Seasonal fluctuations of macroinvertebrate drift in a South Carolina Piedmont stream

The seasonal fluctuations of larval macroinvertebrate drift, exuvial drift and larval benthic density were quantitatively examined over a 1-year period in a fourth order, spring-fed stream in the Piedmont area of South Carolina. The drift was dominated by the mayfly Baetis spp. and by two species of blackfly (Prosimulium mixtum and Simulium jenningsi). Peak drift densities were noted during early spring and especially late summer. Strong correlations were noted between larval drift densities and exuvial drift, indicating a relationship between drift and seasonal growth and emergence patterns. Seasonal trends in drift and benthic densities, though less strongly correlated, were also generally similar.     

Stable baselines of temporal turnover underlie high beta diversity in tropical arthropod communities

While the high species diversity of tropical arthropod communities has often been linked to marked spatial heterogeneity, their temporal dynamics have received little attention. This study addresses this gap by examining spatio‐temporal variation in the arthropod communities of a tropical montane forest in Honduras. By employing DNA barcode analysis and Malaise trap sampling across 4 years and five sites, 51,596 specimens were assigned to 8,193 presumptive species. High beta diversity was linked more strongly to elevation than geographic distance, decreasing by 12% when only the dominant species were considered. When sampling effort was increased by deploying more traps at a site, beta diversity only decreased by 2%, but extending sampling across years decreased beta diversity by 27%. Species inconsistently detected among years, likely transients from other settings, drove the low similarity in species composition among traps only a few metres apart. The dominant, temporally persistent species substantially influenced the cyclic pattern of change in community composition among years. This pattern likely results from divergence–convergence dynamics, suggesting a stable baseline of temporal turnover in each community. The overall results establish that large sample sizes are necessary to reveal species richness, but are not essential for quantifying beta diversity. This study further highlights the need for standardized methods of sampling and species identification to generate the comparative data required to evaluate biodiversity change in space and time.     

Rainfall homogenizes while fruiting increases diversity of spore deposition in Mediterranean conditions

There is a lack of knowledge regarding the main factors modulating fungal spore deposition in forest ecosystems. We have described the local spatio-temporal dynamics of fungal spore deposition along a single fruiting season and its relation with fruit body emergence and rainfall events. Passive spore traps were weekly sampled during autumn and analysed by metabarcoding of the ITS2 region in combination with qPCR. There were larger compositional changes of deposited spores across sampling weeks than amongst sampling plots. Spore diversity and abundance correlated with mushroom emergence and weekly rainfall. Spore compositional changes were related to rainfall, with lower spatial compositional heterogeneity across plots during weeks with higher rainfall. Soil saprotrophs, and amongst them, puffball species, showed the strongest positive correlation with rainfall across fungal guilds. We saw high fine-scale temporal changes of deposited spores, and both mushroom emergence and rainfall may be important factors driving airborne spore deposition.     

Diel variation in chironomid (Diptera: Insecta) exuviae abundance and taxonomic richness in near-pristine upland streams of the Greater Blue Mountains World Heritage Area,South-Eastern Australia

We assessed diurnal variation of Chironomidae exuviae in two small upland streams in temperate Australia, during summer. Understanding the diel periodicity of exuviae can be an important consideration for biomonitoring purposes or to investigate adult emergence patterns. We collected 1,813 floating exuviae, comprising 54 taxa from four subfamilies, from flowing water using a drift net. Unlike many northern hemisphere temperate studies, we observed that peak exuviae abundance (7.3 exuviae per m3) and taxon richness (1.7 taxa per m3) occurred in the dusk and night hours, with the lowest numbers (0.9 exuviae per m3) and taxon richness (0.6 taxa per m3) recorded in the late morning to early afternoon. We suggest that this could be an adaptation to avoid stressful weather during the heat of summer days, or it could be to avoid visual predators. The numerically dominant taxa exhibited peak abundance in the dusk/night samples which indicates predominant crepuscular/nocturnal patterns of adult emergence. This pattern was consistent across both streams surveyed. Our taxon inventory rose steeply during the first 24-h occasion, then at a reduced rate during the second and third days of sampling. For flowing water collections of exuviae that utilise drift-netting, we suggest that sampling at all sites includes at least three 24-h cycles and avoids periods of heavy rainfall and increased stream flow.     

