bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mass loss and macroinvertebrate colonisation of Pacific salmon carcasses in south‐eastern Alaskan streams
Authors: Chaloner Dominic T. , Wipfli Mark S. , Caouette John P. 
Published: March 2003

1. We examined the spatial and temporal dynamics of pink salmon (Oncorhynchus gorbuscha) carcass decomposition (mass loss and macroinvertebrate colonisation) in south‐eastern Alaskan streams. Dry mass and macroinvertebrate fauna of carcasses placed in streams were measured every two weeks over two months in six artificial streams and once after six weeks in four natural streams. We also surveyed the macroinvertebrate fauna and wet mass of naturally occurring salmon carcasses.2. Carcass mass loss in artificial streams was initially rapid and then declined over time (k=–0.033 day–1), and no significant differences were found among natural streams.3. Several macroinvertebrate taxa colonised carcasses, but chironomid midge (Diptera: Chironomidae) and Zapada (Plecoptera: Nemouridae) larvae were found consistently and were the most abundant (on average 95 and 2%, respectively, of the invertebrates found). Chironomid abundance and biomass increased over time, whereas Zapada abundance and biomass did not. Significant differences in abundance were found among natural streams for Baetis (Ephemeroptera: Baetidae) and Sweltsa (Plecoptera: Chloroperlidae) larvae, while no significant differences were found for chironomid and Zapada abundance or biomass.4. Our results suggest that salmon carcasses initially undergo a high rate of mass loss that tapers off with time. Chironomid and Zapada larvae are likely to be important in mediating nutrient and energy transfer between salmon carcasses and other components of the freshwater‐riparian food web in south‐eastern Alaskan streams.
Simple predictions of instream habitat model outputs for fish habitat guilds in large streams
Authors: LAMOUROUX NICOLAS , SOUCHON YVES 
Published: March 2003

1. In the context of a generalised modification of hydraulic conditions in medium to large streams, modelling the impacts of stream regulation on fish communities in multiple streams is an important challenge for basic and applied freshwater ecology. Conventional instream habitat models such as PHABSIM link a hydraulic model with preference curves for various species to estimate habitat value changes with discharge in stream reaches. Despite world‐wide applications, they have been scarcely used in multiple sites with multiple species.2. We assigned 21 size classes of European fish species to four habitat guilds (cluster analysis grouping size classes with comparable microhabitat preference curves). Then, we ran a conventional instream habitat model on 28 French stream reaches belonging to the `barbel zone', to estimate habitat values versus discharge curves for the 21 size classes. We summarised the outputs as mean habitat values for guilds, and tested if they were predictable from average characteristics of reaches (discharge, depth, width, particle size).3. As was obtained elsewhere for populations, habitat values for guilds were strongly related to average, dimensionless characteristics of reaches. The Reynolds number of reaches, equivalent to a discharge per width unit, reflected most of the discharge‐dependent changes in habitat values (within reaches). In particular, habitat values of species preferring bank (respectively midstream) microhabitats decreased (respectively increased) with increasing Reynolds number. The Froude number at median discharge was the major predictor of reach‐dependent but discharge‐independent variations in habitat values. Habitat values of species preferring riffle versus pool or bank microhabitats were higher in reaches with high Froude numbers. These relationships were consistent with existing knowledge on the different species.4. Such results suggest that the input variables required to estimate habitat values for fish communities can be greatly simplified, as illustrated by a general estimation of the sensitivity of species preferring midstream habitats to discharge changes in any reach. Cost‐efficient alternatives to conventional instream habitat models should facilitate their validation in multiple sites, a point that remains critical in instream habitat modelling of fish communities.
Effects of longitudinal variations in stream habitat structure on fish abundance: an analysis based on subunit‐scale habitat classification
Authors: Inoue Mikio , Nunokawa Masanori 
Published: March 2003

