Stream invertebrate diversity reduces with invasion of river banks by non‐native plants

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The influence of riparian vegetation on macroinvertebrate community structure in four Hong Kong streams

The benthic macroinvertebrate communities of four Hong Kong streams with similar water chemistry but differing riparian conditions were investigated. Differences in chlorophylls and detritus standing stocks reflected the degree of shading by riparian vegetation; Tai Po Kau Forest Stream (TPKFS) and Bride's Pool (BP) had an allochthonous food base while autochthonous energy sources were relatively more important in Lam Tsuen River (LTR) and Pui O Stream (POS). The macrobenthos was dominated by aquatic insects and morphospecies richness (excluding Chironomidac) ranged from 70 (POS) to 94 (TPKFS). Differences in total macroinvertebrate abundance across sites were not related to chlorophylls or detritus.
Highly significant differences in the morphospecies comprising the most numerous taxa at each site were observed, and TPKS and BP were more similar to each other than to the LTR-POS pair with respect to top-ranked taxa. Intraspecific comparisons of the abundance of these taxa revealed significant differences for 23 out of 30 morphospecies. Multiple regression of the abundance of key morphospecies against independent variables (chlorophylls a , b and c , total chlorophyll and detritus) yielded significant best-fit models for all taxa showing intersite differences in abundance. These data can be interpreted as reflecting the influence of riparian vegetation on stream community structure via an effect on food supply. The results were discussed with reference to the applicability of the River Continuum Concept in the tropics.     

The influence of riparian vegetation on macroinvertebrate community structure and functional organization in six new Guinea streams

Information on the ecology of New Guinea streams is meagre, and data are needed on the trophic basis of aquatic production in rivers such as the Sepik in Papua New Guinea which have low fish yields. This study investigates the relationship between riparian shading (from savanna grassland to primary rainforest), algal and detrital food, and macroinvertebrate abundance and community structure in 6 Sepik River tributary streams. A particular aim was to elucidate macroinvertebrate community responses to changes in riparian conditions. All streams supported diverse benthic communities, but morphospecies richness (overall total 64) was less than in streams on the tropical Asian mainland; population densities of benthic invertebrates, by contrast, were similar to those recorded elsewhere. Low diversity could reflect limited taxonomic penetration, but may result from the absence of major groups (Plecoptera, Heptageniidae, Ephemerellidae, Psephenidae, Megaloptera, etc.) which occur on the Asian mainland. Population densities of all 19 of the most abundant macroinvertebrate taxa varied significantly among the 6 study streams, but community composition in each was broadly similar with dominance by Baetidae and (in order of decreasing importance), Leptophlebiidae, Orthocladiinae, Elmidae and Hydropsychidae. Principal components analysis (PCA) undertaken on counts of abundant macroinvertebrate taxa clearly separated samples taken in two streams from the rest. Both streams contained high detrital standing stocks and one was completely shaded by rainforest. Stepwise multiple-regression analysis indicated that population densities of the majority of abundant taxa (11 out of 19) across streams (10 samples per stream; n = 60) were influenced by algae and/or detritus, although standing stocks of these variables were not clearly related to riparian conditions. When regression analysis was repeated on mean counts of taxa per stream (dependent variables) versus features of each stream as a whole (thus n = 6), % shading and detritus were the independent variables yielding significant regression models most frequently, but pH, total-nitrogen loads and algae were also significant predictors of faunal abundance. Further regression analysis, undertaken separately on samples (n = 10) from each stream, confirmed the ability of algae and detritus to account for significant portions of the variance in macroinvertebrate abundance, but the significance of these variables varied among streams with the consequence that responses of individual taxa to algae or detritus was site-specific.Community functional organization — revealed by investigation of macroinvertebrate functional feeding groups (FFGs) — was rather conservative, and streams were codominated by collector-gatherers (mean across 6 streams = 43%) and grazers (36%), followed by filter-feeders (15%) and predators (7%). The shredder FFG was species-poor and comprised only 0.4% of total macroinvertebrate populations; shredders did not exceed 2% of benthic populations in any stream. PCA of FFG abundance data was characterized by poor separation among streams, although there was some evidence of clustering of samples from unshaded sites. The first 2 PCA axes accounted for 84% of the variation in the data suggesting that the poor separation resulted from the general similarity of FFG representation among streams. Although stepwise multiple-regression analysis indicated that algae and detritus accounted for significant proportions of the variations in population density and relative abundance of some FFGs, the response of community functional organization to changes in riparian conditions and algal and detrital food base was weak — unlike the deterministic responses that may be typical of north-temperate streams.     

