Contribution to the stone-fly (Plecoptera) fauna of the Volga and Don river basins

In the Volga and Don river basins, 17 stonefly species are known: 16 from the Volga, and 6 from the Don basin. The fauna is dominated by the species with wide, European (Isogenus nubecula, Nemoura flexuosa, N. dubitans, Amphinemura sulcicollis, Brachyptera braueri, Isoperla difformis, I. grammatica, Leuctra hippopus, Xanthoperla apicalis, Siphonoperla burmeisteri) and Transpalaearctic ranges (Taeniorterykh nebulosa, Nemurella pictetii, Amphinemura borealis, Nemoura cinerea, Capnia atra, Leuctra fusca, Isoperla obscura).     

The Plecoptera of Øvre Heimdalsvatn

The stonefly fauna was studied in the exposed zone and on soft bottom in deeper waters. Emergence was recorded by traps. Ten species were found. All were recorded in the exposed zone. Diura bicaudata (L.) and Nemoura avicularis Morton dominated.
During the winter N avicularis occurred in large numbers on soft bottom at nearly all depths while D. bicaudata was only recorded on stony substratum in shallow water. N. avicularis was therefore more susceptible to predation and was recorded in trout stomachs during most of the year, while D. bicaudata was preyed upon only during the short emergence and flight period.
The growth of the most numerous plecopteran species took place partly while the lake was covered by ice. D. bicaudata had two thirds of its growth during this period, while N. avicularis only had one third of its growth during the same period.     

Flight activity of insects along a mountain stream: is directional flight adaptive?

1. Flight activity of Trichoptera, Plecoptera and Ephemeroptera was studied by sticky trapping for 12 months at five sites along a New Zealand mountain stream. Over 19 000 insects were captured by the traps, which were located in forest and grassland reaches, including a reach with intermittent flow.
2. Most species occurred predominantly in forest or grassland, although some were trapped throughout the stream. Longitudinal distributions of adults and their larvae were strongly correlated.
3. Flight periods of 24 caddisflies, three mayflies and four stoneflies ranged from 2 to 12 months. Six species were trapped in all months and 17 (55%) in more than 5 months.
4. The most abundant forest-dwelling caddisfly species were over-represented on the downstream sides of sticky traps located in, and immediately below, forest indicating a majority was flying upstream. Upstream flight compensates for downstream drift of larvae and should maximize the likelihood that forest-dwelling species will locate preferred habitat for egg, larval and/or adult development. Unlike the caddisflies, the stonefly Spaniocerca zelandica was over-represented on the upstream sides of traps, suggesting that some adults may float or fly downstream following emergence.
5. In contrast to forest-dwelling species, only one common caddisfly ( Oxyethira albiceps ) was over-represented on the downstream sides of traps at grassland sites. Unlike the forest-dwelling species, most species taken at the downstream sites probably came from a variety of sources, including a nearby stream.     

Distribution Patterns,Species Assemblages and Habitat Selection of the Stoneflies (Plecoptera) from Two Mediterranean River Basins in Southern Spain

The stonefly distribution and its relationship with habitat changes, based on stream physico chemical features, were investigated in two Mediterranean river basins (Guadaira and Guadalete, S Spain). Plecopteran nymph distribution varied along an elevation gradient. Both stonefly species richness and species diversity increased with altitude. Stoneflies were able to tolerate a wide range of environmental conditions but were absent from low altitude sites, temporary streams with high salinity values and high water temperature. A total of 13 stonefly species were found in the study area, from which Tyrrhenoleuctra minuta (Klapálek ) and Protonemura sp. were dominant. The most widespread species were Nemoura lacustris and Capnioneura mitis. Three distinct species assemblages were observed according to their distribution patterns, but with similar environmental preferences. Capnioneura petitpierreae and T. minuta showed preferences to low altitude sites, whereas C. mitis and N. lacustris were found throughout all sites. T. minuta and N. lacustris inhabited permanent and temporary sites, while the same species and C. mitis also were found in semipermanent streams. Temporally, most stoneflies were caught during winter (85.9%), especially at the low altitude sites.     

