bluuebunny/crossref_metadata_2025_split huggingface dataset:
0+ perch predation on 0+ bream: a case study in a eutrophic gravel pit lake
Authors: Beeck Peter , Tauber Sandra , Kiel Stephanie , Borcherding Jost 
Published: March 2003

SUMMARY 1. We studied the population dynamics of 0+ fish in a eutrophic gravel pit lake in which predation of 0+ Eurasian perch on other 0+ fish was suspected to influence perch growth and the structure of the fish community, with effects on the lake food web.2. The adult fish community was dominated by piscivorous species, especially perch, and the 0+ fish community was dominated by perch and bream. Bream grew to a total length of 80 mm between May and the end of August, gradually decreased in numbers during the summer, and completely disappeared in autumn. Stomach analysis revealed that 0+ perch ≥28 mm fed on 0+ bream.3. The initially unimodal cohort of 0+ perch gradually broadened and became bimodal by the end of July. Fish of the larger, piscivorous cohort grew faster (1.4 mm day−1) than the smaller, zooplankton‐consuming fish (0.6 mm day−1). Although individuals of both cohorts later consumed zooplankton and grew at similar rates (0.5 mm day−1), only perch of the large cohort (mean TL 125 mm) were found by mid‐October. Intraspecific competition for food or cannibalism of older perch may have contributed to the disappearance of the smaller perch.4. Early piscivory of the fast‐growing 0+ perch apparently resulted in the disappearance of 0+ bream by the end of the growing season and precocious maturation of male perch. In contrast to findings in other studies, these large 0+ perch thus avoided the juvenile bottleneck by switching to piscivory early during their ontogenetic development.5. The observations of this study suggest that early piscivory of 0+ perch can have a long‐lasting impact on fish communities in eutrophic lakes, particularly if prey fish are abundant and the structural complexity of the lake is low. Furthermore, early piscivory of 0+ perch may help prevent the expected increase in 0+ cyprinids following reduction of adult cyprinids, which is considered important to ensure the long‐term success of biomanipulation experiments.
Contribution of omnivorous tilapia to eutrophication of a shallow tropical reservoir: evidence from a fish kill
Authors: Starling Fernando , Lazzaro Xavier , Cavalcanti Cristine , Moreira Ricardo 
Published: March 2003

SUMMARY 1. We examined whether a large stock of tilapia (>750 kg ha−1, in littoral areas >1300 kg ha−1), mostly Oreochromis niloticus (L.) and Tilapia rendalli (Boulenger), could contribute to the eutrophication of a tropical reservoir (Lago Paranoá, Brasília, Brazil) by enhancing P‐loading.2. We took advantage of an extensive fish kill (>150 tons removed) during May–August 1997 in a hypereutrophic branch of the reservoir to compare water quality characteristics 1 year before and after this event by means of BACI statistics. We also measured P‐excretion rates in laboratory trials to assess the P‐loading of the reservoir by the tilapia relative to tributary inputs and loading from a sewage treatment plant.3. Concentrations of chlorophyll a (decline from 84 to 56 μg L−1, P=0.018) and total P (decline from 100 to 66 μg L−1, P < 0.001) decreased significantly in the branch of the reservoir affected by the fish kill, compared with a similar but unaffected branch that served as a control. Because P‐loading by both a sewage treatment plant and tributaries remained high after the incidence, the fish kill was likely to contribute to the observed water quality improvement.4. Removing 150 tons of dead tilapia corresponded to 20 days of external total phosphorus load (TP‐load) to the branch, and resulted in a reduction of 5.1 kg P day−1 in internal recycling via tilapia excretion, which is equivalent to 12% of the external TP‐load.5. Implementing professional tilapia cast‐net fisheries could be an efficient biomanipulation approach to improve water quality and limit the occurrence of cyanobacteria blooms and fish kills in hypereutrophic branches of Lago Paranoá and similar tropical lakes.
Spatial and temporal patterns of light attenuation among lakes of the Mackenzie Delta
Authors: Squires Margaret M. , Lesack Lance F. W. 
Published: March 2003

