bluuebunny/crossref_metadata_2025_split huggingface dataset:
Maternal basking opportunity affects juvenile phenotype in a viviparous lizard
Authors: Wapstra E. 
Published: March 2003

Abstract1. The effects of external conditions on embryonic development have been repeatedly examined in oviparous reptile species, but the effect of gestation conditions on offspring traits in viviparous species has rarely been examined.2. The influence of maternal basking opportunities on gestation length and juvenile phenotype was investigated in a viviparous scincid lizard,Niveoscincus ocellatus. Females were housed under one of two experimental regimes (10 or 4 h access to basking) which reflected the natural variation in temperature, potentially one of the most important proximate sources of life‐history variation.3. Females with longer access to basking gave birth significantly earlier than those with reduced basking opportunities. Maternal access to basking significantly affected the phenotype and growth rate of her offspring.4. Offspring born after relatively rapid development were longer, heavier and in better condition than offspring born after slower development.5. In standard laboratory conditions, offspring born after rapid development grew more rapidly than those born after slower development, thus amplifying the difference in body size between these two groups postpartum.6. These results suggest the existence of a strong selective pressure on female basking behaviour through the effect of the maternal environment on embryo development and offspring phenotype and highlight the role of temperature as a proximate source of variation in both the timing of reproductive events and in key life‐history traits of neonates.
The use of anhydrobiosis by soil nematodes in the Antarctic Dry Valleys
Authors: Treonis A. M. , Wall D. H. , Virginia R. A. 
Published: March 2003

Abstract1. Anhydrobiosis is a survival strategy used by soil nematodes that confers protection from environmental stress and is induced by desiccation.2. To study the use of anhydrobiosis by soil nematodes from the Antarctic Dry Valleys, soil was collected from field sites, and nematodes were extracted using an anhydrobiotic extraction technique. Nematodes were found in a coiled form that characterizes the anhydrobiotic state.3. The proportion of nematodes coiled ranged from 30 to 80% and appeared to reach a maximum in soils drier than 2% gravimetric soil moisture content.4. Wetting of dry soils to 12% gravimetric soil moisture content resulted in rapid uncoiling of nearly 100% of nematodes within 6 h.5. In this cold desert ecosystem, long periods of inactivity appear to be an important aspect of soil nematode life history as their activity may be restricted to the period following infrequent snowfall and melt.
Effects of growing conditions and source habitat on plant traits and functional group definition
Authors: A. R. Dyer , D. E. Goldberg , R. Turkington , C. Sayre 
Published: March 2003

Summary

Plant functional groups are used to describe patterns of community organization. However, they are defined either by suites of correlated traits or by species groupings, and the responses of these two definitions to changing environmental conditions are unknown.
We assessed 14 growth and morphological traits under low‐ and high‐resource conditions of 42 annual plant species from two source communities in Israel that differed in resource availability. As current theory predicts, plants growing in the high‐resource treatment were larger, had twofold greater relative growth rate (RGR) and thinner leaves, and allocated less biomass to roots than plants grown in the low‐resource treatment. Differences in these traits were less consistent between the two source communities. Instead, taxonomic groups (grasses, legumes and a group of other forbs), regardless of source, differed in most characteristics.
Three general groups of species (functional groups) were identified in both resource treatments using cluster analysis on all 14 traits. In both resource treatments monocots were almost completely separated into one distinct cluster, regardless of source habitat, while the two other, mainly dicot, clusters were partially separated by habitat. However, the species composition and trait characterization of the dicot clusters differed strongly between treatments. Under low‐resource conditions the two dicot clusters were separated by size traits and seed mass, but under high‐resource conditions, they were separated by above‐ground size, morphology and RGR.
Principal components analysis demonstrated inconsistency in relationships among traits and species groupings between treatments. The first two principal components emphasized different aspects of growth depending on the treatment; the third axis was defined by growth rates. As with the cluster analysis, plots of species scores revealed relatively little separation of species by habitat.
The response of each species varies for different traits and with growing conditions. Variation may differ among species within a functional group, producing different definitions of functional groups under different experimental conditions. Because most functional group analyses are performed on data collected without manipulation of growing conditions, conclusions concerning the response of species or communities to changes in environmental conditions may be problematic.
Plasticity in reproductive effort of male dung flies (Scatophaga stercoraria) as a response to larval density
Authors: Stockley P. , Seal N. J. 
Published: March 2003