Variability In the rate of egg development of the stonefly, Nemoura cinerea (Plecoptera)

SUMMARY. 1. The egg development of the widely distributed European stonefly. Nemoura cinerea Retzius. was investigated in the laboratory. There was a significant relationship between water temperature (T°C) and incubation period (Ydays), expressed by the regression equation: Y = 239 T^−0.85 (r²= 0.85. P<0.001).
2. The number of day-degrees above 0°C required for hatching showed a curvilinear relationship with water temperature, with a minimum requirement around 12°C.
3. Nemoura cinerea shows more variation in the rate of egg development than most other stoneflies. This, in part, explains the wide size range in nymphal populations and the species' extended emergence period. Flexibility in life cycle and asynchrony in egg development enable this species to colonize a wide range of freshwater habitats.     

Effects of simulated N deposition on understorey vegetation of a boreal coniferous forest

1. We report the short-term effects of simulated nitrogen (N) deposition on the understorey of a boreal forest in northern Sweden. Doses of ¹⁵N double-labelled NH₄NO₃ (0·5, 12·5, 25·0 and 50·0 kg N ha^–1) were applied to 1 m² plots in the summer of 1995 and plants were harvested the following autumn.
2. No significant treatment effects were found in either above- or below-ground biomass which was distributed as follows: the ericaceous shrub Vaccinium myrtillus contributed 76%, the grass Deschampsia flexuosa 4%, and the bryophytes Dicranum majus and Pleurozium schreberi 20%.
3. The recovery of applied N in these species was 24, 27, 27 and 32% of the 0·5, 12·5, 25·0 and 50·0 kg N ha^–1 applications, respectively, and thus the recovery increased with the N dose.
4. In the 0·5 kg N ha^–1 treated plots, the highest concentrations of fertilizer-derived ¹⁵N were found in the bryophytes, while in plots given the three higher N applications, leaves of D . flexuosa had the highest concentrations.
5. N application resulted in elevated concentrations of free amino acid N, which indicate increased storage of N in plant tissues. Furthermore, the N application resulted in increased damage to V . myrtillus by natural enemies. The severity of disease caused by two foliar parasitic fungi showed a clear numerical response to N treatment, as did the amount of herbivory as a result of Lepidoptera larvae.     

Mass aerial migration in the carabid beetle Notiophilus biguttatus

Abstract.  1. Catches in traps at 12 and 200 m above ground, and observations with entomological radar, were used to document the high-altitude windborne movements of carabid beetles over agricultural land in south-east U.K. during July 1999, 2000, 2002, and 2004.
2.  Notiophilus biguttatus (Fabricius) was found to be the most abundant species at altitude, with flights by reproductively immature adults resulting in millions of beetles passing through a 1 km² window during the brief migration period in July 2002.
3. This result was unexpected in view of the conclusions of an earlier, classic Dutch study by den Boer and colleagues that classified N. biguttatus as a poorly dispersing species that tended to become isolated in remnants of natural habitat.
4. Reasons for the discrepancy between the two studies are discussed. It is hypothesised that the high mobility seen in the N. biguttatus populations results from a recent adaptation of the beetle's migration syndrome allowing it to exploit the mosaic of temporary habitat patches making up the increasingly intensive agroecosystems of northern Europe.     

The influence of copper exposure on predator-prey interactions in aquatic insect communities

SUMMARY. 1. Vulnerability of two species of net-spinning caddisflies (Chimarra sp. and Hydropsyche morosa) to predation by the stonefly, Paragnetina media , was significantly greater in experimental streams dosed with copper (target concentration=6 μg 1^-1) than in control streams.
2. Results of stomach analyses showed that Hydropsychidae was the major component of stonefly diets in experimental streams and that the number of Hydropsychidae per stonefly gut was significantly greater in dosed streams than controls.
3. Since these results could not be predicted using single species bioassays, we suggest that such simple tests be supplemented with more environmentally realistic procedures that account for species interactions.     

