bluuebunny/crossref_metadata_2025_split huggingface dataset:
Why do shore crabs not prefer the most profitable mussels?
Authors: Smallegange Isabel M. , Van Der Meer Jaap 
Published: July 2003

SummaryWe examined the link between handling time (Th), adopted feeding techniques, profitability curves and prey size selection to further understand the constraints that influence bivalve prey selection in shore crabs (Carcinus maenas L.).Blue mussels (Mytilus edulis L.) of different sizes were used as prey. Prey size was generalized to the ratio between mussel width and major chela length (MW : MCL) and prey profitability standardized to the ratio between prey mass eaten per unit breaking time and predator mass (1/h Tb).Crabs either crushed the mussel with their claws or opened the mussel using the more time‐consuming cutter technique. The latter technique was employed above a critical MW : MCL ratio (0·24). This threshold appeared to coincide with the ratio where prey profitability is maximal.When a range of prey sizes were offered simultaneously, an observed MW : MCL ratio (0·14–0·16) turned out to be lower than the predicted optimal MW : MCL ratio (0·16–0·22) and lower than the MW : MCL ratio where the first crab switched feeding techniques (0·16). Crabs preferred a MW : MCL ratio of 0·16 over the optimal ratio of 0·24 when given dichotomous choices between different MW : MCL ratios.Although larger and more profitable mussels can be crushed, we suggest that crabs select small crushable mussels to prevent claw wear and tear. Claw damage has a considerable effect on mating success and hence on an individual's fitness. Risk of claw damage may thus be of greater importance to a foraging shore crab than energy maximization.
Isotope trophic‐step fractionation: a dynamic equilibrium model
Authors: Olive Peter J. W. , Pinnegar John K. , Polunin Nicholas V. C. , Richards Gareth , Welch Rachel 
Published: July 2003

SummaryTrophic position is a fundamental feature of food‐web structure, knowledge of which is being improved by stable isotope approaches which assume a constant enrichment in heavier isotopes in consumers relative to their diet.We argue that the typical enrichment reflects a dynamic equilibrium between fractionation vectors associated with assimilation and excretion.We develop a linear model to characterize the relationship between the equilibrium isotopic signature and the feeding rate influenced by isotopic discrimination during assimilation and excretion.We present new data for both diet switching and starvation experiments using a marine worm Nereis virens and use this, and previously published data for a fish, bird and mammal to calculate controlling parameters from observations of the isotopic signature following diet‐switching and the onset of starvation.We show that the observed variance in isotopic signatures at each trophic step carries substantially more information than has been used hitherto and is influenced by feeding rate in addition to the isotopic signature of the food source.Using the linear model as a tool we predict that parasitic organisms may be depleted relative to the tissues of their host.
A comparative analysis of patch‐leaving decision rules in a parasitoid family
Authors: Wajnberg Eric , Gonsard Pierre‐Alexis , Tabone Elisabeth , Curty Christine , Lezcano Nathalie , Colazza Stefano 
Published: July 2003

SummaryThe proximate behavioural rules adopted by parasitoid females to manage their foraging time on patches of hosts were studied, under standardized laboratory conditions, in different species (and populations) of the Trichogrammatidae (Hymenoptera) family.Seventeen species/populations were compared and the behavioural mechanisms adopted by the females were identified by means of a Cox's proportional hazards model.On average, females increased their patch‐leaving tendency each time a healthy host was attacked and each time a parasitized host was rejected.Strong variation was observed in these patch‐leaving mechanisms among the different species.Moreover, the interspecific variation in these two behavioural mechanisms showed a significant positive correlation, and this correlation remained significant when the phylogenetic relationship between the strains was controlled with the use of phylogenetic comparative methods.The adaptive and evolutionary meanings of these results are probably related to the ecological features and distribution patterns of the hosts attacked by the species/populations compared.
The relationship between the floristic composition of rain forests and the abundance of folivorous marsupials in north‐east Queensland
Authors: Kanowski J. , Irvine A. K. , Winter J. W. 
Published: July 2003