SUMMARY 1. Stream reaches contain assortments of various habitat types that can be defined at different spatial scales, such as channel unit (e.g. pools, riffles) and subunit (patches within channel units). We described longitudinal (upstream–downstream) patterns of stream habitat structure by considering subunits as structural elements, and examined their effects on the abundance of masu salmon (Oncorhynchus masou) and rosyface dace (Leuciscus ezoe) in a third‐order tributary of the Teshio River in northern Hokkaido, Japan.2. Nine subunit types were determined on the basis of water depth, current velocity and substrate, using 0.5 × 0.5 m grids. Although both masu salmon and rosyface dace used pools as a major habitat, the former preferred a subunit type occurring at pool heads (PH subunit) while the latter preferred a slow‐current edge type (SE‐2 subunit).3. Along the course of the stream, slow‐edge subunits (SE‐1, 2 and 3) increased in frequency downstream while fast‐edge subunits (FE‐1 and 2) decreased, suggesting a downstream development of slow‐current edges. Regression analyses indicated that longitudinal variation in masu salmon abundance was explained by the area of PH, rather than pools. Masu salmon density increased with the area of PH. Rosyface dace abundance was explained by a combination of water depth and the area of SE‐2, both effects being positive.4. Longitudinal variations in the abundance of both species were related to the abundance of their preferred habitat at the subunit scale, rather than channel‐unit scale. The results emphasise the importance of fine‐scale patchiness when examining stream fish habitats.
Effects of augmentation of coarse particulate organic matter on metabolism and nutrient retention in hyporheic sediments
Authors: Crenshaw C. L. , Valett H. M. , Webster J. R. 
Published: March 2003

SUMMARY 1. Metabolic and biogeochemical processes in hyporheic zones may depend on inputs of coarse particulate organic matter. Our research focused on how differing quantity and quality of organic matter affects metabolism and nutrient retention in the hyporheic zone of a first‐order Appalachian stream.2. Sixteen plots were established on a tributary of Hugh White Creek, NC, U.S.A. Sediment was extracted and treated with leaves, wood, plastic strips or remained unamended. Following treatment, sediment was returned to the stream and, approximately 3 months later, samples were removed from each plot.3. Aerobic and anaerobic metabolism were measured as the change in O2 and CO2 in recirculating microcosms. At the same time, we monitored other possible terminal electron accepting processes and changes in nutrient concentrations. Aerobic metabolism was low in all treatments and respiratory quotients calculated for all treatments indicated that metabolism was dominated by anaerobic processes.4. Rates of anaerobic respiration and total (combined aerobic and anaerobic) respiration were significantly greater (P < 0.05) in plots treated with leaf organic matter compared to controls.5. Addition of leaves, which had a low C:N ratio, stimulated respiration in hyporheic sediments. Anaerobic processes dominated metabolism in both control and amended sediments. Enhanced metabolic rates increased retention of many solutes, indicating that energy flow and nutrient dynamics in the subsurface of streams may depend upon the quantity and quality of imported carbon.
Effects of experimentally induced cyanobacterial blooms on crustacean zooplankton communities
Authors: Ghadouani Anas , Pinel‐Alloul Bernadette , Prepas Ellie E. 
Published: March 2003

SUMMARY 1. Large in situ enclosures were used to study the effects of experimentally induced cyanobacterial blooms on zooplankton communities. A combination of N and P was added to shallow (2 m) and deep enclosures (5 m) with the goal of reducing the TN : TP ratio to a low level (∼5 : 1) to promote cyanobacterial growth. After nutrient additions, high biomass of cyanobacteria developed rapidly in shallow enclosures reaching levels only observed during bloom events in eutrophic lakes.2. In the shallow enclosures, particulate phosphorus (PP) was on average 35% higher in comparison with deep enclosures, suggesting that depth plays a key role in P uptake by algae. Phytoplankton communities in both deep and shallow enclosures were dominated by three cyanobacteria species –Aphanizomenon flos‐aquae, Anabaena flos‐aquae and Microcystis aeruginosa– which accounted for up to 70% of total phytoplankton biomass. However, the absolute biomass of the three species was much higher in shallow enclosures, especially Aphanizomenon flos‐aquae. The three cyanobacteria species responded in contrasting ways to nutrient manipulation because of their different physiology.3. Standardised concentrations of the hepatotoxic microcystin‐LR increased as a result of nutrient manipulations by a factor of four in the treated enclosures. Increased biomass of inedible and toxin producing cyanobacteria was associated with a decline in Daphnia pulicaria biomass caused by a reduction in the number of individuals with a body length of >1 mm. Zooplankton biomass did not decline at moderate cyanobacteria biomass, but when cyanobacteria reached high biomass large cladocerans were reduced.4. Our results demonstrate that zooplankton communities can be negatively affected by cyanobacterial blooms and therefore the potential to use herbivory to reduce algal blooms in such eutrophic lakes appears limited.
Exotic crayfish in a brown water stream: effects on juvenile trout, invertebrates and algae
Authors: Stenroth Patrik , Nyström Per 
Published: March 2003

