bluuebunny/crossref_metadata_2025 huggingface dataset:
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.
Growth dynamics and mortality of the encrusting sponge Crambe crambe (Poecilosclerida) in contrasting habitats: correlation with population structure and investment in defence
Authors: Turon X. , Tarjuelo I. , Uriz M. J.
Published: March 2003

1. A trade‐off was predicted between investment in defence and growth rate in the encrusting sponge Crambe crambe (Schmidt), while survival rates were expected to correlate positively with the production of defences. Previous studies have demonstrated that this sponge is better defended (chemically and physically) in shaded animal‐dominated habitats than in well‐illuminated habitats, dominated by algae. It was determined whether these habitat‐associated differences in investment correlate with differences in growth, regeneration and mortality rates of small specimens (initial average area less than 100 mm2) of this sponge.

2. In the 2 years of the study the sponge grew slowly (size increased 2·5 times on average), and showed high interindividual variation in growth rates. A seasonal pattern was evident, with marked size increases from May to October. Significantly higher growth rates (on a monthly basis) were found in the well‐illuminated habitat during the second year of study. There was also a negative relationship between monthly growth rate and toxicity (measured in previous studies). No differences were found in sponge regeneration rates between communities.

3. Mortality was significantly higher in individuals from the well‐illuminated habitat, and mainly affected the smallest sponges (< 150 mm2).

4. This sponge was significantly more abundant in the shaded habitat, but the mean size of the sponges was greater in the well‐illuminated habitat. The size distributions in the two communities were also significantly different. Sponges of the smallest size classes were more abundant in the shaded community.

5. It is concluded that sponges in the shaded habitat, in which investment in defence was greatest, featured higher survival but grew more slowly than those in the well‐illuminated habitat. Differential mortality and growth observed in the study were sufficient to explain the patterns of abundance and size distributions of the established sponge populations from these two habitats.
Granivore impact on soil‐seed reserves in the central Monte desert, Argentina
Authors: Marone L. , Rossi B. E. , Lopez DE Casenave J.
Published: March 2003

1. Mechanisms of grass‐ and forb‐seed input and output in the central Monte desert of Argentina were studied in 1995 to test the hypothesis that seed consumption by autumn–winter granivores, especially birds, has qualitative as well as quantitative effects on soil‐seed reserves.

2. The abundance of perennial grass seeds in late summer soils (≈ 2400 seeds m–2 or 0·36 g m–2) remained unchanged the following early spring (≈ 2700 seeds m–2 or 0·39 g m–2), despite the incorporation of about 3000 seeds m–2 or 0·71 g m–2 newly produced grass seeds during autumn–winter. Grass seeds appeared to be heavily consumed, especially the medium‐sized ones.

3. The annual forb‐seed bank was about the same size in late summer (≈ 5500 seeds m–2 or 1·34 g m–2) as in early spring (≈ 6500 seeds m–2 or 1·53 g m–2). Since forb‐seed production had been relatively low (≈ 400 seeds m–2 or 0·12 g m–2), these seeds apparently suffered negligible postdispersal losses.

4. This pattern of grass‐ and forb‐seed loss coincides with the pattern of seed consumption by granivorous birds – on average, 93% of seed mass in bird stomachs was from grass seeds, while only 7% was from forb seeds.

5. Further evidence of a major impact of bird foraging on seed reserves is that the mass of particular grass seeds that was lost from soils was positively correlated with the mass of such seeds in bird diets, and that the main target of bird consumption, i.e. medium‐sized grass seeds, suffered the highest postdispersal loss.

6. It is concluded that autumn–winter granivores in the central Monte desert, particularly birds, mainly consume newly produced grass seeds and that they might have major qualitative as well as quantitative impacts on soil‐seed reserves.
Variation in energy intake and basal metabolic rate of a bird migrating in a wind tunnel
Authors: LindstrÖM Å. , Klaassen M. , Kvist A.
Published: March 2003

1. We studied the changes in body mass, metabolizable energy intake rate (ME) and basal metabolic rate (BMR) of a Thrush Nightingale, Luscinia luscinia, following repeated 12‐h migratory flights in a wind tunnel. In total the bird flew for 176 h corresponding to 6300 km. This is the first study where the fuelling phase has been investigated in a bird migrating in captivity.

