bluuebunny/crossref_metadata_2025_split huggingface dataset:
Whitemere, a lake that defies some conventions about nutrients
Authors: Kilinc Sabri , Moss Brian 
Published: March 2003

1. Whitemere, a kettle‐hole lake in north‐west England (zm,14 m, area 22.5 ha) has extremely high maximal concentrations (around 1 mg L−1) of total phosphorus (TP) and soluble reactive phosphorus (SRP), and comparatively low maximal concentrations of dissolved inorganic nitrogen (<0.5 mg N L−1). Bioassays indicate that its phytoplankton is nitrogen limited, and it has surface blue‐green algal blooms in summer. Palaeoecological investigations have shown that high populations of cyanophytes occurred more than 6000 years ago, even before human settlement of the catchment.2. The reasons for this combination of features are not immediately clear. This paper attempts to distinguish between two hypotheses: that the high phosphorus concentrations arise from input of phosphate‐rich groundwater; and that the high phosphorus concentrations arise from concentration and recycling mechanisms within the lake.3. The lake is entirely fed by ground water, direct rainfall and surface sheet flow. The concentrations of phosphorus in the ground water are much lower than in the lake water. The lake is stratified and has high phosphorus concentrations in the anaerobic hypolimnion in summer as a result of substantial release from the sediment. Vertical turbulence in the relatively weakly stratified water column may transfer substantial amounts to the epilimnion.There is also substantial phosphorus release from the sediments under the aerobic epilimnion.4. There is little outflow of water and phosphorus. Most of the phosphorus is returned to the sediment under winter isothermal conditions, to be released again the following summer. The lake has probably maintained these mechanisms for millennia. Recent eutrophication is likely to have been driven by nitrogen inputs from greater intensification of agriculture in the catchment.
Chlorella‐bearing ciliates dominate in an oligotrophic North Patagonian lake (Lake Pirehueico, Chile): abundance, biomass and symbiotic photosynthesis
Authors: Woelfl Stefan , Geller Walter 
Published: March 2003

1. Large mixotrophic ciliates (Stentor araucanus, S. amethystinus and Ophrydium naumanni) were a characteristic component of a temperate, oligotrophic lake in North Patagonia. During a 1‐year study, the abundance, biomass and primary production of these large Chlorella‐bearing ciliates were compared with those of the total plankton community.2. Mixotrophic ciliates peaked in spring and from late summer to autumn, accounting for 1.6–43% (annual average: 16.3%) and 67–99% (annual average: 92%) of total ciliate abundance and biomass, respectively. Their contribution to total zooplankton biomass, including flagellates, rotifers, ciliates and crustaceans, was 14–76%, or 47% as an annual average. Endosymbiotic algae accounted for up to 25% of total autotrophic biomass (annual mean: 3.9%).3. Maximum cell‐specific photosynthetic rates of S. araucanus and S. amethystinus at light saturation varied between 80 and 4400 pg C ciliate–1 h–1 with high values during autumn and winter, and low values during summer. The depth‐integrated rates of photosynthesis (0–40 m) of algal endosymbionts contributed 1–25% to total photosynthesis (annual mean: 6.5%).4. A comparison of calculated ingestion rates with photosynthetic rates of Stentor indicates that photosynthate produced by endosymbionts generally exceeded heterotrophic food supply of Stentor during autumn and winter, but was much lower during summer, when food supply was high.5. The mixotrophic ciliates represent an important ‘link’ between nanoplankton and higher trophic levels within the plankton community because of their high heterotrophic biomass and considerable contribution to total photosynthesis.
Seasonal patterns in macroinvertebrate drift and seston transport in streams of an alpine glacial flood plain
Authors: ROBINSON C. T. , TOCKNER K. , BURGHERR P. 
Published: March 2003

