bluuebunny/crossref_metadata_2025 huggingface dataset:
Top‐down effects on pelagic heterotrophic nanoflagellates (HNF) in a large river (River Rhine): do losses to the benthos play a role?
Authors: WEITERE MARKUS , ARNDT HARTMUT
Published: March 2003

1. The abundance, production and control of pelagic heterotrophic nanoflagellates (HNF) in the Lower River Rhine (Germany) were investigated. Field samples (live‐counting technique) were taken at least every 2 weeks at Cologne (km 685) over a period of 20 months. In addition, Lagrangian sampling was carried out 160 km downstream of Cologne (Kalkar–Grieth, km 845) over a period of 12 months. Potential HNF growth rates and loss rates caused by planktonic predators were estimated in the laboratory (size fractionation experiments) and compared with the changes in HNF‐density in a water parcel flowing downstream.

2. Mean abundance (±SD) ranged from 7 ± 6 to 4890 ± 560 individuals mL–1 and was positively correlated with discharge. Heterotrophic nanoflagellates abundance increased up to 30‐fold during flood events, whereas there were only minor changes in the taxonomic composition.

3. HNF growth rate ranged from 0.16 ± 0.12 to 1.98 ± 0.10 day–1. Between 0 and 95% (mean: 32%) of the gross production was lost to planktonic predators; a larger portion between 0 and 195% (mean: 64%) of the HNF gross production was lost by other means.

4. There may be an important role for benthic predators in the control of pelagic HNF. First, production of HNF was high and grazing losses to planktonic predators low at times when HNF abundance was low. Secondly, high in situ loss rates (not explicable by planktonic predators), which were positively related to temperature, indicate the importance of biotic interactions. Thirdly, the dependence of HNF abundance on discharge indicated a decrease grazing intensity with rising water levels (increase in water volume/colonised river bed ratio).

5. The impact of discharge on planktonic HNF mediated by the grazing impact of benthic predators was modelled, showing a good fit with the field data.
Characteristics of oligotrophic hardwater lakes in a postglacial land‐rise area in mid‐Sweden
Authors: BRUNBERG A.‐K. , NILSSON E. , BLOMQVIST P.
Published: March 2003

1. We describe some remarkable ephemeral, oligotrophic hardwater lakes formed because of land rise in the coastal areas of the Baltic Sea, that are unique in Sweden and probably also worldwide. Two younger, coastal lakes were studied by regular sampling for 1 year and compared with an older (i.e. greater altitude) lake, that passed through the oligotrophic hardwater stage some 3–4000 years ago.

2. Despite some differences in composition of the catchment, the two younger lakes were similar with regard to water chemistry and plankton community composition. The concentration of phosphorus was low while nitrogen was high, resulting in very high N/P quotients (101 and 131). Although water colour was moderate, the concentration of organic carbon was extremely high (average values of ≥ 20 μg TOC L–1), consisting mainly of dissolved compounds (DOC).

3. While the plankton was poorly developed, sediments in both lakes were covered by a layer of photosynthesising micro‐organisms. This substantial `microbial mat', which has not been described in detail before, was up to 15 cm thick and dominated by cyanobacteria and purple sulphur bacteria. The concentration of sediment phosphorus was extremely low (352 μg g–1 dw) in one of the lakes and dominated by organic‐bound (residual) phosphorus.

4. Deep sediments in the older lake, representing its oligotrophic hardwater period, differed in phosphorus composition from the currently oligotrophic hardwater lakes by having a strong dominance of HCl‐extractable (Ca‐bound) phosphorus. This indicates that phosphorus, initially organic‐bound within the microbial mat, is subsequently bound to calcium. We hypothesise that this is promoted by the environmental conditions created by the benthic photosynthetic activity, in combination with the prevailing hardwater conditions.

5. The rich and flourishing microbial community on the sediments may also explain the high concentration of DOC in the lake.
The relative importance of lethal and non‐lethal effects of fish on insect colonisation of ponds
Authors: ÅBJÖRNSSON KAJSA , BRÖNMARK CHRISTER , HANSSON LARS‐ANDERS
Published: March 2003

1. We hypothesised that adult insects actively monitor potential habitats for the presence of fish by means of chemical cues and avoid sites that pose significant risks. This was examined by quantifying colonisation of insects in outdoor pools with no fish (controls), fish (direct predation effect) or caged fish (chemical predator cues).

2. A significant direct effect of predation was found, but no indirect effect (avoidance of chemical cue pools), on the total biomass of colonising insects. However, predatory insects avoided fish‐cue pools, thus releasing non‐predatory insects from predation. This resulted in significantly greater biomass of non‐predatory insects in fish‐cue pools than control pools.

3. Fish reduced the number of species of colonising insects in pools through predation. This negative influence of fish implies that caution is necessary when stocking wetlands and ponds with fish if the goal is to maximise biodiversity.