Temporal consistency in the long-term spatial distribution of macroinvertebrate drift along a stream reach

Previous studies of the spatial pattern of stream invertebrate drift have focused on spatial variation at microhabitat scales or landscape scales, or temporal variation over diel or seasonal scales. None have examined consistency in spatial variation over longer time scales (>1 year). This study examined invertebrate drift density and composition at fixed locations (terminal ends of 10 riffles) each month at day and night along a 1 km reach of a 2nd order stream over a period of nearly 2 years. Consistent differences in the density of macroinvertebrate drift between riffles over 2 years were observed. The only habitat characteristic observed to be related to invertebrate drift density was the length and size of riffles above sampling sites, with larger and longer riffles producing the highest drift densities. Consistent differences in the supply of drifting macroinvertebrates along a stream reach may have implications for the supply of colonists to substrate patches and the profitability of feeding positions for drift-feeding fish and other predators. Handling editor: D. Dudgeon     

Long-term patterns of invertebrate stream drift in an Australian temperate stream

1. Invertebrate stream drift was sampled bimonthly in the Acheron River, Victoria, Australia, over a period of 18 months. Replicated hourly samples were collected over a 25-h period on each sampling date. A total of 194 taxa were identified in the drift. However, total drift density was dominated by few taxa. 2. Some evidence was obtained for a seasonal pattern in drift: this was most pronounced in relative abundances of individual taxa and the composition of the drift, rather than in total drift densities. Most of the commonly collected taxa reflected the seasonal pattern of total drift. However, some of the common taxa did not. 3. A small number of taxa showed behavioral drift, with a nocturnal increase in drift densities. One species of ‘Baetis’ drifted in high densities over short periods of time around dusk and dawn. It did not drift in higher densities during the night than during the day. The results emphasize the need for drift studies to be more rigorously designed than is typically the case.     

Species turnover in lake littorals: spatial and temporal variation of benthic macroinvertebrate diversity and community composition

Aims Despite wide consensus that ecological patterns and processes should be studied at multiple spatial scales, the temporal component of diversity variation has remained poorly examined. Specifically, rare species may exhibit patterns of diversity variation profoundly different from those of dominant taxa. Location Southern Finland. Methods We used multiplicative partitioning of true diversities (species richness, Shannon diversity) to identify the most important scale(s) of variation of benthic macroinvertebrate communities across several hierarchical scales, from individual samples to multiple littorals, lakes and years. We also assessed the among‐scale variability of benthic macroinvertebrate community composition by using measures of between‐ and within‐group distances at hierarchical scales. Results On average, a single benthic sample contained 23% of the total regional macroinvertebrate species pool. For both species richness and Shannon diversity, beta‐diversity was clearly the major component of regional diversity, with within‐littoral beta‐diversity (β₁) being the largest component of gamma‐diversity. The interannual component of total diversity was small, being almost negligible for Shannon index. Among‐sample (within‐littoral) diversity was related to variation of substratum heterogeneity at the same scale. By contrast, only a small proportion of rare taxa was found in an average benthic sample. Thus, dominant species among lakes and years were about the same, whereas rare species were mostly detected in a few benthic samples in one lake (or year). For rare species, the temporal component of diversity was more important than spatial turnover at most scales. Main conclusions While individual species occurrences and abundances, particularly those of rare taxa, may vary strongly through space and time, patterns of dominance in lake littoral benthic communities are highly predictable. Consequently, many rare species will be missed in temporally restricted samples of lake littorals. In comprehensive biodiversity surveys, interannual sampling of littoral macroinvertebrate communities is therefore needed.     