SUMMARY 1. The seasonal dynamics of light attenuation, and the relative roles of total suspended solids (TSS), dissolved organic carbon (DOC) and chlorophyll as light attenuators among two sets of lakes in the Mackenzie Delta, were assessed during the open‐water periods of 1998 and 1999.2. The first set consisted of 40 spatially discrete lakes where the frequency of flooding with river water was controlled by sill height (‘sill‐set lakes’). The second set consisted of a chain of six lakes connected to a main river channel (frequently flooded, all with same frequency), but where riverine influence was controlled by the distance from the channel connection point (‘chain‐set lakes’).3. As the flooding frequency of lakes decreased (sill‐set), and as the distance from the channel connection point increased (chain‐set), lake water became increasingly transparent and the stability (decreasing temporal variability) of underwater light increased.4. The effect of flooding on transparency was greater in years with a high minimum summer water level. However, the effect of river flooding on lake water transparency was damped more by an increase in the frequency and duration of flooding than by an increase in distance from the channel connection point.5. The index of scattering was linearly related to TSS over the common range of concentrations in both sets of lakes. The specific attenuation coefficient for TSS (and scattering) increased substantially from the most turbid to the most transparent waters.6. During the summer, DOC provided an approximate index of water colour in the sill‐set lakes but not in the chain‐set lakes, where the gradient of DOC ran counter to the gradient of water colour. The specific attenuation coefficient for water colour was roughly constant among both sets of lakes.7. Calculations of partial attenuation show that, during the spring flood peak, TSS is the dominant attenuator among most lakes, other than those with high sills or positioned far from channel connection points. During the lengthy summer period of open water, however, water colour appeared to be the most important light attenuator among almost all of the lakes in the central delta, with chlorophyll a of only minor importance.8. Lakes of the Mackenzie Delta may be quite sensitive to changes in climate and ultraviolet‐b (UV‐b) radiation in the circumpolar arctic because of the role of DOC as an attenuator of photosynthetically active radiation and UV‐b irradiance and as an energy source for microbial foodwebs in this system.
Daphnia population growth but not moulting is a substantial phosphorus drain for phytoplankton
Authors: Sommer F. , Santer B. , Jamieson C. , Hansen T. , Sommer U. 
Published: March 2003

SUMMARY 1. Negative effects of zooplankton on the availability of phosphorus (P) for phytoplankton as a result of the retention of nutrients in zooplankton biomass and the sedimentation of exoskeletal remains after moulting, have been recently proposed.2. In a mesocosm study, the relative importance of these mechanisms was tested for the freshwater cladoceran Daphnia hyalina×galeata. A total of 13 mesocosm bags was suspended in a mesotrophic German lake during summer 2000 and fertilised with inorganic P in order to obtain a total nitrogen to total P ratio closer to the Redfield ratio. D. hyalina×galeata was then added at a logarithmically scaled density gradient of up to 40 ind. L−1. Zooplankton densities, dissolved inorganic, particulate organic (seston <100 μm), as well as total nutrient concentrations were monitored. Additionally, nutrient concentrations of sediment water removed from the bottom of the mesocosm bags via a manual pump were determined.3. Seston carbon (C), seston P and total P were significantly negatively correlated with Daphnia densities. The amount of particulate P (∼5–6 μg P L−1) sequestered from the seston compartment by Daphnia corresponded roughly to the increase of zooplankton biomass (population growth). Soluble reactive phosphorous (SRP) was at all times high (∼25–35 μg P L−1) and possibly unavailable to phytoplankton as a result of P adsorption to calcite during a calcite precipitation event (whiting). P concentrations determined in sediment water were generally <60 μg P m−2 and thus never exceeded 1% of the total amount of P bound in particulate matter of the overlying water column.4. Seston C : P ratios followed a polynomial second‐order function: At Daphnia densities <40 ind. L−1 a positive linear relationship was evident, which is explained by the stronger reduction of P compared with C in seston, and transfer of seston P to zooplankton. Highest seston C : P ratios of ∼300 : 1 were observed at Daphnia densities of ∼30–50 ind. L−1, which is in agreement with proposed threshold values limiting Daphnia reproductive growth. At Daphnia densities >40–50 ind. L−1 C : P ratios were decreased because of the strong reduction of seston C at close to constantly low seston P‐values of ∼3–4 μg P L−1.5. At least for Daphnia, it may be concluded that – unlike population growth – the sedimentation of faecal pellets and carapaces after moulting seem negligible processes in pelagic phosphorus dynamics.
Causes of episodic acidification in Alpine streams
Authors: Lepori Fabio , Barbieri Alberto , Ormerod S. J. 
Published: March 2003

