bluuebunny/crossref_metadata_2025_split huggingface dataset:
Importance of consumptive and non‐consumptive prey mortality in a coupled predator–prey system
Authors: MCKEE MALCOLM , WRONA FREDERICK , SCRIMGEOUR GARRY , CULP JOSEPH 
Published: November 2003

1. Laboratory experiments were completed to identify the mechanisms by which the predatory flatworm, Dugesia tigrina, imposes mortality on its Aedes aegypti and Daphnia magna prey. Feeding trials were completed in glass microcosms which contained one of three – nine densities of small or large individuals of each prey species.2. Mortality by Dugesia on small and large Aedes followed a type II functional response, whereas the mortality of Daphnia resembled a type III functional response. Prey mortality imposed by Dugesia consisted of consumptive and non‐consumptive elements. Non‐consumptive mortality occurred when prey individuals trapped in mucus trails subsequently died but were not ingested.3. Additional experiments were conducted to quantify consumptive (capture followed by ingestion) and non‐consumptive mortality (death not followed by ingestion).4. Consumptive mortality followed a type II functional response for small and large individuals of both prey species, whereas non‐consumptive mortality increased with prey density, although the relationships differed with prey species and size. The non‐consumptive mortality of large Daphnia increased at an accelerating rate with prey density and exceeded consumptive mortality at intermediate prey abundances. In contrast, non‐consumptive mortality of small Aedes and small Daphnia was lower than consumptive mortality and either increased with prey density at a decelerating (small Aedes) or accelerating (small Daphnia) rate.5. These results suggest that the importance of consumptive and non‐consumptive mortality to total prey mortality needs to be considered when modelling predator–prey dynamics.
Predation by underyearling perch (Perca fluviatilis) on a Daphnia galeata population in a short‐term enclosure experiment
Authors: HÜLSMANN STEPHAN , MEHNER THOMAS 
Published: November 2003

1. The predation impact of underyearling perch (20 mm total length) on the dynamics of Daphnia galeata was studied in three 6.5‐m3 enclosures during a 17‐day experiment in June 1995. These data were compared with zooplankton succession in three fish‐free control enclosures and in the pelagic zone of Bautzen reservoir, Germany.2. Due to individual growth during the experiment, fish biomass in the enclosures increased from 210 mg wet body mass (w.b.m.) m–3 to 830 mg w.b.m. m–3, equivalent to an increase from 20 kg ha–1 to 75 kg ha–1.3. In the enclosures with fish, biomass of daphnids decreased steadily to values below 1 mg wet weight (w.w.) l–1 within 17 days, whereas in the fish‐free controls and in Bautzen reservoir the Daphnia biomass fluctuated around 8 mg w.w. l–1. Other zooplankton species exhibited little or no change. Approximately 60 kg ha–1 was calculated as the critical underyearling perch biomass which may induce a drastic decline of the Daphnia galeata population in Bautzen reservoir. Comparison with values from other lakes is difficult due to differences in water depths and Daphnia biomasses.4. Mean individual biomass of daphnids, egg ratio and proportion of adult daphnids were significantly lower in the enclosures with fish compared with the control enclosures at the end of the experiment. This may be explained partly by preferential predation of the large, egg‐carrying daphnids by fish. However, no difference was found in clutch size and size at first reproduction, possibly due to the short duration of the experiment.5. It must be assumed that the ‘summer depression’ of daphnids observed in many waters is not the exclusive effect of direct reduction of daphnids by fish predation. Even the high biomass of underyearling perch stocked in the enclosures did not completely account for Daphnia mortality. Instead, the selective loss of large size classes, combined with low food resources and reduced reproduction rates, may induce the marked declines in daphnids.
Environmentally induced spatio‐temporal variations in the fecundity of brown trout Salmo trutta L.: trade‐offs between egg size and number
Authors: LOBON‐CERVIA JAVIER , UTRILLA CARMEN , RINCÓN PEDRO , AMEZCUA FELIPE 
Published: November 2003

