findings of this study emphasize the close trophic linkages between zooplankton and zooplanktivorous fishes under changing estuarine environmental conditions, particularly river flow and provide important baseline information for similar studies elsewhere in South Africa and the rest of the world.     

Longitudinal patterns of fish assemblages in a large tropical river in southeastern Brazil: evaluating environmental influences and some concepts in river ecology

This study aimed to evaluate environmental influences on fish distribution and to assess the extent to which concepts in river ecology accommodate levels of spatio-temporal heterogeneity of fish assemblages in a 1,080-km long tropical river. A total of 25 sites were sampled between November 2002 and March 2003 in two seasons (summer/wet versus winter/dry). A thermal gradient separating the upper reaches from the lower reaches was detected. The middle-upper reaches showed higher conductivity and lower dissolved oxygen and pH levels compared with the other reaches. Although some significant associations were found between some fish abundance and environmental variables, the most abundant species (Tilapia rendalli, Geophagus brasiliensis, and Oligosarcus hepsetus) occurred in most sites and under most environmental conditions. Fish community structure varied more in space (longitudinal) than through time (seasonal). The community in the lower reach species was more diverse in comparison with the other reaches. Differences in the fish assemblage structure among the longitudinal river sections appear to have been influenced by the effects of damming, and seem to be partially consistent with the Serial Discontinuity Concept, which views dams as discontinuities within the river continuum. Only the lower river reach showed seasonal differences in the fish community structure, attributable to the influence of flooding. Management plans and biodiversity conservation will benefit by considering the effects of dam disruption and flood increased connectivity to the lotic systems. Handling editor: J. Trexler     

基于eDNA metabarcoding探究北京市主要河流鱼类分布及影响因素

使用eDNA宏条形码(eDNA metabarcoding)和地笼法检测了北京市3条水系在夏季和秋季两个季节的鱼类多样性, 旨在研究北京市鱼类群落的空间格局特征, 探索适用于北京鱼类生物多样性监测及保护的新方法。结果表明: 在北京市的34个采样点中, 利用eDNA metabarcoding共检测出鱼类55种, 显著高于传统方法所捕获的鱼类种数(35种), 鱼类组成以鲤形目和鲈形目为主。山区河流清水鱼的多样性要显著高于城区河流, 城区河流(北运河水系)群落结构较为单一, 以鲫(Carassius auratus)、麦穗鱼(Pseudorasbora parva)、泥鳅(Misgurnus anguillicaudatus)等耐污种为优势种; 山区河流(潮白河水系及大清河水系)以宽鳍鱲(Zacco platypus)、拉氏鱥(Rhynchocypris lagowskii)、马口鱼(Opsariichthys uncirostris)等为优势种。不同季节影响清水鱼群落结构的环境因子不同, 夏季主要是总溶解固体和电导率, 秋季主要是海拔和温度。清水鱼丰富度与环境因子及人类活动的相关性表明, 清水鱼的丰富度随着总溶解固体及灯光指数增加而显著降低, 且均与海拔、温度等存在显著相关性。本研究证明了eDNA metabarcoding方法用于监测北京市鱼类多样性及其时空分布的可行性。     

Altitudinal gradients in stream fish diversity and the prevalence of diadromy in the Sixaola River basin,Costa Rica

Landscape-scale patterns of freshwater fish diversity and assemblage structure remain poorly documented in many areas of Central America, while aquatic ecosystems throughout the region have been impacted by habitat degradation and hydrologic alterations. Diadromous fishes may be especially vulnerable to these changes, but there is currently very little information available regarding their distribution and abundance in Central American river systems. We sampled small streams at 20 sites in the Sixaola River basin in southeastern Costa Rica to examine altitudinal variation in the diversity and species composition of stream fish assemblages, with a particular focus on diadromous species. A set of environmental variables was also measured in the study sites to evaluate how changes in fish assemblage structure were related to gradients in stream habitat. Overall, fish diversity and abundance declined steeply with increasing elevation, with very limited species turnover. The contribution of diadromous fishes to local species richness and abundance increased significantly with elevation, and diadromous species dominated assemblages at the highest elevation sites. Ordination of the sampling sites based on fish species composition generally arranged sites by elevation, but also showed some clustering based on geographic proximity. The dominant gradient in fish community structure was strongly correlated with an altitudinal habitat gradient identified through ordination of the environmental variables. The variation we observed in stream fish assemblages over relatively small spatial scales has significant conservation implications and highlights the ecological importance of longitudinal connectivity in Central American river systems.     