4. Our data suggest that although predatory aquatic insects may use chemical signals to assess the quality of potential habitats with respect to predation risk, direct predation is the main method by which fish affect insect assemblages in ponds. Because fish and invertebrate predators may both have strong effects on prey mortality, behavioural adjustment by insects to the actual predator regime within a habitat should be more important than avoiding colonisation of habitats with fish.
How can dragonflies discern bright and dark waters from a distance? The degree of polarisation of reflected light as a possible cue for dragonfly habitat selection
Authors: Bernáth Balázs , Szedenics Gábor , Wildermuth Hansruedi , Horváth Gábor
Published: March 2003

SUMMARY 1. Based on the findings that some dragonflies prefer either ‘dark’ or ‘bright’ water (as perceived by the human eye viewing downwards perpendicularly to the water surface), while others choose both types of water bodies in which to lay their eggs, the question arises: How can dragonflies distinguish a bright from a dark pond from far away, before they get sufficiently close to see it is bright or dark?

2. Our hypothesis is that certain dragonfly species may select their preferred breeding sites from a distance on the basis of the polarisation of reflected light. Is it that waters viewed from a distance can be classified on the basis of the polarisation of reflected light?

3. Therefore we measured, at an angle of view of 20° from the horizontal, the reflection‐polarisation characteristics of several ponds differing in brightness and in their dragonfly fauna.

4. We show that from a distance, at which the angle of view is 20° from the horizontal, dark water bodies cannot be distinguished from bright ones on the basis of the intensity or the angle of polarisation of reflected light. At a similar angle of view, however, dark waters reflect light with a significantly higher degree of linear polarisation than bright waters in any range of the spectrum and in any direction of view with respect to the sun.

5. Thus, the degree of polarisation of reflected light may be a visual cue for the polarisation‐sensitive dragonflies to distinguish dark and bright water bodies from far away. Future experimental studies should prove if dragonflies do indeed use this cue for habitat selection.
The effects of bankside management on chalk stream invertebrate communities
Authors: Harrison Simon S. C. , Harris Iain T.
Published: March 2003

SUMMARY 1. Communities of aquatic macroinvertebrates and the terrestrial adult phases of aquatic insects were investigated from short stretches of English chalk streams with two different bankside vegetation types: simply structured grazed grass (grazed) and structurally complex herbaceous vegetation with scattered trees (ungrazed). Macroinvertebrates were sampled in spring, summer, autumn and winter 1996–97 from three aquatic habitats: mid‐channel gravel, patches of the aquatic macrophyte Ranunculus and marginal emergent macrophytes. The terrestrial adult phases of aquatic insects were sampled in spring, summer and autumn from bankside vegetation.

2. Total macroinvertebrate abundance did not differ between stretches with different bankside vegetation. Taxon richness of mid‐channel gravel was, however, significantly higher in ungrazed compared with grazed stretches and Shannon diversity (H′) of mid‐channel gravel and marginal vegetation was significantly higher in ungrazed compared with grazed stretches. Total abundance, taxon richness and Shannon diversity (H′) of the terrestrial adult phases of aquatic insect were significantly higher from the bankside vegetation of ungrazed compared with grazed stretches.

3. Ordination of communities of aquatic macroinvertebrates and terrestrial adults demonstrated that individual families of both groups were generally more abundant in ungrazed stretches. Many more families were significantly associated with ungrazed stretches than with grazed stretches.

4. This investigation has shown that high structural diversity of bankside vegetation along lowland chalk streams is accompanied at the reach scale by increased diversity of both aquatic macroinvertebrates and the terrestrial adult phases of aquatic insects. The conservation potential of such streams may thus be lowered by management practices that result in the removal or simplification of bankside vegetation along extensive stream stretches.
The influence of water transparency on the distribution and abundance of macrophytes among lakes of the Mackenzie Delta, Western Canadian Arctic
Authors: Squires M. M. , Lesack L. F. W. , Huebert D.
Published: March 2003

SUMMARY 1. Macrophyte abundance and distribution was assessed in a chain of six interconnected lakes (all with the same flooding frequency) in the Arctic, where increasing distance from the Mackenzie River channel resulted in a gradient of water transparency (‘chain‐set’ lakes), and in a group of 26 spatially discrete lakes where increasing frequency and duration of lake flooding with river water (controlled by sill height) also resulted in a transparency gradient (‘sill‐set’ lakes).

2. Among the chain‐set lakes, above‐ground macrophyte biomass increased from 0 to 1000 g m−2 with increasing water transparency. Among the sill‐set lakes, the transparency gradient among the lakes was less well defined and the relations with biomass were more varied. A decrease in flooding was associated with increasing water transparency and an increasing biomass of macrophytes from about 0 to over 2000 g m−2. For a specific flood frequency, however, the effect of flooding was much greater when lakes were directly connected to a river channel than when floodwaters flowed first through an intervening lake. Among infrequently flooded lakes the effect of flooding on water transparency and biomass was negligible.

3. Among relatively clear lakes in both sets of lakes, biomass increased with increasing water transparency and decreasing lake depth. Among relatively turbid lakes, however, biomass increased with the combined effect of increasing water colour (decreasing water transparency) and increasing lake water depth. The increases in biomass with increasing water colour (coloured dissolved organic matter) and increasing depth, which together result in reduced light at the bed, may be explained by reduced exposure to ultra violet light.

