bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of growth pattern, sampling interval and number of size classes on benthic invertebrate production estimated by the size‐frequency method
Authors: MOTHIVERSEN TORBEN , DALL PETER 
Published: May 2006

SUMMARY. 1. A hypothetical leech population with known initial density, initial weight, final weight and cohort production interval (CPI) was established. Production estimated by the size‐frequency method for various growth patterns, mortalities, number of samples per CPI and number of size classes was compared with actual production estimated from daily growth and mortality by the increment‐summation method. The population had either perfectly continuous reproduction or a perfectly synchronous cohort.2. When size‐classes were delimited in order to equalize the time spent in each size class, the deviations from actual production increased with decreasing number of size‐classes and increasing mortality. For a population with perfectly continuous reproduction, production was only overestimated by 32% with an extreme mortality of 2.0% day−1 and three size‐classes. For a perfectly synchronous cohort, production was either underestimated or overestimated, depending on the first day of sampling. The deviations from actual production increased considerably with decreasing number of size‐classes, increasing mortality and decreasing number of samples per CPI.3. Differences between actual and assumed growth patterns may give underestimates or overestimates of more than one order of magnitude at high mortalities and few size‐classes. It is concluded that knowing the actual growth pattern, the size frequency method will give realistic estimates of production in cases when normal cohort methods cannot be used. The estimate can be improved significantly by increasing the number of size classes and the number of samples per CPI.
Life‐history patterns of the mosquito‐fish, Gambusia affinis, in the estuary of the Guadalquivir river of south‐west Spain
Authors: FERNÁNDEZ‐DELGADO C. 
Published: May 2006

SUMMARY. 1. The age, growth and reproduction of the small, introduced fish Gambusia affinis (Baird & Girard, 1853) were studied in the estuary of the Guadalquivir river.2. The life‐span was very short, the stock contained only two age groups: with annulus (1+ group; 10–12 months old) and without annulus (0+ group).3. In both sexes growth restarted in April when the annulus appeared, but whilst 1+ males stopped growth, 1+ females grew steadily to June. Growth of 0+ spawners was only evident in September, the last month of the reproductive period. A differential growth rate between sexes was also evident.4. 1+ specimens reproduced during May and June and their offspring from July to September. In both age groups somatic condition progressively declined during the spawning period.5. The loss of condition and the disappearance of 1 + and the larger 04‐specimens after reproduction may indicate the cost of a prolonged high level of reproductive effort.6. The total fecundity (taken as the number of embryos) of 1 + females was represented by the formula: Fec=5.08 T.L. (mm) ‐170.07 and that of 0+ specimens by: Fec=2.23 T.L. (mm) ‐42.92. The maximum average monthly fecundity was reached in June when the length of the mother was at its greatest.7. Length at first maturity was smaller in 0+ group than in the 1 + group; the difference between the two groups was greater in males (≅5 mm, T.L.) than in females (≅3 mm, T.L.). Also the average total length of 14‐spawners was greater than 0+ spawners. There were significant differences in the overall sex ratio of 956 males to 2057 females.8. The differences found in growth and reproduction between the two age groups suggest that life‐history tactics may vary not only between different stocks but also within the same stock among its different components.
Comparisons of the diets and reproductive performances of two sympatric rotifers, Asplanchna girodi and Asplanchna priodonta
Authors: SALT GEORGE W. 
Published: May 2006

SUMMARY. 1. Diet composition and the production of embryos were measured in Asplanchna girodi and Asplanchna priodonta collected through 3 years in the San Joaquin‐Sacramento delta of California. The two species are sympatric in low to moderate densities for 5 months of the year.2. Despite marked differences in the structure of the trophi, both species consumed the same array of prey species. Percentage composition of the diet varied both intra‐ and interspecifically. The food niches of the two species appear to differ little from one another.3. Individuals of Asplanchna girodi had a larger mean number of prey in the gut per individual than did those of A.priodonta, due to their larger size. Per unit volume, each species prey gathering performance was the same. Asplanchna priodonta produced more embryos per calculated unit volume of prey ingested than did A.girodi.4. During spring, when both species were present in the plankton, A.priodonta did not capture Size Class 2 and 5 animals (volumes 0.09–1.0 μm3×106 and 3.0–3.5 μm3X106 respectively) nor large Synchaeta. Both these prey classes were in the diet during the summer and autumn months. Several hypotheses are examined as possible explanations for this phenomenon.
Periphyton responses to invertebrate grazing and riparian canopy in three northern California coastal streams
Authors: FEMINELLA JACK W. , POWER MARY E. , RESH VINCENT H. 
Published: May 2006

