Spatial and Temporal Variation of Macroinvertebrate Drift in Two Neotropical Streams1

The detection of spatial variation in macroinvertebrate drift depends on the spatial scale of investigation in streams of the La Selva Biological Station, Costa Rica. Drift samples were taken in a spatially nested design, with two streams, two reaches per stream, two riffles per reach, and four replicate samples per riffle. Drift showed little variation among streams, but varied significantly at the scales of reach and riffle, with variation among samples also high. In addition, sampling took place at two temporal scales: diel and at two different periods that differed in rainfall conditions. Drift diel periodicity was a clear pattern, while only density of individuals varied among sampling periods. This is the first study of macroinvertebrate drift at multiple spatial scales, despite the recognition that multi‐scale studies are essential for a more complete understanding of community patterns and processes.     

Temporal and Spatial Distribution Patterns of Larval Trichoptera in Madeiran Streams

Temporal and spatial distribution patterns of lotic larval trichopteran assemblages in relation to environmental variables were investigated in Madeiran streams using multivariate analyses. TWINSPAN classification detected distinct faunal assemblages related to spatial factors between non-polluted high altitude sites and lower lying enriched sites where tolerant taxa were predominant but showed strong seasonal shifts in species composition and abundance. The 15 TWINSPAN end groups were grouped into five arbitrary clusters based upon the seasonal and spatial changes in the trichopteran assemblages detected by the analysis. Significant differences between environmental variables (distance from source, altitude, temperature, conductivity, alkalinity and nitrate) and the trichopteran assemblages (using trichopteran based metrics) of these clusters were confirmed by the Kruskal-Wallis test (H) and Dunn’s test. Chemical classification of samples within the clusters revealed a strong association between trichopteran assemblages and water quality. Canonical Correspondence Analysis and Monte Carlo global permutation tests also identified significant associations between the larval assemblages and physicochemical variables such as temperature and conductivity along a strong physical gradient (altitude, slope) and nitrate along a weaker seasonal gradient. Analysis of functional feeding group distribution patterns clearly showed that mid to high altitude indigenous woodland sites were trophically diverse whilst the lower reaches of the islands streams are trophically impoverished with strong seasonal shifts between two feeding groups of enrichment tolerant taxa. Trichopteran shredders are exclusive to indigenous woodland sites, indicating a limited distribution associated with land use, allochthonous input and habitat destruction. The results indicate that several ‘environmental filters’ operate at different levels upon the islands trichopteran fauna, producing temporally and spatially distinct ‘subsets’ of species best able to exploit conditions and resources at a given site or time, confounding the direct comparison of these insular systems with the findings of the River Continuum Concept, traditionally associated with unaffected continental lotic systems.     

Functional Differences Among Benthic Macroinvertebrate Communities in Reference Streams of Same Order in a Given Biogeographic Area

Ecological theory (Southwood, 1977. Journal of Animal Ecology 46: 337–365, 1988. Oikos 52: 3–18; Townsend, 1989. Journal of the North American Benthological Society 8: 36–50; Townsend & Hildrew, 1994. Freshwater Biology 31: 265–275) considers that spatio-temporal variations in habitats act as evolutionary forces on organisms, selecting for traits that maximize fitness. As a consequence, communities developed under same environmental conditions should present the same combination of species bio-ecological characteristics. The objective was to verify, using data from the same biogeographical zone, (1) if there was a unique suite of bio-ecological profiles for reference macrobenthic communities of `comparable' rivers or (2) if the distribution of bio-ecological traits within reference communities was significantly influenced by geology. The variability of 22 bio-ecological traits in 12 different sites was tested to evaluate the potential influence of geological substrate on biological and ecological features of reference stream communities. Observed patterns suggested that communities displayed highly stable bio-ecological profiles among sites (within a given biogeographical zone) whatever the substrate was, even if communities on clayey substrate exhibited slightly different bio/ecological characteristics than on others geologies. Nevertheless, the functional structure of macrobenthic communities in reference sites was quite stable in this biogeographical area. This study was restricted to the selected stream types and its results may not directly be transferred to other biogeographical areas and stream types. However, the perspective of a unique functional reference for streams of the same order in a given biogeographical area, improve functional comparison between observed vs. reference communities. This could simplify and objectively define the ecological status of a given site.     

