bluuebunny/crossref_metadata_2025_split huggingface dataset:
An experimental study of the breakdown of submerged leaves by hyphomycetes and invertebrates in Morocco
Authors: CHERGUI HASSAN , PATTEE ERIC 
Published: May 2006

SUMMARY.
1. Mechanisms of the breakdown of submerged leaves under the warm and dry Moroccan climate, including the interaction between hyphomycetes and invertebrates, were investigated.2. Laboratory experiments were performed on dried leaves of Salix sp. and Nerium oleander.3. During the first month under the experimental conditions, Melanopsis praemorsa, Physa acula (Gastropoda) and Hydropsyche maroccana (Trichoptera), respectively, were responsible for a loss of weight of 38, 21 and 13% in willow leaves, and 40, 15 and 8% in oleander leaves.4. The weight lost by willow leaves inoculated with the fungi Alatospora acuminata, Anguillospora longissima, Lemonniera aquatica and Tetracladium marchalianum increased with time, but varied according to the fungal species. Loss of weight and increase in nitrate and phosphate content of the leaves were greatest with Lemonniera and smallest with Tetracladium.5. When the leaves thus colonized by each of the four fungal species were exposed to each of the three invertebrates, the amount of material consumed increased with the time of fungal conditioning and varied according to the fungus and to the invertebrate. Greatest consumption was by Melanopsis feeding on leaves conditioned by Lemonniera, in which case assimilation percentage by the gastropod was as high as 75%.6. Owing to their numbers in the field, and to the quantity of leaf material they ingest, gastropods appear as the main shredders in the streams considered, thus replacing the Crustacea that often play this part under temperate climates. Breakdown seems faster in Morocco than in France, mainly because of a shorter initial time lag in weight loss.
Influence of food density on the effects of a Chaoborus‐released chemical on Daphnia ambigua
Authors: HANAZATO TAKAYUKI 
Published: May 2006

SUMMARY 1. Daphnia ambigua was reared individually at four different food levels in water conditioned by a predator, Chaoborus flavicans. Daphnia ambigua developed spike‐like helmets during the first four instars in each treatment with the Chaoborus‐conditioned water, but only during the first instar in untreated water. The helmet development at instars 2–4 was probably induced by a chemical released from the Chaoborus.2. The helmets decreased in size with decreasing food levels, but never ceased to form, even at a very low food concentration.3. Daphnids cultured in the Chaoboras‐conditioned water exhibited reduced growth, reproduction and survival rates at low food levels. These results might be induced by the energy loss associated with producing the helmets.4. It is suggested that the predator releases a chemical, which reduces the tolerance of the cyclomorphic Daphnia to food deficiency, thus accentuating the summer decline in the Daphnia population caused by food shortage.
Laboratory studies of egg development and diapause in Isoperla obscura (Plecoptera) from a mountain stream in Norway
Authors: ØKLAND BØRN 
Published: May 2006

SUMMARY 1. A laboratory study of egg development of the stonefly Isoperla obscura (Zetterstedt) collected from the stream Flybekken (southern Norway, 61°25'N, 8°48'E, 1373 m a.s.l.) showed a short diapause followed by a prolonged period of postdiapause quiescence.2. Diapause occurred over a wide range of temperatures (−20°C to +8°C), but 0–1°C was the most favourable for fast diapause development and successful hatching. Diapause development required temperatures below 12°C, but sub‐zero diapause temperatures increased mortality during the postdiapause phase, as well as reducing hatching success.3. The threshold for initiation of postdiapausal development was about 1–2°C. Development rate increased and variation in development time decreased at higher water temperatures. These may be important characteristics to ensure seasonal and geographical synchrony of development in individual populations. Low postdiapausal temperatures were unfavourable, despite a subsequent increase in water temperature. No response to postdiapausal photoperiod was detected.4. The results agreed well with conditions noted in the natural environment, and with the abundance of this species at high altitudes and latitudes in Fennoscandia. Nevertheless, Isoperla obscura also occurs in streams in the maritime parts of western Norway. The results of the present study suggest that egg development in these populations will prove to be different.
The effect of the acanthocephalan parasite (Pomphorhynchus laevis) on the drift of its intermediate host (Gammarus pulex)
Authors: McCAHON C. P. , MAUND S. J. , POULTON M. J. 
Published: May 2006