4. An average light attenuation of 1.3 m−1 (Secchi depth about 1 m) over the growing season appears to represent a threshold water transparency which, in combination with water depths early in the growing season, is consistent with a light supply on the bed required for growth of the common macrophytes in lakes of the Mackenzie Delta. However, a comparison with other systems indicates that macrophytes among lakes of the Mackenzie Delta grow deeper, for a given level of transparency, than is reported in lakes at lower latitude, despite the lower sun angles and increased reflectivity of water surfaces in the arctic.

5. A complete accounting of water transparency (at PAR and UV wavelengths), lake depth, summer sun angle and duration of sunlight may be necessary to explain patterns of macrophyte growth among lakes across a full range of latitudes.
Nutrient limitation of phytoplankton and periphyton growth in upland lakes
Authors: Maberly S. C. , King L. , Dent M. M. , Jones R. I. , Gibson C. E.
Published: March 2003

SUMMARY 1. Thirty small upland lakes in Cumbria, Wales, Scotland and Northern Ireland were visited three times between April and August 2000. On each occasion water chemistry was measured and phytoplankton bioassays were performed in the laboratory to assess growth‐rate and yield limitation by phosphorus and nitrogen. In addition, yield limitation of periphyton growth was investigated twice, in situ, using nutrient‐diffusing substrata.

2. Over the whole season the percentage frequency of P, N and co‐limitation was 24, 13 and 63%, respectively, for phytoplankton rate limitation and 20, 22 and 58%, respectively, for phytoplankton yield limitation.

3. A clear response of periphyton yield to nutrient additions was found in 75% of all cases and of these, co‐limitation was most common (54%). Average percentage frequency for P and N limitation was 26 and 20%, respectively.

4. Phytoplankton and periphyton showed seasonal changes in nutrient limitation within sites. In particular, co‐limitation became progressively more common as the season progressed.

5. The response of phytoplankton growth rate to ammonium and nitrate addition was identical, but ammonium was a slightly better source of nitrogen than nitrate for phytoplankton yield on 7% and for periphyton yield on 10% of the occasions. However, the magnitude of the effect was small.

6. The concentration of dissolved inorganic nitrogen (DIN) and the molar ratio of DIN to total dissolved phosphorus (TDP), appeared to be the main environmental factors controlling the extent of nitrogen or phosphorus limitation at a given site. Nitrogen limitation was more likely than phosphorus limitation where the DIN was <6.5 mmol m−3 and the ratio of DIN : TDP was <53. Co‐limitation was the most likely outcome at a DIN concentration <13 mmol m−3 and at a DIN : TDP molar ratio <250. Above these values phosphorus limitation was most likely.

7. The relatively high frequency of nitrogen limitation and co‐limitation at higher N : P ratios than previously reported, may result from the inability of nitrogen‐fixing cyanobacteria to thrive in these upland lakes where pH and the concentration of phosphorus tended to be low and where flushing rates tended to be high.
Breakdown of wood in the Agüera stream
Authors: Díez Joserra , Elosegi Arturo , Chauvet Eric , Pozo Jesús
Published: March 2003

SUMMARY 1. Breakdown of wood was compared at three sites of the Agüera catchment (Iberian Peninsula): two oligotrophic first‐order reaches (one under deciduous forest, the other under Eucalyptus globulus plantations) and one third‐order reach under mixed forest, where concentration of dissolved nutrients was higher.

2. Branches (diameter = 3 cm, length = 10 cm) of oak (Quercus robur), alder (Alnus glutinosa), pine (Pinus radiata) and eucalyptus, plus prisms (2.5 × 2.5 × 10 cm) of alder heartwood were enclosed in mesh bags (1 cm mesh size) and placed in the streams. Mass loss was determined over 4.5 years, whereas nutrient, lignin and ergosterol were determined over 3 years. In order to describe fungal dynamics, ergosterol was also determined separately on the outer and inner parts of some branches.

3. Breakdown rates ranged from 0.0159 to 0.2706 year−1 with the third‐order reach having the highest values whatever the species considered. The most rapid breakdown occurred in alder heartwood and the slowest in pine branches; breakdown rates of oak, eucalyptus and alder branches did not differ significantly.

4. The highest nitrogen and phosphorus contents were found in alder, followed by oak, while pine and eucalyptus had low values. During breakdown, all materials rapidly lost phosphorus, but nitrogen content remained constant or slightly increased. Lignin content remained similar.

5. Peaks of ergosterol ranged from 0.023 to 0.139 mg g−1 and were higher in alder than in other species in two of the three sites. The third‐order reach generally had the greatest increase in ergosterol, especially in alder branches, eucalyptus and alder heartwood. The overall species/site pattern of fungal biomass was thus consistent with the observed differences in breakdown.

6. When compared with leaves of the same species decomposing at these sites, wood breakdown appeared to be less sensitive to the tree species but more sensitive to stream water chemistry. Although wood breakdown is slower and its inputs are lower than those of leaf litter, its higher resistance to downstream transport results in a relatively high standing stock and a significant contribution to the energy flux.
Drag and reconfiguration of freshwater macrophytes
Authors: Sand‐Jensen Kaj
Published: March 2003

SUMMARY 1. Submerged freshwater macrophytes face large hydrodynamic forces in flowing waters in streams and on wave‐swept lake shores and require morphological adaptations to reduce the drag and the physical damage. This experiment studied five species of freshwater macrophytes and strap‐formed plastic leaves to test the predictions that: (i) increasing flexibility leads to greater reconfiguration and lower drag coefficients, (ii) flexible plants experience a steeper decline of drag coefficients with increasing water velocity than unflexible plants and (iii) plants mounted vertically on a horizontal substratum bend over in fast flow attaining a shielded position of low drag.