Summary

Explaining variation in reproductive effort is fundamental to understanding diversity in male mating and life‐history strategies, although relatively little is known about environmental influences on such variation and associated trade‐offs.
Plasticity in reproductive effort was examined in male Yellow Dung Flies (Scatophaga stercoraria) reared under two larval density treatments. Relative testis size, thorax size and mate‐searching effort were compared, and relationships between these traits examined to look for correlational evidence of predicted trade‐offs in gonadal and mate‐searching expenditure.
Males reared under high larval density conditions developed relatively larger testes than those reared at low density but no evidence was found for a corresponding reduction in mean mate‐searching effort at the population level.
A negative relationship was found between testis size and mate‐searching activity among males within the high larval rearing density treatment but not among those reared at low density.
Willingness to engage in struggles for possession of females increased in relation to body size among males reared at high larval density, and the opposite relationship was found among those reared at low density.
Plasticity in male reproductive effort in relation to environmental conditions may be more widespread among insects than has previously been appreciated.
Light‐dependent changes in biomass allocation and their importance for growth of rain forest tree species
Authors: L. Poorter 
Published: March 2003

Summary

Sapling growth of six rain forest tree species was compared to evaluate whether species respond in a similar way to a natural light gradient. Saplings were measured non‐destructively; production and loss of leaves, stem and branches were analysed in detail.
Sapling height growth was positively related to light environment and leaf area. No single descriptor of light environment explained sapling growth best. Direct or diffuse light could explain plant growth, depending on species.
Seventeen percent of the saplings had negative relative biomass growth rates, although they occurred in fairly bright conditions. Negative growth rates were caused by leaf shedding and stem breakage. Sapling relative growth rate increased with irradiance, mainly because of an increase in net assimilation rate.
On a shoot basis, shaded plants had a smaller leaf mass fraction (LMF) and a larger specific leaf area, resulting in similar leaf area ratios (LAR) to those of sun plants. This contrasts with the results of seedling studies under controlled conditions, where LMF and LAR increased with shade.
Biomass partitioning to leaf growth decreased with irradiance and relative growth rate of the sapling. This leaf partitioning ratio was better correlated with RGR than with irradiance.
Species differed in the effect of light‐dependent changes in specific leaf area (SLA) on growth. This underscores the importance of SLA in explaining differences in species performance in a forest environment. Nevertheless, the effect of SLA was not related to the shade tolerance of the species.
Origins of interspecific variation in lizard sprint capacity
Authors: Van Damme R. , Vanhooydonck B. 
Published: March 2003

Abstract1. Data were compiled on maximal sprint speed, body mass and temperature in squamate lizards from the literature and from our own data on lacertid lizards.2. Both traditional (i.e. non‐phylogenetic) and phylogenetic statistical analyses showed that sprint speed is positively correlated with body mass (‘bigger is better’) and temperature (‘hotter is better’).3. Additionally, we tested whether sprint speed correlates with behavioural and ecological characteristics, i.e. foraging mode (sit‐and‐wait or active), activity (diurnal or nocturnal), microhabitat use (saxicolous, arboreal or terrestrial) and climate (Mediterranean, xeric, cool or temperate). Lizards from Mediterranean and xeric climates, diurnal lizards, sit‐ and wait predators and terrestrial species are expected to run the fastest. Traditional tests suggest that lizards from Mediterranean and desert areas are faster than lizards from cool and tropical regions; that diurnal species are faster than nocturnal species; and that saxicolous animals have higher sprint capacities than do arboreal and terrestrial species. No difference was found between sit‐and‐wait predators and actively foraging animals.4. However, the effects of climate, activity period and microhabitat use were no longer significant when the data were analysed in a proper phylogenetic context. This seems to suggest that differences in sprint speed reflect phylogeny, rather than ecology. The discrepancy between the results of phylogenetic and traditional analyses forms a strong case for the use of phylogenetic information in comparative studies.
Foraging effort, food intake and lactation performance depend on maternal mass in a small phocid seal
Authors: Bowen W. D. , Iverson S. J. , Boness D. J. , Oftedal O. T. 
Published: March 2003

Summary

Female mammals increase energy expenditure during lactation to support the high cost of milk production. The extent to which lactation in a small phocid species, the Harbour Seal Phoca vitulina L., was fuelled by food vs body stores, how this allocation varied with maternal body mass and the consequences of maternal expenditure on offspring growth were studied.
The proportional body composition of 30 females was independent of initial postpartum body mass, but larger females had absolutely more stored energy than smaller ones.
Females lost 32% of postpartum body mass and 62% of body energy by late lactation; 97% of energy loss was derived from body fat. Percentage loss of body energy was independent of initial body mass, indicating that females limit their allocation of body stores to offspring by expending a constant proportion of stores rather than a constant amount.
Females spent more time diving and individual dives were deeper and longer as lactation progressed. By late lactation, these characteristics of diving were inversely proportional with initial postpartum mass.
During early lactation, female expenditures were covered mainly by a reduction in body energy stores. By late lactation, food intake increased six‐fold but the extent of this increase varied inversely with postpartum mass.
Pup growth rate and weaning mass were positively related to postpartum mass and total daily energy expenditure of females, but were independent of the source of energy used by females during lactation. Pups of heavy females had higher survival than pups of light females.
Our results support the hypothesis that maternal body mass is an important determinant of lactation strategies in pinnipeds.
Adaptive self superparasitism in a solitary parasitoid wasp: the influence of clutch size on offspring size
Authors: Mackauer M. , Chau A. 
Published: March 2003