SUMMARY 1. The drift of Gammarus pulex in a population in which approximately 20% of adults are infected with the acanthocephalan parasite Pomphorhynchus laevis was monitored at margin and mid‐river sites in the River Teme, England over a 24‐h period in mid‐summer.2. Drift densities showed a diurnal pattern with a large increase at night, independent of parasite burden.3. There was no significant effect of site (margin or mid‐river) on the proportion of parasitized and unparasitized G. pulex found in the drift or the benthos.4. The drift of parasitized G. pulex was significantly greater than unparasitized animals. Gammarids harbouring only one parasite were found in significantly higher proportions in the drift than those with two or more parasites.5. At both sites (margin and mid‐river) the proportion of unparasitized adult G. pulex in the drift was significantly lower than that in the benthos. However, there was a significantly higher proportion of parasitized animals in the drift than in the benthos.
Spatial distribution of freshwater mussels: the role of host fish and metabolic rate
Authors: BAUER G. , HOCHWALD S. , SILKENAT W. 
Published: May 2006

SUMMARY.
1. Three species of the superfamily Unionacea live in Bavarian trout streams: the freshwater pearl mussel Margaritifera margaritifera which usually occurs alone, and the unionids Unio crassus and Anodonta piscinalis which are frequently associated.2. We found no evidence for competition between M. margaritifera and the unionids. Two types of habitat factors were analysed: (i) the occurrence of host fish, which does not explain the distributional relationships of mussels; and (ii) hydrochemical factors indicating a lower productivity in the rivers inhabited by M. margaritifera.3. With respect to physiological differences, M. margaritifera is separated from the other two species by low growth constants and low metabolic rates. We conclude, therefore, that the metabolic rate is an important factor governing distribution of the species: M. margaritifera is able to grow in rivers with low food availability, whereas the higher metabolic rates of U. crassus and A. piscinalis presumably necessitate a richer food supply.
Bryophytes as invertebrate habitat in two New Zealand alpine streams
Authors: SUREN ALASTAIR M. 
Published: May 2006

SUMMARY.
1. Quantitative samples of lotic benthic invertebrates and associated organic material were taken monthly for 18 months from bryophyte and gravel habitats in two New Zealand alpine streams in Arthur's Pass National Park, South Island; an unshaded site above the tree‐line and a shaded stream flowing through mountain beech forest. This was to assess the ecological role of bryophytes in these habitats and to determine the relative effects on the fauna of algal and detrital resources.2. Bryophytes were confined to stable bedrock substrata in shallow (mean depth of 4.5 and 10.5 cm), fast water (mean velocity of 0.21 ms−1 and 0.30ms−1) at the unshaded and shaded sites. Mean ash‐free dry weight (AFDW) of organic material from bryophyte areas was similar at the unshaded and shaded sites (335.6 and 272.4 gm−2). Low stream‐bed stability of the gravel areas resulted in poor retention of organic matter, with average AFDW of 59.1 and 77.9 gm−2 at the unshaded and shaded sites, respectively. Periphyton biomass, however, was much higher at the unshaded site.3. Within bryophytes, water velocity is reduced and large quantities of periphyton and detritus accumulate. This explains the greatly enhanced invertebrate densities within bryophytes (218400 and 53500 individuals m−2), compared with gravel areas (20900 and 7400 individuals m−2) in the unshaded and shaded sites, respectively. The higher invertebrate densities at the unshaded site reflect greater periphyton biomass there.4. Invertebrate densities followed clear seasonal patterns, attributable to changes in chironomid densities. These reflected larval chironomid hatching following adult oviposition. This illustrates the importance of these plants as oviposition sites, and as protective nurseries for small larvae where they can obtain shelter during floods and consume the abundant food sources available to them.5. DECORANA ordination revealed taxonomically distinct invertebrate communities in each stream, and in bryophytes and gravels. Several taxa appeared restricted to either the unshaded site (e.g. Acroperla spiniger and Hydrobiosis silvicola) or the shaded site (e.g. Zelolessica
The impact of three‐spined sticklebacks on the Zooplankton of a previously fish‐free pool
Authors: PONT D. , CRIVELLI A. J. , GUILLOT F. 
Published: May 2006