Spatio‐temporal scaling of biodiversity and the species–time relationship in a stream fish assemblage

1. The increase of species richness with the area of the habitat sampled, that is the species–area relationship, and its temporal analogue, the species–time relationship (STR), are among the few general laws in ecology with strong conservation implications. However, these two scale‐dependent phenomena have rarely been considered together in biodiversity assessment, especially in freshwater systems. 2. We examined how the spatial scale of sampling influences STRs for a Central‐European stream fish assemblage (second‐order Bernecei stream, Hungary) using field survey data in two simulation‐based experiments. 3. In experiment one, we examined how increasing the number of channel units, such as riffles and pools (13 altogether), and the number of field surveys involved in the analyses (12 sampling occasions during 3 years), influence species richness. Complete nested curves were constructed to quantify how many species one observes in the community on average for a given number of sampling occasions at a given spatial scale. 4. In experiment two, we examined STRs for the Bernecei fish assemblage from a landscape perspective. Here, we evaluated a 10‐year reach level data set (2000–09) for the Bernecei stream and its recipient watercourse (third‐order Kemence stream) to complement results on experiment one and to explore the mechanisms behind the observed patterns in more detail. 5. Experiment one indicated the strong influence of the spatial scale of sampling on the accumulation of species richness, although time clearly had an additional effect. The simulation methodology advocated here helped to estimate the number of species in a diverse combination of spatial and temporal scale and, therefore, to determine how different scale combinations influence sampling sufficiency. 6. Experiment two revealed differences in STRs between the upstream (Bernecei) and downstream (Kemence) sites, with steeper curves for the downstream site. Equations of STR curves were within the range observed in other studies, predominantly from terrestrial systems. Assemblage composition data suggested that extinction–colonisation dynamics of rare, non‐resident (i.e. satellite) species influenced patterns in STRs. 7. Our results highlight that the determination of species richness can benefit from the joint consideration of spatial and temporal scales in biodiversity inventory surveys. Additionally, we reveal how our randomisation‐based methodology may help to quantify the scale dependency of diversity components (α, β, γ) in both space and time, which have critical importance in the applied context.     

The effect of sample duration on the quantification of stream drift

1. We performed computer simulations and a field experiment to determine the effect that sample duration and, thus, sample volume had on estimates of drift density and sample variance. 2. In computer simulations, when the spatial arrangement of individuals in the water column approximated a random and a contagious-random distribution, estimated mean drift density was not significantly affected by sample duration, but sample variance decreased curvilinearly as sample duration increased. 3. Similar results were obtained in field experiments in habitats of high and low water velocity. 4. Our findings from an Albertan stream indicate that the relationship between sample variance (i.e. coefficient of variation) and duration of drift samples is curvilinear. This relationship affected the number of samples required to achieve a specific level of precision (i.e. a standard error within 10% of the mean). For estimates in low and high current velocities, sample variation was halved by increasing the duration of sample collections from 10 to 20 min. The increased precision obtained with samples of 20 min duration reduced the amount of drift material that needed to be processed by approximately 50% compared with an equivalent 10% level of precision for samples of 10 min duration. This reduction in the number of samples required to obtain a given level of precision has important consequences to the cost of processing drift samples. 5. Thus to optimize studies of stream invertebrate drift, both in terms of sample precision and processing effort, researchers must consider the effect that sample volume has on the variance of drift density estimates. Because researchers generally use drift nets with similar-sized apertures (>300cm²), the problem for specific field applications becomes one of optimizing sample duration relative to variance estimates for drift density.     

Environmental and spatial controls of taxonomic versus trait composition of stream biota

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Spatial heterogeneity reduces temporal variability in stream insect communities

Although all natural systems are heterogeneous, the direct influence of spatial heterogeneity on most ecological variables is unknown. In many systems, spatial heterogeneity is positively correlated with both microhabitat refugia and species richness. Both an increased number of microhabitat refugia and the effects of statistical averaging via increased species richness should lead to an inverse relationship between spatial heterogeneity and variability in community composition. To test this prediction, I measured diversity and temporal variability of invertebrate communities in a northern New Hampshire stream along a natural gradient of spatial heterogeneity formed by variation in stream substrates. On average, there was a 42% decrease in community variability along a gradient of increasing heterogeneity. This pattern was robust to changes in metrics of both heterogeneity and community variability. There was also a significant positive relationship between taxon richness and spatial heterogeneity with predicted taxon richness increasing c. 1.5× along the heterogeneity gradient. By resampling community abundance data, I estimated that statistical averaging accounted for only 4% of the observed decrease in community variability in this study. I concluded that the remaining decrease was very likely explained by a greater number of refugia from predation and/or flooding in high‐heterogeneity habitats. The results of this study suggest that maximizing heterogeneity in ecological restoration programmes may promote temporally stable and diverse communities and may aid in responsible management of aquatic resources.     