Summary

In solitary parasitoid Hymenoptera, normally only one offspring per host survives. Parasitism with more than one egg by the same female results in siblicide and hence is generally maladaptive.
The braconid wasp Monoctonus paulensis Ashmead is a solitary parasitoid of aphids, including the Pea Aphid. Although all but one offspring are eliminated by competition between first‐instar larvae, females often produce a multiple‐egg clutch, even when searching alone. The hypothesis that the size and, presumably, the fitness of the surviving offspring in a clutch are greater than that of singly developing counterparts was tested in the laboratory. Adult size was measured as dry mass in parasitoids developing in Pea Aphids that differed in size (instar) and growth potential.
Parasitoid size increased with host size, and females were larger than males. Parasitoids developing in aphids reared under crowded conditions (which had low growth potential) were smaller relative to initial host size. As predicted, the male offspring of virgin mothers developing in a clutch were 4–5% larger than counterparts developing alone. Clutch size had no consistent effect on the size of male or female offspring of mated mothers, however.
A female of M. paulensis laying a multiple‐egg clutch can gain in fitness in terms of increased offspring size. The surviving offspring has access to greater nutritional resources because superparasitized aphids feed more than single‐parasitized aphids; the former also contain proportionately more teratocytes, which are egg‐derived cells aiding in parasitoid nutrition.
Evidence that some species of solitary parasitoids do better when developing in a clutch suggests that the solitary lifestyle may not be an evolutionary absorbing state.
Hormonal modification of resource sharing in the clonal plant Fragaria chiloensis
Authors: Alpert P. , Holzapfel C. , Benson J. M. 
Published: March 2003

Summary

Clonal plants can share resources such as carbon and nitrogen among connected, separately rooted plant units or ramets. In many cases, resource sharing tends to equalize the performance of ramets, suggesting that differences in resource supply drive the sharing process, with resources moving from ramets with high access to resources to those with low access to resources. However, some patterns of apparent C and N sharing in the stoloniferous wild strawberry Fragaria chiloensis make the growth of ramets less equal, which is inconsistent with this model of resource sharing. As hormones are a mechanism by which non‐clonal plants can make the growth of the branches of a shoot less equal, we hypothesized that clonal plants might use hormones to modify patterns of resource sharing between ramets.
Auxin (IAA) or cytokinin (BA) was applied to the shoot tip of ramets using a non‐invasive protocol previously shown to increase internal hormone concentrations. 14C or 15N was then fed to connected ramets, and the amounts of 14C or 15N imported by the hormone‐treated ramets and by suitable controls were measured.
Ramets treated with IAA showed greater C import from connected ramets than did control ramets when the IAA‐treated and control ramets were shaded and the connected ramets were not. Ramets treated with IAA showed increased N import from connected ramets compared with the controls when the IAA‐treated and control ramets were given less N than the connected ramets, and were also younger than the connected ramets. IAA had no consistent effect on C or N sharing between ramets given the same resource treatments as one another and did not affect the direction of N sharing, which is strongly acropetal in F. chiloensis. BA showed little effect on resource sharing.
The results supported the hypothesis that hormones can modify patterns of resource sharing between ramets in clonal plants. In F. chiloensis, auxin can enhance resource import by ramets in relatively resource‐poor microsites. Clonal plants may use hormones as a mechanism for physiological integration of connected ramets.
Nutrient allocation of Macaranga triloba ant plants to growth, photosynthesis and indirect defence
Authors: Heil M. , Hilpert A. , Fiala B. , Bin Hashim R. , Strohm E. , Zotz G. , Linsenmair K. E. 
Published: March 2003