Why does the hoverfly Metasyrphus corollae migrate?

Abstract. 1. Migration pattern and mass appearance of the hoverfly Metasyrphus corollae (F.) (Diptera, Syrphidae) were investigated on the SE coast of Sweden in 1981. In total, 4433 hoverflies, belonging to fifteen species, were collected in water traps during 4–6 August. All but 2.2% were M.corollae , 3282 specimens being caught on 4 August, 1021 on 5 August and thirty-five on 6 August.
2. The sex ratios ( ♂/♀ ) on these dates were 1/1.6, 1/1.3 and 1/1.7. The average dry weights did not significantly differ between sexes (males 4.01 mg, females 4.02 mg).
3. M.corollae females were reproductively immature.
4. Females mostly had Senecio pollen in their guts while males mainly had Rubus pollen. The average number of pollen grains per specimen was 210 for females and 1100 for males.
5. In the summer 1980 aphids were numerous, forming a basis for a high abundance of adult hoverflies (with hibernating larvae) in 1981. Aphid density in 1981 was low and stimuli inducing egglaying were sparse. It is suggested that this pattern of aphid abundance triggers migration in M.corollae and in other aphidophagous species at irregular intervals.     

Field experiments on the mobility of benthic invertebrates in a southern English stream

1. In each of twenty-six week-long experiments, the colonization by macroinvertebrates of boxes of natural sediment in a stony stream was measured. The experiments took place between February and November 1992 and environmental conditions prevailing during the weeks (particularly discharge and temperature) differed widely.
2. Colonization rate also varied widely between the weekly experiments and was sensitive to discharge, temperature and background benthic density, depending on the taxa considered.
3. A 'mobility index' measured colonization rate independently of background benthic density. This index was most strongly and positively correlated with discharge for the abundant stonefly Leuctra nigra, the net-spinning caddis Plectrocnemia conspersa and the Chironomidae, perhaps indicating that their mobility is physically driven by the influence of flow on drift.
4. Mobility in a second stonefly ( Nemurella pictetii ) was greatest in summer, when flows were low but temperature was high. Peak mobility in this species occurred during an ochreous bloom on the stream bed. It is likely the mobility of N. pictetii is more active than the other taxa.
5. There were thus differences among taxa in their mobility at baseflow and in their susceptibility to flow fluctuations. The population consequences of differences in mobility among taxa are discussed.     

FIELD OBSERVATIONS OF SENOSTOMA SPP. (DIPTERA: TACHINIDAE) AT KATOOMBA, N.S.W.

Habitats, microhabitats and behaviour of Senostoma longipes (Macquart), S. pallidihirtum (Malloch) and S. tessellatum (Macquart) at Katoomba Falls Reserve, N.S.W. are reviewed. All species favour dry sclerophyll forest on ridge-tops. Males aggregate on Eucalyptus trunks, females on trunk bases and surrounding substrate. Orientation and postures on trunk surfaces are described. Males compete intraspecifically for apparently favoured sectors of trunk (territories). Competition involves interactions of specimen pairs in flight and on the bark. Trunks are postulated to be leks, as symbolic territories competed for here are devoid of resources for females.     

Effects of age and body size on gonadal development of Atlantic sturgeon

Three hundred and five Atlantic sturgeon caught in the Hudson River and Hudson Bight were examined for age, body size and gonadal development (histology). Sampled fish ranged in age from 1·5 to 43 years and fork length (LF) 48–244 cm, and included 144 females and 161 males. All young sturgeon (age 1·5–4 years) caught in the river had sexually differentiated gonads. Age and size distributions of subadults and adults at different stages of gametogenesis were sex-specific and conformed with von Bertalanffy growth curves. Males mature faster and at a younger age compared to the females. Females with mid-vitellogenic ovaries were not found and their absence may be related to fishing gear selectivity or out-migration into the ocean during ovarian recrudescence. Mature males and females caught during the spring spawning migration into the Hudson River, ranged in age from 12 to 19 and from 14 to 43 years, and LF 117–185 and 173–244 cm, respectively. Individual fecundity and diameter of fully grown ovarian follicles increased with age and body size, but this increase was dampened in older females. Three hermaphroditic fish were found and all exhibited sparse pre-vitellogenic ovarian follicles embedded in normally developing testicular tissue.     