Evaluating ecosystem effects of climate change on tropical island streams using high spatial and temporal resolution sampling regimes

Climate change is expected to alter precipitation patterns worldwide, which will affect streamflow in riverine ecosystems. It is vital to understand the impacts of projected flow variations, especially in tropical regions where the effects of climate change are expected to be one of the earliest to emerge. Space‐for‐time substitutions have been successful at predicting effects of climate change in terrestrial systems by using a spatial gradient to mimic the projected temporal change. However, concerns have been raised that the spatial variability in these models might not reflect the temporal variability. We utilized a well‐constrained rainfall gradient on Hawaii Island to determine (a) how predicted decreases in flow and increases in flow variability affect stream food resources and consumers and (b) if using a high temporal (monthly, four streams) or a high spatial (annual, eight streams) resolution sampling scheme would alter the results of a space‐for‐time substitution. Declines in benthic and suspended resource quantity (10‐ to 40‐fold) and quality (shift from macrophyte to leaf litter dominated) contributed to 35‐fold decreases in macroinvertebrate biomass with predicted changes in the magnitude and variability in the flow. Invertebrate composition switched from caddisflies and damselflies to taxa with faster turnover rates (mosquitoes, copepods). Changes in resource and consumer composition patterns were stronger with high temporal resolution sampling. However, trends and ranges of results did not differ between the two sampling regimes, indicating that a suitable, well‐constrained spatial gradient is an appropriate tool for examining temporal change. Our study is the first to investigate resource to community wide effects of climate change on tropical streams on a spatial and temporal scale. We determined that predicted flow alterations would decrease stream resource and consumer quantity and quality, which can alter stream function, as well as biomass and habitat for freshwater, marine, and terrestrial consumers dependent on these resources.     

Emigration and immigration can be important determinants of benthic diatom assemblages in streams

SUMMARY.

• 1 Interspecific differences in diatom abundances in stream drift (plankton), immigration, and natural benthic assemblages were compared to assess the importance of emigration and immigration in benthic diatom community dynamics. Water samples were collected throughout a 24-h period to measure diel changes in diatom drift abundances and to estimate benthic diatom emigration rates. Immigration was assessed with 24-h colonization of bare tiles.
• 2 Dissimilarity in species composition of drift, immigration, and natural substrate assemblages indicated differential emigration and immigration among diatom species.
• 3 A mathematical model indicated that reproduction by diatoms in the plankton could not account for diel drift peaks and that diel variation in drift was an informative measure of benthic diatom emigration.
• 4 Emigration and immigration of some species constituted substantial proportions of diatom abundances on natural substrata. We conclude that emigration into the drift and immigration onto substrata can be important processes that regulate benthic diatom species composition and standing crop in streams.

     

Spatiotemporal changes of beetle communities across a tree diversity gradient

Aim Plant and arthropod diversity are often related, but data on the role of mature tree diversity on canopy insect communities are fragmentary. We compare species richness of canopy beetles across a tree diversity gradient ranging from mono‐dominant beech to mixed stands within a deciduous forest, and analyse community composition changes across space and time. Location Germany’s largest exclusively deciduous forest, the Hainich National Park (Thuringia). Methods We used flight interception traps to assess the beetle fauna of various tree species, and applied additive partitioning to examine spatiotemporal patterns of diversity. Results Species richness of beetle communities increased across the tree diversity gradient from 99 to 181 species per forest stand. Intra‐ and interspecific spatial turnover among trees contributed more than temporal turnover among months to the total γ‐beetle diversity of the sampled stands. However, due to parallel increases in the number of habitat generalists and the number of species in each feeding guild (herbivores, predators and fungivores), no proportional changes in community composition could be observed. If only beech trees were analysed across the gradient, patterns were similar but temporal (monthly) species turnover was higher compared to spatial turnover among trees and not related to tree diversity. Main conclusions The changes in species richness and community composition across the gradient can be explained by habitat heterogeneity, which increased with the mix of tree species. We conclude that understanding temporal and spatial species turnover is the key to understanding biodiversity patterns. Mono‐dominant beech stands are insufficient to conserve fully the regional species richness of the remaining semi‐natural deciduous forest habitats in Central Europe, and analysing beech alone would have resulted in the misleading conclusion that temporal (monthly) turnover contributes more to beetle diversity than spatial turnover among different tree species or tree individuals.     

