bluuebunny/crossref_metadata_2025_split huggingface dataset:
Correlations between observed dispersal capabilities and patterns of genetic differentiation in populations of four aquatic insect species from the Arizona White Mountains, U.S.A.
Authors: Miller Mark P. , Blinn Dean W. , Keim Paul 
Published: March 2003

SUMMARY 1. Dispersal ability is an important ecological factor that can influence population structure. In an attempt to determine the extent that the pattern of genetic differentiation is correlated with dispersal ability in stream‐dwelling aquatic insects, we used the amplified fragment length polymorphism (AFLP) technique to characterise genetic variation in four aquatic insect species: Gumaga griseola (Trichoptera: Sericostomatidae), Helicopsyche mexicana (Trichoptera: Helicopsychidae), Psephenus montanus (Coleoptera: Psephenidae) and Ambrysus thermarum (Hemiptera: Naucoridae). Individuals were sampled from several sites within two adjacent catchments in the Arizona White Mountains. In addition to the genetic analyses, a 20‐week‐long trapping study was used to determine the relative dispersal ability of adults of the four species examined.2. We obtained hierarchical indicators of genetic differentiation for catchments, sites within catchments and sites across the region examined. Overall, average estimators of genetic differentiation (F‐statistics) were consistent with direct observations of organismal movement, although it was our direct observations on adult insect flight that permitted us to interpret our results correctly. This was because of the fact that a lack of genetic differentiation across watersheds can be interpreted in two ways.3. In contrast to F‐statistics, patterns of genetic isolation by distance for each species more clearly reflected dispersal ability, suggesting that such analytical approaches provide less ambiguous information about the importance of gene flow in the hierarchical partitioning of genetic variation in stream organisms.
Geomorphic dynamics of floodplains: ecological implications and a potential modelling strategy
Authors: RICHARDS KEITH , BRASINGTON JAMES , HUGHES FRANCINE 
Published: March 2003

1.  The dynamics of channel migration and floodplain renewal constitute an important control of the ecological diversity of river corridors. Restoration initiatives should therefore assess whether these dynamics must be reinstated in order to address the cause rather than the symptoms of floodplain biodiversity decline.2.  Restoration of reach‐scale dynamism in rivers where this is a natural behavioural process will restore smaller‐scale geomorphological and sedimentological processes that encourage vegetation regeneration, but may require catchment‐scale management of material flows.3.  Channel dynamics depend on the style of river–floodplain interaction, and this may be summarised in qualitative, classificatory, sedimentological models of floodplain architecture that have been somewhat neglected in the ecological literature.4.  One approach to the assessment of floodplain biodiversity and its restoration would be through the development of simulation models based on specified channel styles, and involving simplified hydrodynamics and successional changes. Such models, currently the subject of research as a spin‐off from modelling studies of landscape evolution, would permit evaluation of the consequences for ecological diversity of implementing various management options that may affect the dynamics of channel migration.
Functional heterogeneity of dry‐season fish refugia across a Mediterranean catchment: the role of habitat and predation
Authors: Magalhães M. Filomena , Beja Pedro , Canas Catarina , Collares‐Pereira Maria João 
Published: March 2003

SUMMARY 1. Fish in Mediterranean streams survive through the summer in residual surface waters, encompassing a broad range of abiotic and biotic conditions. Yet, the extent to which fish assemblages may be shaped by functional heterogeneity in dry‐season refugia is largely unknown. This study addresses this issue, by examining fish assemblage and population attributes, and predation patterns in residual summer habitats (12 pools and six runs) across a Mediterranean catchment in south‐west Portugal.2. Species richness was fairly constant among runs but increased with pool size, with the addition of exotics and rare natives to large pools resulting in nested subsets. The four most common species (chub, nase, loach and eel) were considered generalists in terms of their use of dry‐season refugia. Conversely, rare species presented more specialised habitats, with barbel and exotics favouring pools and stickleback favouring runs.3. Age and size of the two most common species varied among dry‐season habitats. Age 0 chub were restricted to runs, where spawning stages (age 2 and older fish) were also more represented. Age 0 nase also concentrated in runs, but the individuals collected in pools exhibited greater growth. Conversely, age 2 and older nase were proportionally more abundant in pools, but with greater growth and better condition in runs.4. The otter was the main fish predator, consuming fish of all species and size classes, irrespective of habitat. Otter activity concentrated in pools, where predation risk for cyprinids seemed to be much higher than in runs.5. Dry‐season refugia apparently vary in functional importance for different fish species and life stages, acting as complementary units in the landscape. Therefore, the presence of both pool and run refugia trough the summer dry season may play a critical role in promoting the persistence of native species in Mediterranean streams.
Temperature‐ and predator‐induced phenotypic plasticity in Bosmina cornuta and B. pellucida (Crustacea: Cladocera)
Authors: Kappes Heike , Sinsch Ulrich 
Published: March 2003

