bluuebunny/crossref_metadata_2025_split huggingface dataset:
Manipulation of habitat quality: effects on chironomid life history traits
Authors: Stanko‐Mishic Sandra , And J. Kevin Cooper , Silver Pamela 
Published: March 2003

1. To understand how habitat heterogeneity affects organisms, the present authors measured the response of chironomid life‐histories to single patch types in a controlled laboratory experiment. The objective was to determine whether the size and type of leaf particles in the substratum affect development rate and survival of larvae, and the fecundity of the resulting adults.2. Chironomus riparius larvae were raised in sand supplemented with dogwood, Cornus florida, (a rapid decomposer) or American sycamore, Platanus occidentalis, (a refractory decomposer) leaves fully crossed in a factorial design with four leaf particle sizes (0.2, 0.5, 1 and 5 cm2), or in sand only.3. Development time was shorter in dogwood habitats than sycamore habitats, and shorter in sycamore habitats than in sand habitats. Survival was higher and larval head capsule lengths of instars III and IV were larger in dogwood than in sycamore or sand habitats. Development time was longer and head capsule lengths of instars III and IV were smaller in habitats with 5‐cm2 leaf particles than in 0.2‐, 0.5‐ and 1‐cm2 particle size treatments. Female thorax length (a measure of fecundity) did not differ among treatments.4. The present authors conclude that, for C. riparius confined to a single patch type, fitness is significantly enhanced when the patch contains small particles of dogwood (labile) leaves.
Examination of endopelic and epilithic algal community structure employing scanning electron microscopy
Authors: Greenwood J. L. , Clason T. A. , Lowe R. L. , Belanger S. E. 
Published: March 2003

1. Biological community structure within a stream periphyton mat and sediment core was examined using scanning electron microscopy. Samples were fixed, freeze‐fractured and viewed under normal conditions with a scanning electron microscope.2. This technique enabled the analysis of orientation and spatial distribution of algal cells within the three‐dimensional algal communities.3. Fractured samples from a periphyton mat and sediment core at the Procter & Gamble Experimental Stream Facility showed layering of some dominant diatom species, such as Nitzschia dissipata, Melosira varians and Gyrosigma attenuatum. The spatial relationship of nematodes as potential algal predators was also revealed.4. Advantages, disadvantages and potential future applications of this freeze fracture technique are discussed.
Demographic responses of adult Mesocyclops thermocyclopoides (Copepoda, Cyclopoida) to different plant and animal diets
Authors: Kumar R.A.M. , Ramakrishna Rao T. 
Published: March 2003

1. We studied the effects of food type on adult females of the cyclopoid copepod Mesocyclops thermocyclopoides.2. The test diets, covering a size range of 5–1250 μm, included a toxic strain of Microcystis aeruginosa, three algae (i.e. Chlorella vulgaris, Scenedesmus acutus and Chlorogonium elongatum), three ciliates (i.e. Tetrahymena pyriformis, Stylonychia notophora and S. mytilus), two rotifers (i.e. Brachionus angularis and B. calyciflorus) and two cladocerans (i.e. Ceriodaphnia cornuta and Moina macrocopa), and a selected subset of them in a second experiment.3. Experimental diets were started with the last juvenile instar (C5) and data were collected on the newly moulted adult females. The survival of the copepod was less affected by food type than its reproductive output. Net reproductive rate was significantly higher with animal than with plant food. Algal diets enriched with organic extracts supported higher reproductive rates than unenriched diets of the same algal species. The large and motile alga Chlorogonium gave performances which approached those of ciliate diets.4. The pre‐reproductive period of M. thermocyclopoides was shorter and its post‐reproductive period longer with animal than with plant diets, the latter being chiefly caused by a briefer period between clutches.5. The frequency of infertile clutches increased in later clutches, indicating possible sperm limitation in females which have mated only once.6. There was a significant, positive correlation between the size of food particles and the lifetime reproductive output of M. thermocyclopoides, with more than an order of magnitude difference in the total fecundity between the largest and the smallest food items.7. Mesocyclops thermocyclopoides achieved the highest total fecundity with ‘mixed’ food, and thus, reflected the adaptive value of omnivory for this species.
Diversity, distribution and larval habitats of North Swedish blackflies (Diptera: Simuliidae)
Authors: Malmqvist Björn , Zhang Yixin , Adler Peter H. 
Published: March 2003