2. ME was very high, supporting earlier findings that migrating birds have among the highest intake rates known among homeotherms. ME was significantly higher the second day of fuelling, indicating a build‐up of the capacity of the digestive tract during the first day of fuelling.

3. Further indications of an increase in size or activity level of metabolically active structures during fuelling come from the short‐term variation in BMR, which increased over the 2‐day fuelling period with more than 20%, and in almost direct proportion to body mass. However, mass‐specific BMR decreased over the season.

4. The patterns of mass change, ME and BMR of our focal bird following two occasions of 12‐h fasts were the same as after flights, indicating that fast and flight may involve similar physiological processes.

5. The relatively low ME the first day following a flight may be a contributing factor to the well‐known pattern that migrating birds during stopover normally lose mass the first day of fuelling.
Sexually dimorphic growth in the dioecious tropical shrub, Siparuna grandiflora
Authors: Nicotra A. B.
Published: March 2003

1. To demonstrate evolved sex‐based differences in vegetative traits of dioecious plant species, one must consider both pre‐reproductive and reproductive individuals, as dimorphic patterns commonly arise secondarily from different effects of reproduction on resource balance.

2.
Siparuna grandiflora, a neotropical dioecious shrub in which females allocate significantly more biomass to reproduction than males, was studied for 2 years (three reproductive events) to determine whether sex‐based differences in stem growth, leaf production and allocation pattern could be detected in pre‐reproductive individuals grown from cuttings in field plots or in mature naturally occurring individuals.

3. Among pre‐reproductive individuals, females accumulated more stem and leaves than males, but among mature individuals, no sex‐based growth differences were apparent. In mature individuals, both growth and leaf longevity were positively correlated with reproductive frequency. With regards allocation, pre‐reproductive males had larger leaves than females, and mature females allocated less biomass per unit stem length than males.

4. The capacity of pre‐reproductive females to grow faster than males demonstrates innate differences between the sexes. That mature females achieved equivalent growth to males, despite higher reproductive allocation, indicates that the greater growth capacity of young females is sustained in older females and enables them to compensate for greater reproductive allocation.
HOBOs, Tidbits and lizard models: the utility of electronic devices in field studies of ectotherm thermoregulation
Authors: Vitt L. J. , Sartorius S. S.
Published: March 2003

1. A replicated experiment tested the null hypothesis that stand‐alone electronic temperature recording devices produce sets of operative temperatures similar to those produced using lizard models.

2. Commercially available electronic temperature recording devices (HOBO XT™ with external probe and Tidbit™) produced sets of operative temperatures nearly identical to models designed to mimic the size, shape, scale architecture and colour of two species of common North American lizards.

3. Tidbits™ performed better than external probes.

4. These results suggest that electronic devices (especially Tidbits™) can be substituted for models in many applications and that size, morphology, scale architecture and colour contribute very little to temperature change in small‐sized life‐like models widely used in field‐based studies on the thermal ecology of vertebrates.

5. Small differences between temperatures recorded by electronic devices and detailed lizard‐shaped models fitted with thermal probes suggest that these models may nevertheless be necessary for certain kinds of studies.
Effects of age and size at metamorphosis on performance and metabolic rates of Southern Toad, Bufo terrestris, metamorphs
Authors: Beck C. W. , Congdon J. D.
Published: March 2003

1. Southern Toad, Bufo terrestris, tadpoles were reared at two temperatures and two food levels in a 2 × 2 factorial design. Effects of treatments on age and size at metamorphosis, metabolic rate (MR), sprint speed and endurance of metamorphs were measured.

2. Across all treatments, MR, sprint speed and endurance were negatively related to age at metamorphosis and positively related to mass at metamorphosis. Therefore, decreases in larval period duration and increases in mass at metamorphosis may be advantageous in terms of locomotor performance, but disadvantageous because of the cost of increased energy expenditure on maintenance, all else being equal.