SUMMARY 1. Despite their global importance as mountain landscapes, the effect of acid deposition on running waters in the Alps is still incompletely described. The acid–base status of 30 clearwater streams in Canton Ticino (Switzerland) was therefore assessed at low and high flow across a south/north gradient of acid deposition in 2000.2. At low flow, no stream was acidic, alkalinity being ≥29 μeq L−1 and pH ≥6.4. However, NO3– was present in streamwater at these flows in concentrations that suggested anthropogenic enrichment, and its concentration correlated with spatial patterns of N deposition from the atmosphere.3. Severe loss of alkalinity occurred in most streams at high flow during snowmelt (spring) or rainstorms (spring and autumn). Autumn episodes were because of dilution of streamwater alkalinity by rainwater. By contrast, spring episodes involved dilution and NO3– titration, the increase in nitrate being correlated with patterns of N deposition. SO42– declined during most episodes.4. High NO3– leaching at low flow suggests that catchment soils in Canton Ticino are approaching saturation in N. These data are among the first to illustrate that NO3– can drive episodic acidification in Europe, paralleling locations in north‐eastern United States.
Caddisfly life histories along permanence gradients in high‐altitude wetlands in Colorado (U.S.A.)
Authors: Wissinger S.A. , Brown W.S. , Jannot J.E. 
Published: March 2003

SUMMARY1. Larvae of cased caddisflies (Limnephilidae and Phryganeidae) are among the most abundant and conspicuous invertebrates in northern wetlands. Although species replacements are often observed along permanence gradients, the underlying causal mechanisms are poorly understood. In this paper, we report on the distributional patterns of caddisflies in permanent and temporary high‐altitude ponds, and how those patterns reflect differences in life history characteristics that affect desiccation tolerance (fundamental niches) versus constraints related to biotic interactions (realised niches).2. Species (Hesperophylax occidentalisandAgrypnia deflata) that were encountered only in permanent ponds are restricted in distribution by life history (no ovarian diapause, aquatic oviposition, and/or inability to tolerate desiccation). Although the egg masses ofH. occidentalistolerate desiccation, the larvae leave the protective gelatinous matrix of the egg mass because adults oviposit in water.3. Three species (Asynarchus nigriculus, Limnephilus externusandL. picturatus) have life history characteristics (rapid larval growth, ovarian diapause and terrestrial oviposition of desiccation‐tolerant eggs) that should facilitate the use of both permanent and temporary habitats. However,A. nigriculusis rare or absent in most permanent ponds, andL. externusandL.picturatusare rare or absent in most temporary ponds. Experimental data from a previous study on the combined effects of salamander predation and interspecific interactions among caddisflies (e.g. intraguild predation) suggest that biotic interactions limit each species to a subset of potentially exploitable habitats.4. Many wetland invertebrates exhibit species replacements along permanence gradients, but few studies have separated the relative importance of the effects of dryingper sefrom the effects of biotic interactions. Our results emphasise the complementary roles of comparative data on life histories and experimental data on competition and predation for understanding invertebrate distributions along permanence gradients.
Particulate fatty acids in two small Siberian reservoirs dominated by different groups of phytoplankton
Authors: Sushchik Nadezhda N. , Gladyshev Michail I. , Kalachova Galina S. , Kravchuk Elena S. , Dubovskaya Olga P. , Ivanova Elena A. 
Published: March 2003