1. We measured drift of macroinvertebrates and organic matter in five different channel types (upper and lower main channel, intermittent side‐channel, side‐slope tributary, and a groundwater channel) draining a glacial flood plain in the Swiss Alps. Samples were collected seasonally over 3 years (May 1997 to November 1999) to encompass major periods of floodplain expansion and contraction.2. Total wetted channel length ranged from ≤ 5 km during maximum floodplain contraction to ≥ 24 km under system expansion. Principal components analysis (PCA) of key physical and chemical measures collected over an annual cycle showed that the main and side channel sites differed spatially and seasonally from the tributary and groundwater sites, reflecting the glacial influence on the former.3. Two‐way ANOVA indicated a significant Site × Date interaction for all measured variables. Transported organic matter, caused by blooms of Hydrurus foetidus, was typically five to 10 times higher in the lower main channel and side‐channel than the other channel types, and was least variable among dates in the groundwater and tributary channels.4. The number of drifting macroinvertebrates was usually highest in the groundwater channel, although highly variable among years. Other channel types had highest drift rates in November and lowest rates in May, reflecting seasonal changes in the life cycles of particular taxa, such as Baetis alpinus and the Simuliidae. The lower main channel exhibited the greatest, and the groundwater the lowest, seasonality in drift compared with the other channels.5. The Chironomidae displayed the highest drift rates in most seasons, especially in summer when other taxa were relatively low in the drift. The number of taxa in the drift also varied among channel types and season, ranging from less than two in early spring to four to six in other seasons.6. The observed differences in drift rate and transported organic matter among channel types and seasons have important implications for ecosystem dynamics, through its effect, for instance, on dispersal among channel types or on organic matter exchange.
Exotic riparian vegetation lowers fungal diversity but not leaf decomposition in Portuguese streams
Authors: BÄRLOCHER FELIX , GRAÇA MANUEL A. S. 
Published: March 2003

1. We characterised the fungal communities of eight streams in Portugal, four bordered by native deciduous forest and four bordered by pure stands of Eucalyptus globulus.2. Aquatic hyphomycete species richness and evenness, but not numbers of water‐borne conidia, of aquatic hyphomycetes were significantly lower in eucalypt bordered streams.3. Multivariate analyses subdivided the fungal communities into two distinct groups corresponding to riparian vegetation.4. Despite these differences in the dominant decomposer community, decay rates of eucalypt leaves (accounting for ≥98% of naturally occurring leaves in eucalypt bordered streams, absent in native forest) and chestnut leaves (occurring naturally in native forests) did not differ between the two groups of streams.
A simple method for approximating the supportive capacities and metabolic constraints in lakes and reservoirs
Authors: REYNOLDS C. S. , MABERLY S. C. 
Published: March 2003

1. A method for calculating and comparing the stoichiometric yields of phytoplankton standing crop (as chlorophyll a) is presented.2. Some worked examples show how the model distinguishes lakes in which the supportive capacity is constrained mainly by the available phosphorus or by the nitrogen supply or by the light availability. Sites are identified where control moves among the constraining factors.3.  An instance of lake management is given where the diagnosis, remedy and the remediation have conformed closely to the model predictions.
Macro‐zooplankter responses to simulated climate warming in experimental freshwater microcosms
Authors: MCKEE D. , ATKINSON D. , COLLINGS S. , EATON J. , HARVEY I. , HEYES T. , HATTON K. , WILSON D. , MOSS B. 
Published: March 2003

1. We report data collected from 48 replicated microcosm communities created to mimic plant‐dominated shallow lake and pond environments. Over a 2‐year period, the microcosms were subjected to warming treatments (continuous 3 °C above ambient and 3 °C above ambient during summer only), a nutrient addition treatment and the presence or absence of fish. We tracked macro‐zooplankter dynamics, censusing cladoceran populations at the species level, copepods at the order level and ostracods as a class.2. Responses to warming were subtle. Cladoceran diversity and overall abundance were not significantly affected by warming, although measures of community evenness increased. Warming effects on patterns of population trajectories tended to be strongly seasonal and most apparent during periods of pronounced increase. Populations of the prevalent cladocerans, Chydorus sphaericus and Simocephalus vetulus, displayed idiosyncratic patterns, with evidence in the case of S. vetulus for a negative relationship between warming and body‐size at maturity. Copepod populations were reduced in size by warming, but those of ostracods increased.3. The effects of the nutrient addition and fish treatments were strong and consistent, interacting little with warming effects in statistical models. Zooplankter abundance tended to be the highest in the fish‐free microcosms receiving additional nutrient inputs and lowest when fish were present and no nutrients were added. Both treatments reduced cladoceran diversity and community evenness.4. We suggest that warming, independently, is unlikely to supplant the effects of changing nutrient loading and fish predation as the major driver of zooplankter dynamics in shallow lakes and ponds. Moreover, in the situations where warming was of significant influence in our experiment, the distinction between summer‐only warming and year‐around warming was blurred. This suggests that warming effects were most pervasive during the summer, at the upper end of the temperature spectrum.
Image analysis of Daphnia populations: non‐destructive determination of demography and biomass in cultures
Authors: Færøvig Per J. , Andersen Tom , Hessen Dag O. 
Published: March 2003