SUMMARY1. The impact of the introduced omnivorous signal crayfish (Pacifastacus leniusculus) on trout fry, macroinvertebrates and algae was evaluated in a brown water stream in southern Sweden usingin situenclosures. We also examined the gut content of all surviving crayfish in the enclosures. Two crayfish densities in addition to a control without crayfish were used in replicate enclosures (1.26 m2) in a 1‐month experiment. Additionally, 20 trout fry (Salmo trutta) were stocked in each enclosure to assess the effects of crayfish on trout survival and growth.2. Detritus was the most common food item in crayfish guts. Animal fragments were also frequent while algae and macrophytes were scarcer. Crayfish exuviae were found in crayfish guts, but the frequency of cannibalism was low.3. Trout survival in enclosures was positively related to water velocity but was unaffected by crayfish.4. Total invertebrate biomass and taxon richness were lower in crayfish treatments. The biomass of all predatory invertebrate taxa was reduced but only three of six non‐predatory taxa were reduced in the crayfish treatments.5. Epiphytic algal biomass (measured as chlorophylla, on plastic strips) was not related to crayfish density, whereas the biomass of epilithic algae (measured as chlorophylla) was enhanced by high water velocity and high crayfish density. The latter was possibly mediated via improved light and nutrient conditions, as active crayfish re‐suspend and/or remove detritus and senescent algal cells during periods of low water velocity.6. We conclude that the introduced signal crayfish may affect stream communities directly and indirectly. Invaded communities will have reduced macroinvertebrate taxon richness and the signal crayfish will replace vulnerable invertebrate predators such as leeches. In streams that transport large amounts of sediment or organic matter, a high density of crayfish is likely to enhance benthic algal production through physical activity rather than via trophic effects.
Stem CO2 fluxes in two Sahelian shrub species (Guiera senegalensis and Combretum micranthum)
Authors: Levy P. E. , Jarvis P. G. 
Published: March 2003

1. Measurements are presented of CO2 flux from woody stems of two shrub species in the Sahelian zone of West Africa (Guiera senegalensis and Combretum micranthum). Measurements were made on excised stems and in situ. 2. An experiment suggested that the respiration rate was closely related to the stem surface area but showed little relationship with stem volume, and was therefore associated with the cambium and phloem rather than the sapwood. This contrasts with several studies in which sapwood volume appeared to be the dominant component and the difference is attributed to the comparatively small diameter of stems in the shrubs studied here. 3. Measurements were made of the response of stem CO2 flux to photosynthetic photon flux density (Q) and gave evidence of corticular photosynthesis in the stems. 4. The response of stem respiration to temperature was determined in situ. The data were analysed using a variant on the standard exponential relationship with temperature, R = (Rom + Rog) exp(k T), where R is respiration rate, Rom is maintenance respiration rate at 0 °C, Rog is growth respiration rate at 0 °C, k is a temperature coefficient and T is temperature. Data from the dry season were assumed to represent maintenance respiration and used to define Rom and k. The Rog term thus quantifies the increase in respiration during the wet season beyond this baseline level, presumably attributable to growth. Values of Rom were 0·054 and 0·074μmol m–2 s–1 in G.senegalensis and C. micranthum, respectively, whilst Rog ranged between 0·061 and 0·96μmol m–2 s–1 during the wet season. 5. At ecosystem scale on an annual basis, stem respiration represented 17% of leaf photosynthesis, whilst corticular photosynthesis was at most 11·1% of stem respiration.
Regulation of integumentary colour and plasma carotenoids in American Kestrels consistent with sexual selection theory
Authors: Negro J. J. , Bortolotti G. R. , Tella J. L. , Fernie K. J. , Bird D. M. 
Published: March 2003