The immigration of spiders (Araneida) into a new polder

Abstract. (1) The immigration of spiders into the Lauwerszeepolder (constructed in 1969) was studied during four years in four areas. The spider fauna was sampled weekly and 65 000 specimens of eighty-four species were caught using strip traps, window traps, simple pitfall traps and fences.
(2) About sixty species from all kinds of habitats were caught rarely; nineteen species were caught in numbers that suggest that they had established populations in the study areas.
(3) The four successful pioneer species, plus two marsh-dwelling species, were most abundant during 1969 and 1970. The 1971 catch was dominated by species from saline habitats; they became less abundant in 1972 when species from non-saline habitats increased. Only halotolerant species established populations.
(4) No evidence was found that dispersing spiders select certain areas. The differences between the spider fauna of the differennt study areas arise from degrees of success in colonization by immigrants. Pioneer species are least influenced by the abiotic environment.
(5) A greater aeronautic dispersal power is found in species inhabiting unstable habitats than in species from stable habitats.
(6) Aeronautic activity in adult linyphiids (s.l.) is not restricted to a special season, but is related to definite phases of the phenology.
(7) Male and female erigonids are equally active in aeronautic behaviour. In erigonids and linyphiids intense aeronautic activity coincides with great ground activity; on the ground males are more active than females.     

Experimental manipulation of breeding density and litter size: effects on reproductive success in the bank vole

1. Reproductive success of individual females may be determined by density-dependent effects, especially in species where territory provides the resources for a reproducing female and territory size is inversely density-dependent.
2. We manipulated simultaneously the reproductive effort (litter size manipulation: ± 0 and + 2 pups) and breeding density (low and high) of nursing female bank voles Clethrionomys glareolus in outdoor enclosures. We studied whether the reproductive success (number and quality of offspring) of individual females is density-dependent, and whether females can compensate for increased reproductive effort when not limited by saturated breeding density.
3. The females nursing their young in the low density weaned significantly more offspring than females in the high density, independent of litter manipulation.
4. Litter enlargements did not increase the number of weanlings per female, but offspring from enlarged litters had lower weight than control litters.
5. In the reduced density females increased the size of their home range, but litter manipulation had no significant effect on spacing behaviour of females. Increased home range size did not result in heavier weanlings.
6. Mother's failure to successfully wean any offspring was more common in the high density treatment, whereas litter manipulation or mother's weight did not affect weaning success.
7. We conclude that reproductive success of bank vole females is negatively density-dependent in terms of number, but not in the quality of weanlings.
8. The nursing effort of females (i.e. the ability to provide enough food for pups) seems not to be limited by density-dependent factors.     

Spawning Periodicity, Spawning Migration, and Size at Maturity of Green Sturgeon, Acipenser medirostris, in the Rogue River, Oregon

