Species richness and spatial distribution of blackflies (Diptera: Simuliidae) in streams of Central Amazonia, Brazil

1. The spatial distribution and species richness of blackflies were evaluated at 58 stream sites in Central Amazonia, Brazil. Samples were taken along a north–south axis of approximately 130 km and a east–west axis of approximately 220 km.
2. Based on stream-site characteristics, the occurrence of larvae of the six most frequently collected species was highly predictable (79.3–91.5% accuracy in prediction of occurrence). The predictive value of stream size and the presence of impoundments agrees with results of similar work in the Holarctic Region, suggesting a general responses of blackflies to environmental parameters.
3. Although only 19.0% of interstream variation in species richness was explained by a regression model, results suggested that species richness was greater in larger, cooler, faster, covered streams with rocky beds than in smaller, warmer, slower, open streams with sandy bottoms. Overall, the species richness of blackflies (11 species in total) was lower than in the temperate zone suggesting, for some taxa at least, that aquatic communities do not follow the terrestrial pattern of greater species richness in the tropics.     

An exploration of factors influencing lotic insect species richness

An understanding of factors that influence species richness of lotic insects is generally lacking. We present comparative data on aquatic insect species richness from several North American and other streams. Factors such as large sample numbers and drainage area (species area relationships) are not significant predictors of species richness across the streams we examined. We explore several hypotheses regarding the origins and maintenance of species richness using Upper Three Runs Creek (UTR), South Carolina, USA, as a reference stream. UTR has the highest species richness of any stream in the Western Hemisphere. Hypotheses examined included historical, regional and local processes such as: (1) Evolutionary time, (2) disturbance regime/environmental variability, (3) temperature/evolutionary-speed, (4) productivity, and (5) habitat heterogeneity. Of these hypotheses, we suggest that productivity and habitat heterogeneity appear to contribute most to the high species richness found in UTR. We believe that multidisciplinary analysis of other streams is necessary because without this crucial information our knowledge of, and desire to protect biodiversity in streams will be wanting.     

The effect of long pools on the drift of macro-invertebrates in a mountain stream

Macro-invertebrate drift was measured entering and leaving two pools on the Middle Fork of the Cosumnes River, a third order California stream. Drift rates for Baetis spp., Chironomidae, Simulium spp., Capniidae and total drift were calculated. Significant differences in the numbers of organisms entering the two pools were found for Baetis, Chironomidae, and Capniidae. Comparisons of drift rates at the upstream and downstream ends of each pool showed that the abundance of Chironomidae, Simulium, Capniidae and total drift changed in different directions across the pools. The numbers of organisms leaving the two pools, however, were not significantly different for Baetis, Simulium, Capniidae and total drift. These findings lead us to hypothesize that long pools act as barriers, not filters, to stream macro-invertebrate drift. The composition of drift leaving the pools in this experiment appeared to be controlled by the composition of the benthic habitat at the tail of the pool and not by the composition of upstream drift entering the pools.     

Relationships between labral fan morphplogy, body size and habitat in North Swedish blackfly larvae (Diptera: Simuliidae)

A comparison was made of the labral fan morphology of 29 populations belonging to at least 21 different simuliid species present as mature larvae in spring-early summer in North Swedish streams and rivers. The study revealed that there are both adaptive, morphological and phylogenetic traits evident in the material. Two basically different particle capture techniques can be deduced from morphology, where two prosimuliids, Cnephia pallipes and Metacnephia trigonia , represent species which mainly rely on a sieving technique, whereas all other species investigated capture particles by some other process, such as diffusional deposition. Within tribe Simuliini there are significant relationships between several fan traits and habitat. Thus, fast rivers are inhabited by species with small fans, having short and stout rays, whereas small, slow streams harbour species with large fans consisting of elongated, delicate rays. The finer morphology of the fan rays in terms of secondary structures, the microtrichia, appears to be more related to phylogeny than" habitat. Since a phylogeny of blackfly species still is lacking, this conclusion cannot be tested. In two subgenera, however, which are particularly well represented in the present material ( Simulium s. str. and Nevermannia ), and whose taxonomy is based on criteria other than fan morphology, there is consistent support for the conclusions about habitat-morphology relations.     

Regional patterns of diversity and estimates of global insect species richness

The total number of insect species in the world is an important if elusive figure. We use a fresh approach to estimate global insect species richness, based on biogeographic patterns of diversity of well or better documented taxa. Estimates generated by various calculations, all variations on a theme, largely serve to substantiate suggestions that insect species are likely to number around 10 million or less.     