SUMMARY 1. Clones of Bosmina cornuta and B. pellucida (B. longirostris species complex) were derived from samples collected from Scheuermühlenteich and Lake Windsborn(westernGermany). Experimental temperature change (to 10 °C and 20 °C) and exposure to Acanthocyclops vernalis copepods (12 L−1) significantly altered external morphology in laboratory cultures of the two species. Morphological traits were derived from eight log10‐transformed and standardised morphometric distances by factorial analysis: factor 1 represented body size, factor 2, size of appendages and factor 3, the head size.2. Acclimation of clones to cold water (10 °C, >14 days) led to an increase in body, antennule and mucrone size in B. cornuta and B. pellucida. Moreover, at 10 °C, B. cornuta cultures usually collapsed within a few weeks. Compared to the trials at 10 °C, acclimation to 20 °C (the two species) and to 15 °C (B. pellucida only) left the size of body appendages unchanged. Individuals were unequivocally assigned to each species by discriminant functions. Conspecific individuals that were acclimated to different temperatures between 10 and 20 °C also differed in external morphology, but discriminant analysis yielded misclassification rates of 5.3–23.3%.3. Morphological response to the presence of copepod predators was weaker than that caused by temperature change. Long‐term exposure of clones to copepod predators induced a significant increase in size of appendages in the two species but left body size unaffected. Again, species identification by discriminant functions could be made without any error, whereas conspecific controls and experimentals were misclassified at rates between 19.4 and 29.5%.4. It is suggested that temperature is the main proximal cue for Bosmina cyclomorphosis. The distinct response to temperature of B. pellucida and B. cornuta may also account for seasonal differences in abundance observed in field.
Genetic and morphological differentiation of Dikerogammarus invaders and their invasion history in Central Europe
Authors: Müller Jakob C. , Schramm Stephanie , Seitz Alfred 
Published: March 2003

SUMMARY 1. Biological invasions often involve close taxonomic relatives either as native/invader pairs or as invader/invader pairs. Precise identification and differentiation of species is therefore of paramount importance to reconstruct the invasion history. Genetic studies are indispensable in the case of morphologically conservative taxonomic groups.2. We analysed the Pontocaspian freshwater amphipods Dikerogammarus that have successfully invaded the benthos of large Central European rivers. Taxonomic uncertainties were clarified by phylogenetic analyses of mitochondrial 16S and COI genes. The three‐way partitioning of allozyme genotypes in a syntopic population further corroborated the taxonomic status of the three species Dikerogammarus haemobaphes, D. villosus and D. bispinosus. Dikerogammarus bispinosus had been prior misidentified as a subspecies of D. villosus. The conspicuous colour types of D. villosus, however, appeared to be conspecific.3. The genetic identification of the previously more abundant D. haemobaphes individuals in old samples supported the ‘successive invasion wave’ hypothesis with D. haemobaphes as the first invader displaced by the second invader D. villosus. Dikerogammarus bispinosus could be a potential future invader.4. Haplotype differentiation was apparent between two invasion lines of D. haemobaphes, but the occurrence of a single widespread haplotype indicates genetic impoverishment during rapid colonisation.
Water temperature, light intensity and zooplankton density and the feeding activity of juvenile brook charr (Salvelinus fontinalis)
Authors: Marchand F. , Magnan P. , Boisclair D. 
Published: March 2003