The influence of habitat structure and flow permanence on invertebrate communities in karst spring systems

The macroinvertebrate fauna of five karst (limestone) springbrook systems with contrasting physical habitat and discharge patterns were investigated to examine the role of flow permanence and habitat structure on macroinvertebrate community composition. Clear physical differences were identified between perennial and intermittent springs and individual sampling stations. However, flow permanence, water temperature and the input of leaf litter exerted a greater influence on the aquatic invertebrate community than habitat structure. Perennial sites were characterised by a greater abundance of macroinvertebrates and greater Ephemeroptera, Plecoptera and Trichoptera (EPT) richness than intermittent sites. The fauna of all of the springbrook systems examined were dominated by relatively common and ubiquitous taxa (e.g. Gammarus pulex) although a number of taxa displaying life cycle adaptations to ephemeral aquatic habitats (e.g. Limnephilus auricula and Stenophylax permistus) were recorded at intermittent sites.     

Influence of environmental variables on macroinvertebrate community structure in Lianhuan Lake

The structural characteristics of the macroinvertebrate community can effectively reflect the health status of lake ecosystems and the quality of the lake ecological environment. It is therefore important to identify the limiting factors of macroinvertebrate community structure for the maintenance of lake ecosystem health. In this study, the community composition of macroinvertebrate assemblages and their relationships with environmental variables were investigated in 13 small lakes within Lianhuan Lake in northern China. A self‐organizing map and K‐means clustering analysis grouped the macroinvertebrate communities into five groups, and the indicator species reflected the environmental characteristics of each group. Principal component analysis indicated that the classification of the macroinvertebrate communities was affected by environmental variables. The Kruskal–Wallis test results showed that environmental variables (pH, total phosphorus, nitrate, water temperature, dissolved oxygen, conductivity, permanganate index, and ammonium) had a significant effect on the classification of the macroinvertebrate communities. Redundancy analysis showed that mollusks were significantly negatively correlated with pH and chlorophyll a, while annelids and aquatic insects were significantly positively correlated with chlorophyll a and dissolved oxygen. Spearman correlation analysis showed that the species richness and Shannon''s diversity of macroinvertebrates were significantly negatively correlated with total phosphorus, while the biomass of macroinvertebrates was significantly negatively correlated with pH. High alkalinity and lake eutrophication have a serious impact on the macroinvertebrate community. Human disturbances, such as industrial and agricultural runoff, negatively impact the ecological environment and affect macroinvertebrate community structure. Thus, macroinvertebrate community structure should be improved by enhancing the ecological environment and controlling environmental pollution at a watershed scale.     

Factors influencing macroinvertebrate assemblages in artificial subtropical ponds of Taiwan