SUMMARY. 1. Field experiments were conducted to examine the impact of grazing invertebrates on periphyton biomass in twenty‐one pools across three northern California coastal streams (U.S.A.): Big Sulphur Creek, the Rice Fork of the Eel River, and Big Canyon Creek. Periphyton accrual on artificial substrate tiles was compared in each stream between two treatments: those elevated slightly above the stream bottom to reduce access by grazers (= platforms) and those placed directly on the stream bottom to allow access by grazers (=controls).2. Crawling invertebrate grazers (cased caddisflies and snails) were numerically dominant in each stream (86% of all grazers in Big Sulphur Creek, 61% in the Rice Fork, 84% in Big Canyon Creek). Platforms effectively excluded crawling grazers, but were less effective in excluding swimming mayfly grazers (Baetidae).3. Periphyton biomass (as AFDM) on tiles was significantly lower on controls compared to platforms for the Rice Fork, an open‐canopy stream, and Big Sulphur Creek, a stream with a heterogeneous canopy. In contrast, no grazer impact was found for Big Canyon Creek, a densely shaded stream. Here, extremely low periphyton biomass occurred for both treatments throughout the 60 day study.4. The influence of riparian canopy on periphyton growth (i.e. accrual on platforms), grazer impact on periphyton, and grazer abundance was examined for Big Sulphur Creek. As canopy increased (15–98% cover), periphyton biomass on platforms decreased. In contrast, canopy had little influence on periphyton accrual on controls; apparently, grazers could maintain low periphyton standing crops across the full range of canopy levels. The abundance of one grazer species, the caddisfly Gumaga nigricula, was highest in open, sunlit stream pools; abundance of two other prominent grazers, Helicopsyche borealis (Trichoptera) and Centroptilum convexum (Ephemeroptera), however, was unrelated to canopy.
The natural regulation of numbers and growth in contrasting populations of brown trout, Salmo trutta, in two Lake District streams
Authors: ELLIOIT J. M. 
Published: May 2006

SUMMARY. 1. This short review summarizes a long‐term investigation of brown trout in two populations that probably represent opposite extremes of life histories in this polymorphic species; Bhick Brows Beck serves as a nursery for the progeny of migratory trout (mixture of sea and estuarine trout) and Wilfin Beck is populated by resident trout.2. Population density in Black Brows Beck was always much higher than that in Wilfin Beck, and was regulated by density‐dependent survival in the early stages of the life cycle. There was no evidence for similar density‐dependent regulation in Wilfin Beck; simple proportionate survival occurred with fairly constant loss‐rates. Survival was reduced in both populations by summer droughts and also by spates in Wilfin Beck.3. Black Brows trout were always larger than Wilfin Beck trout of similar age; fry size at the start of the growth period was chiefly responsible for these differences. Variations in water temperature were chiefly responsible for differences in growth rates between year‐classes within each population. Food intake was not a limiting factor, except in the first winter of the life cycle and for adults over 3 years old in Wilfin Beck. Variation in individual size was inversely density‐dependent in Black Brows Beck and decreased with age in Wilfin Beck, these changes being due to natural (stabilizing) selection.4. There is strong evidence for genotypic differences between the populations. The implications of this are discussed, especially the need to conserve different populations that may contain unique genetic material, and the importance of restocking with fish reared from the indigenous population that should always contain the optimum genotypes for a particular habitat. Restocking with juveniles should be done with caution because it could lead to a decrease in both numbers and size variation when the population is regulated by density‐dependent mechanisms.5. One major objective of future work should be the development and improvement of mathematical models that can be used to predict the optimum density for trout in different populations, the maximum attainable growth rate in different habitats, and the effects on trout populations of environmental changes due to natural causes (e.g. droughts and spates) or human activities.
The ecology of brown trout Salmo trutta in English chalk streams
Authors: MANN R. H. K. , BLACKBURN J. H. , BEAUMONT W. R. C. 
Published: May 2006