The Ability of Aquatic Macrophytes to Assess Fish Farm Pollution in Two Salmon Rivers

The wastewater from freshwater fish farming is responsible for important water quality modifications in receiving ecosystems. These point source pollution cause local problems for the management of the freshwater environment, especially in salmon rivers. The aim of this paper is to study the relationship between plant communities and environmental factors in two rivers basins on which seven fish farms are located and to assess the relative part of water pollution compared to other environmental factors involved in water plant distribution. The disturbance due to fish farming wastewater increased both richness and diversity of aquatic plant communities and modified the distribution of 11 aquatic macrophytes. Nevertheless, the main factors involved in the aquatic plant distribution in the whole data set were not the location upstream or downstream from one point source pollution but the belonging to one river system and the habitat physical features. Relevant prediction of macrophytic communities is a useful tool for bioindication purposes but several groups of variables that manifest themselves at different spatial levels must be considered.     

Spatio-temporal distribution patterns and conservation of fish assemblages in a Chilean coastal river

River environments are characterized by extreme spatial and temporal variation in the physical environment. The relationship of fish assemblages to environmental variation is poorly understood in many systems. In Chile zonation patterns of fish assemblages have been documented in several Andean river drainages. Coastal river drainages are comparatively small, but inordinately important because of their highly endemic flora and fauna and their proximity to major human populations. For conservation purposes it is important to understand what environmental factors affect assemblage structure of fishes especially in the comparatively high diversity coastal drainages. We studied patterns of fish distribution and abundance in three rivers of the coastal, Andalien drainage near Concepción, Chile. We used multi-dimensional scaling analyses to compare patterns among zones (rithron, transition and potamon) and high and low flow seasons. Species assemblages differed by zone, but not with season. Assemblages consisted of nested subsets of species characterized by their range of distribution among zones. One species group was composed of widespread species that occurred in all three zones, another species group consisted of species found only in transitional and potamal zones, and a final group was comprised of species found only in the potamal zone. The potamal zone contained the most diverse and abundant fish assemblage. Fish assemblages were related to both water quality and habitat structure variables. This study suggests that the key to conserving the diversity of native fish communities in coastal Chilean rivers is in the conservation of potamal regions. Unfortunately, most protected areas in Chile are in the depauperate headwaters of drainages. Protection of only headwaters is clearly inadequate and will not contribute to the conservation of this unique freshwater fish fauna.     

Resource partitioning between unionid mussels in a Swedish lake outlet

Partitioning of food and space resources of two dominating unionid mussel species, Anodonta piscinalis and Unio pictorum , was investigated in a South Swedish lake outlet. Differences in diurnal activities were not considered to be a mechanism for niche segregation. The two species ingested particles of almost identical size distribution indicating a high overlap in food. Mussel distribution was correlated to environmental variables including substrate properties, water depth, current velocity, and distance from the lake, the latter being a relative measure of food quality and quantity, U. pictorum dominated near the lake and in the centre of the river while A. piscinalis had its peak density ca. 500 m below the lake and was relatively more abundant along the river margins. At maximum mussel densities, which were found near the lake, a separation in space was more obvious than downstream, implying possible interspecific interactions.     

Local and ecoregion effects on fish assemblage structure in tributaries of the Rio Paraíba do Sul, Brazil