2. The results confirmed all three predictions. In fast flow, plants mounted upright on a horizontal platform gradually approached a position aligned with the flow, depending on their flexibility. In the range 8–50 cm s−1 the deflection followed an interspecific negative linear relationship between log (tangent Φ) and velocity, where Φ represents the shoot angle normal to the horizontal level. Above 50 cm s−1, further deflection was reduced perhaps by a combination of the elasticity and packing of shoots and the increasing lift generated by fast flow.

3. Drag coefficients of plants ranged between 0.01 and 0.1, typical of moderately to very streamlined objects. Drag coefficients declined log‐log linearly at increasing velocity, following negative slopes between −0.67 and −1.24 (median: −1.0) because of reconfiguration and formation of a shielding canopy. Drag coefficients declined much less (median: −0.55) for plants floating freely in the streaming water and which were capable of changing their shape but unable to form a shielding canopy. Drag coefficients declined even less for relatively unflexible plastic leaves (−0.30 to −0.40), and they remained constant for stiff, bluff objects.

4. The experiments suggest that flow resistance of flexible, submerged macrophytes in natural streams may increase in direct proportion to water velocity because they form a shielding submerged canopy, and high water stages at peak flow may result in greater proportions of the water passing unimpeded above the canopy. In contrast, stiff amphibious and emergent reed plants should experience an increase of flow resistance with at least the square of velocity as reconfiguration is small and former aerial plant surfaces come into contact with the streaming water at higher water stages. Field experiments to test these predictions are urgently needed.
Longevity of the freshwater anostracan Streptocephalus mackini (Crustacean: Anostraca) in relation to food (Chlorella vulgaris) concentration
Authors: Anaya‐Soto Alejandro , Sarma S. S. S. , Nandini S.
Published: March 2003

SUMMARY 1. Temporary ponds are inhabited by a variety of invertebrates, of which anostracans are an important group. We studied the lifetables of male and female anostracan Streptocephalus mackini at 3 algal concentrations (0.5 × 106, 1.0 × 106 and 1.5 × 106 cells mL−1).

2. Regardless of sex, S. mackini showed better survivorship at lower food levels. The longest average lifespan observed was 85 ± 2 days for males fed Chlorella at 0.5 × 106 cells mL−1.

3. Both net reproductive rate and generation time decreased with increasing food level. The highest net reproductive rate was about 120 cysts per female. The longest generation time of about 40 days, observed at 0.5 × 106 cells mL−1, was more than three times that at 1.5 × 106 cells mL−1.

4. The rate of population increase (r) was nearly the same (0.31 ± 0.06) at high (1.5 × 106 cells mL−1) and intermediate (1.0 × 106 cells mL−1) food levels. The r‐value at low food level (0.5 × 106 cells mL−1 of Chlorella) was 0.20 ± 0.01 per day.
Estimation of the in‐situ settling velocity of particles in lakes using a time series sediment trap
Authors: Douglas Richard W. , Rippey Brian , Gibson Christopher E.
Published: March 2003

SUMMARY 1. We outline a simple method for estimating the in‐situ settling velocity of particles in wind disturbed lakes. The total sedimentation rate (primary and secondary sedimentation) was measured during storm events in two lakes using a time series sediment trap.

2. The sediment trap had 12 sample bottles which were programmed to open for periods of 3–4 h, giving total deployment times ranging from 36 to 48 h.

3. Wave mixed layer theory was used to infer if and when sediment resuspension occurred and the first order rate equation was used to estimate the settling velocity of resuspended particles.

4. The settling velocity during three resuspension events in Lough Neagh and one in Lough Macnean were 34.3, 29.5, 24.1 and 77.3 m day−1, respectively. These are similar to values obtained using recent in‐situ video imaging in marine environments, but much larger than previous lake sediment trap studies.
Response of bee‐flies to the shape and pattern of model flowers: implications for floral evolution in a Mediterranean herb
Authors: Johnson S. D. , Dafni A.
Published: March 2003

1. The functional significance of floral traits in Linum pubescens (Linaceae), a Mediterranean annual that is pollinated almost exclusively by the bee‐fly Usia bicolor (Bombyliidae), was investigated. The flies feed on both pollen and nectar, and use the flowers as mating rendezvous sites in the afternoon.

2. Choice experiments with model flowers were used to determine the response of U. bicolor to visual cues, such as shape, size, colour and pattern.

3. Bee‐flies strongly preferred models with a dissected outline over models with a simple outline. They also preferred pink models over other colours, and larger models over smaller models.

5. Flies landing on models with converging lines (‘nectar guides’) tended to follow the lines to the point where they meet in the centre of the model, while flies landing on plain models showed undirected behaviour, often moving to the edge of the model.