Elmidae (Coleoptera, Byrrhoidea) larvae in the state of São Paulo, Brazil: Identification key, new records and distribution

The family Elmidae Curtis, 1830 has cosmopolitan distribution and most species inhabit riffles on streams and rivers, hence the name “riffle beetle”. In recent years, this family has been featured in papers addressing the assessment and environmental monitoring of water quality. In Brazil, studies on the family remain scarce and the present investigation is a pioneering study in the state of São Paulo. This study aims to propose a taxonomic key for the identification of larvae of Elmidae genera known to occur in the State, as well as to report new records and the distribution of these genera. The material analyzed was collected from various locations in each of 15 drainage basins from 2005 to 2010. The identification key includes 12 genera (Austrolimnius Carter & Zeck, 1929, Heterelmis Sharp, 1882, Hexacylloepus Hinton, 1940, Hexanchorus Sharp, 1882, Huleechius Brown, 1981, Macrelmis Motschulsky, 1859, Microcylloepus Hinton, 1935, Neoelmis Musgrave, 1935, Phanocerus Sharp, 1882, Potamophilops Grouvelle, 1896, Stegoelmis Hinton, 1939 and Xenelmis Hinton, 1936) known in Brazil as well as three morphotypes designated herein as Genus A, Genus M and Genus X. The genus Hexanchorus is recorded for the first time in the state of São Paulo.     

Characterization of benthic microhabitat: An experimental system for aquatic insects

An experimental system used to determine microhabitat current velocity and microhabitat selection by aquatic insects is described. The experimental system includes a microvelocity probe and a hydraulically calibrated artificial substrate. A thermistor velocity probe detects flow velocities to 0.5 m s^–1 near the surface of substrates at locations inhabited by aquatic insects. The artificial substrate was designed to provide two major habitat types, highly turbulent vortex areas and regions with unidirectional, near laminar flow. Substrate calibration and microhabitat characteristics of the substrates are demonstrated. Experimental studies of Simulium sp. location on substrates indicated that while simuliid larvae are characteristic of lotic, erosional habitats, actual microhabitats selected are governed by substantially lower flow velocity.     

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.     

Effects of flooding on avian top-predators and their invertebrate prey in a monsoonal Taiwan stream

1. The effects of flooding on top predators are poorly understood globally, but particularly in monsoonal streams. We therefore attempted to assess how inter-annual and intra-annual variations in flood magnitude affected an obligate riverine predator, the brown dipper ( Cinclus pallasii ), and its invertebrate prey, in the mountain Tachia River, Taiwan. Major flooding in one of the study years (2005) allowed an insight into the effects of abnormally large flows.
2. The abundance and biomass of insects, and the abundance of dippers, decreased steadily from 2003 to 2005 as flood magnitude grew, but then increased in 2006 when more typical discharge returned. Dipper abundance, insect abundance and insect biomass were all strongly positively inter-related, but negatively related to discharge. Insect biomass, rather than abundance, was more useful in predicting brown dipper abundance.
3. Aquatic insect composition fluctuated among sampling years, revealed by non-metric multidimensional scaling, and these fluctuations were also related to discharge. In turn, dipper abundance and the mean body size of aquatic insects declined with the shift in insect composition as flow increased.
4. These data illustrate how discharge fluctuations can have pronounced effects on top predators in streams, mediated in this case by fluctuating prey abundance. While contributions from bird movement, breeding performance and mortality were not clearly differentiated, our data reveal how dippers have strategies to accommodate varying discharge in river systems. We suggest that the effects of floods on dippers should be taken into account when using this group as indicators of river quality.     

Sex ratio and maturity indicate the local dispersal and mortality of adult stoneflies

1. Despite a recent upsurge in interest, there remains remarkably little information about the dispersal and survival of the adults of most stream‐dwelling insects, although this is a basic requirement for understanding their long‐term population dynamics. 2. Using Malaise traps for a whole annual flight period, we captured adult stoneflies (Leuctra nigra) along transects perpendicular to three upland Welsh streams. We assessed spatial and temporal patterns in sex ratio to infer local dispersal and, using maturity as an age marker, estimated the mortality of adult females. 3. Nearly all adult stoneflies (99%) were taken in the period 26 April–23 July, and the onset of the male and female flight periods was the same. Most males (90%) had been caught by late June. Females were classified as immature (without ripe eggs) or mature, and 90% of immature females had been caught by mid‐late June (depending on catchment). As immature females declined in the catch, mature females increased, 10% having been caught by late‐May to early June and 90% by early to mid‐July. The median catches of immature and mature females were separated by 32 days in all three catchments. 4. There was a female bias in the sex ratio overall, which increased as time passed and was attributable partially to the greater longevity of females. Late in the flight period, however, female bias was also greater near the stream channel implying a return of mature females (but not males) from the riparian vegetation, presumably to oviposit. 5. The number of mature females was less than the number of immatures in two of the three channels. Over all three catchments, the overall mortality of females over the 32 days taken to mature was estimated at 29%, equivalent to an exponential daily rate of 1.1% day^?1. The apparently negative mortality rate in one catchment (i.e. more matures than immatures being caught) could be due to an influx of adult females from elsewhere along the channel to oviposit. 6. Natural markers of age and population structure, such as sex ratio and female maturity, thus enabled us to detect a return of females to the stream to oviposit, after prior limited dispersal into the riparian zone, and to infer longitudinal movements in search of suitable sites. We were also able to estimate mortality in the field. Such natural markers seem to have been underexploited in the study of adult aquatic insects.     