SUMMARY 1. An image analysis technique was developed for the semiautomatic determination of abundance, size distribution and biomass in Daphnia cultures. This allowed detailed observations of growth, demography and biomass accumulation in live populations, avoiding artifacts caused by subsampling and sampling losses.2. The image analysis method gave fast, non‐destructive and reliable individual counts, even in cultures with high density and a large fraction of juveniles.3. In Daphnia, animal width changes with nutritional status and growth within instar, while length changes only at the moult. Thus, estimation of individual biomass using an ellipsoidal model based on animal width gave improved biomass calculations compared to manual counting, sizing, and length : weight regressions.4. The power of the image analysis technique for assessing population growth and size structure was demonstrated in two 40‐day experiments, with Daphnia magna feeding on the green algae Selenastrum capricornutum in a two‐stage chemostat system.
Effects of waterfowl and fish on submerged vegetation and macroinvertebrates
Authors: Marklund Ola , Sandsten Håkan , Hansson Lars‐Anders , Blindow Irmgard 
Published: March 2003

SUMMARY 1. With the aim to assess the combined and separate effects of waterfowl and fish on submerged vegetation and macroinvertebrates, we performed a replicated selective exclosure study in a shallow, eutrophic lake in southern Sweden. Our results are presented together with a literature review of the effects of fish and waterfowl on macroinvertebrates and submerged vegetation.2. Based on our experiment and on published data, we conclude that waterfowl normally will reduce submerged vegetation only at high waterfowl densities, at very low vegetation densities, or in the colonisation phase of the vegetation.3. Further, we conclude that in shallow temperate eutrophic lakes, a naturally occurring mixed fish assemblage rarely reduces submerged vegetation. Unless the vegetation is very sparse, the risk of severe reduction of submerged vegetation as a result of waterfowl or fish grazing, should thereby be low.4. Even relatively low densities of fish seem to reduce macroinvertebrate biomass, while a mixed waterfowl assemblage rarely has a significant effect on macroinvertebrate biomass.
On the cost of vertical migration: are feeding conditions really worse at greater depths?
Authors: Winder M. , Boersma M. , Spaak P. 
Published: March 2003

SUMMARY 1. The ultimate explanation for diel vertical migration (DVM) of zooplankton is the avoidance of visual predation in surface waters. Studies on migrating zooplankton have shown that remaining in the cold and food‐poor hypolimnion during the day, however, has demographic costs. Higher temperatures and greater food concentrations in the surface waters are thought to be the main reasons why Daphnia species move upwards at night.2. In this study, we investigated the growth condition of daphniids raised on seston taken from different depths from a lake with and without a deep‐water chlorophyll maximum.3. Juvenile growth rates of Daphnia galeata x hyalina from the lake without a deep‐water chlorophyll maximum were similar for all treatments. After temperature correction, however, growth rates were significantly higher on seston taken from the surface layers.4. In contrast, in the lake with the deep‐water chlorophyll maximum, D. galeata growth rates were higher in deeper strata, even after temperature correction. Although this lake had a weak temperature gradient, D. galeata left the food‐rich strata at night and migrated into the surface food‐poor environment. Invertebrate predation and oxygen depletion are probably not the reasons for the nocturnal upward migration into the surface strata. Therefore, we assume that D. galeata migrates upwards to take advantage of higher temperatures. Using several temperature–egg‐development models, we could not, however, fully explain this behaviour.
Optimal diet choice for large herbivores: an extended contingency model
Authors: Farnsworth K. D. , Illius A. W. 
Published: March 2003