6. Flies were strongly attracted to flowers of L. pubescens which had a fly glued on to one of the petals, as well as flowers with a dark spot painted onto one of the petals. In addition, models with a dark spot were strongly preferred over plain models during the afternoon when flies exhibit mating behaviour. This evidence suggests that the dark centre of the L. pubescens flower may function as an attractant to mate‐seeking bee‐flies.
IsEcheveria gibbiflora(Crassulaceae) fecundity limited by pollen availability? An experimental study
Authors: Parra‐Tabla V. , Vargas C. F. , Eguiarte L. E.
Published: March 2003

1.An experimental approach, manually pollinating all the flowers of individual plants, was used to measure the effect of pollen limitation on female fecundity of the hummingbird‐pollinated perennial shrubEcheveria gibbiflorain the ecological preserve of Pedregal de San Angel around México City, México. Eleven randomly selected plants were manually over‐pollinated in all their flowers and another 11 were left to be freely visited by natural pollinators.

2.Manually pollinated plants produced significantly more fruit and seeds than control plants (1·38 and 1·74 times, respectively). There was no change in average mass of fruits.

3.Considering individual fruit production per plant sampled three times in one season, decreases in fruit mass and average seeds per fruit were observed within the same reproductive season for both treatments. For the manually pollinated plants, from the start to the end of the reproductive season, seed set decreased 55·9%; while in control plants seed set decreased 33·4% in the same period. For both treatments, average fruit mass decreased 26%.

4.Vegetative growth was not significantly different between control and experimental plants but hand‐pollinated plants showed a smaller reproduction probability for the following year.

5.It is concluded that female fecundity inE. gibbiflorais limited by pollen early in the reproductive season and by resources in the middle and the end of the season.
Induced thermotolerance and associated expression of the heat‐shock protein Hsp70 in adult Drosophila melanogaster
Authors: Dahlgaard J. , Loeschcke V. , Michalak P. , Justesen J.
Published: March 2003

1. Inducible heat‐shock proteins are synthesized when temperatures are increased to levels substantially above normal. The functional role of these proteins is well known at the cellular level. Today increasing interest has been directed towards the importance of heat‐shock proteins for resistance of whole organisms to high‐temperature stress and other environmental stressors.

2. Here the functional relationship between the heat‐shock protein, Hsp70, and thermal resistance in adult Drosophila melanogaster was examined by comparing thermal resistance, i.e. survival at 39 °C for 85 min, and levels of Hsp70 at various times elapsed (2, 4, 8, 16, 32 and 64 h) after thermotolerance was induced by short‐term acclimation/heat hardening at 37 °C for 55 min.

3. Levels of Hsp70 in both males and females were highest 2 h after heat hardening and declined with longer times elapsed. The rate of decrease initially was very fast but diminished with increasing time. After 32 h the level of Hsp70 approached the level in flies that were not hardened. Levels of Hsp70 in males exceeded that of females during the entire period.

4. Survival of both sexes increased with increasing time after heat hardening and reached an optimum between 8 and 32 h. Thereafter resistance decreased with longer times elapsed. Survival of females generally exceeded that of males except after 16 and 64 h.

5. Regression analysis applied to the data on Hsp70 levels revealed that the model describing these data could not explain the data for survival. Also, higher levels of Hsp70 in males compared with females were not associated with greater survival in males. However, statistical analysis on paired measurements of Hsp70 and survival revealed a positive association between Hsp70 level and survival at each time elapsed after induction of thermotolerance.
Modelling the time–temperature relationship in cold injury and effect of high‐temperature interruptions on survival in a chill‐sensitive collembolan
Authors: Nedve˘D O. , Lavy D. , Verhoef H. A.
Published: March 2003

1. Temperature‐ and time‐dependent mortalities were studied and modelled in insects exposed in regimes with constant and alternating temperatures. In these experiments, freezing was not a cause of death.

2. Survival rates at a range of constant low temperatures (– 5 to + 1 °C) and for different exposure periods (1–14 days) were measured in the summer acclimated springtail Orchesella cincta.

3. Daily interruptions of the cold exposure with short intervals at high temperature reduced mortality or slowed the increase of mortality. This effect was stronger at higher temperature (19 vs 5 and 12 °C) and increased with the duration of the interruption (0·25–2 h).

4. The injury was reversible when the cold exposure was limited to 2 days.

5. Survival in desiccated animals (14% water loss) was reduced.

6. It is suggested that the mortality of summer acclimated springtails is caused by a complex metabolic disorder and membrane changes at low temperatures.
Using elasticity analysis of demographic models to link toxicant effects on individuals to the population level: an example
Authors: HANSEN F. , FORBES V. E. , FORBES T. L.
Published: March 2003

1. A simple two‐stage population model was applied to data from a previously published life‐table response experiment (LTRE), which examined the toxicity of 4‐n‐nonylphenol to life‐history traits of the polychaete Capitella sp. I. Population growth rates (λ) and the relative sensitivities (= elasticities) of λ to changes in each of the individual life‐history traits were calculated.

2. In the present study, the life‐history parameters measured in laboratory‐reared individuals were manipulated to simulate potential effects of competition and predation on fecundity, time to reproductive maturity and juvenile survival to explore how such factors might influence the sensitivity of population growth rate to toxicant‐caused changes in individual life‐history traits.

3. Dramatic changes in elasticity patterns among simulations indicate that population growth rates may respond very differently to toxicant exposure depending on the extent to which other demographically limiting factors (e.g. competitors and/or predators) are operating on the population.