SummaryThree species of folivorous ringtail possums (Marsupialia: Pseudocheiridae) inhabit higher elevation rain forests on the Atherton Tablelands, north‐east Queensland, Australia. Each possum is thought to specialize on a restricted suite of host plants. It has been hypothesized that the absence of the possums from lowland forests may reflect the absence or ‘inappropriate combination’ of their host plants in lowland forests.We test this ‘floristics hypothesis’ using data from published dietary studies, herbarium records and field surveys. Studies of the possums’ diets show that each possum eats a wide variety of plant species. However, the majority of each possum's diet comes from a few genera or families of plants and there is considerable dietary partitioning between the possums. These data are consistent with the hypothesis that the possums are specialists on a restricted suite of plant taxa.The altitudinal ranges of plants known to be important in the diets of the ringtail possums were compiled from herbarium records. Several plant species eaten by the possums are absent from lowland forests, but all genera and families of plants important in the possums’ diets occur in lowland forests.The relationship between the floristic composition of forests and the abundance of the ringtail possums was examined at 16 sites on the Atherton Tablelands. The floristic composition of forests varied primarily with geology and secondarily with altitude. This was true whether the entire plant assemblage was considered, or just those families known to be important in each possum's diet. Possum abundance varied primarily with altitude and secondarily, for two species, with geology. There was no correlation between the abundance of ringtail possums and the floristic composition of forests, whether the entire plant assemblage was considered, or just those families known to be important in each possum's diet.Altitudinal variation in the abundance of ringtail possums in north Queensland does not appear to be a response to variation in the floristic composition of those forests.
Parasitism and developmental plasticity in Alpine swift nestlings
Authors: Bize Pierre , Roulin Alexandre , Bersier Louis‐Felix , Pfluger Dominik , Richner Heinz 
Published: July 2003

SummaryDevelopment plasticity is a common evolutionary and phenotypic response to poor growth condition, in particular in organisms with determinate growth such as most birds and mammals. Because various body structures can contribute differently to overall fitness, natural selection will adjust the degree of plasticity of each structure to its proportionate contribution to fitness at a given life stage.Two non‐mutually exclusive mechanisms can account for plasticity in the growth of offspring to compensate for the effect of parasites. First, if parasite infestation levels fluctuate over the nestling period, parasitized young may show reduced growth until peak parasite infestation, and accelerated growth once the conditions improve (the accelerated growth hypothesis). Secondly, if the period of tissue maturation is not fixed in time, hosts may grow slower than parasite‐free hosts but for a longer period of time (the delayed maturation hypothesis).To test whether hosts compensate for the effects of parasites on their development, the load of the blood‐sucking louse‐flyCrataerina melbaeRondani in the nests of Alpine swifts,Apus melbaLinnaeus, was increased or decreased experimentally. Parasite prevalence was 100% in both treatments, but intensity (no. of parasites per nestling) was significantly lower for deparasitized nestlings. In both treatments, parasite intensity increased up to halfway through the rearing period (i.e. 30 days of age) and decreased afterwards.In line with the accelerated growth hypothesis, wings of parasitized nestlings grew at a lower rate than those of deparasitized ones before the peak of parasite infestation, but at a greater rate after the peak. Louse‐flies had no significant effect on the growth of body mass. In agreement with the delayed‐maturation hypothesis, wings of parasitized nestlings grew for 3 additional days and were of similar size at fledging as in deparasitized birds.In summary, the present study shows in a wild bird population that nestling hosts can compensate for the effect of parasitism on their phenotype. It emphasizes the need to take the dynamics of parasite populations into account in studies of host–parasite relationships, and to investigate the effect of parasites on host development over the entire growing period rather than only at fledging, as employed traditionally.
Variable age structure and apparent density dependence in survival of adult ungulates
Authors: Festa‐Bianchet Marco , Gaillard Jean‐Michel , Côté Steeve D. 
Published: July 2003