1. Blackfly species richness and community structure were analysed at fifty‐six sites in northern Sweden in two seasons. The sites were situated in a wide range of streams and rivers from small springbrooks, bog streams and lake‐outlet streams to medium‐sized forest rivers and large rivers draining montane regions.2. Thirty‐nine blackfly species were found, with between two and thirteen species per site. Neither species richness nor abundance could be related to the environmental variables measured.3. An analysis of labral fan size of blackflies indicated a clear trend for the prevalence of larvae with small fans in large rivers and larvae with larger fan size in small streams. Similarly, fan size related to current velocities so that large fans were associated with slow current velocities and small fans with high velocities.4. A strong relationship existed between species composition and habitat, as seen in ordination by non‐metric multidimensional scaling. The relationship found between fan size and habitat size‐related variables, such as channel width, depth, velocity and substratum particle size, along with longitude and altitude, in partial least squares regression analysis offered an explanation of the species composition–habitat relationship.5. In addition to testing that distributions of blackfly larvae reflect morphological traits, we tested two general hypotheses pertaining to distribution patterns: (a) that blackfly communities show bimodal distributions; and (b) that their distributions are nested. Neither of these two hypotheses was supported by our observations. However, widespread blackfly species were locally more abundant than those found at relatively few sites, thus showing a positive abundance–occupancy relationship.
Community concordance between the fish and aquatic birds of lakes in northern Alberta, Canada: the relative importance of environmental and biotic factors
Authors: Paszkowski Cynthia A. , Tonn William M. 
Published: March 2003

1. Community concordance measures the degree to which patterns in community structure in a set of sites are similar between two different taxonomic groups. Although seldom incorporated into studies of lake ecosystems, aquatic birds can be influenced by the same environmental features of lakes which affect fish and invertebrates, and can interact with these organisms directly as predators, competitors or prey. We surveyed lakes in north‐central Alberta, Canada, to determine if co‐occurring fish and aquatic bird assemblages displayed concordance, and assessed the relative importance of environmental and biotic factors in contributing to observed concordance.2. In 41 lakes (3–305 ha), we encountered seven species of fish and thirty‐one avian taxa which subsequently were used in multivariate analyses. Fish assemblages dominated by large piscivores were in large deep lakes, whereas fishless lakes and lakes with only small‐bodied fish were small and shallow, and thus, prone to winter hypoxia. Bird assemblages displayed three general patterns: (a) small shallow lakes supported a ‘core’ of widespread species (between three and eight species per lake); (b) large, deep lakes supported more species (between 11 and 16), including large, aerially foraging piscivores; and (c) large, shallow lakes supported the most species (between 15 and 23), including many ducks.3. Randomization tests of matrix concordance and Mantel tests both showed that fish and bird assemblages were significantly concordant. Concordance reflected the fact that both groups were strongly affected by the same key environmental factors, principally lake size and maximum depth, and to a lesser extent, productivity and geographic isolation. Direct interactions between birds and fish, such as predation and competition, appeared to play much smaller roles in shaping the two assemblages.
Calcium carbonate deposits reduce predation pressure on Gammarus fossarum from salamander larvae
Authors: Ruff Heike , Maier Gerhard 
Published: March 2003