The Rogue River, Oregon represents one of three important spawning systems for green sturgeon, Acipenser medirostris, in North America. In this paper we describe the spawning migration, spawning periodicity, and size at maturity for green sturgeon caught in the Rogue River during 2000–2004. Green sturgeon were caught by gill net or angling; 103 individuals were tagged with radio or sonic transmitters (externally or internally). Green sturgeon caught by gill net and angling ranged from 145 cm to 225 cm total length. Histological and visual examinations of gonad tissues indicated that most green sturgeon were spawning or post-spawning adults that entered the Rogue River to spawn. Ripe individuals were caught when water temperature was 10–18°C. Specimens carrying transmitters migrated 17–105 km up river; reaches consisting of likely spawning sites were identified based on sturgeon migratory behavior. Most green sturgeon remained in the Rogue River until late fall or early winter when flows increased, after which they returned to the ocean. Eight green sturgeon (males and females) returned to the Rogue River 2–4 years after leaving, entering the river during March, April, and May when water temperatures ranged from 9°C to 16°C. None of the 103-tagged individuals entered the Rogue River during successive years. There appear to be few known natural threats to adult green sturgeon in the Rogue River. However, our data suggest that a high percentage of adults that spawn in the Rogue River (particularly males) were susceptible to harvest by commercial, Tribal, and sport fisheries after leaving the system because they were not adequately protected by maximum size limits during the period of this study. The implications of maximum size limits (or lack of size limits) to green sturgeon are discussed, and recent actions taken by Oregon and Washington Fish and Wildlife Commissions to manage green sturgeon more conservatively are presented.     

Filters and templates: stonefly (Plecoptera) richness in Ouachita Mountains streams, U.S.A.

1.  We collected adult stoneflies periodically over a 1-year period at 38 sites in two headwater catchments in the Ouachita Mountains, Arkansas, U.S.A. The 43 species collected were a subset of the Ozark-Ouachita fauna and the much larger fauna of the eastern U.S.A. We estimated 78–91% species coverage in the two catchments using jackknife extrapolation of species richness from our survey.
2.  Many streams, especially small ones, lacked surface water for months, but others, both small and large, flowed permanently.
3.  Using published regional presence–absence and coarse ecological data in a discriminant function analysis (DFA), we identified stream size (negative) and regional frequency of occurrence (positive) as predictors of presence in these headwater catchments. For the combined catchments, the extrapolated richness (51 spp.) was similar to an estimate (48 spp.) based on predicted absences from DFA and the Ouachita provincial total of known stonefly species (57 spp.).
4.  Local species richness (1–27 spp. per site) was correlated strongly with stream size (catchment area) but was independent of stream drying. Generic richness was correlated negatively with stream drying and positively, but less strongly, with stream size.
5.  Regionally endemic stoneflies dominated in drying streams, and widely distributed species dominated in more permanent streams. The composition of stonefly assemblages was associated with regional factors (species pools, regional abundance, evolution of tolerant endemic species, regional climate) and local factors (drying, stream size).     

Direct interference or indirect exploitation? An experimental study of fitness costs of interspecific competition in voles

Studies on competing mammalian species in the past have focused mainly on the competitive exclusion of one species from the preferred habitat of the other. Investigations on effects of competition and coexistence on individual fitness are rare . In this study we were able to measure effects of interspecific competition on major fitness components, using a system with two vole species in asymmetric competition. Survival, reproduction and space use of bank vole Clethrionomys glareolus females were monitored in 32 enclosed populations over four replicates of eight parallel run enclosures. Into half of the enclosures we introduced an additional number of field voles Microtus agrestis , a dominant competitor.
Survival of bank vole females was lower under competitive conditions. Total number of breeding females was lower in populations coexisting with competitors. Territory size of bank vole females decreased. Females body weight and litter size bank vole litters conceived during the experiment were not affected by interspecific competition. These characteristics should respond to differences in food resources, and territory size should increase if food was scarce, thus we found no indication of direct exploitation competition between the two species. Space use was overlapping between the species, but individuals of both species were never caught together in the same trap, indicating avoidance behaviour.
We conclude that adult bank vole females do suffer fitness consequences through interference competition with field voles, probably basing on increased number of aggressive encounters in the presence of the dominant species. Our results suggest, that direct interference rather than indirect exploitation competition may be the cause for observed fitness decrease in bank vole females.     