Macroinvertebrate assemblages and its association with environmental factors at the 11 artificial subtropical ponds of Taiwan were examined using the multivariate analysis software STATICO. The aims of the study were to determine whether spatial and seasonal variation of macroinvertebrate assemblages changed seasonally, to examine which environmental factors determined the spatial and temporal structure of maroinvertebrate assemblages, and to compare between-pond variations in the taxon composition of macroinvertebrates. Macroinvertebrates were collected seasonally by a corer and a sweep net in 2007, and 13 physical and chemical factors were measured at the same time. A total of 31 macroinvertebrate taxa were collected during the sampling period, and the most dominant taxa were Chironomidae (31.7% of total animal abundance) and Tubificidae (22.4%). STATICO identified pond size, pond depth, sediment depth, and altitude as the major abiotic factors and Bufo melanostictus (Amphibia) as the major biotic factor to influence macroinvertebrate assemblages at these ponds. These factors changed with seasonality. For example, the abundance of B. melanostictus was the most important factor during the spring but became much less important in other seasons. According to the spatial distribution patterns of macroinvertebrate assemblages, macroinvertebrates could be split into two groups based on their dispersal. The active dispersers, such as insect taxa, were strongly associated with pond size and the passive dispersers, such as non-insect taxa, were strongly associated with the pond depth and/or sediment depth. The results of this study suggested that pond size might influence macroinvertebrate assemblages through their dispersal mechanisms and that the environmental factors which influenced the macroinvertebrate assemblages most changed with seasons in this study area.     

Relative influence of variables at multiple spatial scales on stream macroinvertebrates in the Northern Lakes and Forest ecoregion, U.S.A.

• 1 We used 94 sites within the Northern Lakes and Forests ecoregion spanning Minnesota, Wisconsin and Michigan to identify environmental variables at the catchment, reach and riparian scales that influence stream macroinvertebrates. Redundancy analyses (RDA) found significantly influential variables within each scale and compared their relative importance in structuring macroinvertebrate assemblages.
• 2 Environmental variables included landcover, geology and groundwater delivery estimates at the catchment scale, water chemistry, channel morphology and stream habitat at the reach scale, and landcover influences at three distances perpendicular to the stream at the riparian scale. Macroinvertebrate responses were characterised with 22 assemblage attributes, and the relative abundance and presence/absence of 66 taxa.
• 3 Each scale defined macroinvertebrates along an erosional to depositional gradient. Wisconsin's macroinvertebrate index of biotic integrity, Ephemeroptera–Plecoptera–Trichoptera taxa and erosional taxa corresponded with forest streams, whereas organic pollution tolerant, Chironomidae and depositional taxa corresponded with wetland streams. Reach scale analyses defined the gradient similarly as dissolved oxygen and wide, shallow channels (erosional) opposed instream macrophytes and pool habitats (depositional). Riparian forests within 30 m of the stream coincided with an erosional assemblage and biotic integrity.
• 4 Next, we combined all significant environmental variables across scales to compare the relative influence of each spatial scale on macroinvertebrates. Partial RDA procedures described how much of the explained variance was attributable to each spatial scale and each interrelated scale combination.
• 5 Our results appeared consistent with the concept of hierarchical functioning of scale in which large‐scale variables restrict the potential for macroinvertebrate traits or taxa at smaller spatial scales. Catchment and reach variables were equally influential in defining assemblage attributes, whereas the reach scale was more influential in determining relative abundance and presence/absence.
• 6 Ultimately, comprehending the relative influence of catchment and reach scale properties in structuring stream biota will assist prioritising the scale at which to rehabilitate, manage and derive policies for stream ecosystem integrity.

     

Predicting the constraint effect of environmental characteristics on macroinvertebrate density and diversity using quantile regression mixed model

Various factors, such as habitat availability, competition for space, predation, temperature, nutrient supplies, presence of waterfalls, flow variability and water quality, control the abundance, distribution and productivity of stream-dwelling organisms. Each of these factors can influence the response of the density of organisms to a specific environmental gradient, inflating variability and making difficult to understand the possible causal relationship. In our study, we used quantile regression mixed models and Akaike’s information criterion as an indicator of goodness to examine two different datasets, one belonging to Italy and one belonging to Finland, and to detect the limiting action of selected environmental variables. In the Italian dataset, we studied the relationships among five macroinvertebrate families and three physical habitat characteristics (water velocity, depth and substratum size); in the Finnish dataset the relationships between taxa richness and 16 environmental characteristics (chemical and physical). We found limiting relationships in both datasets and validated all of them on different datasets. These relationships are quantitative and can be used to predict the range of macroinvertebrate densities or taxa richness as a function of environmental characteristics. They can be a tool for management purposes, providing the basis for habitat-based models and for the development of ecological indices.     