4. Effectively predicting the population‐level consequences arising from toxicant effects measured on individuals can be improved by exploring the elasticity pattern of λ for the population over a range of realistic ecological situations.
Differential fractionation of δ13C and δ15N among fish tissues: implications for the study of trophic interactions
Authors: PINNEGAR J. K. , POLUNIN N. V. C.
Published: March 2003

1. Stable isotopes of nitrogen and carbon are widely used in the evaluation and understanding of trophic interactions, and especially so in aquatic food‐webs. However, differences among tissues which occur in consumers such as fish may confound resolution of these ecological relationships, and greatly affect dietary compositions calculated through mass‐balance equations.

2.δ13C and δ15N were determined for homogenized whole fry (≈ 2·7 g) and particular tissues (white muscle, red muscle, liver and heart) of juveniles (≈ 20·6 g) of Rainbow Trout Oncorhynchus mykiss.

3. Differences in δ13C and δ15N were observed among tissues; removal of lipid resulted in these tissues becoming statistically indistinguishable but more variable in δ13C, particularly in tissues with higher lipid content. Differences in δ15N among tissues may be related to the relative composition of ‘essential’ and ‘non‐essential’ amino acids.

5. Acidification, which is used to reduce variability caused by the presence of inorganic carbonate, had a significant effect on δ15N, while having a non‐significant effect on the δ13C. This was the case for whole ground fish‐fry, which contained 22·6% inorganic carbonates in the form of bones and scales, and for individual fish tissues which contained only very small amounts of inorganic carbonate.

6. White muscle was found to be less variable in δ13C and δ15N than all other tissues, and is probably the best tissue for use in ecological work. Red muscle, which is often closely associated with white muscle, is more variable in δ13C and may constitute a source of significant error in source material identification and dietary overlap.
Life‐history variation in closely related generalist predators living in the same habitat: a case study with three Cyclosa spiders
Authors: Miyashita T.
Published: March 2003

1. Generalist predators sharing similar food resources and phenologies as well as having no competitive interactions are expected to have a similar life‐history pattern, but some closely related web spiders show different life‐history traits. The present paper clarifies possible selection pressures affecting life‐history traits of the three coexisting Cyclosa spiders and explores the significance of the life‐history variation.

2.
Cyclosa argenteoalba had lower daily survival rate and higher growth rate, C. sedeculata had higher daily survival rate and lower growth rate, and C. octotuberculata showed intermediate levels. This implies that the selection pressures these spiders experience differ appreciably even in the same habitat.

3. The significance of the life‐history characteristics of the three species was evaluated by general life‐history theories. Cyclosa argenteoalba showed distinguishing reproductive traits: shorter time to maturation, larger reproductive effort, larger relative clutch size, decreased clutch size with the number of clutches, and smaller egg size. These characteristics may have evolved in response to the larger ratio of juvenile to adult survivorship. Cyclosa octotuberculata had a clutch size much larger than the other two species, but relative clutch sizes accounting for body size were similar between C. octotuberculata and C. sedeculata. Also, the two species showed a similar time to maturation despite having different selection pressures. Probably, higher growth rate compensates for lower survivorship, leading to the similarity in some reproductive traits.
Decomposition and nutrient dynamics of Quercus pubescens leaf litter in a naturally enriched CO2 Mediterranean ecosystem
Authors: Cotrufo M. F. , Raschi A. , Lanini M. , Ineson P.
Published: March 2003

1. The chemical composition (i.e. N, P, C, lignin and polyphenol concentrations) of Quercus pubescens leaf litter derived from a natural CO2 spring in Tuscany (Italy) was analysed and compared to litter from a nearby reference site. Litter was incubated for 25 months at both the natural CO2 spring and the reference site, and monitored for decomposition rates, nutrient and lignin concentrations.

2. Long‐term exposure to elevated CO2 concentrations from the natural spring was associated with a change in the chemical composition of the Oak leaf litter, with decreases in P and polyphenol concentrations and increases in lignin. No differences in N concentrations were observed between the enriched CO2 litter from the natural spring and the reference litter.

3. Decomposition was reduced in the CO2 spring, with the lower P concentration of the native litter, combined with the lack of soil fauna observed at that site, being the factors most probably responsible for the measured decreases in mass loss. However, litter from the CO2 spring and reference litter decomposed at the reference site showed similar rates of decomposition.

4. All litter showed similar N concentrations during decomposition, with N being mineralized throughout the incubation period from both litter regardless of the site of incubation. In contrast, P dynamics differed between litter, with P being immobilized in the litter derived from the spring, and mineralized from the reference litter. When the litter from the spring was incubated at the reference site, there was a trend for net P uptake from the surrounding environment. The chemical composition of decomposing litter from the spring appeared to match that of the reference litter after 3 months of incubation at the reference site.

5. The results from the CO2 spring suggest that litter decomposition may be retarded under elevated levels of atmospheric CO2. However, results from field surveys around CO2 vents should be viewed with caution because differences may relate to factors other than the known differences in CO2 concentrations.
Metabolic costs of growth in free‐living Garter Snakes and the energy budgets of ectotherms
Authors: Peterson C. C. , Walton B. M. , Bennett A. F.
Published: March 2003

1. The metabolic or respiratory cost of growth (RG) is the increase in metabolic rate of a growing animal, and it represents chemical potential energy expended in support of net biosynthesis but not deposited as new tissue.