Stoneflies as ecological engineers – hungry predators reduce fine sediments in stream beds

1. We conducted experiments in a Colorado Rocky Mountain stream to measure the effect of foraging by predatory stoneflies ( Megarcys signata ) on fine sediment deposition and removal.
2. Cages containing one of four treatments were placed in the stream substratum and removed 3 days after fine sediment load to the stream was experimentally increased. Cages containing a stonefly but no prey accumulated less sediment than cages initially with no benthic invertebrates. Although cages with Megarcys plus prey also tended to have less sediment than controls, sediments were not reduced in cages with prey only.
3. Distance from sediment source, depth and current velocity at cages, final prey density and numbers of prey per predator gut at the end of the experiment had no effects on sediment accumulation in cages.
4. To determine the mechanisms underlying this effect, behavioural tests were conducted in a stream-side artificial stream system. To simulate the different hunger levels of stoneflies in cages, Megarcys were fed or starved for 3 days before behavioural trials that were repeated during high (night) and low (day) stonefly feeding periods. During night trials, foraging movements by starved Megarcys were more prolonged and active than those of fed stoneflies, regardless of the presence of prey. However, neither hunger level nor prey presence affected stonefly foraging behaviour during day trials.
5. Results of field experiments suggest that the presence of stoneflies enhances sediment removal from interstitial spaces. Behavioural observations indicate that nocturnal searching for prey by hungry Megarcys dislodges fine sediments from interstitial spaces.
6. Future studies should explore beyond the direct impacts of predators on stream invertebrate communities, and investigate the potential impact of predators on benthic microhabitat quality.     

Relationships among the seed rain,seed bank and vegetation of a Hawaiian forest

Abstract. Hawaiian ecosystems are prone to invasion by alien plant species. I compared the seed rain, seed bank, and vegetation of a native Hawaiian forest to examine the potential role that seed ecology plays in allowing alien species to invade native forest. Absolute cover of seed plants in the forest was 126 %, annual seed rain was 5 713 seeds m^-2 yr^-1, and the mean density of seedlings emerging from the seed bank averaged across four seasons was 1 020/m². The endemic tree Metrosideros polymorpha was the most abundant species in the vegetation, seed rain and winter seed bank. Overall, native seed plants comprised 95 % of the relative cover in the vegetation and 99 % of the seeds in the seed rain, but alien species comprised 67 % of the seeds in the seed bank. Alien species tended to form persistent seed banks while native species formed transient or pseudo-persistent seed banks. Dominance of the seed bank by alien species with persistent seed banks suggests that aliens are favorably placed to increase in abundance in the vegetation if the forest is disturbed.     

Stoneflies as ecological engineers – hungry predators reduce fine sediments in stream beds

1. We conducted experiments in a Colorado Rocky Mountain stream to measure the effect of foraging by predatory stoneflies ( Megarcys signata ) on fine sediment deposition and removal.
2. Cages containing one of four treatments were placed in the stream substratum and removed 3 days after fine sediment load to the stream was experimentally increased. Cages containing a stonefly but no prey accumulated less sediment than cages initially with no benthic invertebrates. Although cages with Megarcys plus prey also tended to have less sediment than controls, sediments were not reduced in cages with prey only.
3. Distance from sediment source, depth and current velocity at cages, final prey density and numbers of prey per predator gut at the end of the experiment had no effects on sediment accumulation in cages.
4. To determine the mechanisms underlying this effect, behavioural tests were conducted in a stream-side artificial stream system. To simulate the different hunger levels of stoneflies in cages, Megarcys were fed or starved for 3 days before behavioural trials that were repeated during high (night) and low (day) stonefly feeding periods. During night trials, foraging movements by starved Megarcys were more prolonged and active than those of fed stoneflies, regardless of the presence of prey. However, neither hunger level nor prey presence affected stonefly foraging behaviour during day trials.
5. Results of field experiments suggest that the presence of stoneflies enhances sediment removal from interstitial spaces. Behavioural observations indicate that nocturnal searching for prey by hungry Megarcys dislodges fine sediments from interstitial spaces.
6. Future studies should explore beyond the direct impacts of predators on stream invertebrate communities, and investigate the potential impact of predators on benthic microhabitat quality.