3. After removing the effects of age and size at metamorphosis, neither of the treatments nor their interaction significantly affected locomotor performance. In contrast, MRs of metamorphs were significantly affected by the interaction between the food and temperature treatments, independent of age and size at metamorphosis. Thus, aspects of the larval environment may affect metamorph physiology, and possibly fitness, via mechanisms other than differences in age and size at metamorphosis.
The metabolic cost of reproduction in an oviparous lizard
Authors: Angilletta M. J. , Sears M. W.
Published: March 2003

1. Studies of reproductive effort in ectotherms have focused primarily on the energetic investment in gamete production; much less is known about the indirect energetic costs of reproduction, such as increased metabolic costs of maintenance or activity.

2. The metabolic cost of reproduction in the oviparous lizard, Sceloporus undulatus, was investigated by measuring the metabolic rate of females prior to and following oviposition.

3. The metabolic rates of gravid females were adjusted for embryonic metabolism by subtracting the metabolic rate of egg clutches, measured immediately after oviposition.

4. The metabolic rate of females when gravid was elevated by 122% compared with that when non‐gravid. The difference was not detected until the metabolic rates of gravid females were adjusted for the metabolic rates of the embryos.

5. The increment in metabolic rate associated with reproduction was not correlated with clutch mass or body mass, indicating that different components of reproductive effort (i.e. metabolism vs gametic investment) may not covary in a predictable fashion.

6. Indirect energetic costs of reproduction constitute a substantial portion of the reproductive effort of female S. undulatus, and should be incorporated into theoretical considerations of life history.
Cross‐species relationships between seedling relative growth rate, nitrogen productivity and root vs leaf function in 28 Australian woody species
Authors: Wright I. J. , Westoby M.
Published: March 2003

1. Seedling relative growth rate (RGR) is often decomposed into the product of specific leaf area (leaf area per leaf mass, SLA), net assimilation rate (rate of mass increase per unit leaf area per unit time, NARa) and leaf mass ratio (ratio of leaf to total dry mass, LMR). Commonly, most cross‐species variation in RGR is accounted for by variation in SLA, while no general relationships occur between RGR and either NARa or LMR. NARa can be factored into the product of leaf nitrogen productivity (rate of mass increase per unit leaf nitrogen per unit time, LNP) and leaf nitrogen concentration (area basis, LNCa). In this way the influence on RGR of leaf nitrogen – how it is displayed, and how it is utilized – can be investigated.

2. Seedlings of 28 Australian woody dicot species were grown under controlled, favourable conditions. Variation in SLA, LNP, LNCa and LMR explained c. 44%, 22%, 19% and 15% of variation in RGR, respectively. SLA and LNP were positively associated with RGR, while LNCa was negatively associated with RGR. LNP and LNCa were negatively correlated, the counteracting trends between RGR and each of these attributes resulting in no relationship between RGR and NARa. It is argued that this phenomenon may be widespread and may contribute to the inconsistency of reported relationships between NARa and RGR.

3. The functional balance between leaves and roots can be described in terms of mass allocation and morphology (static ratios or allometric coefficients) or, alternatively, in terms of leaf ‘activity’ (NAR) and root ‘activity’ (nitrogen uptake rate, NUR). At any given time most species allocated greater mass to leaves than to roots, but species with low RGR tended to be partitioning a greater ongoing proportion of new biomass to the roots rather than to the leaves, resulting in a proportionally greater increase in root surface compared with leaf surface over time. Nitrogen uptake rate was correlated with leaf and whole‐plant nitrogen concentration, but not with other attributes. While it is clear that root and leaf functions must be co‐ordinated (and thus in balance) for growth to occur, there is little evidence that this balance varies systematically with RGR across all species.
Spatial aggregation and temporal migration of free‐living stages of the parasitic nematode Trichostrongylus tenuis
Authors: Saunders L. M. , Tompkins D. M. , Hudson P. J.
Published: March 2003

1. Predicting outbreaks of Trichostrongylus tenuis in Red Grouse from larval counts has been hampered because of the poor recovery of the third‐stage infective larvae from heather vegetation. Two possible explanations for this poor recovery were examined: (i) larvae are spatially aggregated; (ii) larvae exhibit temporal variability in abundance and may be missed by sampling at the wrong time.