Summary

We studied the lime deposits on Gammarus fossarum from a tufa brook in Southern Germany. Between 20 and 75% of the gammarids collected carried calcium carbonate deposits at the dorsal part of the pleon segments. Average weight of deposits ranged between 0.6 mg on small and 1.7 mg on large specimens and constituted 60–20% of specimens' dry weights.
Predator‐prey experiments with salamander larvae and gammarids showed that significantly fewer prey with deposits were eaten than without deposits and that the differences in predation risks between prey with vs. prey without deposits were greatest in small and medium sized specimens.
Lime deposits changed the feel or taste and the activity patterns of gammarids. Gammarids with deposits were rejected significantly more often by the predators than gammarids without deposits. Medium sized specimens with deposits, which suffered a great predation risk, were significantly less active than specimens of the same size category without deposits.
Lime deposits did not increase conspicousness or decrease escape ability of prey. Prey with deposits were attacked by predators with the same frequency and captured with the same success as prey without deposits.
Lime deposits may afford effective protection from salamander predation in some natural habitats. Predation impact on gammarids by salamander larvae may be low, however, because larval density was very low in most places (< 1 m‐2) and because larvae are only present for a limited time until they start metamorphosis.
Littoral microcrustacea in Lake 302S in the Experimental Lakes Area of Canada: acidification and recovery
Authors: Hann Brenda J. , Turner Michael A. 
Published: March 2003

Summary

The littoral microcrustacean community (Cladocera and Copepoda) was examined from 1989 to 1991 in a lake experimentally acidified to pH 4.5, and from 1992 to 1997 during the early stages of pH recovery.
Cladoceran abundance declined significantly from 1989 to 1991 (pH 4.5), but species richness did not change. Acantholeberis curvirostris, Simocephalus serrulatus, Latona spp. (Latona setifera, L. parviremis), and all species of chydorid Cladocera declined markedly in abundance while at pH 4.5. The abundance of cyclopoid copepods was low and Ceriodaphnia and calanoid copepods were absent.
Recovery of the community was subsequently monitored as pH was incrementally changed to a target pH 5.1 in 1992 and 1993, and to 5.8 in 1994–97. Species richness remained unchanged. Chydorid cladocerans remained at low abundance in 1992, and only Chydorus cf. brevilabris increased substantially from 1993 to 1996. Non‐chydorid Cladocera increased in abundance in 1992, declined again in 1993, then gradually increased (mainly due to Ophryoxus gracilis) in 1994–96. All species declined in 1997 as minnows recolonized the lake. The calanoid copepod Leptodiaptomus minutus was present in low numbers in 1997.
The microcrustacean community in the littoral zone of Lake 302S has not yet shown consistent signs of recovery from acidification.
Factors governing nutrient status of mountain lakes in the Tatra Mountains
Authors: Kopàcöek JiR. öå , Stuchlåk& Evzö.E. N. ,   dagger, Strasökrab VeörA. , Psöenàk Petra 
Published: March 2003

1. Nutrient and chlorophyll a levels, and bacterial numbers of 84 glacial lakes in the Tatra Mountains (Slovakia and Poland, Central Europe) were determined to assess the impact of catchment vegetation and water acidity on lake trophic status.2. Catchment vegetation was the crucial factor governing nutrient content of lakes.3. Concentrations of organic carbon, organic nitrogen, and chlorophyll a, and bacterial numbers were tightly correlated with total phosphorus (TP) content. Their levels were the highest in forest lakes, then decreased in alpine lakes with decreasing amount of catchment vegetation and soil cover, and were the lowest in lakes situated in bare rocks.4. The above pattern was further modified by lake water acidity. Concentrations of TP, organic carbon, and chlorophyll a were lower in alpine lakes with pH between 5 and 6 than in more or less acid alpine lakes. Zooplankton was absent in all alpine lakes with pH between 5 and 6.5. Nitrate concentrations followed an inverse trend to TP; lowest values were in forest lakes, then increased with decreasing amount of catchment soils and vegetation. Within the lakes of the same type of catchment vegetation, nitrate concentrations were negatively correlated to TP. N‐saturation of catchment areas and lake primary production were dominant processes controlling nitrate levels in lakes and nitrate contribution to lake acidification.
A model for accurate drift estimation in streams
Authors: Faulkner Hazel , Copp Gordon H. 
Published: March 2003