1. Resident brown trout Salmo trutta in the Esva River basin (north Spain) live in a patchy environment with tracts of riparian forest or meadow along stream banks. This study assessed whether the reproductive traits of brown trout from four contrasting sites reflected site‐specific factors.2. Length at maturity (10.5–11 cm of 1 + individuals) was the same in the four sites examined but slowest growers in slow‐growing sub‐populations delayed maturity for 1 year relative to fast‐growing fish. The analysis of monthly variations in egg size and number suggest that two ‘decisions’ in two consecutive years are required to complete spawning. The first concerns the number of eggs, determined when trout are still 0 +, and the second concerns egg size.3. At three sites, egg size and number did not differ significantly between years but highly significant interannual variations were apparent at another site. Fish length was the major determinant of egg size and number at all sites but for any given length, brown trout at sites where the fish exhibited higher growth rates spawned more, but smaller, eggs than those at slow‐growing sites. This spatial pattern was identical to the temporal pattern exhibited by trout at another site. The combination of temporal (year‐to‐year) and spatial (between rivers) variations in egg size and number showed a significant negative correlation, supporting the operation of a trade‐off between these two traits.4. The trade‐off between egg size and number seems to be determined by site‐specific factors, with slow‐growing trout at sites which are fully covered by canopy spawning fewer, but larger, eggs than fast‐growers in unshaded sites.
Planktonic green algae in western Lake Erie: the importance of temporal scale in the interpretation of change
Authors: NICHOLLS KEN 
Published: November 2003

1. Total densities of planktonic Chlorophyceae collected in weekly sampling of the Kingsville (Ontario) municipal water intake in western Lake Erie were evaluated for potential effects of the recent zebra mussel (Dreissena polymorpha) invasion and for the longer term effects of the Lake Erie phosphorus loading control programme.2. At a relatively small temporal scale of about 10 years, an apparent zebra mussel‐related impact was clearly revealed in 1988 as an inflection point on the cumulative sum chlorophyte density curve. However, at a temporal scale of nearly three decades, this inflection point was not distinct. There was a steady decline in total Chlorophyceae throughout the 1970s which accelerated during the early 1980s; this corresponds to declining western Lake Erie phosphorus loading rates and phosphorus concentrations reported by others over the same period. In the absence of zebra mussels, average annual chlorophyte density decreased by 94% between the early 1970s and the mid‐1980s.3. The dramatic long‐term decline of planktonic chlorophytes in western Lake Erie reveals the success of the phosphorus control programme, places the recent impact of the zebra mussels in its proper perspective and underscores the need for and value of long‐term limnological data for management of the Laurentian Great Lakes.
Feeding ecology of the freshwater detritivore Ptychoptera paludosa (Diptera, Nematocera)
Authors: WOLF BEATE , ZWICK PETER , MARXSEN JÜRGEN 
Published: November 2003

1. We examined selected aspects of the nutritional ecology of larval Ptychoptera paludosa and their role in nutrient cycling in the Breitenbach, a first‐order stream in Hesse, Germany.2. Food preference experiments demonstrated significant preference for sediments with a high organic matter content and live bacteria.3. pH was circumneutral in all sections of the gut.4. Enzymatic activity (β‐glucosidase and amino‐peptidase) in different parts of the gut was measured using 4‐methylumbelliferyl‐β‐D‐glucopyranoside (MUF‐Glc) and leucine‐4‐methylcoumarinyl‐7‐amide (Leu‐MCA). β‐glucosidase activity was highest in the hindgut.5. The mean larval gut passage time was between 7 and 8 h.6. The egestion rate of last instar larvae was about 0.35 mg dry weight (DW) faeces per larva h–1 and about 1.25 mg ash‐free dry weight (AFDW) faeces per mg larval AFDW day–1.7. Larval faeces contained at least 4–18 times more organic matter than the average in the sediments in which they were feeding, that is, larvae fed selectively, extracting organic matter from sediments.8. P. paludosa larvae are important in the dynamics of detritus in slow‐flowing reaches of the Breitenbach. They gather organic material from the sediment to a depth of 3 cm, and release it as faeces onto the sediment surface. A total of 770 g DW faeces m–2 yr–1, comprising about 16% organic matter, was produced by the Ptychoptera population.
Comparison of diatoms, fossil pigments and historical records as measures of lake eutrophication
Authors: HALL ROLAND , LEAVITT PETER , SMOL JOHN , ZIRNHELT NORMAN 
Published: November 2003