2. Heather vegetation was intensively sampled and infective larvae were found to be spatially aggregated. The temporal distribution of T. tenuis also varied, with greater numbers of larvae present on heather sampled in the afternoon than the morning.

3. In a series of laboratory experiments the diurnal availability of T. tenuis larvae were examined on two plant species with differing physical structures: heather and wheat. These trials were tested against infective larvae of Haemonchus contortus, a related nematode known to exhibit diurnal migration patterns. Larvae were exposed to diurnal variations in light and temperature.

4. Infective larvae of both species were recovered in greater numbers during periods when the lights were on. Temperature did not have a significant influence on H. contortus larval availability but greater numbers of T. tenuis L3 were recovered at low temperature (10 °C) than at higher temperature (20 °C).

5. Both temporal variation in the presence of T. tenuis larvae on vegetation and the spatial variation in larval distribution may account for poor recovery of Trichostrongylus tenuis L3 in the field.
The influence of millipedes on selected soil elements: a microcosm study on three species occurring on coastal sand dunes
Authors: A.‐M. Smit , R. J. Van Aarde
Published: March 2003

The effect of mechanical breakdown of detritus by the millipedes Centrobolus fulgidus, Centrobolus richardii and Spinotarsus sp. on selected soil elements was investigated in the laboratory.

 Microcosms containing soils, detritus and millipedes from areas undergoing vegetation regeneration were set up in a climate chamber. Short‐term changes in soil concentrations of ammonia (NH4+), nitrates (NO3−), phosphorus (P), calcium (Ca), potassium (K), magnesium (Mg), nitrogen (N) and carbon (C) in the presence and absence of millipedes were determined.

Soil concentrations of the elements investigated were higher in microcosms subjected to millipede activity than in controls. Microcosms containing Spinotarsus sp. and C. richardii were found to have the highest concentrations of Mg, K, N and C.

 The results further illustrated no major sex‐specific differences for individual species.

 For most elements, rates of change were not affected by millipede biomass. However, the largest effect was in rate of change of Mg and K measured at 5–15 g of millipedes per microcosm.

 Compositional effects (species present) were recorded for rates of change in K concentrations.

 Influence of species richness on rates of change was only recorded for K and N, with rates for both increasing as the number of species increased. The predictability of rate of change diminished for K with an increase in the number of species.

 It is concluded that millipedes influence concentrations of soil elements through species‐specific differential effects. Patterns related to composition and species richness only reflect species‐specific differences. Nevertheless, the rate at which these soil elements increase in the microcosms suggests that millipede activity may accelerate the release of elements in areas undergoing vegetation development on coastal dune forests.
Carbon isotope discrimination by a sequence of Eucalyptus species along a subcontinental rainfall gradient in Australia
Authors: MIller J. M. , Williams R. J. , Farquhar G. D.
Published: March 2003

1. The 13C/12C discrimination (Δ) by a series of co‐occurring and replacement Eucalyptus species was measured across an eightfold decrease in rainfall. As Δ is a measure of the stomatal limitation on photosynthesis, it should provide a subcontinental scale measure of water‐limited plant physiological performance.

2. Leaf Δ of five of 13 species decreased with decreasing rainfall, seven exhibited no trend, and one increased. Wood Δ decreased in eight species, showed no trend in four, and increased in one species.

3. Species replacements were marked by a shift in Δ reflecting greater stomatal limitation on carbon assimilation.

4. Wood Δ was less variable than leaf Δ.

5. There was a non‐linear response of the multispecies average leaf and wood Δ to decreasing total annual rainfall. This response reflected the spatial pattern of the sensitivities of Δ to decreasing rainfall of the individual species. It was not the result of a proposed emergent behaviour where the trend in the multispecies average differed from that of the individual species.