Rainbow Trout diets and macroinvertebrates assemblages responses from watersheds dominated by native and exotic plantations

Over the past few decades, land-use changes through conversion of global forest cover to exotic plantations is contributing to both habitat and biodiversity loss and species extinctions. To better understand human influences on ecosystem, we use diet composition from introduced Rainbow Trout Oncorhynchus mykiss as indicator of potential changes in the composition of stream-macroinvertebrates due to land use changes from native to exotic vegetation (eucalyptus plantations) in southern Chile. Water quality variables, aquatic macroinvertebrates and Rainbow Trout diet were studied in 12 sites from mountain streams located in two watersheds including one dominated by native riparian vegetation and the other dominated by exotic vegetation. As expected, richness and abundance of macroinvertebrates were clearly higher at sites in native forest than in those with exotic vegetation. Collector-gatherer was the most abundant functional feeding group, but there was no statistical difference in the functional composition between the two watersheds. Differences in in-stream macroinvertebrate availability was more higher correlated with changes in Rainbow Trout diets. Specifically, taxa consumed from the watershed dominated by native forests was higher than from the watershed with exotic vegetation. Additional environmental variables showed statistical differences between watersheds. The exotic vegetation sites had the highest concentrations of dissolved solids, suspended solids, nitrates, chlorides and sulphates. Our findings show that macroinvertebrate assemblage structure and trout diets can be altered by changes in riparian vegetation. The absence of specific macroinvertebrate taxa in streams with exotic vegetation was captured by the composition of trout diets. This suggest that Rainbow Trout diets can be a good biological indicator of land use practices and thus, diet can be used as a rapid and effective tool for evaluate environmental quality. Our findings provide insights about the design of aquatic monitoring programmes to improve detection of anthropogenic impacts in streams in South America and elsewhere.     

渤海湾大型底栖动物调查及与环境因子的相关性

对渤海湾大型底栖动物和环境因子进行调查,利用多元分析技术对大型底栖动物与环境因子之间的关系进行研究。调查期间共发现大型底栖动物45种,平均密度为406个/m2。大型底栖动物数量空间变化明显,呈现从近岸到外海降低的变化特征。运用典范对应分析(CCA)探讨大型底栖动物与环境因子之间的关系,并采用向前引入法对环境因子进行逐步筛选,Monte Carlo置换检验结果显示,水深、无机氮和溶解氧是影响渤海湾大型底栖动物空间分布的关键环境因子。     

Probabilistic modeling and mapping of plant indicator species in a Northeast Oregon industrial forest,USA

Managing forest ecosystems for sustainable, multiple use requires forest resource managers to understand and predict how plant species composition and distribution varies across environmental gradients and responds to landscape scale disturbances. This study demonstrates predictive vegetation modeling and mapping for a Northeast Oregon forest using non-parametric Multiplicative Regression (NPMR) with presence/absence data for the species Clintonia uniflora (CLUN) and a set of stand structural and raster-based predictor variables. NPMR is a flexible probability modeling system that can find the best subset of habitat factors influencing species occurrence. NPMR was compared with logistic regression (LR) by building reduced models from variables selected as best by NPMR and full models from variables identified as significant with a forward stepwise process and further manual testing. log β was used to select models with the highest predictive capability. NPMR models were less complex and had higher predictive capability than LR for all modeling approaches. Spatial coordinates were among the most powerful predictors and the modeling approach with physiographic and stand structural variables together was the most improved relative to the average frequency of occurrence. GIS probability maps produced with the application of the physiographic models showed good spatial congruence between high probability values and plots that contained CLUN. NPMR proved to be a reliable probability modeling and mapping tool that could be used as the analytical link between monitoring and quantifying the status and trends of vegetation resources.     