1. Analysis of fossil diatoms and pigments was used to examine the effects of land‐management practises on the trophic status of Williams Lake, a eutrophic lake in central British Columbia, Canada. Published weighted‐average (WA) models were used to infer changes in total phosphorus concentration (TP) during the past 200 years.2. Diatom‐inferred TP (DI‐TP) was compared to 20 years of direct chemical TP measurements to determine the accuracy of diatom‐TP models in inferring mean summer TP in Williams Lake. Plant pigments were measured using high performance liquid chromatography (HPLC) to quantify historical changes in gross algal community composition and abundance and to evaluate further diatom‐TP inferences.3. Palaeolimnological analyses showed that Williams Lake has been productive throughout the last 200 years. Diatoms characteristic of alkaline, eutrophic conditions were continuously present c. 1765–1990 AD. Carotenoids from filamentous cyanobacteria (myxoxanthophyll, aphanizophyll) were regularly present in Williams Lake sediments, although cryptophytes (alloxanthin), diatoms (diatoxanthin), chlorophytes (lutein‐zeaxanthin, b‐phorbins), and siliceous algae (diatoms, chrysophytes) or dinoflagellates (fucoxanthin) were also important components of past algal communities. Terrestrial disturbance (railway and road constructions, cattle ranching) increased lake production, but resulted in relatively little permanent environmental change.4. Comparison of DI‐TP with measured TP (1972–91) showed that inferences from simple WA models were similar to average summer TP (39.1 vs. 35.2 μg TP l–1). Inferences resulting from data manipulations that down‐weighted eutrophic lakes (outlier elimination, bootstrapping) or diatom species (square‐root transformation, tolerance‐weighting) were weakly and negatively correlated with measured TP, introduced bias into inference models, or underestimated measured TP. These patterns suggest that, when using diatom‐TP models developed from sparsely populated regions, accurate palaeoecological inferences for TP in eutrophic lakes should avoid data manipulations which down‐weight the most productive sites and taxa.5. Comparison of DI‐TP and fossil‐inferred algal abundance during the past 200 years suggested that changes in nutrient inputs accounted for relatively little variation in past algal abundance. Although past changes in total algal biomass (as β‐carotene) and DI‐TP were broadly similar, the two variables were not significantly correlated (α = 0.05). In contrast, changes in DI‐TP were significantly correlated with mean concentrations of diatom‐specific carotenoids (diatoxanthin), although the explanatory power was low (r2 = 0.16). These patterns suggest that the DI‐TP model reflects more closely environmental conditions in Williams Lake during periods of diatom growth, and not necessarily those when total algal biomass is greatest.
Shredder–collector interactions in temporary streams of western Oregon
Authors: DIETERICH MARTIN , ANDERSON N.H. , ANDERSON TRACEY 
Published: November 2003

1. Field data and results from laboratory rearing are combined to describe shredder–collector interactions in western Oregon temporary streams.2. The composition of functional feeding groups in the temporary streams conforms to that predicted for permanent headwaters by the River Continuum Concept (RCC).3. A distinct functional feeding group phenology was found, with shredders emerging first and collectors emerging last in the season. Scrapers were intermediate.4. Presence of shredders enhanced collector growth in laboratory experiments (P < 0.01;n = 12). The species reared in the study trials accounted for 67% of the shredder biomass and 76% of the collector biomass in the natural systems.5. Field data and laboratory rearing trials both support the hypothesis of a close shredder–collector interaction in the processing of allochthonous material in the summer‐dry headwaters studied.
A yellow–green algal symbiont in the freshwater sponge, Corvomeyenia everetti: convergent evolution of symbiotic associations
Authors: FROST THOMAS , GRAHAM LINDA , ELIAS JOAN , HAASE MARK , KRETCHMER DONALD , KRANZFELDER JAMES 
Published: November 2003