Macroinvertebrate Responses to Algal and Bacterial Manipulations in Streams

Our study was designed to assess the relative importance of algae and bacteria as sources of energy for stream macroinvertebrates. In one experiment, we manipulated algae by artificially shading six sections in each of two streams, one stream with an open canopy (clear-cut drainage basin) and the other with a closed canopy (forested drainage basin); both streams were in Hubbard Brook Experimental Forest, New Hampshire, USA. Chlorophyll a concentrations were reduced from 0.2 to 0.05 μg/cm² in artificially shaded sections of both streams. However, macroinvertebrates showed no response to these algal manipulations in either the clear-cut or forested stream. Nutrient concentrations (N and P) were low and limiting to primary production in both the clear-cut and forested streams. Additionally, both streams had relatively low macroinvertebrate densities suggesting bottom-up controls were important in macroinvertebrate abundance. However, the forested stream did have higher macroinvertebrate densities presumably because of higher inputs of coarse particulate organic matter from the riparian vegetation. In a second experiment, in Augusta Creek, Michigan, we manipulated both algae and bacteria. To reduce algae, we artificially shaded experimental stream channels so that chlorophyll a was reduced from natural levels of 3.0–5.6 to 0.4–0.7 μg/cm². Half of the shaded channels had dissolved organic carbon (DOC – sucrose) dripped into them to raise DOC levels by 2–3 mg/l and thus stimulate bacterial abundance. Open channels, with higher algal abundance, had higher densities of Ephemerella, but only in November when nymphs were larger. Channels with increased DOC had higher bacterial abundances, higher densities of Chironomidae and lower densities of Heptageniidae. Several other macroinvertebrate taxa that were at relatively low abundance in our samples showed no significant response to these manipulations. Our results suggest that early instar Ephemerella may not rely as heavily on algae as later instars. Also, certain taxa were able to use the heterotrophic microbial community, especially chironomids which increased in numbers when bacterial density increased; thus, the bacterial carbon source may be more important to some stream macroinvertebrates than previous studies have suggested.     

Comparative Environmental Assessment in the Studies of Benthic Diatom,Macroinvertebrate, and Fish Communities

Community response to environmental gradients operating at hierarchical scales was assessed in studies of benthic diatoms, macroinvertebrates and fish from 44 stream sites in the New York City watershed. Hierarchical cluster analysis (TWINSPAN) of diatoms and fish partitioned the study sites into four groups, i.e., acid streams, reservoir outlets and wetland streams, large eutrophic streams, and small eutrophic streams; macroinvertebrate TWINSPAN distinguished an additional group of silty eutrophic streams. The correspondence among the three assemblage TWINSPAN groupings was moderate, ranging from 51 to 57%. The similarity across the four major group types was the highest among large eutrophic stream and acid stream assemblages, and the lowest among small eutrophic stream assemblages. Stepwise discriminant function analysis revealed that environmental factors discriminated most effectively the diatom grouping and least effectively the fish grouping. The best environmental predictors for diatom and macroinvertebrate grouping were conductance and percent surface water, while population density was most powerful in separating the fish groups. Carbaryl was the only pesticide that correlated with macroinvertebrate grouping. Partial redundancy analyses suggested a differential dependence of freshwater communities on the scale of the environmental factors to which they respond. The role of small‐scale habitat and habitatland cover/land use interaction steadily increased across the diatom, macroinvertebrate, and fish assemblages, whereas the effect of large‐scale land cover/land use declined.     