6. Patterns of Δ across the distributions of species (reflecting increasing stomatal limitation on assimilation) did not provide a simple measure of the physiological limits of the distribution of eucalypts in north‐western Australia.
Interspecific carbon exchange and cost of interactions between basidiomycete mycelia in soil and wood
Authors: Wells J. M. , Boddy L.
Published: March 2003

1. The outcome of interactions between wood decay basidiomycete fungi is affected by the size of territory held by a mycelium. We investigated the outcomes of interactions between the cord‐forming saprotrophs Phanerochaete velutina (DC: Pers.) Parm., Phallus impudicus (L.) Pers. and Hypholoma fasciculare (Huds: Fr) Kumner over 152–155 days, determined as ability to capture or share territory in soil and wood, in terms of decay partitioning and the carbon cost of interactions.

2. The outcome of interactions in wood alone differed from those in which the fungi competed for an opponents’ inoculum in soil microcosms. Competitive ability (the ability to capture or co‐occupy an opponent’s inoculum) varied according to species and inoculum age. In wood block pairings in the absence of soil there was evidence that P. velutina opportunistically utilized C previously mobilized within an opponent’s inoculum.

3. In soil systems, short‐term (28‐day) respiratory losses of preloaded 14C (supplied as glucose) indicated that interaction could have a substantial C cost, depending on the resource quality of the opponents’ inocula. Phallus impudicus inocula accumulated 14C from opponents’ mycelia during ‘deadlock’ interactions, although reciprocal interspecific 14C transfer was not observed.

4. Saprotrophic cord‐forming basidiomycetes are considered to be highly conservative of acquired nutrients, representing a significant nutrient reservoir in woodland ecosytems. Here we demonstrate that a potential major pathway for nutrient mineralization by this group is nutrient loss during competitive interactions in soil.
Desert shrub water relations with respect to soil characteristics and plant functional type
Authors: Sperry J. S. , Hacke U. G.
Published: March 2003

1. Soil characteristics influence plant communities in part through water relations. Hypothetically, finer textured soils in arid climates should be associated with more negative plant and soil water potentials during drought, greater resistance of xylem to cavitation, and shallower root systems than coarse soils.

2. These hypotheses were tested by comparing the water relations of Great Basin shrubs growing in sand versus loam soils. The eight study species (Chrysothamnus nauseosus, Chrysothamnus viscidiflorus, Chrysothamnus parryi, Tetradymia glabrata, Atriplex canescens, Atriplex confertifolia, Grayia spinosa and Sarcobatus vermiculatus) varied in typical rooting depth and vegetative phenology.

3. Xylem pressures for a species were, on average, 1·1 MPa more negative in the loam versus the sand site, despite greater precipitation at the loam site. Root xylem at the loam site was, on average, 0·9 MPa more resistant to cavitation than at the sand site for the same species. There was a strong trend for shallower rooting depths at the loam versus the sand site. Within a species, roots were consistently more vulnerable to cavitation than stems, and experienced more cavitation during the growing season.

4. Over most of the summer there was much more cavitation at the loam site than at the sand site. More than 80% loss of xylem conductivity (PLC) was estimated in shallow roots of three species at the loam site by the end of July, with two of the three showing extensive leaf drop and branch mortality. Transpiration rate was negatively correlated with PLC, with a tendency for lower gas‐exchange rates in loam versus sand.

5. At the sand site, cavitation resistance was negatively correlated with estimated rooting depth. Drought‐deciduous species had the shallowest root systems and greatest resistance to cavitation. In contrast, two species with phreatophytic tendencies were summer‐active and were the most vulnerable to cavitation.

6. The cavitation resistance of roots determines the minimum water potential permitting hydraulic contact with soil. Differences in cavitation resistance of roots between desert species may contribute to differences in sensitivity of gas exchange to soil drought, ability to perform hydraulic lift, and response to late summer rain pulses.
Why are species’ body size distributions usually skewed to the right?
Authors: Kozłowski Jan , Gawelczyk Adam. T.
Published: March 2003

1. Species’ body size distributions are right‐skewed, symmetric or left‐skewed, but right‐skewness strongly prevails.

2. Skewness changes with taxonomic level, with a tendency to high right‐skewness in classes and diverse skewness in orders within a class. Where the number of lower taxa allows for analysis, skewness coefficients have normal distributions, with the majority of taxa being right‐skewed.