1. A more general contingency model of optimal diet choice is developed, allowing for simultaneous searching and handling, which extends the theory to include grazing and browsing by large herbivores. 2. Foraging resolves into three modes: purely encounter‐limited, purely handling‐limited and mixed‐process, in which either a handling‐limited prey type is added to an encounter‐limited diet, or the diet becomes handling‐limited as it expands. 3. The purely encounter‐limited diet is, in general, broader than that predicted by the conventional contingency model. 4. As the degree of simultaneity of searching and handling increases, the optimal diet expands to the point where it is handling‐limited, at which point all inferior prey types are rejected. 5. Inclusion of a less profitable prey species is not necessarily independent of its encounter rate and the zero‐one rule does not necessarily hold: some of the less profitable prey may be included in the optimal diet. This gives an optimal foraging explanation for herbivores’ mixed diets. 6. Rules are shown for calculating the boundary between encounter‐limited and handling‐limited diets and for predicting the proportion of inferior prey to be included in a two‐species diet. 7. The digestive rate model is modified to include simultaneous searching and handling, showing that the more they overlap, the more the predicted diet‐breadth is likely to be reduced.
An experimental device for studying seed responses to naturally fluctuating temperature of surface soil under a constant water table
Authors: Araki S. , Shiozawa S. , Washitani I. 
Published: March 2003

1. A simple experimental device was designed, in which seeds can be exposed to natural fluctuation of surface soil temperature under a constant soil moisture condition maintained by an automatic water supply system based on the principle of a Mariotte siphon. 2. Except for the period during summer drought, surface soil temperature at a depth of 5 cm and its fluctuation within the device were largely similar to the temperature of the surface soil subjected to natural fluctuation of moisture. 3. The seeds of Persicaria lapathifolia placed at the depth of 0·5 cm in the soil within the device germinated during the natural germination season of the species, while the seeds placed at the depth of 5 cm or beneath the 10 cm‐thick layer of litter failed to germinate. 4. The ungerminated seeds retrieved in August did not germinate at the favourable alternating temperature in the laboratory test unless exposed to previous moist chilling, suggesting the induction of secondary dormancy. Therefore, higher summer temperatures but not summer drought or moisture fluctuation seem to have been responsible for the dormancy induction, because the dormancy was induced in the fully hydrated seeds.
Oocyte maturation and ovariole number in lines of Drosophila melanogaster selected for postponed senescence
Authors: Carlson K. A. , Nusbaum T. J. , Rose M. R. , Harshman L. G. 
Published: March 2003

1. Postponed senescence lines of Drosophila melanogaster have previously been generated by selection for delayed female reproduction. 2. This study addresses the question of whether the selection regime has differentiated lines with respect to oocyte maturation or ovariole number. 3. Oocyte stage and ovariole number were characterized in replicate postponed senescence lines (O) and in replicate control lines (B). 4. Oocyte maturation is delayed in O females. 5. The delay in oocyte maturation in O lines corresponds to reduced early age fecundity. 6. Selection may have resulted in an increased number of ovarioles in O females.
Impact of an ecological factor on the costs of resource acquisition: fighting and metabolic physiology of crabs
Authors: Sneddon L. U. , Huntingford F. A. , Taylor A. C. 
Published: March 2003