Summary 1. Allocation patterns are an important aspect of plant life strategies. In particular, many hypotheses on plant antiherbivore defence – such as the growth differentiation balance hypothesis and the resource availability hypothesis – concern constraints on resource allocation to defence, and assume defence to be limited by nutrient supply under most, yet not all, conditions. 2. Field‐grown Macaranga triloba saplings were fertilized, and temporal and spatial patterns in the response of growth, photosynthesis and investment in biotic defence against herbivores and pathogens were measured simultaneously. Macaranga triloba produces food bodies to nourish mutualistic ants which protect their hosts against herbivores and pathogens. Food body production rate is quantitatively related to ant colony structure, and the latter is correlated with defensive efficacy. Food body production can therefore serve as a measure of the plant's investment in defence. 3. Food body production responded quickly, and on all food body‐producing stipules, to increased nutrient supply. In contrast, photosynthetic capacity responded much more slowly, to a smaller degree, and only in leaves that emerged after the onset of fertilization. No significant effects on plant growth were seen. 4. Our results show that food body production by M. triloba is regulated directly by nutrient availability. There was no evidence that increased nutrient supply was preferably allocated to growth and/or photosynthesis, which forms a central assumption of most hypotheses on plant antiherbivore defence. 5. Phenotypic plasticity and the ability to make use of short pulses in nutrient supply are of particular importance in pioneer plants inhabiting rapidly changing habitats. New theoretical frameworks are required for the inclusion of phenotypically plastic defence traits in the theory of plant antiherbivore defence.
Linkages between plant litter decomposition, litter quality, and vegetation responses to herbivores
Authors: Wardle D. A. , Bonner K. I. , Barker G. M. 
Published: March 2003

Summary

There is increasing awareness that similar suites of plant traits may govern foliage palatability and litter decomposability, but whether there is an association between the response of vegetation to herbivory and litter decomposition rates across plant species remains unexplored.
We collected 141 samples of litter from 59 understorey and 18 canopy tree species from a total of 28 sites under natural forest throughout New Zealand. We assessed whether variables related to decomposition and quality of litter of the understorey species showed a statistical relationship with the response of vegetation density (assessed using a pole‐intercept method) of the same species at the same locations to browsing by deer and goats. Decomposition and nutrient‐loss data from litter were obtained using standardized laboratory bioassays.
There was a significant positive correlation between litter decomposition rate and the extent to which vegetation density was reduced by browsing mammals (r = 0·488, P < 0·001). Further, decomposition rate and vegetation response to herbivory were both correlated with several of the same litter quality variables.
The proportion of total initial phosphorus and nitrogen released from litter during decomposition was correlated with litter decomposition rate, but not with vegetation density response to browsing. This suggests that effects of browsers on vegetation composition are more likely to influence ecosystem carbon flow than nitrogen or phosphorus flow.
Litter‐mixing experiments showed that good quality litters produced by plant species reduced by browsers tended to promote the decomposition of other litters. Meanwhile, poor quality litters from species promoted by browsers tended to decompose more rapidly when mixed with other litter types than when by themselves. However, these effects were weak and likely to be less important than the more direct effects of browsing mammals on vegetation composition.
The relationships between litter decomposition and effect of herbivory on vegetation density were driven primarily by differences among the main plant functional groups, which showed the same decreasing rank order for both variables: large‐leaved dicots, small‐leaved dicots, Nothofagus, ferns, and monocots.
The implications of these results for understanding how herbivores affect the decomposer subsystem are considered. Because the results of this work are only partially consistent with those of an earlier study on how browsers affect decomposer organisms and processes, conducted at the same 28 field sites, other mechanisms through which browser effects are manifested below‐ground must often override that investigated in this study.
Temporospatial constraints in resources available to and used by hermit crabs: tests of models
Authors: Barnes D. K. A. , De Grave S. 
Published: March 2003

Summary

Resources vary critically in space and time so the ability of animals to utilize them necessarily does so in sympathy. For hermit crabs in coastal SW Madagascar, a critical resource is a suitable shell to habit, as is typical of the group. Quantification of resource status should therefore be as straightforward as counting shells on a beach. Only certain shells are exploitable, however, based on their condition, occupier status and attributes (such as size).
The total, total exploitable and empty shell densities (size classed) per unit area were measured from the shallow subtidal to landward range (100 m inland) of hermit crabs. The population density of resource exploiters (hermit crabs) was also measured (grouped by size classes) over a similar area, enabling calculation of the total number of exploitable shells per individual (based on appropriate match of resource and resource user) and the nested subset of empty exploitable shells per individual.
Resource bottlenecks and surpluses occurred at different (resource exploiter) life stages and at different positions on the shore. The proportion of available shell types used by hermit crabs was found to increase down shore despite the number of shell types availability showing the converse pattern.
4.  Multiple regression models of shell use by hermit crabs were constructed that showed species and genus level trends. Five or more variables were almost equally significant in each of the models. Overall hermit crab size, site, habitat and local shell diversity were most important in determining the number of shell types used.
The proportion of interspecific vs intraspecific competition at each shore level was estimated using observed species‐specific shell use patterns and population size class sizes. Observed competition followed the predicted sigmoidal pattern across the littoral zone but that of intensity of competition was different and bimodal.
Ordination (detrended correspondence analysis) showed that resource exploiter (species) specific shell suites heavily overlap in multidimensional niche space as is near universally described in the literature. When shell suites are ordinated by size class, however, species niches separate, even across sites, except at sizes where resources are not restricted. Niches are distinct but cryptic.