SUMMARY.
In the Camargue (southern France), most invertebrates inhabiting temporary shallow oligohaline marshes and pools are large‐bodied, conspicuous and defenceless taxa that are restricted to fish‐free environments. Management practices, by creating drainage canals, strongly affect the invertebrate community by allowing colonization by fish.
Sticklebacks colonizing the study pool were sampled daily and Zooplankton sampling was carried out at weekly intervals. From early October until the pool dried in June, 1365 sticklebacks entered and only 139 stickleback's fry and seven adults left the pool. Zooplankton abundance was high during the whole study period with a mean density of 1360 ind. 100cm−2. Larger forms (Daphnia magna, Simocephalus vetulus, Arctodiaptomus wierzejskii) quickly disappeared after the first wave of sticklebacks entered the pool in November. Subsequently, smaller species (Diacyclops bicuspidatus odessanus, Chydorus sphaericus and ostracods) replaced the larger ones until the pool dried.
Food selectivity of sticklebacks and daily Zooplankton consumption were investigated under experimental conditions within the pool in spring. After introduction of sticklebacks, densities of Zooplankton species dropped quickly (D. b. odessanus, C. sphaericus) with the exception of Ostracoda. Estimates of daily Zooplankton consumption by adult sticklebacks varied between 2.8 and 10.7% of fish body weight. Examination of gut contents showed that fry mainly ingested Chydorus sphaericus.
Given that the stickleback is an annual species in the Camargue, and that few fry are able to leave the pool due to the early drying out, the colonization of such a former fish‐free pool is not beneficial for the stickleback population. However, a more serious effect of such colonization is the progressive local extinction of the most typical Zooplankton species inhabiting these formerly fish‐free environments.
Invertebrate colonization of a new, man‐made stream in southern Sweden
Authors: MALMQVIST BJÖRN , RUNDLE SIMON , BRÖNMARK CHRISTER , ERLANDSSON ANN 
Published: May 2006

SUMMARY.
The invertebrate colonization of a man‐made stream, Flugströmmen, in southern Sweden was monitored for 18 months in 1988 and 1989. Benthic samples were taken on twelve occasions from three sites (upstream, middle and downstream) and community structure was compared with that at ten natural, permanent reference sites nearby.
The number of species colonizing increased rapidly during the first 3 months. The increase was most rapid upstream but levelled off during the second year at this site, while numbers continued to increase downstream.
Simuliid species were the earliest colonizers and reached high densities at upstream and middle sites during the first year. Ephemeropteran and plecopteran species also occurred early on, whereas Coleoptera, Odonata and Trichoptera were, on average, slower to colonize. Blackfly densities decreased upstream after the first year and hydropsychids became numerically dominant.
The colonization order of functional feeding groups was as predicted: filter feeders first, grazers/collectors intermediate, predators and shredders last.
After a year, the community structure in Flugströmmen closely resembled that in lake‐outlet streams situated in the area, although communities at the three sites within the stream were most similar to one another.
The possible role of competitive and predatory processes in determining the observed successional patterns are discussed.
Growth enhancement of the macrophyte Ceratophyllum demersum in the presence of the snail Planorbis planorbis: the effect of grazing and chemical conditioning
Authors: UNDERWOOD GRAHAM J.C. 
Published: May 2006

SUMMARY
The effects of epiphyton grazing and nutrient recycling by the freshwater snail Planorbis planorbis on the growth of the macrophyte Ceratophyllum demersum were examined in laboratory experiments.
Ceratophyllum plants grown in the presence of snails, or in water chemically conditioned by snails, were significantly longer, had more healthy nodes of leaves, and more growing tips than Ceratophyllum plants grown in isolation. There were no significant differences between the growth of plants that were grazed by snails, and those plants which received water chemically conditioned by snails.
Adult P. planorbis released 3.74 × 10−4μg phosphate, 23.9 × 10−4μg nitrate, 4.38 × 10−4μg ammonia, and 0.79 × 10−4μg of urea mg−1 wet weight of snail h−1. Measurements of these chemicals in the experimental systems suggested that ammonia was an important nutrient in stimulating the growth of Ceratophyllum.
Removal of epiphyton by grazing snails significantly prolonged the life of individual Ceratophyllum leaves compared to ungrazed leaves.
Patch distribution of interstitial communities: prevailing factors
Authors: DOLE‐OLIVIER M.J. , MARMONIER P. 
Published: May 2006