SUMMARY. .1. Chalkstream trout are fast‐growing, short‐lived with a stable age structure that is a consequence of the lack of extremes in the abiotic environment, especially of water temperature and flow.2. Levels of secondary (invertebrate) production arc high and there is no evidence that interspecific or intraspecific competition for food resources limits growth.3. Dietary studies show a broad similarity between trout and other species, but indicate differences that reflect variations in the micro‐habitat distributions between fish species.4. Trout numbers appear to be limited initially by the availability of gravel spawning areas, and then by areas suitable for newly‐emerged fry. Reduction in stream discharge in the spring, either naturally or by man, can lower the number of 0+ trout that survive.5. Eels are not important predators on trout eggs or fry. but a reduction in pike numbers can lead to a decrease in the mean weight of pike. Small pike do not pose a serious threat to stocked yearling trout.
Lake restoration by reducing external phosphorus loading: the influence of sediment phosphorus release
Authors: MARSDEN MARTIN W. 
Published: May 2006

SUMMARY. 1. This review considers the factors which determine the recovery of eutrophic lakes following a reduction in the external phosphorus loading.2 The mean phosphorus content of a lake should decrease roughly in proportion to the reduction in phosphorus input. Where the lake phosphorus concentration does not decrease as predicted, then the release of phosphorus from the sediment is implicated.3. The current understanding of the processes by which sediment phosphorus is mobilized and transported into the photic zone is described. The extent to which phosphorus release can maintain lake phosphorus concentrations following the reduction in external loading is influenced by: lake morphometry, flushing rate, sediment type, trophic state and history of enrichment.4. A reduction in the phytoplankton biomass of a lake is dependent upon the size of the decrease in lake phosphorus concentration and the degree to which phosphorus limits primary production. The importance of phosphorus in limiting phytoplankton production tends to decrease with increasing lake trophic status.5. Improvements in the condition of highly eutrophic lakes require very large reductions in external phosphorus loading, whereas in mildly enriched lakes moderate changes in the supply of phosphorus have noticeable effects on phytoplankton biomass.
The abundance and temporal distribution of caddisflies (Insecta: Trichoptera) caught by light traps on the Austrian Danube from 1986 to 1987
Authors: WAR1NGER J. A. 
Published: May 2006

SUMMARY. 1. Adult Trichoptera were caught for 1 year (May 1986 to June 1987) on the banks of the Danube at Altenwörth, Lower Austria, using a set of three Jermy‐type light traps. From a total of 62,693 specimens caught, the most abundant species were Brachycentrus subnubilus Curtis (Brachycentridae), the two hydropsychids Hydropsyche bulgaromanorum Mal. and Hydropsyche contubernalis McL., Tinodes waeneri L. (Psychomyidae) and the leptocerid Ceraclea dissimilis Steph.2. The total catch included sixty‐five of the 278 Austrian species from thirteen families. Hydroptila pulchricornis Pictet and Oecetis notata Ramb. were new to the Austrian fauna.3.Of the meteorological parameters tested, only air temperature seemed to influence flight activity.4. Twenty‐four species were studied in detail; Halesus tesselatus Ramb. was the only autumn species, the remainder being summer species. In Tinodes waeneri, the flight period was divided into two well‐defined peaks.5. Of the total, 49.9% were caught during the first third of the night, 39.1% in the second and 11.0% in the last third.6. In seventeen species the sex ratio was significantly different from 1:1, and it changed during the night.7. The indication of water quality by light trap catches of caddisflies is discussed.
Long‐term studies on the Windermere populations of perch (Perca fluviatilis), pike (Esox lucius) and Arctic charr (Salvelinus alpinus)
Authors: MILLS CHRIS A. , HURLEY MARGARET A. 
Published: May 2006