1. This paper explores the experimental difficulties involved with the use of drift nets in small streams, and outlines a method whereby the estimation of drift density (number of specimens m−3 of water) can be improved.2. Changes in the filtering efficiency of the net caused by trapping of organic debris (‘clogging’) has the effect of reducing net entrance velocities, causing errors in the calculation of sampled water volume, and thus drift density. A model of the reductions in net entrance velocity based on empirical measurements of trapped debris is developed.3. Cross‐sectional velocity calculations suggest that errors can also be introduced into drift density calculations by positioning sampling nets only on the bed. A method to allow this effect is demonstrated.4. As adjustments to the calculation of sampled volume are required when sampling in rivers that undergo marked changes in discharge during the sampling period, a method whereby these effects can be accommodated to improve drift density estimations is also outlined.5. The results of this study imply that theoretical links between flow hydraulics and short‐term drift behaviour are poorly understood.
The mating and reproductive biology of the freshwater planktonic calanoid copepod Eudiaptomus gracilis
Authors: Berger Irmgard , Maier Gerhard 
Published: March 2003

1. Quantitative aspects of the mating and reproductive biology of the freshwater planktonic calanoid copepod Eudiaptomus gracilis, including duration and frequency of mating, duration of various phases of the oviducal cycle, egg production rate and adult longevity were studied under laboratory conditions. One set of copepods was fed the alga Chlamydomonas reinhardtii whose density was adjusted to 2 × 105 cells mL−1 (about 10 mg C L−1), another set was fed a mixed diet consisting of natural plankton (copepod nauplii, small rotifers and large algae) in the size range of 50–150 μm (dry mass approximately 90 mg L−1).2. The entire mating process, from the grasping of the female by the male’s right geniculate antennule to the separation of the pair, lasted about 2 min. Spermatophore placement started at about 30 s to 1 min after mating began and took approximately 1 min. Immediately after the spermatophore had been fixed in the female’s genital segment, the pair separated.3. The total oviducal cycle, including the gravid phase where the female carried ripe oocytes and the non‐gravid phase where the female did not carry ripe oocytes, lasted about 5–6 days. The non‐gravid phase was particularly long; it was longer than the gravid phase and constituted 62–72% of the total cycle.4. Mating and spermatophore placement usually occurred with gravid females although occasionally (in 30 of 200 observations) spermatophores were attached in the genital segment of non‐gravid females. Generally two to four, but up to seven, spermatophores were observed at a female’s genital segment at the same time.5. Clutch size, rate of egg production and adult longevity depended on food. When fed on C. reinhardtii, females carried 7–8 eggs clutch−1, produced a mean of 1.3 clutches and lived 14 days on average. When fed natural mixed food, females carried 10 eggs clutch−1, produced 5.6 clutches and lived 37 days on average.6. Removal of males after the first clutch resulted in no further egg production. Re‐mating is necessary in E. gracilis for continuous clutch production and the production of fertile eggs.7. Mating duration is comparatively short and the non‐gravid phase comparatively long in E. gracilis. This could be an adaption to the life in the pelagic zone of the lake, where fish predators are present. Fish select ovigerous females, pairs in copula and, probably, females with ripe oocytes which make them conspicuous. Thus, a short mating duration and a prolonged period without conspicuous oocytes, can be advantageous.
Behaviour of roach (Rutilus rutilus L.) altered by Ligula intestinalis (Cestoda: Pseudophyllidea): a field demonstration
Authors: Loot Géraldine , Brosse Sébastien , Lek Sovan , Guégan Jean‐François 
Published: March 2003

1. We studied the influence of a cestode parasite, the tapeworm Ligula intestinalis (L.) on roach (Rutilus rutilus L.) spatial occupancy in a French reservoir (Lake Pareloup, South‐west of France).2. Fish host age, habitat use and parasite occurrence and abundance were determined during a 1 year cycle using monthly gill‐net catches. Multivariate analysis [generalized linear models (GLIM)], revealed significant relationships (P < 0.05) between roach age, its spatial occupancy and parasite occurrence and abundance.3. Three‐year‐old roach were found to be heavily parasitized and their location toward the bank was significantly linked to parasite occurrence and abundance. Parasitized fish, considering both parasite occurrence and abundance, tended to occur close to the bank between July and December. On the contrary, between January and June no significant relationship was found.4. These behavioural changes induced by the parasite may increase piscivorous bird encounter rate and predation efficiency on parasitized roach and therefore facilitate completion of the parasite’s life cycle.
How well do laboratory experiments explain field patterns of zooplankton emergence?
Authors: Cáceres Carla E. , Schwalbach Michael S. 
Published: March 2003