SUMMARY1. Community structure of interstitial invertebrates was studied in the sediments of two gravel bars in a bypass section of the Rhone River (France), in relation to hydrological patchiness and to major geomorphological characteristics of the sampling areas. Hydrological patchiness was characterized by upweiling or downwelling zones while geomorphological characteristics were concerned mainly with position towards the head or tail of each bar, which presented different environmental conditions.2. Longitudinal profiles of the two bars, at 0.5 and 1.0m below the substrate surface, were compared. At each station 10‐l samples were taken using mobile standpipes and a Bou—Rouch pump. During low‐water conditions, replicate samples were taken in both the head‐bar and tail‐bar regions to confirm the results. Physicochemical parameters were used to differentiate surface water from ground water (conductivity, alkalinity, silica, nitrates, sulphates and temperature) and to detect hydrological patterns.3. Two different situations were observed within the gravel bars. In the first one, the upweiling zone was situated in the tail bar and downwelling zone in the head bar. The reverse was observed in gravel bar 2 where the head‐bar region formed the upweiling zone and the tail‐bar region formed the downwelling zone.4. In the first situation, the distribution of interstitial assemblages corresponded with the observed hydrological patterns: epigean fauna characterized the downwelling zone and stygofauna characterized the upweiling zone. The interstitial fauna seemed to be strictly linked to the mode of water movement within the sediments. Hydrological patchiness therefore appeared to be an important factor for the structure of interstitial assemblages.5. In the second case there was no relationship between the hydrological and the biological pattern. Epigean fauna and hypogean fauna were scattered all along the gravel bar. These results suggest that geomorphology is a second important factor governing the composition and structure of interstitial assemblages. A precise structure was obtained when hydrological and geomorphological characteristics were superimposed (case 1). When they were opposed (case 2) all the species responded according to their individual ecological requirements.
Physiological characteristics of inorganic nitrogen uptake by spatially separate algal communities in a nitrogendeficient lake
Authors: REUTER JOHN E. , AXLER RICHARD P. 
Published: May 2006

SUMMARY1. The physiological characteristics of nitrogen uptake by sublittoral and eulittoral (splash zone) epilithic periphyton as well as epipelic periphyton in N‐deficient Castle Lake, California were determined by evaluating the half‐saturation constants (Kt) and initial slopes (Vmax/Kt) of uptake kinetics curves. These results were compared to similar studies of phytoplankton nitrogen uptake in this lake.2. The strategies of nitrogen uptake differed among the various communities and were largely determined by the proximity of each to pools of available dissolved inorganic N (DIN).3. The sublittoral algae did not have a high biological affinity for either NH4 or NO3 and depended on nitrogen fixation for their N supply. The eulittoral community showed an increased capacity for DIN uptake at low substrate concentration, but not as high as measured for the phytoplankton community. Epipelic algae live immediately adjacent to a large pool of interstitial sediment NH4 and showed no physiological adaptations for surviving in a N‐deficient environment.4. Kt values for all benthic communities were approximately two orders of magnitude greater than ambient substrate levels. In contrast, the half‐saturation constants for NH4+ NO3 uptake by phytoplankton were very similar to in situ levels of these nutrients.
Plant—herbivore interactions in streams near Mount St Helens
Authors: LAMBERTI G.A. , GREGORY S.V. , HAWKINS C.P. , WILDMAN R.C. , ASHKENAS L.R. , DENICOLA D.M. 
Published: May 2006