1. Sexually selected traits are expected to vary seasonally, with the maximal expression of the character being evident during mate choice; however, the mechanisms controlling or regulating such traits are generally poorly known. 2. Carotenoid pigments responsible for bright red or yellow coloration in the feathers, skin or other integumentary structures of birds are generally believed to vary seasonally because of diet. 3. Variation in carotenoid‐dependent skin colour between winter and spring (mating season) was investigated, as was variation in plasma carotenoids across the breeding season in captive American Kestrels, Falco sparverius, fed a uniform diet. 4. Kestrels were more brightly coloured in the mating period than in winter, and plasma carotenoid concentrations declined from the time of mating to the rearing of young. 5. Although carotenoid levels were highly sexually dimorphic during mating and laying, males and both breeding and non‐breeding females all had similar levels by the incubation period, and the pattern of variation over time suggests rheostatic regulation. 6. These results suggest kestrels may have the ability to regulate (rather than merely control) their colour physiologically, the variation in colour and carotenoids is consistent with that expected of a sexually selected trait, and the loss of colour after breeding may suggest a trade‐off between the show and health functions of carotenoids.
A satiation model for the temporal organization of grazing in limpets
Authors: Chelazzi G. , Parpagnoli D. , Santini G. 
Published: March 2003

1.A compartmental model of the limpet alimentary system was designed to simulate the effects of functional constraints and substrate characteristics on the temporal patterning of grazing in these gastropods. Limitations are imposed by gut capacity and processing time. A maximum operating frequency is set for the radula activity, and a negative feedback on the grazing frequency is related to gut replenishment.2.When holding constant the ‘morphofunctional’ parameters of the model, variations in the ‘richness’ of the substrate (i.e. in the amount of matter extracted per single rasp) generated different patterns of grazing activity, from constant grazing at different frequencies, to the appearance of distinct grazing–non‐grazing subphases with a periodicity corresponding to the processing time. Moreover, when varying the digestibility of the matter (i.e. its processing time), temporary saturations were produced.3.Automatic recording of radula activity in specimens ofPatella caeruleaL. collected from a Mediterranean boulder beach and transferred to tidal tanks showed that each activity phase (performed during the high‐tide period) may be differently structured: from almost continuous grazing, with more or less pronounced and sometimes periodic oscillations, to alternation of grazing and non‐grazing subphases. Continuous and non‐continuous grazing patterns are shown also by the same specimen during subsequent activity phases.4.The results of the model are consistent with empirical observations and suggest that satiation events related to the characteristics of the substrate encountered by the limpets when foraging, can produce highly variable grazing patterns with implications for the energetics of foraging in this group of grazers.
Close association of RGR, leaf and root morphology, seed mass and shade tolerance in seedlings of nine boreal tree species grown in high and low light
Authors: Reich P. B. , Tjoelker M. G. , Walters M. B. , Vanderklein D. W. , Buschena C. 
Published: March 2003