SummaryLarge herbivores have strongly age‐structured populations. Because recruitment often decreases as population density increases, in unexploited populations the proportion of older adults may increase with density. Because survival senescence is typical of ungulates, ignoring density‐dependent changes in age structure could lead to apparent density‐dependence in adult survival.To test for density dependence in adult survival, we used data from three populations that underwent considerable changes in density. Bighorn sheep (Ovis canadensis) on Ram Mountain, Alberta, ranged from 94 to 232, mountain goats (Oreamnos americanus) on Caw Ridge, Alberta, varied from 81 to 147, and estimates of roe deer (Capreolus capreolus) older than 1 year at Chizé, France, ranged from 157 to 569.We used recent developments of capture–mark–recapture modelling to assess the response of adult survival to changes in density when age structure was and was not taken into account.Survival rates were 10–15% higher during the prime‐age stage than during the senescent stage for all sex‐species combinations. When adults were pooled into a single age class there was an apparent negative effect of density on female survival in bighorns and roe deer, and negative trends for female mountain goats, male roe deer and male bighorn sheep. When age class was taken into account, there were no significant effects of density on adult survival. Except for male mountain goats, the strength of density dependence was lower when age was taken into account.In ungulate populations, age structure is an important determinant of adult survival. Most reports of density dependence in adult survival may have been confounded by changes in age structure.
Determinants of colobine monkey abundance: the importance of food energy, protein and fibre content
Authors: Wasserman Michael D. , Chapman Colin A. 
Published: July 2003

SummaryA fundamental ecological question is what determines the abundance of animals? Answering this question is vital in the formulation of effective management plans for endangered or threatened species. However, there are few general hypotheses proposed to account for variation in animal abundance. Studies of folivorous primates are a notable exception. In this group, the protein to fibre ratio of mature leaves is a significant predictor of biomass. However, Dasilva (1992) suggested that the availability of energy may play a critical role in colobine behaviour and ecology.Here we evaluate the importance of food energy content for the red colobus (Procolobus badius) and black‐and‐white colobus (Colobus guereza) monkeys of Kibale National Park, Uganda.Energy was found to be of little importance. None of the eight groups studied selected high‐energy foods: there was no correlation between food energy content and foraging effort. For all groups, estimates of energy expenditure [daily energy expenditure (DEE) and average daily metabolic needs (ADMN)] were less than estimates of energy consumption. Finally, the average energy content of mature leaves from the 20 most abundant tree species at four sites was not related to colobine biomass.In contrast, the protein and fibre content of foods was important to both colobine species. Seven of the eight groups selected foods with a high‐protein, low‐fibre content. The average protein to fibre ratio of mature leaves from the 20 most abundant tree species at four sites was correlated positively with colobine biomass.This study provides further validation of the protein to fibre model, suggesting the importance of this model for conservation and management of colobus monkeys, with the potential application to other small mammalian herbivores.
Seasonal range size in relation to reproductive strategies in brown bears Ursus arctos
Authors: Dahle Bjørn , Swenson Jon E. 
Published: July 2003

SummaryData on seasonal ranges of 93 radio‐collared adult brown bears (Ursus arctos) were used to test hypotheses explaining variation in range size in relation to male and female reproductive strategies.Both males and oestrous females used large ranges in the mating season, but decreased their ranges after the mating season. These results suggested that both sexes in this species roam to mate, because the results could not be explained by a seasonal change in food availability nor by increased foraging movements of oestrous females to replenish body reserves after previous cub raising.Females with cubs‐of‐the‐year (cubs) restricted their range size in the mating season and increased their ranges in the post‐mating season. This finding suggests that females with cubs restricted their ranges to avoid contact with infanticidal males, an important cause of cub mortality, because the proposed alternative explanation − limited mobility of small cubs − was unable to explain the small size of mating season ranges.Our results suggest that range size in females is influenced by sexually selected infanticide, selecting for large mating season ranges and multiple mating in oestrous females to hide paternity and for restricted mating season ranges in females with cubs to avoid infanticidal males.To our knowledge, we are the first to report a significant relationship between seasonal range size and reproductive status in female brown bears and the first to report an effect of oestrus on seasonal range size in female carnivores.
Population‐level mechanisms for reddened spectra in ecological time series
Authors: Akçakaya H. Resit , Halley John M. , Inchausti Pablo 
Published: July 2003

SummaryThe temporal variability of many animal populations increases with the length of census period. This pattern is associated with the reddened spectral colour, quantified by the spectral exponent, which is typically around + 1.We used simulation models to explore the effects of various population‐level processes on the spectral colour of the simulated time series of abundances.Our results showed that the observed spectral exponents could be explained as the effect of a combination of measurement error and natural variability (in the form of white environmental noise).Thus, it may not be necessary to invoke complex varieties of environmental noise to explain the observed spectral exponents.
Variability in marine resources affects arctic fox population dynamics
Authors: Roth James D. 
Published: July 2003