SUMMARY1. In four separate field experiments near Mount St Helens (Washington, U.S.A.) during 1986, the grazing effects of two large benthic herbivores, tadpoles of the tailed frog Ascaphus truei and larvae of the caddisfly Dicosmoecus gilvipes, were investigated using streamside channels and in‐stream manipulations. In the experimental channels, abundances of periphyton and small benthic invertebrates declined significantly with increasing density of these larger herbivores.2. In eleven small, high‐gradient streams affected to varying degrees by the May 1980 eruption, in‐stream platforms were used to reduce grazing by A, truei tadpoles on tile substrates. Single platforms erected in each tributary and compared to grazed controls revealed only minor grazing effects, and no significant differences among streams varying in disturbance intensity (and, consequently, tadpole density). However, results probably were confounded by high variability among streams in factors other than tadpole abundance.3. Grazing effects were further examined in two unshaded streams with different tadpole densities, using five platforms per stream. In the stream with five tadpoles m−2, grazing reduced periphyton biomass by 98% and chlorophyll a by 82%. In the stream lacking tadpoles, no significant grazing effects were revealed. Low algal abundance on both platforms and controls, and high invertebrate density in that stream (c. 30000m−2) suggests that grazing by small, vagile invertebrates was approximately equivalent to that of tadpoles.4. The influence of large benthic herbivores on algal and invertebrate communities in streams of Mount St Helens can be important, but reponses vary spatially in relation to stream disturbance history, local environmental factors, and herbivore distributional patterns and abundance.
Patch dynamics of the stream macrophyte, Callitriche cophocarpa
Authors: SAND‐JENSEN KAJ , VINDBÆK MADSEN TOM 
Published: May 2006

SUMMARY1. We examined changes in position and growth of Callitriche cophocarpa patches in a shallow section of a small Danish stream during the main expansion of plant cover between April and June. Mean upstream growth of patches was only 7.5% of downstream growth. The mean growth rate was 1,02cm day−1 in length and 0.55 cm day−1 in width and the growth rates were not significantly dependent on patch size. For patches with an area (A) above 100cm2, the growth rates in patch area (dA/dt) was proportional to patch circumference and thus √Aand the relative growth rate (dA/dt A−1) was inversely proportional to √A.The smallest patches (<100cm2), however, expanded less than expected because of their combined tendency to grow more slowly in patch length and width than larger patches.2. The expansion of plant cover will be much more rapid in many medium‐sized patches compared to few large patches of a similar combined area, because internal selflimitation by light and space is partially relieved in smaller patches. We anticipate that recruitment and mortality of new‐formed patches are critical steps preceding areal expansion. Quantification of these processes are needed fully to evaluate patch dynamics and space occupation.
The influence of periphyton, detritus and shelter on invertebrate colonization of aquatic bryophytes
Authors: SUREN ALASTAIR M. , WINTERBOURN MICHAEL J. 
Published: May 2006

SUMMARY1. Artificial bryophytes were placed in a shaded and an unshaded New Zealand alpine stream to investigate why invertebrates colonized these structures and, by inference, real plants. Three experiments were conducted to investigate the influence of (i) periphyton and detritus (ii) shelter, and (iii) time, on invertebrate colonization.2. In the first experiment, seven taxa at the unshaded site displayed a preference for substrata with high detrital and periphyton biomass, presumably reflecting a food relationship. At the shaded, less stable site, only two taxa displayed such a relationship.3. Reducing substratum ‘stem’ density (i.e. ‘shelter’) in the second experiment had little effect on the biomass of periphyton at each site, and only at the shaded site was detrital biomass reduced on low‐density substrata. Abundances of most of the twenty‐two invertebrate taxa analysed were unaffected by stem density reduction: densities of only four taxa at the unshaded site, and two at the shaded site were reduced.4. Stepwise multiple regression showed that invertebrate abundance was little affected by stem density at either site. Indeed, shelter was the primary factor influencing abundance of only two of twenty‐two taxa at the unshaded site, and none at the shaded site. Abundances of most taxa were related to periphyton or detrital biomass at each site.5. The third experiment investigated temporal relationships between invertebrate density, periphyton and detrital biomass, and exposure time of artificial bryophytes. Regression analyses indicated that of twenty‐two taxa at the stable, unshaded site, eight were influenced by periphyton biomass, three by detrital biomass, and two by exposure time. At the unstable shaded site, abundances of only eight of twenty‐two taxa were significantly related to the measured variables, of which exposure time was most important (four taxa).