Structure of Macroinvertebrate Communities in Relation to Environmental Variables in a Subtropical Asian River System

Subtropical Asian rivers support a highly diverse array of benthic macroinvertebrates. Yet, their biodiversity and functionality has been poorly investigated. We choose the Chishui River system, one of the largest un‐dammed, first level branches upstream of the Yangtze River, China, to: 1) determine the spatial pattern of macroinvertebrate diversity and community structure, and 2) examine the influence of variables at local habitat and basin scales on the distribution of macroinvertebrate communities. Samples were collected from 43 sites in spring of 2007. After Canonical Correspondence Analysis, two basin and five habitat variables were found to be significant predictors of the macroinvertebrate community structure. Variance partitioning analysis showed that habitat physical variables had a greater influence than other environmental variables in macroinvertebrate community, which suggested that preserving habitat, especially upstream, should be strongly considered in biological conservation. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparing the Fish and Benthic Macroinvertebrate Diversity of Restored Urban Streams to Reference Streams

Urbanization is associated with substantial losses to stream biological diversity throughout the United States' mid‐Atlantic. Stream restoration has been used to improve stream conditions and, in part, to ameliorate these losses. However, the relationship between restoration and recovery of biological diversity is unclear. Our objective was to critically examine the efficacy of urban stream restorations with regard to biological diversity. We compared restored urban streams to urban nonrestored, nonurban, and reference (minimally degraded) streams using five measures each of fish and benthic macroinvertebrate diversity. Both multivariate and univariate statistical analyses show biological diversity of restored urban streams to be similar to nonrestored urban streams and lower than nonurban and reference streams. Restored urban sites showed no apparent increase in biological diversity through time, while diversity decreased at two of the reference streams coincident with increased urban development within their catchments. Our results indicate that restoration approaches commonly used regionally as in these urban streams are not leading to recovery of native stream biodiversity. Evidence from several sources indicates a need for dramatic changes in restoration approach, and we argue for a watershed‐scale focus including protection of the least impacted streams and adopting other land‐based actions within the watershed where possible.     

Patterns in the Composition of Microbial Communities from a Subtropical River: Effects of Environmental,Spatial and Temporal Factors

Microbes are key components of aquatic ecosystems and play crucial roles in global biogeochemical cycles. However, the spatiotemporal dynamics of planktonic microbial community composition in riverine ecosystems are still poorly understood. In this study, we used denaturing gradient gel electrophoresis of PCR-amplified 16S and 18S rRNA gene fragments and multivariate statistical methods to explore the spatiotemporal patterns and driving factors of planktonic bacterial and microbial eukaryotic communities in the subtropical Jiulong River, southeast China. Both bacterial and microbial eukaryotic communities varied significantly in time and were spatially structured according to upper stream, middle-lower stream and estuary. Among all the environmental factors measured, water temperature, conductivity, PO₄-P and TN/TP were best related to the spatiotemporal distribution of bacterial community, while water temperature, conductivity, NO_x-N and transparency were closest related to the variation of eukaryotic community. Variation partitioning, based on partial RDA, revealed that environmental factors played the most important roles in structuring the microbial assemblages by explaining 11.3% of bacterial variation and 17.5% of eukaryotic variation. However, pure spatial factors (6.5% for bacteria and 9.6% for eukaryotes) and temporal factors (3.3% for bacteria and 5.5% for eukaryotes) also explained some variation in microbial distribution, thus inherent spatial and temporal variation of microbial assemblages should be considered when assessing the impact of environmental factors on microbial communities.     

False Correlates of Nested Patterns: A Case Study Using Temporary Pond Microcrustaceans

Nestedness analysis is a popular tool for inferring spatial species distributions, and therefore has management and conservation relevance. Ecologists frequently compute nestedness and subsequently use Spearman rank correlations for inferring relationships between the observed nested ranks of sites with biogeographic and environmental variables. Using temporary pond microcrustaceans hatched from microcosms as a case study, this paper shows that the application of this method can be problematic. While the overall degree and significance of nestedness was robust against a statistical error, the results obtained from randomly generated matrices, in which community structure from the original microcrustacean incidence matrix was maintained (fixed rows –fixed columns constraints), showed that rank correlations of observed nested patterns can be vulnerable to a Type 1 error (detecting an effect when there is none). Using expected nestedness patterns derived from rarefied original matrices to control for sample size effects did not change this result. This problem may have arisen as a result of a quantitative bias related to the disproportionate impact of rank positions of individual ponds in the analysis. Future extensive simulations studies, involving different community structures, should help identify the general reliability of rank correlation results in nestedness analyses. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Natural‐Channel‐Design Restorations That Changed Geomorphology Have Little Effect on Macroinvertebrate Communities in Headwater Streams