Phenological patterns of neotropical lotic chironomids: Is emergence constrained by environmental factors?

Abstract In this paper we analyzed the emergence phenology of a highly diverse chironomid assemblage to test for association between emergence and some environmental variables and for the presence of synchrony in emergence. We used a time series of 48 weekly samples from a tropical low order forested stream (south‐eastern Brazil) to describe how this assemblage varied in an intra‐annual scale. An eigenvector‐based filtering approach was adapted to create temporal variables that could be used in our multiple regression analyses, trying to overcome the problems of temporal autocorrelation. Emergence of the Chironomidae, two subfamilies, concordant species, and of dominant species was not related to rainfall, temperature, moon phase or photoperiod. Taxonomic composition and species richness did not change across time. The number of emerging individuals of the subfamily Orthocladiinae was significantly related to temperature and to temporal filters. The inclusion of the temporal filters into the analyses almost eliminated autocorrelation in the regression residuals. We detected interspecific synchrony in a group of species, but an absence of trends and periodicity in chironomid emergence, which was not related to environmental variables. This suggests that unknown factors, differing from those known to control emergence in temperate regions, operate in the tropics. The erratic behaviour of the analyzed series raises the question of whether chaotic dynamics may generate this variability.     

Drift dynamics of Chironomidae larvae: I. Preliminary results and discussion of importance of mesh size and level of taxonomic identification in resolving Chironomidae diel drift patterns

Diel drift samples utilizing nets with mesh size less than 200 microns were taken in Linesville Creek, Pennsylvania, an eastern deciduous forest stream, and Inlet Run, Wyoming, an alpine snow melt stream. Identification of drifting Chironomidae larvae to lowest level taxonomic categories indicated 51 species or species group categories representing 51.95% of the total insect drift in Linesville Creek and 18 species or species group categories representing 70.47% of the total insect drift in Inlet Run. Orthocladiinae were the predominant larvae in the drift in Linesville Creek, with 19 species comprising 43.84% of the Chironomidae drift. In decreasing abundance were Chironomini (12 species, 40.36% of Chironomidae drift), Tanytarsini (10 species, 8.89%), and Tanypodinae (10 species, 6.91%). By contrast, Diamesinae were the predominant larvae in the drift in Inlet Run, (5 species, 71.43%) followed by Orthocladiinae (10 species, 27.25%), Tanytarsini (2 species, 1.20%), and Podonominae (1 species, 0.12%). Comparison of drift composition with substrate samples and/ or emergence data indicated a close relationship between relative abundance in drift and relative abundance in the benthos. Behavioral drift patterns with nocturnal peaks were seen for 3 species or species groups in Linesville Creek. Four species with diurnal drift peaks were present in Inlet Run. Analysis of the size distribution of drifting larvae indicates that a mesh size as small as 200 microns is required to resolve diel drift patterns. It is postulated that random factors greatly influence the apparent diel drift pattern of Chironomidae when nets with mesh size in excess of 400 microns are employed in drift studies. Conflicting literature reports of behavioral drift for Chironomidae may be due to differing species composition of drifting larvae and net mesh size related artifacts.     

The spatial scaling of beta diversity

Beta diversity is an important concept used to describe turnover in species composition across a wide range of spatial and temporal scales, and it underpins much of conservation theory and practice. Although substantial progress has been made in the mathematical and terminological treatment of different measures of beta diversity, there has been little conceptual synthesis of potential scale dependence of beta diversity with increasing spatial grain and geographic extent of sampling. Here, we evaluate different conceptual approaches to the spatial scaling of beta diversity, interpreted from ‘fixed’ and ‘varying’ perspectives of spatial grain and extent. We argue that a ‘sliding window’ perspective, in which spatial grain and extent covary, is an informative way to conceptualize community differentiation across scales. This concept more realistically reflects the varying empirical approaches that researchers adopt in field sampling and the varying scales of landscape perception by different organisms. Scale dependence in beta diversity has broad implications for emerging fields in ecology and biogeography, such as the integration of fine‐resolution ecogenomic data with large‐scale macroecological studies, as well as for guiding appropriate management responses to threats to biodiversity operating at different spatial scales.     