SUMMARY 1. The objective of this study was to evaluate the effects of zooplankton biomass (as a measure of density), fish biomass, light intensity and water temperature on the attack rate and swimming characteristics (i.e. swimming speed and angle of turn) of juvenile (1+) brook charr (Salvelinus fontinalis) in field enclosures. We used a portable underwater camera system in a series of pelagic enclosures to quantify the feeding behaviour of brook charr over a gradient of natural conditions.2. In simple linear or non‐linear regression models we found (i) that attack rate and angle of turn were positively related to water temperature, (ii) that attack rate and swimming speed were positively related to zooplankton biomass and light intensity and (iii) that attack rate was positively related to swimming speed. In multiple regression models, fish biomass, light intensity and variance of the angle of turn accounted for 87% of the variation in attack rate. Light intensity and water temperature accounted for 86% of the variation in swimming speed. Fish gut fullness and attack rate accounted for 83% of the variation in the variance of the angle of turn executed by fish.3. The increase in the number of attacks as zooplankton biomass increases conforms to the general positive functional response observed in other fish species. Our results also support the hypothesis that swimming speed increases with prey biomass. We did not observe a plateau in attack rate as zooplankton biomass increased. As our experiments were performed under natural biotic and abiotic conditions, factors other than zooplankton biomass might affect or limit this response, such as water temperature and light intensity.4. Because zooplankton biomass was correlated with water temperature and light intensity, it was not possible to evaluate the independent contribution of these factors on the attack rate and swimming characteristics (swimming speeds and angle of turn) of brook charr. However, this study highlighted the impact of these factors on the feeding behaviour of juvenile brook charr when feeding in the pelagic habitat under natural conditions, and their importance in future models of optimal foraging and fish habitat quality.
Effect of wave exposure on vegetation abundance, richness and depth distribution of shallow water plants in a New Zealand lake
Authors: Riis Tenna , Hawes IAN 
Published: March 2003

SUMMARY 1. The effects of physical disturbance in terms of wave exposure, shore slope and substrate mobility on the presence, species richness, cover and depth limits of the low‐growing, shallow water macrophyte community (called the low mixed community) were examined at 41 shore sites in Lake Wanaka, South Island, New Zealand.2. Wave exposure at a site was described by the previous year's maximum depth of sediment motion and maximum vertical extension of waves, determined from a computer wave model. Shore slope at each site was recorded from −1 to 0 m depth, and sediment stability was assessed as the cover of small gravel.3. The low mixed community was only present on sites where the previous year's maximum depth of sediment motion was <8 m, maximum wave run‐up was <0.3 m, shore slope <0.12 m m−1, and small gravel cover <78%.4. Species richness, cover and depth limits of the low mixed community decreased with increasing disturbance on the sites. Sixty‐two percentage of the variation in species richness could be explained by physical disturbance variables when all sites were included (N=41). When only sites with a low mixed community were included (N=22), only 18% of the variation was explained. Species richness within sites supporting a low mixed community is thus poorly explained by physical disturbance, whereas presence or absence is better explained. There was no evidence to support the intermediate disturbance hypothesis in this study.5. Disturbance as a result of waves explained 86% of the variation in cover among sites with a low mixed community and accounted for 68 and 58% of the variation in upper and lower depth limit of the low mixed community, respectively.6. The models obtained in this study can be used as predictive models for the low mixed community in New Zealand lakes in relation to natural physical disturbance on the shore. By integrating these results with previous studies on the effect of water level fluctuation, we describe a generalised optimum physical habitat for the low mixed community in New Zealand lakes.
Effects of livestock grazing on benthic invertebrates from a native grassland ecosystem
Authors: Scrimgeour Garry J. , Kendall Sharon 
Published: March 2003