Stream restorations that increase geomorphic stability can improve habitat quality, which should benefit selected species and local aquatic ecosystems. This assumption is often used to define primary restoration goals; yet, biological responses to restoration are rarely monitored or evaluated methodically. Macroinvertebrate communities were inventoried at 6 study reaches within 5 Catskill Mountain streams between 2002 and 2006 to characterize their responses to natural‐channel‐design (NCD) restoration. Although bank stability increased significantly at most restored reaches, analyses of variation showed that NCD restorations had no significant effect on 15 of 16 macroinvertebrate community metrics. Multidimensional scaling ordination indicated that communities from all reach types within a stream were much more similar to each other within any given year than they were in the same reaches across years or within any type of reach across streams. These findings indicate that source populations and watershed‐scale factors were more important to macroinvertebrate community characteristics than were changes in channel geomorphology associated with NCD restoration. Furthermore, the response of macroinvertebrates to restoration cannot always be used to infer the response of other stream biota to restoration. Thus, a broad perspective is needed to characterize and evaluate the full range of effects that restoration can have on stream ecosystems.     

Wood‐Associated Macroinvertebrate Fauna in Central European Streams

An overview of macroinvertebrates associated with wood debris is given, with the main focus on Central European fauna. In general, three categories of macroinvertebrate wood relations are distinguished: taxa frequently associated with wood but not xylophagous, facultative xylophagous taxa and obligate xylophagous taxa. The adaptations in the life history, ethology and physiology of species representing these three groups are reviewed. From literature and our own investigations, 15 taxa inhabiting Central European freshwater ecosystems are known to be obligate xylophagous, 22 taxa are facultatively xylophagous. From field observations another 41 taxa presumably feed on wood although no gut content analyses and laboratory experiments have yet been carried out. From 25 taxa other forms of close association to CWD are known (feeding on epixylic biofilm, use as a refuge, or as an attachment point). Possible pathways of xylophagy evolution are discussed and unresolved aspects of aquatic invertebrate wood relations are listed.     

Bacterial Communities in Acidic and Circumneutral Streams

The relationship between pH and the abundance and activity of bacteria in streams was examined as part of a study of the effect of acidification on stream communities. Of the bacterial communities examined, the epilithic community appeared to be the most significantly affected by acidification. Microbial biomass, as quantified by measuring the ATP level, on rock surfaces was significantly correlated with pH. Also, bacterial production by the epilithic bacteria, indicated by incorporation of tritiated thymidine into DNA, was always higher at high-pH sites than at low-pH sites of the same stream order and elevation. Bacterioplankton concentrations varied between 0.53 × 10⁵ and 9.42 × 10⁵ cells · ml⁻¹ in the first- to fourth-order streams examined. The bacterioplankton concentration in one sample from a spring was 0.17 × 10⁵ cells · ml⁻¹. Bacterioplankton concentrations were not correlated with pH but were significantly correlated with seston concentrations. The correlation with seston is a result of increases in particle-associated bacteria at high seston concentrations. The proportion of bacterioplankton attached to particles varied from 0 to 70%. Bacterial numbers and production in the sediments were significantly correlated with the organic content of the sediment rather than with the pH of the overlying water. Thus, reduced abundance and activity of bacteria as a result of acidification could be detected only for the relatively active community on rock surfaces; this community was exposed to the low pH because of the unbuffered nature of its environment.     