Measuring Spider Richness: Effects of Different Sampling Methods and Spatial and Temporal Scales

Assessing the richness of invertebrate taxa to aid conservation and management requires a better understanding of the potential sources of error. Patterns of richness for heathland spiders at the species and family levels were compared across three sampling methods, four spatial scales, and monthly intervals (for 16 months). A total of 33 families and 130 species was collected: pitfall traps collected 94% of species, sweep net, 25%, and visual search, 41%. The sampling methods produced variable results. Pitfall trap and sweep net techniques identified significant, yet contrasting spatial differences in the number of families and species at one spatial scale. Pitfall trap data reflected strong temporal variation that influenced spatial patterns in richness (across one spatial scale for families and two for species). The use of broader temporal scales introduced a potential failure to detect significant differences in the richness of ground active spiders, and this risk varied spatially. The sweep net is not recommended for this habitat, although a method that targets the foliage is required for a more complete faunal assessment. Visual searches detected no significant patterns in richness, yet given its potential and increasing use for rapid biodiversity surveys, ways to improve sampling efficiency are suggested.     

Species composition,abundance and emergence phenology of midges (Deiptera: Chironomidae) in a brown-water stream of West-Central Alberta,Canada

Sixteen floating, box type emergence traps, each covering 0.1 m², were placed along 150 m of a third-order stretch of the Bigoray River, a slow-flowing, vegetation-choked, brown-water muskeg stream. Effects of trap design, trap shading, length of sampling interval, and stream velocity on the number of midges caught was examined. Of the 112 species of Chironomidae caught, 32 species made up 90% of the catch and their emergence phenology is described in detail. There were more rare species than expected from Preston's lognormal distribution. Percentage of Bigoray species belonging to Tanypodinae, Orthocladiinae, Chironomini and Tanytarsini was 18%, 43%, 20%, and 19%, and was compared with 27 other studies on lotic chironomids. During the 140-day emergence period an average of 19.3 × 10³ chironomids emerged per square meter of stream. Based on changes in male:female ratios throughout a species emergence period, it was postulated that 30% of the Bigoray chironomid species were univoltine, 50% were bivoltine, and 20% were trivoltine.     

Identifying the scales of variability in stream macroinvertebrate abundance, functional composition and assemblage structure

1. Many natural ecosystems are heterogeneous at scales ranging from microhabitats to landscapes. Running waters are no exception in this regard, and their environmental heterogeneity is reflected in the distribution and abundance of stream organisms across multiple spatial scales. 2. We studied patchiness in benthic macroinvertebrate abundance and functional feeding group (FFG) composition at three spatial scales in a boreal river system. Our sampling design incorporated a set of fully nested scales, with three tributaries, two stream sections (orders) within each tributary, three riffles within each section and ten benthic samples in each riffle. 3. According to nested anova s, most of the variation in total macroinvertebrate abundance, abundances of FFGs, and number of taxa was accounted for by the among‐riffle and among‐sample scales. Such small‐scale variability reflected similar patterns of variation in in‐stream variables (moss cover, particle size, current velocity and depth). Scraper abundance, however, varied most at the scale of stream sections, probably mirroring variation in canopy cover. 4. Tributaries and stream sections within tributaries differed significantly in the structure and FFG composition of the macroinvertebrate assemblages. Furthermore, riffles in headwater (second order) sections were more variable than those in higher order (third order) sections. 5. Stream biomonitoring programs should consider this kind of scale‐dependent variability in assemblage characteristics because: (i) small‐scale variability in abundance suggests that a few replicate samples are not enough to capture macroinvertebrate assemblage variability present at a site, and (ii) riffles from the same stream may support widely differing benthic assemblages.