SUMMARY. 1, Windermere is a glacial valley lake with two basins separated by shallows and a total area of 14.8 km2. Perch, pike and charr are the dominant fish species and have been studied on a continuous basis for over 45 years.2. The initial slow‐growing stocks of numerous small perch and moderate numbers of large pike were subjected to a heavy initial fishing pressure that was subsequently relaxed for perch but not for larger (>550 mm) pike. The number of charr in the lake has increased 6–8‐fold during the study, probably due to the sustained reduction in the abundance of the larger pike that heavily predate the autumn spawning race of charr when it enters the shallow littoral areas to spawn.3. The biomass of perch did not recover from the initial fishery until the late 1950s when strong year‐classes occurred in warm summers. However, it was now composed of larger and faster growing individuals. In 1976, disease killed over 98% of all adult perch in the lake and the subsequent recovery has again been slow.4. Existing models have explained the variation in perch year‐class strength for the years 1959–74 in terms of adult perch biomass, pike cohort strength and temperature in the year of hatch. A new. more generally applicable model, incorporating a stock‐recruitment expression, gives a better fit to the earlier data, particularly from the North Basin, where there have been periods of extremely low adult biomass.5. The importance of continuing to extend these long‐term data sets and the scope for future modelling work are discussed.
Convergence of insular dwarfism in damselflies (Euphaea) and dobsonflies (Protohermes)
Authors: HAYASHI FUMIO 
Published: May 2006

SUMMARY. 1. The life history was compared between mainland and island congeners of Protohermes (Megaloptera: Corydalidae) and also between those of Euphaea (Odonata: Euphaeidae). Larvae of these genera coexisted in stream riffles, and prey availability for them was assessed to examine the effects on their body size at maturation.2. Body size of P. costalis on the ‘mainland’. Taiwan, was larger than that of an insular congener, P. sp., on Iriomotc and Ishigaki Islands about 200 km east from Taiwan. Insular dwarfism also occurred between E. formosa on the mainland and E. yayeyamana on the islands. All species had an annual life cycle.3. Prey availability was much lower in the island streams than in mainland streams throughout the year. Convergence of insular dwarfism in these phylogenetically distant but ecologically similar taxa (both predatory insects) suggested that prey availability is an important factor affecting their body size determination.4. Seasonal changes in body size occurred within a population of Euphaea which lacked synchronous emergence. Adults emerging from larvae spending their late instars in the warm season were smaller than those in the cold season. However, the size differences between species always exceeded the range of such intraspecific variation.5. Dwarfism in E. yayeyamana was probably achieved by decreasing the size of first‐instar larvae without changing the number of instars and with the size ratio at each moult constant. The mechanisms producing the dwarf form of Protohermes are also discussed.
Evidence of induced plant defences in a pondweed
Authors: JEFFRIES M. 
Published: May 2006

SUMMARY. 1. Palatability changes, induced by herbivore damage, have received much attention in terrestrial plant‐insect research but negligible investigation in freshwater systems.2. Potamogeton coloratus (Potamogetonaceae) and the folivorous caddis larva Triaenodes bicolor (Insecta: Trichoptera) were used to duplicate bioassay techniques common in terrestrial plant‐insect research.3. Leaves of P. coloratus were artificially damaged. Grazing on damaged leaves, and undamaged leaves from damaged plants, was compared to that on control leaves from undamaged plants up to 10 days after initial damage.4. The palatability of damaged and undamaged leaves from damaged plants declined compared to control leaves. The differences were significant at 5 days after damage, but had recovered to approximately equal palatability after 10 days.
Prey detection by the water miteUnionicola crassipes(Acari: Unionicolidae)
Authors: PROCTOR HEATHER C. , PRITCHARD GORDON 
Published: May 2006

SUMMARY.1. The importance of different senses in prey detection by the common water miteUnionicola carssipeswas investigated.2. Mechanoreception is likely to be the most important mode of detection; mites preferentially attacked vibrating over non‐vibrating glass probes. The net‐stance, a characteristic posture in which the mite raises its first two sets of legs from the substrate and orients toward vibrations in the water column, is assumed byU. crassipeswhen hunting.3. Chemoreception may have a role in area‐restricted search: mites exposed to prey‐conditioned water were more sedentary than those exposed to unconditioned water. For a sit‐and‐wait predator likeU. crassipes, remaining still in an area that contains prey will result in a greater predator/prey encounter rate. It is possible that contact chemoreception is used to determine the palatability of an already captured prey item, but mites did not attempt to capture prey they had touched unless the prey moved.4. Vision is not necessary for prey capture; however, mites captured more prey in the light than in the dark. It is not clear whether this is because vision plays a part in prey detection or because prey behave differently in the two situations.
Structural, physical and chemical characteristics of Microcystis aeruginosa hyperscums from a hypertrophic lake
Authors: ZOHARY TAMAR , MADEIRA ARCANGELA M. PAIS 
Published: May 2006