Freshwater diatom biogeography in the Canadian Arctic Archipelago

Aim Document the biogeographical distributions of diatoms in the Canadian Arctic in relation to environmental factors. Location The Canadian Arctic Archipelago. Methods Diatoms were extracted from lake sediments and treated using standard methods. Rarefaction‐estimated species richness, diatom concentrations (valves cc^?1), and diatom abundance were mapped using a Geographic Information System. The physical and chemical parameters of the lakes were measured. Results A total of 326 taxa from 63 genera were found in 62 lakes of the study area. Up to 85 and as low as eight taxa were identified in any one lake, and rarefaction‐estimated species richness correlated with lake size. Nearby lakes could have greatly different diatom assemblages. Many taxa showed limited distributions. Response surfaces and ordination techniques indicate that a large number of taxa prefer colder regions of the Arctic while the abundance of others was influenced by lake water chemical parameters such as TKN and SiO₂. Main conclusions Although many taxa were common and found across the study area, diatom assemblages showed regional differences in the Arctic. Some taxa were not found in either the northern or southern parts of the Archipelago and others were restricted to particular regions. Newly delineated genera showed interpretable geographical patterns and could be related to environmental factors, suggesting that this more natural grouping may enhance our understanding of diatom ecology. Geographical, physical, and chemical factors are needed to explain diatom distributions in the Arctic.     

Are there any differences between taxa groups having distinct ecological traits based on their responses to environmental factors?

The aim of this study was to explore the differences between taxa groups with different ecological strategies for persistence, regarding their responses to environmental factors and seasonal variation. We studied the relationship between the seasonal patterns and habitat attributes of the Ephemeroptera, Plecoptera, Trichoptera (EPT) and the Colepotera, Heteroptera (CH) assemblages. Sampling was carried out in May, July and October of 2009. Samples were taken according to the AQEM protocol at 10 stream sections in the Mecsek Mountains. Based on multivariate analyses (RDA, pRDA), distinctive differences were found between the EPT and the CH taxa groups regarding their response to local chemical variables and variables describing the riparian vegetation. The measured environmental variables had a higher relative influence on the distribution patterns of EPT and CH assemblages than spatial variation of species patterns. The physical structure of aquatic habitats, including the type of bedrock, had greater effects on CH than EPT patterns, whereas the structure of riparian vegetation was more important for EPT than CH. Average density and average taxon richness of EPT were seasonally variable, but CH assemblages were not.     

Lake macroinvertebrates and the altitudinal environmental gradient in the Pyrenees

The distribution of different macroinvertebrate groups inhabiting the littoral zone of 82 mountain lakes in the Pyrenees was investigated in relation to the altitudinal environmental gradient. For each lake, altitude, longitude and latitude, together with 28 environmental variables, relating to chemical and physical characteristics and to lake general productivity, were considered. Using Principal Component Analysis (PCA) we showed that the altitudinal environmental gradient (i.e. altitude and altitude-related variables) represented the largest gradient of environmental variability. We found that incidence was related to altitude in about 50% of macroinvertebrate groups, most relationships being inverse, and also that the number of macroinvertebrate groups found per lake was better described by a second-order polynomial function than by simple linear regression. However, this relationship was linear for a subset of high-altitude lakes above 2,500 m a.s.l., suggesting an ecological threshold around this altitude. Redundancy Analyses (RDAs) showed the importance of environmental factors varying with altitude for the distribution of macroinvertebrate groups. Organic matter, salmonid presence, fine substrate dominance, macrophyte coverage, temperature and altitude by itself were, in this order, the most relevant factors. Partial RDAs showed that different combinations of these variables contributed to the explanation of the distribution of each group. However, the variable that uniquely explained most variability differed from group to group. We conclude that the altitudinal gradient is a multi-faceted ecological factor, which impinges on each group by means of some specific environmental variable(s) that are particularly relevant for the life history of that group.     