1. A previously undescribed symbiotic relationship is reported between the freshwater sponge Corvomeyenia everetti, which occurs throughout eastern North America, and a yellow‐green alga.2. Ultrastructural and pigment analyses place the algal endosymbiont within the class Eustigmatophyceae in the division Heterokontophyta.3. The relationship of the alga with C. everetti appears to be specific and it contributes significantly to the energy budget of the host.4. Although the growth form of C. everetti is very similar to other freshwater sponges that usually have green‐algal symbionts, its phylogeny has been proposed to be quite distinct, suggesting convergent evolution by both algae and sponges in the development of symbiotic associations in fresh water.
The influence of catchment land use on stream integrity across multiple spatial scales
Authors: ALLAN DAVID , ERICKSON DONNA , FAY JOHN 
Published: November 2003

1. Despite wide recognition of the need for catchment‐scale management to ensure the integrity of river ecosystems, the science and policy basis for joint management of land and water remains poorly understood. An interdisciplinary case study of a river basin in south‐eastern Michigan is presented.2. The River Raisin drains an area of 2776 km2, of which some 70% is agricultural land. The upper basin consists of till and outwash, and both topography and land use/cover are diverse. The lower basin consists of fine textured lake deposits, is of low relief, and land use is primarily agricultural.3. The River Raisin basin historically was a region of oak‐savannah and wetlands. It was deforested, drained and converted to farmland during the mid‐nineteenth century. Human population reached a plateau at about 1880, and then underwent a second period of growth after 1950, mainly in small urban areas. More recently, the amount of agricultural land has declined and forested land has increased, in accord with a general decline in farming activity.4. It could be suggested that the influence of land use on stream integrity is scale‐dependent. Instream habitat structure and organic matter inputs are determined primarily by local conditions such as vegetative cover at a site, whereas nutrient supply, sediment delivery, hydrology and channel characteristics are influenced by regional conditions, including landscape features and land use/cover at some distance upstream and lateral to stream sites.5. Sediment concentrations measured during low flows were higher in areas of greater agriculture. In a comparison of two subcatchments, sediment yields were up to ten times greater in the more agricultural location, in response to similar storm events. A distributed parameter model linked to a geographical information system predicted that an increase in forested land cover would result in dramatic declines in runoff and sediment and nutrient yields.6. Habitat quality and biotic integrity varied widely among individual stream sites in accord with patterns in land use/cover. Extent of agricultural land at the subcatchment scale was the best single predictor of local stream conditions. Local riparian vegetation was uncorrelated with overall land use and was a weak secondary predictor of habitat quality and biotic integrity.7. Investigation of the regulatory agencies involved in land and water management in the basin revealed a complex web of overlapping political jurisdictions. Most land‐use decision‐making occurs at the local level of township, city or village. Unfortunately, local decision‐making bodies typically lack the information and jurisdictional authority to influence up‐ and downstream events.
Sensitivity of Daphnia to toxic cyanobacteria: effects of genotype and temperature
Authors: HIETALA JAANA , LAURÉN‐MÄÄTTÄ CAMILLA , WALLS MARI 
Published: November 2003

1. We studied the effects of both acute and chronic exposure of Daphnia pulex to toxic Microcystis aeruginosa. We focused on the effects of Daphnia genotype and temperature (19 and 24 °C).2. The study revealed variation among ten Daphnia pulex clones in survivorship under acute Microcystis exposure, measured as EC50. An increase in temperature caused a clear decrease in EC50, although the ranking of clones according to sensitivity remained the same at both temperatures.3. In the chronic exposure of two of the clones, toxic Microcystis reduced survival and reproduction. The two clones differed in their responses, indicating different means of coping with toxic cyanobacteria. Toxic cyanobacteria reduced slightly more at 24 °C than 19 °C.4. The clonal difference in sensitivity to toxic cyanobacteria at acute exposure was reversed at chronic exposure. This indicates that the results from short‐term toxicity cannot be used to predict life history responses under sublethal exposure.
The photosynthetic response of eight species of Acer to simulated light regimes from the centre and edges of gaps
Authors: LEI T. T. , LECHOWICZ M. J. 
Published: November 2003