SUMMARY. 1. This paper examines the structural, physical and chemical characteristics of cyanobacterial hyperscums (floating scums of densely packed eyanobacteria. measuring decimetres in thickness, that are covered by a dry crust of photo‐oxidized cells) from hypertrophic Hartbeespoort Dam, South Africa.2. The hyperscum community was a cyanobacterial‐baclcrial association, in which the cyanobacterium Microcystis aeruginosa comprised 98% of the biovolumc, with cell concentrations exceeding 109 ml−1.3. The buoyancy mechanism of M. aeruginosa and evaporation at the surface led to increasing compaction of the colonies with declining distance from the surface, and the formation of three distinct, but continuous layers: a 1–2 mm dry surface crust (water content: 14%, chlorophyll a concentration: 3 g l−1), a 5–10 mm compact layer just below the crust (77% water, 1 g l−1 chlorophyll a), and a less compact layer (96% water, 200–500 mg l−1 chlorophyll a) from about 1 cm depth to the bottom, comprising the bulk of the hyperscum.4. The crust attenuated all the incident light and reduced free gas exchange. Beneath it continuously dark anaerobic, highly reduced conditions prevailed. As the hyperscum aged over 3 months in 1984, at 10 cm depth the pH gradually declined from 6.6 to 5.9, interstitial water ammonia‐N concentrations increased from 0.45 to 119 mg l−1, soluble reactive phosphorus from 2.8 to 83.3 mg l−1, and dissolved organic carbon reached a maximum of 460 mg l−1. At any point in time these concentrations declined gradually with increasing depth within the hyperscum, and declined dramatically beneath the hyperscum. Similar patterns were recorded in another hyperscum in 1986.5. The chemical and temperature depth profiles indicated that free water movement took place around and under the hyperscum, but within it water movement was restricted to diffusion.6. Gas bubbles composed of 28% methane. 19% CO2, 53% N2, and traces of H2 trapped within the hyperscum, and the presence of volatile fatty acids in the interstitial water were indicative of anaerobic decomposition processes mediated by fermenting and methanogenic bacteria, and N:P ratios below 1.5 in the interstitial water suggested that nitrogen was lost as gas, possibly through denitrification.7. We hypothesize that the major sites of decay of M. aeruginosa were the crust and the compact layer beneath it, while deeper within the hyperscum this cyanobacterium could survive prolonged periods of dark anaerobic conditions. This hypothesis requires confirmation.
Refuge availability: a key to understanding the summer disappearance of Daphnia
Authors: WRIGHT DAVID , SHAPIRO JOSEPH 
Published: May 2006

SUMMARY. 1. The mid‐summer declines of Daphnia species in three small lakes were investigated to examine the relative roles of reduced natality and increased mortality. Reduced natality (assessed by quantifying clutch size, lipid index, and available food) could not account for the decline in daphnid abundance in any of the populations examined.2. The role of increased mortality imposed by zooplanktivorous fish was assessed by estimating the sizes of the mid‐water refuge areas where daphnids could escape fish predation. The boundaries of the refuge areas were estimated from field measurements and literature values and were based on gradients of temperature, dissolved oxygen and light. Observed decreases in refuge thicknesses correlated well with the mid‐summer declines of large‐bodied Daphnia species in all three lakes. Intermediatesized daphnids were less affected as the refuges thinned and small‐bodied species increased in abundance.3. The importance of refuge thickness in modifying zooplanktivore‐induced mortality was further tested in large enclosures where refuge thickness was experimentally modified. In the presence of zooplanktivorous fish, large‐bodied Daphnia, which used the refuge, persisted when the refuge was thick but disappeared when it thinned. Daphnia galeata mendotae, which did not occupy the refuge zone, was rapidly eliminated regardless of refuge thickness. We conclude that refuge availability plays a major role in Daphnia population dynamics.