SUMMARY 1. We studied the composition of fatty acids (FAs) in the seston from two small freshwater reservoirs (Bugach and Lesnoi) with distinct periodicity of domination by cyanobacteria and eukaryotic algae during the growth season.2. The diatoms in the both reservoirs were characterised by a high content of 14:0 and C16 unsaturated acids, whereas that of the essential FA 20:5ω3 [eicosapentanoic acid (EPA)] was low. The correlation between this polyunsaturated FA (PUFA) and diatom biomass was not significant in either reservoir. The percentage of 20:5ω3 in seston significantly correlated with the biomass of euglenophyta in Bugach and dinophyta in Lesnoi. Hence the diatoms, usually referred as a valuable food for zooplankton, were not an important source of the essential PUFA in these systems.3. The dominant cyanobacteria in Bugach, and the green algae in Lesnoi, both contained the same marker acids: 18:3ω3 and 18:2ω6. Hence, a discrimination between these two phytoplanktonic groups on the basis of FA biomarkers may be difficult in some cases.4. We found no significant correlation between the content of 20:5ω3 in seston and the biomass of the dominant daphniids in either reservoir. This is contrary to expectations, based on the literature, that EPA is generally important. Rather, the biomass of the two dominant Daphnia species in Bugach correlated strongly with the content of 18:3ω3 in the seston. The cyanobacteria were a probable source of this ω3 FA for Daphnia. We conclude that EPA is not always important for Daphnia populations although, in such cases, some other PUFA (e.g. 18:3ω3) might be related to their growth.
Lake age and water level affect the turbidity of floodplain lakes along the lower Rhine
Authors: Roozen F. C. J. M. , Van Geest G. J. , Ibelings B. W. , Roijackers R. , Scheffer M. , Buijse A. D. 
Published: March 2003

SUMMARY 1. We sampled a set of 93 lakes situated in the floodplains of the lower River Rhine in search for morphometric and other factors that explain their variation in clarity.2. Lakes with a drop in summer water level were less turbid at the time of sampling, mainly because of a lower concentration of inorganic suspended solids (ISS).3. We also found that older lakes were more turbid than younger lakes and that this was largely because of an increase in phytoplankton.4. Water clarity was positively related to lake depth and the presence of vegetation.5. Model calculations indicated that the underwater light climate was strongly affected by chlorophyll and ISS, the latter being the dominant factor affecting Secchi depth. Dissolved organic carbon (DOC) was less important.6. The high concentration of ISS suggests that intensive resuspension occurs in most of the lakes. Using a simple wave model, and assuming that vegetation protects sediments against resuspension, we could eliminate wind resuspension as an important process in 90% of the lakes, leaving resuspension by benthivorous fish as probably the most important factor determining transparency.7. Chlorophyll a concentration showed a strong positive correlation to ISS concentration, suggesting that resuspension may also have a positive effect on phytoplankton biomass in these lakes.8. In conclusion, in‐lake processes, rather than river dynamics, seem to be driving the turbidity of floodplain lakes along the lower River Rhine.
The effect of mycorrhizal infection of Abutilon theophrasti on competitiveness of offspring
Authors: Heppell K. B. , Shumway D. L. , Koide R. T. 
Published: March 2003

1. Our goal was to determine whether mycorrhizal infection of one generation of plants could influence the competitiveness of the subsequent generation. 2. We grew the offspring of mycorrhizal (M) and non‐mycorrhizal (NM) Abutilon theophrasti plants together in dense populations in large boxes in a greenhouse. 3. Offspring of M plants were larger than offspring of NM plants. As the experiment progressed, the difference in size was magnified and self‐thinning occurred. 4. Compared with offspring of NM plants, offspring of M plants had a twofold greater survival and collectively produced a total of nearly four times as many seeds. 5. We conclude that mycorrhizal infection of the parent generation can increase the competitive ability of the offspring.
Bird predation as a sex‐ and size‐selective agent of the arboreal spider Pityohyphantes phrygianus
Authors: Gunnarsson B. 
Published: March 2003