3. Skewness changes with geographical scale. For a broad range, distributions in a class are usually right‐skewed. For a narrower scale, distributions remain right‐skewed or become symmetric or even close to uniform.

4. The prevailing right‐skewness of species’ body size distributions is explained with macroevolutionary models, the fractal character of the environment, or body size optimization.

5. Macroevolutionary models assume either size‐biased speciation and extinction, or the existence of a constraint on small size. Macroevolutionary mechanisms seem insufficient to explain the pattern of species’ body size distributions, but they may operate together with other mechanisms.

6. Optimization models assume that directional and then stabilizing selection works after speciation events. There are two kinds of optimization approaches to study species’ body size distributions. Under the first approach, it is assumed that a single energetic optimum exists for an entire taxon, and that species are distributed around this optimum. Under the second approach, each species has a separate optimum, and the species’ body size distribution reflects the distribution of optimal values.

7. Because not only energetic properties but also mortality are important in determining optimal sizes, only the second approach, that is, seeking the distribution of optimal values, seems appropriate in the context of life‐history evolution. This approach predicts diverse shapes of body size distributions, with right‐skewness prevailing.
Assembly rules and functional groups at global biogeographical scales
Authors: Bellwood D. R. , Wainwright P. C. , Fulton C. J. , Hoey A.
Published: March 2003

The taxonomic and functional composition of reef fish assemblages are quantified in three biogeographical regions: Great Barrier Reef, French Polynesia and Caribbean. Assemblages are described in three habitats of differing wave exposure. Functional abilities are estimated based on published analyses linking fin morphology and swimming performance.

Two questions were addressed: (1) To what extent are labrid assemblages similar among habitats and regions? (2) To what extent are functional characteristics of fish assemblages shaped by differences in biodiversity, evolutionary history and species composition?

All three regions display highly congruent patterns of habitat use, in terms of assemblage structure and functional characteristics, despite a five‐fold difference in species richness, limited or no species overlap, and a 3·2‐Myear history of isolation. Exposed reef crest assemblages were dominated by fishes with fins reflecting lift‐based high‐speed locomotion. In contrast to abundance‐based patterns, species presence/absence data were uninformative.

The relationship between swimming ability and habitat use reveals underlying assembly rules at a functional level, emphasizing the utility of functional attributes as a metric for comparing system‐level properties in taxonomically distinct faunas.
Nutritional stress changes sex‐specific reproductive allocation in the simultaneously hermaphroditic land snailArianta arbustorum
Authors: Locher R. , Baur B.
Published: March 2003

Sex allocation theory predicts that when resources are limited in simultaneous hermaphrodites, the allocation to one sexual function will automatically reduce the resources available to the other function. This study examines the effect of nutritional stress on mating behaviour and male and female reproductive output (dry mass and nitrogen contents of spermatophores, sperm delivered and eggs deposited) in individuals of the simultaneously hermaphroditic land snailArianta arbustorumkept under three different food regimes: ample (100%), restricted (50%) and extremely restricted (25%) food supply.

Independent of the extent of nutritional stress, 10–12% of the resources taken up were invested in reproductive output (both gender functions together) and 88–90% in maintenance (including faeces and excretion).

Courtship and copulation behaviour was affected by nutritional stress. Snails with an extremely restricted food supply did not mate, except one pair. Individuals with restricted food supply tended to court longer, and copulated for a shorter period, than individuals with ample food supply.

Nutritional stress did not affect the number of sperm delivered. However, snails with a restricted food supply produced fewer eggs. Thus, snails kept under nutritional stress invested relatively more resources in the male function than in the female function. Nevertheless, the absolute reproductive output remained highly female biased (>95% in all experimental groups).

At the individual level, the existence of a trade‐off between resources invested in the malevsthe female function could not be confirmed. However, there was a trade‐off between nitrogen allocated to reproductive function and maintenance in snails with a restricted food supply.