1.  We examined the effects of physical and chemical habitat variables and ecoregions on species occurrence and fish assemblage structure in streams of the Paraíba do Sul basin, in southeast Brazil.
2.  Fish and environmental data were collected from 42 sites on 26 first to fourth order streams (1 : 50 000 map scale) in three ecoregions. The sites occurred in one valley and two plateau ecoregions at altitudes of 40–1080 m and distances of 0.1–188 km from the main channel of the Rio Paraíba do Sul. Physical habitat (substratum, riparian cover, habitat types) and water quality (dissolved oxygen, pH, temperature and conductivity) variables were measured at each sampling site.
3.  A total of 2684 individuals in 16 families and 59 species were recorded.
4.  Ecoregion was a better predictor of the fish assemblage than the other environmental variables, according to the differences between the mean within-class and mean between-class similarities in assemblage data.
5.  Differing landscape characteristics were associated with differing local variables and thereby with differing fish assemblage structures. Riffles, shrub, grass, dissolved oxygen, conductivity and temperature were closely related to fish assemblage structure.
6.  Fish assemblages in sites far from the main river and at higher altitudes also differed from those near the Paraíba do Sul main channel, presumably as a result of differences in connectivity, covarying environmental factors and anthropogenic influence.
7.  These results reinforce the importance of understanding how stream communities are influenced by processes and patterns operating at local and regional scales, which will aid water resource managers to target those factors in their management and rehabilitation efforts.     

Fluctuation and variation in stream-fish assemblages after a catastrophic flood in the Miyagawa River,Japan

In the autumn of 2004, a typhoon caused a catastrophic flood of the Miyagawa River in Japan. Based upon snorkeling surveys conducted every autumn from 2005 to 2009, we monitored the post flood fluctuation of the local fish assemblages at nine sites of both the main stream and subsidiary streams of the river. Results revealed that species richness significantly increased from 2005 to 2009. In addition, the fish densities of eight species significantly increased over the same period, whereas the density of one species decreased, and that of eight others remained unchanged. Categorization based on Euclidean distance revealed five main clusters from the nine sites. Among these sites, fish assemblages within subsidiary streams were stable as they remained within the same clusters while those in the main stream were dynamically variable through time as they changed cluster membership. In addition, the Euclidean distance between two arbitrary fish assemblages was positively correlated with environmental distance (the Euclidean distance calculated based on river width, depth, velocity and pebble size), time distance, and spatial distance along the river. In conclusion, the fish assemblages were dynamically and regularly altered and varied in the five years after the flood, except for those in the subsidiary streams, and such variation was related to environmental, temporal and spatial variation.     

The relative influences of exotic species and environmental factors

Spatial variation in the native fish community of the lower Guadiana basin (southern Iberia) was related to both biotic (abundance of exotic species) and environmental factors using canonical correspondence analysis, CCA. After choosing the best predictors among the environmental and biotic variables, we partitioned the total variation in native species abundances (18 species-size combinations by 44 sampling locations matrix) into that accounted for (1) solely by selected environmental variables, (2) solely by selected biotic variables, (3) by both environmental and biotic variables together, and (4) that unexplained. Of the 22 variables initially considered in the environmental CCA, only RIVER (dummy variable codifying sampling locations belonging to the main river), SALT (dummy variable codifying sampling locations belonging to tributaries that discharge to the brackish Guadiana), substrate heterogeneity, and macrobenthos abundance were selected as best predictors. In the biotic CCA, three species-size combinations were selected from the eight considered: Micropterus salmoides > 150 mm in total length (TL), Lepomis gibbosus > 100 mm in TL and Gambusia holbrooki. The total variation in the native fish community was partitioned into the following components: pure environmental (24.4%), pure biotic (12.4%), shared (9.2%) and unexplained (54.0%). There was a significant influence of exotic fish on native community variation after accounting for the effect of environmental factors. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fish community structure and environmental correlates in the highly altered southern Sacramento-San Joaquin Delta

We sampled 11 sites in the southern Sacramento-San Joaquin Delta from 1992–1999, to characterize fish communities and their associations with environmental variables. Riparian habitats were dominated by rock-reinforced levees, and large water diversion facilities greatly influenced local hydrodynamics and water quality. We captured 33 different taxa, only eight of which were native. None of the native species represented more than 0.5% of the total number of individuals collected. The abundance of native species was consistently low but typically peaked during high outflow periods. Fish communities were predominantly structured along environmental gradients of water temperature and river flow. Native species (tule perch, Hysterocarpus traski, & Sacramento sucker, Catostomus occidentalis) were associated with conditions of high river flow and turbidity, while the majority of the non-native species were associated with either warm water temperature or low river flow conditions. The exceptions were the non-native striped bass, Morone saxatilis, and white catfish, Ameiurus catus, which were positively associated with relatively high river flow. Variation in fish community structure was greater among river locations within years than within river locations among years, thus fish communities at each river location were consistently different each year. Differences in fish communities among river locations were correlated with river flow and turbidity. We predict that the fish communities of this region will remain numerically dominated by non-native species if the environmental conditions we observed persist in the future.     