Patterns and Ecological Correlates of Pollination Modes Among Bromeliad Communities of Andean Forests in Bolivia

Abstract: We studied the distribution of five pollination modes (ornithophily, chiropterophily, entomophily, mixed/unspecific, autogamy) among the bromeliad communities of 74 forest sites in the Bolivian Andes and adjacent lowlands. We recorded a total of 188 bromeliad species belonging to 16 genera, including 115 (61 %) ornithophilous, 14 (7 %) chiropterophilous, 45 (24 %) entomophilous, 8 (4 %) autogamous, and 6 (3 %) species with mixed pollination mode. Ornithophily was the dominant pollination mode at high elevations and in wet regions, while entomophily dominated in arid regions. Chiropterophily was most common in wet lowland regions, autogamy in arid sites, and mixed pollination in the lowlands. Pollination modes were rather evenly distributed among life-forms and ecophysiological types, with a few exceptions: terrestrial forest bromeliads, mostly belonging to unarmed, soft-leaved taxa, had a prevalence of entomophily and few ornithophilous species; large, spiny terrestrial bromeliads of Puya and Bromelioideae showed a prevalence of ornithophily; and autogamy was restricted to the neotenous subgenus Diaphoranthema of Tillandsia. The restriction of unspecific pollination modes to the lowlands is hypothesized to be related to the abundance of pollinators, eliminating the need for specialized co-evolution, or to the overall rarity of bromeliads in this environment, precluding the development of specialized relationships. The low representation of entomophilous species in small dry forest regions compared to extensive areas is assumed to be due to the seasonal influx of hummingbirds and/or bats. Overall, the frequency of individual pollination modes was related to the availability of pollinators as determined by temperatures and humidity.     

Temporal and Spatial Patterns in Inputs and Stock of Organic Matter in Savannah Streams of Central Brazil

Coarse particulate organic matter (CPOM) inputs from riparian vegetation into streams and CPOM benthic stock vary naturally in space and time, but most studies in the tropical savannah (Cerrado) have been done over a small temporal scale (<1 year), which does not allow for the determination of inter-annual patterns. We found that CPOM collected over two years differed temporally and spatially, whereas there was no significant variation between years for the benthic stock, which indicates high stability in the energy balance of streams. The largest monthly inputs occurred between August and October, at the end of the dry season and the onset of the rainy season, which was partially explained by precipitation. Other factors such as photoperiod, which was not studied, could also have important roles in this pattern. Spatial differences in CPOM between streams were attributed to topography and channel morphology. The plant density was lowest in the stream with a more irregular topography and a deeper channel, which results in drier riparian soil. The benthic stock was highest in the stream with a flat channel, where the lower water speed facilitates the accumulation of CPOM in the stream bed. Inter-annual differences in CPOM were attributed more to the differences in the beginning of the dry and wet periods between years than to the average values of precipitation. Longer-term studies are needed to clarify this temporal pattern.     

Temporal Patterns in Bacterial Communities in Three Temperate Lakes of Different Trophic Status

Despite considerable attention in recent years, the composition and dynamics of lake bacterial communities over annual time scales are poorly understood. This study used automated ribosomal intergenic spacer analysis (ARISA) to explore the patterns of change in lake bacterial communities in three temperate lakes over 2 consecutive years. The study lakes included a humic lake, an oligotrophic lake, and a eutrophic lake, and the epilimnetic bacterial communities were sampled every 2 weeks. The patterns of change in bacterial communities indicated that seasonal forces were important in structuring the behavior of the bacterial communities in each lake. All three lakes had relatively stable community composition in spring and fall, but summer changes were dramatic. Summertime variability was often characterized by recurrent drops in bacterial diversity. Specific ARISA fragments derived from these lakes were not constant among lakes or from year to year, and those fragments that did recur in lakes in different years did not exhibit the same seasonal pattern of recurrence. Nonetheless, seasonal patterns observed in 2000 were fairly successful predictors of the rate of change in bacterial communities and in the degree of autocorrelation of bacterial communities in 2001. Thus, seasonal forces may be important structuring elements of these systems as a whole even if they are uncoupled from the dynamics of the individual system components.     