1. Seedlings of eight Acer species grown under two light treatments simulating forest gap edge (photosynthetic photon flux density, PPFD=30μmolm–2s–1; R:FR=0·6) and gap centre (PPFD=400μmolm–2s–1; R:FR=1·1) were studied to explore the effect of growth irradiance on transient‐ and steady‐state photosynthesis. 2. The increase in maximum photosynthetic rate (Amax) from gap edge‐ to gap centre‐grown seedlings ranged between 20% in Acer saccharum and 138% in Acer ginnala. Amax differed significantly among species (2·3 to 12·3μmolm–2s–1) but assimilation rates under dim light (30μmolm–2s–1) were more similar (0·6 to 1·4μmolm–2s–1). 3. Significant differences among species in stomatal conductance indicate that species of high photosynthetic performance maintain higher dim light conductance and show a much greater excursion in stomatal opening under saturating light. 4. Lightfleck response based on actual photosynthetic rates was more rapid in gap centre‐ vs gap edge‐grown plants but the latter demonstrated more rapid rates of photosynthetic induction (PI). 5. We suggest that the estimation of photosynthetic induction state is prone to an inverse relationship with maximum photosynthetic rate (Amax) and so may not be directly related to efficiency in sunfleck response. Conversely, higher Amax can result in low PI but is also associated with higher transient rates of assimilation during a lightfleck and, therefore, be equally relevant as induction properties. 6. It appears that leaves with characters such as greater specific leaf mass and area‐based leaf N, even within the same irradiance treatment, may confer a carboxylation advantage to sunfleck utilization not reflected in PI. However, whether the total carbon return on such a leaf is better assessed by PI or transient photosynthetic rate remains to be determined.
Ecological correlates of the thermal quality of an ectotherm’s habitat: a comparison between two temperate lizard populations
Authors: DÍAZ J. A. 
Published: November 2003

1. Although thermal factors are of paramount importance to the quality of the habitats occupied by small ectotherms (e.g. lizards), the hypothesis that the relative abundance of squamate populations is related to the thermal quality of their habitats remains untested. If differences in the availability of thermally suitable microhabitats was the primary determinant of the overall quality of a lizard’s habitat, population density in a habitat should be proportional to its thermal quality. 2. The influence of the thermal quality of a habitat on thermoregulatory behaviour, body temperatures, expected physiological performance and relative abundance was compared in two populations of the temperate lizard Psammodromus algirus separated by 700 m altitude in central Spain. Habitat thermal quality was estimated with an index of how closely the available operative temperatures in a habitat match the range of body temperatures that lizards attempt to maintain in a laboratory thermogradient (Hertz, Huey & Stevenson 1993). 3. Operative temperatures, measured using copper models, were higher at the lowland site, where a large proportion of readings fell within or above the preferred range, especially in the early morning. Thermal habitat quality was also higher at the low altitude site, with smaller absolute deviations from the preferred range throughout most of the morning hours. Moreover, lizard body temperatures, the accuracy of thermoregulation and the predicted running performance of lizards were somewhat higher at the lowland site, although differences were smaller than expected on the basis of operative temperatures. A log‐linear analysis showed that lizard selectivity for basking sites was more pronounced at the thermally inferior montane site. Thus, the observed differences in the thermal quality of habitats appeared to influence the behaviour of lizards. 4. Nevertheless, the relative abundance of lizards, as estimated by repeated transect counts, was higher at the montane site. This unexpected result suggests that thermal constraints may not be the most important factor determining lizard population densities on a regional scale. Alternatively, food availability and/or predation pressure might have a greater impact on the overall quality of a habitat for temperate lizards.