Littoral benthic macroinvertebrates of mountain lakes in the Tatra Mountains (Slovakia,Poland)

Littoral benthic macroinvertebrates of 45 mountain lakes in the Tatra Mountains were sampled using a semi-quantitative method in September 2000. A total of 32,852 specimens were identified to 93 taxa belonging to 14 higher taxonomic groups. Multivariate statistics (CCA, RDA) and nine biotic metrics (AQEM/STAR) were used to explain relationships between macroinvertebrate assemblages and environmental variables. Up to 57% of the ecological position of littoral macroinvertebrate assemblages were explained by variance of environmental variables divided into chemical, trophic, physical, catchment and location. Five types of Tatra lakes were recognized using CCA: A — strongly acidified lakes (small catchment, low pH, high concentration of TP, DOC, highest amount of POM in littoral); B — alpine acidified lakes (low amount of POM, low values of biotic metrics); C — alpine non-acidified lakes (high value of diversity index, predominance of Diptera); D — subalpine acidified lakes (high values of biotic metrics: number of families, proportion of crenal and rhithral taxa/total taxa); E — subalpine non-acidified lakes (high values of biotic metrics: number of families, number of genera, BMWP score, number of taxa and abundance of EPT taxa). RDA was used to design five levels of macroinvertebrate taxa acidification tolerance. The Tatra Acidification Index (TAI) was established to assess the acidification status of the lakes in the Tatra Mts.     

Response of benthic macroinvertebrates to whole-lake, non-native fish treatments in mid-elevation lakes of the Trinity Alps, California

Introduced fish reduce the abundance and diversity of native aquatic fauna, but the effect can be reduced in complex habitats. We manipulated fish populations in forested mountain lakes to determine whether or not fish affected benthic macroinvertebrate composition across lakes with differing habitat complexity. We compared abundance, biomass, body-length, and community structure of benthic macroinvertebrates from 16 lakes with three treatments (fish stocked, suspended stocking, fish removed) and unstocked fishless “controls”. Over 4 years, we assessed the relative importance of fish and environmental variables influencing the composition of benthic macroinvertebrates. Control lakes had the greatest overall abundance of macroinvertebrates when chironomid midges were excluded. Abundances of insects in the clinger/swimmer functional group and caddisflies were greatest in the control lakes but were primarily influenced by habitat variables including the availability of aquatic vegetation and wood. Total biomass and mean body length of macroinvertebrates were not affected by treatment. Taxon richness of macroinvertebrates was about 40% greater in the control lakes compared to the treatment lakes but did not differ among treatments. Our results suggest that fish reduce susceptible macroinvertebrate richness and abundances, but that changes associated with alterations of fish composition are confounded by other factors in complex lake habitats.     

The Application of Predictive Modelling for Determining Bio-Environmental Factors Affecting the Distribution of Blackflies (Diptera: Simuliidae) in the Gilgel Gibe Watershed in Southwest Ethiopia

Blackflies are important macroinvertebrate groups from a public health as well as ecological point of view. Determining the biological and environmental factors favouring or inhibiting the existence of blackflies could facilitate biomonitoring of rivers as well as control of disease vectors. The combined use of different predictive modelling techniques is known to improve identification of presence/absence and abundance of taxa in a given habitat. This approach enables better identification of the suitable habitat conditions or environmental constraints of a given taxon. Simuliidae larvae are important biological indicators as they are abundant in tropical aquatic ecosystems. Some of the blackfly groups are also important disease vectors in poor tropical countries. Our investigations aim to establish a combination of models able to identify the environmental factors and macroinvertebrate organisms that are favourable or inhibiting blackfly larvae existence in aquatic ecosystems. The models developed using macroinvertebrate predictors showed better performance than those based on environmental predictors. The identified environmental and macroinvertebrate parameters can be used to determine the distribution of blackflies, which in turn can help control river blindness in endemic tropical places. Through a combination of modelling techniques, a reliable method has been developed that explains environmental and biological relationships with the target organism, and, thus, can serve as a decision support tool for ecological management strategies.     