2. Two statistical methods (multiple non‐linear regression and analysis of regression residuals) were used to calculate RG from data (n = 68) from a doubly labelled water study of free‐ranging Garter Snakes (Thamnophis sirtalis fitchi) in northern California.

3. The sample‐wise (‘ecological’) cost of growth was 2·07 kJ per gram of net growth (equivalent to 8·63 kJ g–1 dry tissue); reanalysis of a subset of efficient growers yielded a more conservative ‘physiological’ estimate of 1·67 kJ g–1.

4. Our empirical estimate of RG, among the first reported for squamate reptiles and free‐living animals of any kind, compares closely with published, laboratory‐derived values for ectotherms.

5. The metabolic costs of growth accounted for an average of 30% of total field metabolic rates for these snakes, which were growing at a mean rate of 3% of body mass per day. However, our method probably underestimated the total ecological cost of growth for large animals, because potential growth costs that covary with body size were not included.

6. Distinction between conceptual and empirical energy budgets clarifies relationships among body size, metabolic rates, and the physiological and ecological costs of growth.
Growth hormone‐induced effects on mortality, energy status and growth: a field study on Brown Trout (Salmo trutta)
Authors: Johnsson J. I. , Petersson E. , Jönsson E. , Järvi T. , Björnsson B. TH.
Published: March 2003

1.Growth hormone (GH) treatment increases the growth rate and competitive ability of salmonids under laboratory conditions. Since fast growth should increase fitness, why is endogenous secretion of GH not higher in wild fish? To address this question, three hypotheses were suggested. H1: high GH levels reduce antipredator responses and may therefore increase mortality from predation. H2: high GH levels reduce long‐term (e.g. over winter) survival by reducing allocation to critical energy reserves. H3: GH is not beneficial for growth under natural conditions.

2.To test these hypotheses, the performance of GH‐treated juvenile Brown Trout (Salmo trutta) and control (placebo) trout was compared in an enclosed stream section subjected to natural predation. Four experiments were conducted during winter, spring, summer and autumn, respectively.

3.Mortality rates were not significantly different between GH‐treated and control trout in any of the four experiments so H1was not supported. Energy reserves were generally lower in GH‐treated fish, which is consistent with H2, whereas growth rates in mass were higher in GH‐treated fish than in controls so H3was not supported. This suggests that GH promotes growth at the expense of investment in maintenance.

4.Judging from growth and mortality rates, the fitness of GH‐treated and control trout appeared similar. Thus, escaped GH‐manipulated fish may compete successfully with wild fish.

5.Hatchery‐raised trout with higher initial condition index suffered higher mortality rates than more slender fish. This novel finding may be explained by reduced escape ability related to body morphology, reduced behavioural responses towards predators by high‐condition trout, or predator preferences for high‐condition fish.
Proportional dry‐mass content as an underlying trait for the variation in relative growth rate among 22 Eurasian populations of Dactylis glomerata s.l.
Authors: Ryser P. , Aeschlimann U.
Published: March 2003

1. Relative growth rate (RGR), proportional dry‐mass content of leaf and stem tissues, and biomass‐allocation pattern were assessed under controlled conditions for 22 populations of Dactylis glomerata s.l. from contrasting latitudes and altitudes in Europe, Israel and Kazakstan. Furthermore, width and thickness of leaves were measured in garden‐grown mature plants.

2. All these parameters varied significantly among the populations. RGR correlated negatively with dry‐mass content of leaves and stems, but not with biomass‐allocation parameters, leaf thickness or leaf width. We argue that the close association of RGR with variation in dry‐mass content among species and genetically distinct populations is a result of the larger volume of tissue, and correspondingly larger leaf area and longer root system, that a plant with a low tissue density can build per unit dry mass.

3. Leaf tissue dry‐mass content decreased and RGR increased with increasing latitude and elevation of the originating site, indicating that a high growth rate may be an advantage in habitats with a short growing season. This contrasts with earlier findings of a negative correlation between inherent RGR and altitude.
Thermoregulatory abilities of Alaskan bees: effects of size, phylogeny and ecology
Authors: Bishop J. A. , Armbruster W. S.
Published: March 2003

1. The thermoregulatory capabilities of 18 species of Alaskan bees spanning nearly two orders of magnitude of body mass were measured. Thoracic temperature, measured across the temperature range at which each species forages, was regressed against operative (environmental) temperature to determine bees’ abilities to maintain relatively constant thoracic temperatures across a range of operative temperatures (thermoregulatory performance).

2. Previous studies on insect thermoregulation have compared thoracic temperature with ambient air temperature. Operative temperature, which integrates air temperature, solar radiation and effects of wind, was estimated by measuring the temperature of a fresh, dead bee in the field environment. It is suggested that this is a more accurate measure of the thermal environment experienced by the insect and also allows direct comparisons of insects under different microclimate conditions, such as in sun and shade.

3. Simple regression analysis of species and family means, and analysis of phylogenetically based independent contrasts showed thermoregulatory capability, ability to elevate thoracic temperature, and minimum thoracic temperature necessary for initiating flight all increased with body size.