1. Current game theory models and recent experimental evidence suggests that the strategy an animal adopts in agonistic encounters is determined by individual state. Therefore manipulation of an individual’s state should elicit different behavioural responses. In this paper, mechanisms are examined that underlie state‐dependent strategies using Shore Crabs, Carcinus maenas, and how, by altering the environment, behaviour and physiology are affected. 2. Fights were staged between pairs of male crabs under normoxic and severely hypoxic (<15 torr) conditions to determine if the metabolic costs of fighting and resource acquisition are affected by water PO2. After fighting, blood and tissue samples from each crab were taken and analysed for metabolites associated with anaerobiosis (L‐lactate, glucose and glycogen). 3. The spectrum of behavioural acts performed during contests was unaffected by hypoxic conditions. However, fight duration was significantly shorter in the hypoxic treatment. 4. The phenomenon of being of a larger relative size and winning had a greater influence in the contests staged under hypoxia with 93% of the victors being of a larger size compared to 78% in normoxic conditions. Fight duration and intensity had no relationship with relative size in either treatments. 5. The accumulation of L‐lactate was significantly greater in the blood and tissues of crabs after fighting under hypoxia than in normoxic conditions. In addition, there was greater glycolytic activity in the tissues of these crabs, shown by elevated concentrations of glucose in the blood and increased breakdown of glycogen. 6. This study demonstrates that the internal state of the crabs altered the length of time they were willing to engage in fighting and that fighting was energetically more expensive under hypoxic conditions.
Resistance to thermal stress in desert Drosophila
Authors: Stratman R. , Markow T. A. 
Published: March 2003

1. Four species of Drosophila are endemic to the Sonoran Desert of North America where daily and seasonal high temperatures exceed those experienced by other species in this genus. The close association between these species and their cactus hosts means that they reside only in the desert and raises the question as to whether they are better able to survive heat stress than are non‐desert species of Drosophila. The tolerance of adult flies of the four desert species D. mojavensis, D. nigrospiracula, D. pachea and D. mettleri and the cosmopolitan D. simulans to acute heat stress was tested. 2. There was considerable variability among the desert endemic species with respect to survival following heat exposure. Two species, D. mojavensis and D. pachea, were more resistant at 44 °C and 46 °C than the others, with D. mettleri exhibiting similar heat stress resistance to D. simulans. 3. While there was no consistent influence of gender on heat resistance, younger flies (1‐day‐old) showed significantly greater survival than did older flies (7‐ or 14‐days old).
An energetic evaluation of a predator–prey (leech–amphipod) couple in Montezuma Well, Arizona, USA
Authors: McLoughlin N. J. , Blinn D. W. , Davies R. W. 
Published: March 2003

1. The highly stable conditions in Montezuma Well, Arizona, have contributed to a very close predator–prey relationship between the endemic leech, Erpobdella montezuma, and its endemic amphipod prey, Hyalella montezuma, which forms nearly 90% of the leech diet. 2. Using a simple bioenergetic model, it was determined why a benthic opportunistic foraging strategy, typical of most other erpobdellids, is inferior to the specialized foraging behaviour utilized by E. montezuma and why reproduction by the leech is restricted during certain times of the year. 3. Our model demonstrated that to attain a biomass in excess of 2000 mg (maximum field size) during periods of low amphipod densities in the winter E. montezuma must feed on alternative prey types and have a foraging activity < 4 h per day. 4. Leech reproduction 4–6 months prior to the onset of winter food shortages of prey increases juvenile and adult survivorship with highest reproductive success for E. montezuma occurring in June–July. 5. Rather than being an obligate forager on H. montezuma, E. montezuma exploits a periodically abundant amphipod during most of the year in addition to alternate prey types during the winter thereby achieving an overall higher rate of energy gain than could be achievable by other closely related species of erpobdellids utilizing an opportunistic foraging approach.
Does substrate quality influence take‐off decisions in Common Starlings?
Authors: Bonser R. H. C. , Norman A. P. , Rayner J. M. V. 
Published: March 2003

1. An instrumented perch was used to measure the reaction forces during take‐off of starlings from perches of three thicknesses. There was no significant decrease in reaction force with decreasing perch thickness; however, over the range of perch sizes there was a 10‐fold decrease in safety factor and a 400‐fold increase in the energy of deflection of the thinnest perch. 2. The implications of these results are that birds do not change their take‐off strategy when faced with perches of variable thickness and that, as a result, leaps from thin perches are very much less efficient than those from thicker perches. Birds appear not to adjust their leaping behaviour to minimize the risk of substrate failure during take‐offs.