柳江鱼类群落结构及多样性研究

为了解柳江鱼类群落结构、多样性及其与环境因子的关系, 2018年7月和12月在柳江9个江段(榕江、从江、融安、柳城、象州、永福、鹿寨、河池和宜州)开展鱼类和环境调查。共采集鱼类36474尾, 隶属于5目20科80属115种; 其中, 鲤科鱼类最多(68种), 占59.13%。Shannon-Wiener多样性指数、Simpson指数、Pielou均匀度指数和Margalef丰富度指数的变化范围分别为2.13—3.12、0.81—0.93、0.58—0.80和4.65—7.18。鱼类优势种以银Squalidus argentatus、大眼华鳊Sinibrama macrops、胡Microphysogobio chenhsienensis、银鲴Xenocypris macrolepis和南方拟?Pseudohemiculter dispar等小型鱼类为主。丰度/生物量比较曲线表明, 宜州、榕江、鹿寨、柳城、象州和融安江段鱼类群落受到中度或严重干扰, 河池、从江和永福鱼类群落结构相对稳定。采用非度量多维标度排序(NMDS)方法对鱼类群落的时空分布特征进行分析, 将鱼类划分为3个类群: 柳江上游的从江-榕江类群, 洛清江支流的永福-鹿寨类群, 柳江中下游及龙江支流的融安-柳城-象州-河池-宜州类群。采用典范对应分析(CCA)分析鱼类群落与环境因子的关系, 发现河宽、海拔和pH是柳江鱼类群落结构差异的主要影响因子。与历史资料相比, 柳江鱼类群落结构发生显著变化, 经济鱼类占比减少, 鱼类个体呈现小型化和低龄化。建议从以下几个方面加强柳江鱼类多样性保护: 加强执法力度, 严厉打击偷捕、电捕等非法行为; 对主要经济鱼类开展增殖放流; 恢复河流的连通性; 对流域珍稀特有鱼类进行监测、救护和繁育。     

Elevational Gradients in Fish Diversity in the Himalaya: Water Discharge Is the Key Driver of Distribution Patterns

Background

Studying diversity and distribution patterns of species along elevational gradients and understanding drivers behind these patterns is central to macroecology and conservation biology. A number of studies on biogeographic gradients are available for terrestrial ecosystems, but freshwater ecosystems remain largely neglected. In particular, we know very little about the species richness gradients and their drivers in the Himalaya, a global biodiversity hotspot.

Methodology/Principal Findings

We collated taxonomic and distribution data of fish species from 16 freshwater Himalayan rivers and carried out empirical studies on environmental drivers and fish diversity and distribution in the Teesta river (Eastern Himalaya). We examined patterns of fish species richness along the Himalayan elevational gradients (50–3800 m) and sought to understand the drivers behind the emerging patterns. We used generalized linear models (GLM) and generalized additive models (GAM) to examine the richness patterns; GLM was used to investigate relationship between fish species richness and various environmental variables. Regression modelling involved stepwise procedures, including elimination of collinear variables, best model selection, based on the least Akaike’s information criterion (AIC) and the highest percentage of deviance explained (D²). This maiden study on the Himalayan fishes revealed that total and non-endemic fish species richness monotonously decrease with increasing elevation, while endemics peaked around mid elevations (700–1500 m). The best explanatory model (synthetic model) indicated that water discharge is the best predictor of fish species richness patterns in the Himalayan rivers.

Conclusions/Significance

This study, carried out along one of the longest bioclimatic elevation gradients of the world, lends support to Rapoport’s elevational rule as opposed to mid domain effect hypothesis. We propose a species-discharge model and contradict species-area model in predicting fish species richness. We suggest that drivers of richness gradients in terrestrial and aquatic ecosystems are likely to be different. These studies are crucial in context of the impacts of unprecedented on-going river regulation on fish diversity and distribution in the Himalaya.