1. We conducted a laboratory experiment to explore potential mechanisms driving variation in zooplankton emergence from diapausing eggs observed in Oneida Lake, NY, U.S.A. We hypothesized that variation in timing of ice‐out (date of thawing of ice) between 1994 and 1995, which resulted in variation in photoperiod–temperature cues, contributed to the differences in the observed field patterns. Environmental chambers were used to establish weekly photoperiod–temperature combinations that reproduced natural conditions in Oneida Lake in 1994 and 1995. In addition, a third treatment (‘dark’) exposed eggs only to the changes in temperature. We recorded zooplankton emergence for 2.5 simulated ice‐free seasons.2. Nine cladoceran taxa were found to hatch, but only Daphnia pulicaria in large numbers. Hatching of D. pulicaria was recorded throughout the season in the two light treatments and sporadically in the dark treatment. The early ice‐out treatment had the highest emergence, followed by the late ice‐out and dark treatments. Among taxa, there was temporal segregation with five hatching in the early weeks of sampling and two taxa hatching during the middle weeks. Alona hatched late in the first year, but earlier in the second year.3. We compared our laboratory results of D. pulicaria hatching with the field data obtained by Cáceres (1998). Hatching was continuous in the laboratory, whereas a synchronous spring emergence was found in the field. However, in both the laboratory and the field, more D. pulicaria hatched under conditions reflecting ice‐out occurring in March as opposed to April. Because differences in rates and timing of emergence can affect the population and community dynamics of pelagic systems, we suggest caution when applying laboratory results to field populations.
The relative importance of shading and nutrients on algal production in subtropical streams
Authors: Mosisch Thorsten D. , Bunn Stuart E. , Davies Peter M. 
Published: March 2003

1. We used artificial substrata in forested and open streams in South‐East Queensland, Australia, to determine the relative importance of shading from riparian vegetation and of nutrients on periphyton growth, and whether nitrogen and/or phosphorus limited algal productivity.2. Nutrient‐diffusing substrata consisting of agar enriched with N, P and N + P, and controls without nutrients, were deployed in duplicate at 15 sites in headwater streams with riparian canopy cover ranging from 0 to 88%.3. Shading was the over‐riding factor controlling periphyton biomass accrual on the artificial substrata, with nutrients playing a relatively minor role. Microscopic examination of periphyton scrapings taken after 7 weeks revealed that diatoms dominated on the artificial substrata in shaded streams, whereas filamentous green algae dominated the algal assemblage in the more open canopy streams.4. Whilst nutrients had little effect on the accrual of algal biomass compared with riparian shading, there was evidence that nitrogen, and not phosphorus, stimulated periphyton production in streams with sufficient light.
Phosphorus release from sediments in hardwater eutrophic lakes: the effects of redox‐sensitive and ‐insensitive chemical treatments
Authors: Burley Kim L. , Prepas Ellie E. , Chambers Patricia A. 
Published: March 2003

1. Phosphorus (P) release from bottom sediments is an important source of nutrient enrichment in many lakes in sedimentary basins, such as those in western Canada. On the Boreal Plain, sediment P release is particularly strong during periods of seasonal anoxia.2. In this study, the effects of reduction–oxidation (redox)‐sensitive and ‐insensitive chemicals on P release were examined in sediment cores collected from three eutrophic lakes.3. Contrary to expectations, redox‐sensitive treatments were no more effective at lowering total phosphorus (TP) in sediment cores than some redox‐insensitive treatments. Redox‐sensitive treatments with FeCl3 and FeCl3 + O2 reduced TP to 8 and 6%, respectively, of reference concentrations, whereas redox‐insensitive treatments with alum or lime + alum reduced TP to 14% of reference concentrations. Lime and O2 treatments reduced TP concentrations to 35 and 52% of reference concentrations, respectively.4. The fraction of P that adsorbed and co‐precipitated with iron and aluminium in the sediment cores was low (non‐apatite phosphorus fractions < 5%), suggesting that P release was controlled by apatite solubility and bacterial metabolism.