Reproductive ecology of the freshwater red alga Batrachospermum boryanum Sirodot in a temperature headwater stream

The surface and hyporheic fauna of a second-order reach of a northern California Coast Range stream (Big Canyon Creek, Lake Co., CA, USA) was examined using substrate colonization samplers (i.e. hyporheic pots) during both the wet and dry seasons in the prevailing Mediterranean climate of the region. In terms of total number of macroinvertebrate taxa, the surface (0 cm to −5.0 cm within the stream substrate) level had higher richness than any level within the hyporheic (−5.1 cm to −15.0 cm, −15.1 cm to −25.0 cm, or −25.1 cm to −35.0 cm) from the beginning of the dry season (May) to the beginning of the wet season (October); during this period the surface was not subject to disturbance from wet-season storms. During the wet season, richness at the surface was similar to that observed at any of the three hyporheic levels examined. Macroinvertebrate density at the surface was substantially reduced during the wet season; however, mean surface densities always exceeded those found within the hyporheic zone (from 25% to 78% of total macroinvertebrate numbers were found at the surface). Seasonal fluctuations in abundance of total macroinvertebrates and density of many constituent populations were less within the hyporheic zone than at the surface. Apparently, early instars of abundant surface taxa do not penetrate the interstices, and substrate disturbance due to spates is less in deeper levels. Compared with many hyporheic faunas described from other temperate-zone sites, this hyporheic community shows reduced numerical dominance by the Chironomidae.     

Distribution and systematics of the freshwater red algal family Thoreaceae in North America

North American populations and type specimens of Thorea and Nemalionopsis were compared using multivariate morphometrics and image analysis. We continue to recognise the separation of the two genera based on spore-bearing branch-to-assimilatory filament length ratio and assimilatory filament density (≤0·3 and loose for Thorea and ≥0·6 and compressed for Nemalionopsis, respectively). Four species of Thorea were distinguished worldwide: T. hispida (syn. T. andina, T. lehmannii, T. ramosissima), T. violacea (syn. T. bachmannii, T. brodensis, T. gaudichaudii, T. okadae, T. prowsei and T. riekei), T. clavata and T. zollingeri. The former two species have variable branched, non-clavate assimilatory filaments, whereas the latter two have unbranched, clavate assimilatory filaments. Thorea hispida has copious secondary branches while T. violacea is sparsely branched. Thorea clavata is differentiated from T. zollingeri by having fewer monosporangia per cluster. Two of these species were found in North America: T. hispida in Mexico, Grenada and Jamaica, and T. violacea in Texas and Mexico. Two species of Nemalionopsis were differentiated: N. shawii with long assimilatory filaments composed of barrel-shaped cells and n. tortuosa (syn. N. shawii f. caroliniana) with short assimilatory filaments having cylindrical cells. Only N. tortuosa has been collected on the continent, from Florida, Louisiana and North Carolina.     

The effects of bankside management on chalk stream invertebrate communities

SUMMARY 1. Communities of aquatic macroinvertebrates and the terrestrial adult phases of aquatic insects were investigated from short stretches of English chalk streams with two different bankside vegetation types: simply structured grazed grass (grazed) and structurally complex herbaceous vegetation with scattered trees (ungrazed). Macroinvertebrates were sampled in spring, summer, autumn and winter 1996–97 from three aquatic habitats: mid-channel gravel, patches of the aquatic macrophyte Ranunculus and marginal emergent macrophytes. The terrestrial adult phases of aquatic insects were sampled in spring, summer and autumn from bankside vegetation.
2. Total macroinvertebrate abundance did not differ between stretches with different bankside vegetation. Taxon richness of mid-channel gravel was, however, significantly higher in ungrazed compared with grazed stretches and Shannon diversity ( H ') of mid-channel gravel and marginal vegetation was significantly higher in ungrazed compared with grazed stretches. Total abundance, taxon richness and Shannon diversity ( H ') of the terrestrial adult phases of aquatic insect were significantly higher from the bankside vegetation of ungrazed compared with grazed stretches.
3. Ordination of communities of aquatic macroinvertebrates and terrestrial adults demonstrated that individual families of both groups were generally more abundant in ungrazed stretches. Many more families were significantly associated with ungrazed stretches than with grazed stretches.
4. This investigation has shown that high structural diversity of bankside vegetation along lowland chalk streams is accompanied at the reach scale by increased diversity of both aquatic macroinvertebrates and the terrestrial adult phases of aquatic insects. The conservation potential of such streams may thus be lowered by management practices that result in the removal or simplification of bankside vegetation along extensive stream stretches.