1. To test hypotheses concerning adaptation and acclimation of tree species to shaded habitats we determined the growth, biomass partitioning and morphology of seedlings of nine near‐boreal tree species in high‐ and low‐light greenhouse environment (25 and 5% of full sunlight, respectively), comparable to sunlit gap and shaded microsites in boreal forests. The species differ widely in shade tolerance, seed size and leaf life span. 2. In low light, all species allocated proportionally more biomass to stems and less to roots, but the same to foliage, compared with the high‐light environment. At a common size, all species had finer leaf morphology (higher specific leaf area, SLA) but coarser root morphology (lower specific root length, SRL) in low than high light. From a whole plant perspective, all species enhanced leaf area per unit plant mass (leaf area ratio, LAR) in low light and root length per unit plant mass (root length ratio, RLR) in high light. 3. Shade‐intolerant deciduous species had higher RGR, SLA and SRL than larger seeded evergreens: ranking from Populus, Betula and Larix spp., then to five evergreen Pinus, Picea and Thuja spp., which were generally comparable in these traits. There were no changes in growth rankings of species between high‐ and low‐light environments, nor consistent differences among species in biomass partitioning. Hence, species differences in leaf and root morphology (SLA, SRL) drove whole plant patterns, such as Populus, Betula and Larix had greater total leaf area and root length per unit plant mass (LAR and RLR, respectively) than the evergreens. Interspecific variation in RGR in both high and low light was positively correlated (r≈ 0·9) with SLA, SRL, LAR and RLR, and negatively correlated (r≈–0·9) to seed mass and leaf life span. 4. These data suggest that SLA, SRL, NAR and RGR are closely associated with variation in life‐history traits and that variation in leaf and root structure more strongly influences patterns of RGR among species and light environments than does biomass partitioning.
Effects of defoliation and girdling on fruit production inIlex aquifolium
Authors: Obeso J. R. 
Published: March 2003

1.The effects of defoliation and girdling on fruit production in European hollyIlex aquifoliumwere studied in a northern Spanish population. Three defoliation treatments (control, 50% and 100% leaf removal) were applied at branch level in 10 trees. Six branches were used per treatment in each tree and half of these branches were girdled (a ring of bark and cambium was removed from the branch base).2.Leaf removal from ungirdled branches had little effect on fruit set, fruit production and reproductive allocation at branch level. However, these variables decreased as the extent of defoliation increased on girdled branches.3.Fruit production in undefoliated branches did not differ between girdled and ungirdled branches, showing that girdled branches were autonomous for fruit production when undamaged. Mean fruit mass of girdled‐100% defoliated branches averaged 8% of fruit mass produced by control branches.4.Fruit production of ungirdled‐100% defoliated branches did not differ from control branches, showing the importance of resource importation from other branches. Hence the branches may be regarded as only partially autonomous for fruit production.5.Fruit production of girdled‐50% defoliated branches was 42% of fruit production of control branches, while ungirdled‐50% defoliated branches amounted to 70% of controls. These results also demonstrated resource importation but did not support the existence of photosynthetic compensatory mechanisms.6.The ability of resource importation developed by fruiting branches might be a mechanism to reduce the effect of reproductive costs in this species.
Colour‐associated mating success in a polymorphic Ladybird Beetle, Harmonia axyridis
Authors: Ueno H. , Sato Y. , Tsuchida K. 
Published: March 2003

1. Body size is often an important character in mating success, but has been only infrequently mentioned in regard to colour polymorphism. In this study, mating success was investigated in a colour polymorphic Ladybird Beetle, Harmonia axyridis, with reference both to colour morph and to body size. 2. In the non‐melanic males the mating individuals were significantly larger than solitary individuals, while in melanic males there was no significant difference. 3. The mating pattern was close to random mating with respect to colour morph and there was no significant deviation. 4. The results suggest both body size and colour morph affect the male mating success and males of different body size obtain mating advantage according to the colour morph. Colour polymorphism in this species is controlled by alleles on a single locus. Thus, the alleles on that locus significantly influence the effect of selection on the quantitative character.
Ecological correlates of seed size in the British flora
Authors: Hodkinson D.J. , Askew A.P. , Thompson K. , Hodgson J.G. , Bakker J.P. , Bekker R.M. 
Published: March 2003

1. The association between seed size and habitat shade within the British flora was investigated using a data set of seed masses, life histories and quantitative measures of habitat shade for 504 species; the association between seed size and seed longevity was investigated using a data set of seed masses, life histories and seed longevities for 301 species. 2. The data were analysed using the method of phylogenetically independent contrasts (PICs) calculated using the software package CAIC (Comparative Analysis by Independent Contrasts). 3. Seed mass was found to be positively correlated with habitat shade and negatively correlated with seed longevity, after variation owing to life history had been accounted for.