钱塘江中游流域不同空间尺度环境因子对底栖动物群落的影响

溪流底栖动物群落结构受不同空间尺度环境因子的共同作用。基于2010年钱塘江中游流域60个样点的大型底栖无脊椎动物和环境变量数据,寻找与研究流域底栖动物群落结构变化密切相关的关键环境变量,解析流域尺度和河段尺度的环境因子对底栖动物群落的相对影响。PCA分析表明该区域的主要环境梯度是流域内的土地利用类型及其引起的溪流物理生境退化程度和水体营养状态。CCA分析发现影响底栖动物群落的流域尺度的关键环境变量是纬度、海拔、样点所在流域大小、森林用地百分比,河段尺度是总氮、总磷、钙浓度、二氧化硅浓度和平均底质得分。偏CCA分析得到两种尺度环境因子对底栖动物变异的总解释量为26.4%,流域尺度和河段尺度变量分别为总解释量的50%和31%;方差分解结果表明研究区域大型底栖无脊椎动物受到两种尺度环境因子的综合影响,且流域尺度环境因子较河段尺度环境因子更为重要,体现了其在溪流生态系统保护、恢复、监测和评价中的重要参考价值。     

Assessing abiotic correlations of an indicator species with sympatric riparian birds in a threatened submontane river–forest system using joint species modelling

Aim

To assess the abiotic correlations between indicator species and others in the community. Additionally, we evaluated the importance of environmental variables in driving the co-occurrence patterns of the coexisting riparian bird species within a threatened aquatic and terrestrial system.

Location

Seven classic submontane rivers in riparian ecosystems of the Changbai Mountains in eastern Jilin Province, China, elevation ranging from 351 to 942 m.

Methods

Joint species distribution models (JSDMs) were applied to examine the relative importance of abiotic and potential species associations driving the abundance and cooccurrence of bird species along submontane riparian zones. The abiotic factors were examined with a focus on the scaly-sided Merganser and the coexisting bird species potentially sharing or interacting within the same niche.

Results

We found that the co-occurrence patterns of submontane riparian bird species were dominantly driven by numerous positive correlations when incorporating abiotic variables. The scaly-sided Merganser exhibited the greatest number of correlations with other species and exhibited significant responses to most of the measured environmental variables. Land cover diversity, proportion of gravel bars, and channel width were the most common environmental factors affecting riparian bird species distribution.

Conclusions

Using JSDM, we found that the indicator roles of the scaly-sided Merganser are mainly derived from shared environmental responses with coexisting riparian bird species; moreover, the composition of submontane riparian bird communities is affected by both environmental variables and potential species associations. Our results verified the central role of the scaly-sided Merganser as an indicator species in submontane riparian ecosystems due to their strict physical environment preferences and extensive connections with other sympatric riparian bird species, primarily through shared environmental intersections. Our results emphasize the crucial necessity for simultaneously considering environmental predictors and potential species associations in modelling species distributions and to better realizing the roles of indicators in practical applications.     

Habitat complexity as a determinate of benthic macroinvertebrate community structure in cypress tree reservoirs

We analyzed benthic samples (n = 128) collected from four cypress-tree population areas within a large, shallow Arkansas reservoir over a 2-year period to investigate macroinvertebrate community distribution patterns and their relation to physical and chemical parameters. The calculated biomass, abundance and diversity of the benthic macroinvertebrate community varied significantly both temporally and spatially. Variations of these variables are most likely explained by significant differences in the concentration of carbon and nitrogen in sediments across lake sites, and on a smaller scale, the presence or absence of cypress trees. Benthic macroinvertebrate abundance, biomass, and diversity significantly decreased with distance from tree.