SUMMARY 1. The effects of cattle grazing on stream bank stability, biomass of riparian vegetation, instream vegetation cover, biomass of coarse particulate organic matter (CPOM) and epilithon and benthic invertebrate community structure were investigated over a 2‐year period using: (i) enclosures containing different cattle grazing treatments and (ii) by comparing streams with different grazing intensities in the Cypress Hills Provincial Park, Alberta, Canada.2. Livestock enclosure experiments comprised four treatments of: (1) early season cattle grazing (June–August), (2) late season cattle grazing (August–September), (3) all season cattle grazing (June–September) and (4) cattle‐absent controls. All four treatments were replicated in two streams while two treatments (i.e. cattle‐absent controls, early season cattle grazing) were established in a third stream.3. Bank stability, estimated visually based on sediment inputs to the stream channel, increased significantly in cattle‐absent treatments compared with cattle‐present enclosures over the 2‐year study period.4. Epilithic chlorophyll a was significantly affected by time, but neither cattle nor the interaction of time and treatment were significant.5. At the end of the experiment, total invertebrate biomass in the late and all‐season treatment exceeded that in the early and cattle‐absent treatments. However, excluding cattle from the streams, at any of the different treatments, had little clear impact on the total benthic invertebrate abundance or the abundance of the predominant functional feeding groups over the 2‐year study period.6. In contrast, comparisons of benthic assemblages from streams with different grazing intensities showed that the non‐grazed reach of Storm Creek contained significantly higher biomass of CPOM and shredders compared with the cattle‐absent enclosures in Battle, Graburn and Nine Mile creeks. Redundancy analysis showed that benthic communities from all enclosures and Storm Creek in summer and autumn 2000 were affected primarily by CPOM biomass, pH, nitrate, turbidity and benthic chlorophyll a. Construction of a 99% probability ellipse from enclosure sites showed that invertebrate communities from livestock enclosures differed from that in the non‐grazed Storm Creek.7. Results from stream‐scale comparisons indicate that current livestock grazing practices in the Cypress Hills significantly impact riparian zones, stream channels and benthic invertebrate community structure and that alternative practices, such as rotational grazing, need to be developed.
Invasibility of a reservoir to exotic Daphnia lumholtzi: experimental assessment of diet selection and life history responses to cyanobacteria
Authors: Pattinson K. R. , Havel J. E. , Rhodes R. G. 
Published: March 2003

SUMMARY 1. In reservoirs of the south‐central United States, the exotic cladoceran Daphnia lumholtzi is common during warm midsummer conditions, when cyanobacteria are abundant and native Daphnia are rare. In the current study, we employed surveys, field experiments, and a life table experiment to investigate the role of food quality in explaining the distribution and phenology of D. lumholtzi, relative to two native species (Daphnia parvula and Daphnia mendotae).2. During May–September 2000 in eutrophic McDaniel Lake, Missouri U.S.A., cyanobacteria (primarily Oscillatoria) first appeared at 6‐m depth and then became abundant throughout the epilimnion.3. During the May field experiment, D. lumholtzi, D. parvula and D. mendotae all consumed a similar diet of algae, showing positive selection for small greens (chlorophytes and cryptophytes <20 μm). During the July experiment, when the epilimnion exceeded 25 °C and cyanobacteria were common in the lake, D. lumholtzi consumed significantly more total algae and more cyanobacteria than the two native species. Although the Daphnia selected against cyanobacteria, all three species consumed about 25% of this food in their diet.4. A life table experiment compared the responses of D. lumholtzi and D. parvula with variation in density of high‐quality food (Ankistrodesmus) and concentration of a toxic strain of cyanobacteria (Anabaena flos‐aquae). Both Daphnia species showed reduced survivorship, fertility and intrinsic rates of increase in response to elevated concentrations of cyanobacteria, particularly at the higher food level.5. The results suggest that D. lumholtzi shows similar inhibition from cyanobacteria as does the native Daphnia. However, their continued high in situ feeding rates imply that D. lumholtzi is less affected by midsummer conditions in warm‐water reservoirs than are native Daphnia.
Temporal dynamics in epipelic, pelagic and epiphytic algal production in a clear and a turbid shallow lake
Authors: Liboriussen Lone , Jeppesen Erik 
Published: March 2003