4. Bumble‐bees were better thermoregulators than solitary bees primarily as a consequence of their larger body size. However, their thermoregulatory abilities were slightly, but significantly, better than predicted from body size alone, suggesting an added role of pelage and/or physiology. Large solitary bees were better thermoregulators than small solitary bees apparently as a result of body‐size differences, with small bees acting as thermal conformers.
Dynamics of food availability, body condition and physiological stress response in breeding Black‐legged Kittiwakes
Authors: Kitaysky A. S. , Wingfield J. C. , Piatt J. F.
Published: March 2003

1. The seasonal dynamics of body condition (BC), circulating corticosterone levels (baseline, BL) and the adrenocortical response to acute stress (SR) were examined in long‐lived Black‐legged Kittiwakes, Rissa tridactyla, breeding at Duck (food‐poor colony) and Gull (food‐rich colony) Islands in lower Cook Inlet, Alaska. It was tested whether the dynamics of corticosterone levels reflect a seasonal change in bird physiological condition due to reproduction and/or variation in foraging conditions.

2. BC declined seasonally, and the decline was more pronounced in birds at the food‐poor colony. BL and SR levels of corticosterone rose steadily through the reproductive season, and BL levels were significantly higher in birds on Duck Island compared with those on Gull Island. During the egg‐laying and chick‐rearing stages, birds had lower SR on Duck Island than on Gull Island.

3. The results suggest that, in addition to a seasonal change in bird physiology during reproduction, local ecological factors such as food availability affect circulating levels of corticosterone and adrenal response to acute stress.
A theoretical approach to linking the composition and morphology with the function of leaves
Authors: Roderick M. L. , Berry S. L. , Noble I. R. , Farquhar G. D.
Published: March 2003

1. In this paper we develop a theoretical framework for describing the composition and morphology of leaves on a volumetric basis which is inclusive of both the liquids and internal air space. That framework is then used to link the composition and morphology with the function of leaves.

2. Leaves are segmented into a functional scheme named a–u–s–V (air space–solution–structure–Volume basis) and a measurement scheme named a–q–d–M (air space–liquid–dry matter–Mass basis). Measurements of mass, liquid mass, volume and fractional air space are necessary to (partially) link the two schemes.

3. The liquid content of leaves can be used to infer the mode of mechanical support and, hence, the likely values of air space, solution and structure. For example, if a leaf has a high liquid content, then it cannot have a large volumetric fraction of structure (which is largely made of dry matter) and is unlikely to have large internal air spaces.

4. Based on measurements of individual leaf components, the specific gravity of the non‐gaseous fraction in leaves would usually be in the range 1–1·3. Consequently, the specific gravity of leaves would be most sensitive to variation in fractional air space.

5. For the dimensions typical of most leaves, the surface area to volume ratio of a leaf is determined by leaf thickness (or diameter).

6. Leaf design is considered in terms of light interception and gas exchange. The requirements for each are essentially incompatible and lead to a trade‐off on leaf thickness. However, that relationship is complicated because variation in fractional air space can potentially lead to broad optima for gas exchange at any given leaf thickness.

7. The theoretical predictions have not been assessed owing to a lack of measurements of leaf density, fractional air space and liquid content. However, published data were used to develop the following hypotheses: (1) the mass of nitrogen per unit mass of liquid is relatively constant within leaves; (2) the surface area to volume ratio of leaves is proportional to leaf liquid content. These hypotheses are tested in a subsequent paper.
Evidence for micropatch partitioning and effects of boundaries on patch use in two species of gerbils
Authors: Fierer N. , Kotler B. P.
Published: March 2003

1. Spatial heterogeneity in resource abundance creates opportunities to exploit patchiness at different scales. The ability to subdivide patches into smaller micropatches is termed micropatch partitioning. At various scales, patches can be recognized by distinct boundaries or by vague boundaries delineated by changes in resource abundances. The ability to micropatch partition was tested for and the effect on foraging of vague vs distinct boundaries was assessed for two species of coexisting desert rodents, the gerbils Gerbillus allenbyi and G. pyramidum. To do so, the distribution of seeds in experimental resource patches in a large enclosure were manipulated.

2. Both G. allenbyi and G. pyramidum are imperfect micropatch assessors. When seeds were concentrated into micropatches, there were lower patch‐wide giving‐up densities (GUDs) than if seeds were randomly distributed throughout the patch. Both species could micropatch partition at scales of 0·14 m2.

3. GUDs in experimental micropatches were greater than expected for perfect assessors.

4. With G. allenbyi, a micropatch with fewer vague boundaries was foraged to a lower GUD. In contrast, GUDs for G. pyramidum were similar regardless of the types of patch boundaries.

5.  Gerbillus allenbyi showed greater error in the assessment of micropatch size.

6. These results have implications for diet selection and coexistence. These species coexist via temporal partitioning, with G. pyramidum biasing its activity to early in the night when resource patches are richer and G. allenbyi biasing its activity to later in the night. Gerbillus pyramidum encounters a richer and more variable environment where errors in patch assessment are costlier, and micropatch partitioning is more valuable. Gerbillus allenbyi encounters a poorer environment where resources vary at larger spatial scales.