Temporal Variation and Co-occurrence Patterns of Bacterial Communities in Eutrophic Lake Taihu,China

To understand the long-term and local variations of bacteria under the influence of annually re-occurred water bloom, bacterial community composition (BCC) was investigated monthly for 3 years (2009–2011) at four different sites located across Lake Taihu. The bacterial community composition was analyzed by 16S rRNA gene clone libraries and terminal restriction fragment length polymorphism. Co-occurrence patterns among bacterial taxa and environmental variables were determined through network analysis. Overall, strong seasonal variation patterns of BCC were observed whilst the spatial variations of BCC were slight in the long-term observation. However, core species bacteria persisted throughout the annual variations. Network analysis showed that the highly connected operational taxonomic units in bacteria-environment network included both the numerically dominant taxa and some functional groups with low abundance, such as Methylophilaceae and Nitrospira. Co-occurrence networks further revealed that the correlations of bacteria-bacteria could be more critical than those between environment and bacteria in structuring microbial communities, and would be a crucial driving factor of BCC in Lake Taihu.     

The Ecology of Temporary Streams I. The Faunas of Two Canadian Streams

This, the first of two papers on the ecology of temporary streams, describes, in detail, the faunas of two such habitats in southeastern Canada. The adaptive mechanisms for coping with the summer drought are documented for a variety of species and faunal succession is shown to occur from the stream stage (fall-winter) through the pool stage (spring) to the terrestrial (summer).     

Links Between Anthropogenic Perturbations and Benthic Macroinvertebrate Assemblages in Afromontane Forest Streams in Uganda

Relationships between environmental variables and benthic macroinvertebrate assemblages were investigated among several sites that varied in disturbance history in Bwindi Impenetrable National Park, an Afromontane site in East Africa. Environmental variables were correlated with the level of past catchment disturbance – logging, agricultural encroachment, and present tourism activity. For example, sites in medium and high disturbance categories had higher values of specific conductance and lower water transparency than low disturbance category sites, these environmental variables may therefore act indicators of ecological quality of rivers. Environmental variables such as conductivity and water transparency were found to be good predictors of benthic macroinvertebrate assemblages, with anthropogenically stressed sites having lower diversity than the reference sites. Impacted sites were dominated by tolerant taxa such as chironomid and leeches, while ‘clean water’ taxa such as Ephemeroptera, Plecoptera and Trichoptera dominated at minimally impacted sites. Comparison of sites with different disturbance histories provided evidence for differences in benthic macroinvertebrate communities that reflect the state of forest restoration and recovery. We recommend quarterly monitoring of water quality to act as an early warning system of deterioration and tracking ecological recovery of previously impacted sites.     

The Ecology of Temporary Streams III. Temporary Stream Fishes in Southern Ontario,Canada

The 12 fish species living in three temporary streams in Southern Ontario, Canada, during 1973–1974, are listed. Environmental parameters are recorded together with details of the abundance, distribution, age structure, growth, reproduction and food of the more common species. These species are thought to be either physiologically very tolerant, or to be capable of temporal or spatial migrations. Colonization of temporary streams bestows benefits in terms of plentiful invertebrate food, although resource sharing may occur, earlier spring breeding and reduced predation.     

Classification of Springs in the Lake Baikal Region by Macroinvertebrate Communities

The macrozoobenthos communities in 15 cold fresh, 12 mineral (sodium chloride), and 19 thermal springs of the Baikal Rift Zone and adjacent areas have been investigated. The classification of springs on the basis of quantitative indicators of abundance was proposed. According to the dominant group of fauna, three types of communities were identified for the cold springs; six types, for mineral springs; and four types, for thermal springs. It was established that communities with the dominance of Chironomidae, Turbellaria, and Oligochaeta are formed in cold springs and communities with the predominance of Gastropoda (one or two species) prevail in thermal springs. It was noted that mineral springs of medium mineralization are characterized by communities with a prevalence of Amphipoda (Gammarus lacustris); those with high salinity are dominated by Brachyceran flies (Diptera, Brachycera).