1. The solitary sheetweb spider Pityohyphantes phrygianus (Araneae: Linyphiidae) lives in canopies of coniferous trees. Earlier studies in Scandinavia have shown that bird predation affects the spider abundance negatively. 2. In a large‐scale, 2‐year field experiment, passerine birds were excluded from foraging on spruce branches. The experimental branches were net‐enclosed, which prevented bird predation but left spiders free to leave and enter. Samples were taken in the autumn and spring for 2 years. 3. Removal of bird predation increased the mean number of subadult P. phrygianus per branch between 2·1 and 10·6 times the control number for each sex. Bird predation had approximately similar effects on the sexes, except in the second experimental spring when males were affected twice as much as females, and there was a significantly lower proportion of males on control branches exposed to bird predation than on net‐enclosed branches. 4. The mean size of females was larger on net‐enclosed branches than on controls in both spring samples. In males, this was the case in the first spring sample only. 5. This study shows that there are also mortality costs for both sexes associated with large size in the non‐mating season. In certain winters, however, there is an additional mortality risk to males, presumably caused by a higher activity level than in females.
A comparison of 12 tree species of Amazonian caatinga using growth rates in gaps and understorey, and allometric relationships
Authors: Coomes D. A. , Grubb P. J. 
Published: March 2003

1. The relative growth rate of saplings of 12 species from an oligotrophic lowland rain forest were measured in treefall gaps and understorey. Mean relative height growth (RH) within treefall gaps was found to be slowest for tall‐tree species with branched saplings, intermediate for subcanopy trees and fastest for tall‐tree species with unbranched saplings. Most species had similar RH within the understorey. RH values were not related to leaf mass per unit area (LMA) or foliar N concentrations. 2. Allometric relationships between the total leaf area (TLA) and height were dependent upon light conditions; in general saplings of a given height had a greater TLA in treefall gaps than in understorey. The species with the largest estimated TLA values in gaps tended to have the greatest RH values in gaps; no such trend emerged in the understorey. The values of the allometric coefficients were not related to foliar properties. 3. The relationship between stem diameter and height was only weakly dependent on light conditions and the relationship between the growth rates in these dimensions was also weak. The lack of plasticity may reflect the fact that the height–diameter relationship has little bearing on a sapling’s tolerance of shade. 4. One way of accommodating the dependence of allometry upon irradiance is to add RH as a covariate. We derive a relationship between growth rates from this resource‐dependent allometric equation and show that it reasonably describes measurements taken in the caatinga forest.
Regulation of chick provisioning rate in Manx Shearwaters: experimental evidence and implications for nestling obesity
Authors: Hamer K. C. , Lynnes A. S. , Hill J. K. 
Published: March 2003

1. Procellariiform seabirds such as Manx Shearwater accumulate large quantities of lipid during the nestling period, and a series of recent papers suggests that these lipid reserves provide a buffer against pronounced and unpredictable variation in food provisioning, resulting in part from an inability of parents to regulate food supply to the nest. Supplementary feeding was used to test experimentally whether or not parents were able to adjust their level of food provisioning according to the nutritional requirements of the chick. 2. There was no difference between experimental and control groups in parental provisioning rates before supplementary feeding began. Thereafter, chicks given daily supplements received significantly fewer feeds from their parents, although the mass of food delivered during each feed did not differ between groups. The total amount of food received by chicks in the experimental group (parental delivery plus supplementary food) was only slightly higher than the amount delivered by parents in the control group, indicating that parents adjusted their provisioning rate downwards, although they did not compensate completely for the additional food provided by the supplements. 3. These results indicate that in Manx Shearwaters, nestling obesity is not related to an inability of parents to monitor changes in the chick’s nutritional status. These results are discussed in relation to the optimization of nestlings’ lipid reserves. It is suggested that evidence of a reduction in parental food provisioning in response to a decrease in the food requirements of chicks does not refute the hypothesis that nestling obesity provides a buffer against highly variable food delivery. However, these results do suggest that in species that feed their chicks at comparatively short average intervals, variability in provisioning should be viewed as arising from highly variable and unpredictable foraging success among parents, and not from an inability of parents to assess the nutritional requirements of their offspring.