SUMMARY 1. Pelagic and epipelic microalgal production were measured over a year in a pre‐defined area (depth 0.5 m) in each of two lakes, one turbid and one with clear water. Further estimates of epiphytic production within reed stands were obtained by measuring production of periphyton developed on artificial substrata.2. Total annual production of phytoplankton and epipelon was 34% greater in the turbid lake (190 g C m−2 year−1) than in the clearwater lake (141 g C m−2 year−1). However, the ratio of total production to mean water column TP concentration was two fold greater in the clearwater lake.3. Phytoplankton accounted for the majority of the annual production (96%) in the turbid lake, while epipelic microalgal production dominated (77%) in the clear lake. The relative contribution of epipelic algae varied over the year, however, and in the turbid lake was higher in winter (11–25%), when the water was relatively clear, than during summer (0.7–1.7%), when the water was more turbid. In the clearwater lake, the relative contribution of epipelon was high both in winter, when the water was most clear, and in mid‐summer, when phytoplankton production was constrained either by nutrients or grazing.4. Compared with pelagic and epipelic primary production, epiphytic production within a reed stand was low and did not vary significantly between the lakes.5. The study supports the theory of a competitive and compensatory trade‐off between primary producers in lakes with contrasting nutrient concentrations, resulting in relatively small differences in overall production between clear and turbid lakes when integrating over the season and over different habitats.
Carbon gains by desiccation‐tolerant plants at elevated CO2
Authors: Tuba Z. , Csintalan Z. , Szente K. , Nagy Z. , Grace J. 
Published: March 2003

1. There have been no reports of the long‐term responses of the desiccation‐tolerant (DT) plants to elevated CO2. Xerophyta scabrida is a DT woody shrub, which loses chlorophylls and thylakoids during desiccation: a so‐called poikilochlorophyllous desiccation‐tolerant species (PDT). When the leaves of X. scabria are allowed to desiccate, the species shows many of the normal features of (P)DT plants. 2. However, the duration of photosynthesis in X. scabria is prolonged by 300% when the measurements are made at 700 as opposed to 350p.p.m. CO2. The implication is that the carboxylating enzymes must still have been active at this time to enable appreciable photosynthetic activity. This response could have far‐reaching implications for the success of such species in a future climate. 3. Lichens and mosses, representing the homoiochlorophyllous DTs (HDT), retain their chlorophyll content and photosynthetic apparatus during desiccation. We show the desiccation responses of two common HDT species (Cladonia convoluta and Tortula ruralis) to elevated CO2 for comparison. Both HDT species showed increased net CO2 uptake in the material grown at high CO2 by more than 30% in moss and by more than 50% in lichen. It is concluded that desiccation‐tolerant plants will be among the main beneficiaries of a high CO2 future.
The influence of sex and body size on food habits of a giant tropical snake, Python reticulatus
Authors: Shine R. , Harlow P. S. , Keogh J. S. , Boeadi  
Published: March 2003

1. In many animal species, dietary habits shift with body size, and differ between the sexes. However, the intraspecific range of body sizes is usually low, making it difficult to quantify size‐associated trophic shifts, or to determine the degree to which sex differences in diet are due to body‐size differences. Large snakes are ideal for such a study, because they provide a vast range of body sizes within a single population. 2. More than 1000 Reticulated Pythons (Python reticulatus) from southern Sumatra were examined, with specimens from 1·5 to > 6 m in snout–vent length, and from 1 to 75 kg in mass. Females attained much larger body sizes than did conspecific males (maxima of 20 vs 75 kg, 5 vs 7 m), but had similar head lengths at the same body lengths. 3. Prey sizes, feeding frequencies and numbers of stomach parasites (ascarid nematodes) increased with body size in both sexes, and dietary composition changed ontogenetically. Small snakes fed mostly on rats, but shifted to larger mammalian taxa (e.g. pangolins, porcupines, monkeys, wild pigs, mouse deer) at 3–4‐m body length. 4. Adult males and females showed strong ecological divergence. For some traits, this divergence was entirely caused by the strong allometry (combined with sexual size dimorphism), but in other cases (e.g. feeding frequency, dietary composition), the sexes followed different allometric trajectories. For example, females shifted from rats to larger mammals at a smaller body size than did conspecific males, and feeding frequencies increased more rapidly with body size in females than in males. These allometric divergences enhanced the degree of sex difference in trophic ecology induced by sexual size dimorphism.