SummaryTerrestrial predators in coastal areas are often subsidized by marine foods. In order to determine the potential impact on terrestrial prey, the numerical response of predators to each food source must be determined.In winter, arctic foxes (Alopex lagopus) may forage on the frozen Arctic ocean and scavenge carcasses of seals killed by polar bears (Ursus maritimus), but the importance of this food source and its effect on the population cycles of arctic foxes and lemmings (their primary prey) are unclear.I estimated the marine component of the late winter diet of arctic foxes near Churchill, Manitoba, using stable‐carbon isotope analysis, and compared these estimates to abundance of arctic foxes and collared lemmings (Dicrostonyx richardsoni).From 1994 to 1997, fox density varied with lemming abundance, but following a decline, fox abundance began increasing before lemmings. During this increase marine foods were consumed more than in other years, with over two‐thirds of food intake from marine sources.Arctic and red fox (Vulpes vulpes) harvests in the 1980s to 1990s were correlated with published estimates of polar bear body mass, which varies with seal productivity. However, this relationship disappeared during high lemming years.Thus, variation in marine productivity affects arctic fox abundance, especially when their primary prey are scarce, and this numerical response of arctic foxes to marine resources and lemmings suggests that increased predation by arctic foxes subsidized by seal carrion may delay the recovery of low lemming populations.
Energy dynamics in a parasitoid foraging in the wild
Authors: Casas Jerome , Driessen Gerard , Mandon Nicole , Wielaard Sebastiaan , Desouhant Emmanuel , Van Alphen Jacques , Lapchin Laurent , Rivero Ana , Christides Jean Philippe , Bernstein Carlos 
Published: July 2003

SummaryAlthough parasitoids are used widely as a biological models for understanding the evolution of animal behaviour, most studies have been constrained to the laboratory. The dearth of field studies has been compounded by the almost complete ignorance of the physiological parameters involved in foraging and dispersal, in particular of the energetic constraints imposed by resource limitation.We estimated the dynamics of carbohydrates and lipids reserves ofVenturia canescens (Gravenhorst) females by releasing individuals of known nutritional status in a natural environment and recapturing them using host‐containing traps. The recapture rate was around 30%. These results were compared with the reserves of caged animals kept under different experimental conditions (freshly emerged, starved to death, fedad libitumand partially starved). Wild animals were also sampled in order to estimate the resource levels of the local population.The results show that: (i) wasps are able to maintain a nearly constant level of energy over an extended foraging period; (ii)V. canescenstakes sugars in the field; and (iii) the lipid reserves accumulated during the larval life may be limiting as lipogenesis does not take place in adults even under conditions of high sugar availability.These results demonstrate that wasps can forage for hosts and food and disperse in this habitat for hours and days without running into a severe risk of energy limitation.
Mid‐domain models of species richness gradients: assumptions, methods and evidence
Authors: Zapata F. A. , Gaston K. J. , Chown S. L. 
Published: July 2003

SummaryPatterns of species richness along latitudinal, elevational and depth gradients often exhibit a mid‐gradient peak. Similar patterns with a mid‐domain peak in richness are produced, as a result of geometric constraints on species distributions, by models that randomize species range size and placement over a bounded gradient.Proponents of these so‐called mid‐domain models argue that they provide an appropriate null hypothesis for examining species richness patterns along spatial gradients. Furthermore, some claim that because these models seem to explain a large proportion of the large‐scale spatial variation in richness, geometric constraints on species distribution are in fact the cause of these patterns.A critical examination of model assumptions reveals that some are unrealistic, conceptually flawed or internally inconsistent. Additionally, tests of mid‐domain models have suffered from methodological deficiencies derived from arbitrariness and circularity in the definition of domain boundaries, collapsing two‐dimensional (2‐D) patterns into a single dimension (1‐D), and the use of interpolated ranges, all of which can bias test results in favour of the models. Tests have also been statistically naive by using fairly insensitive measures of deviation between observed and predicted patterns and ignoring the increased probability of Type I error that can result in analyses of spatially autocorrelated data.In spite of this, a review of the empirical evidence indicates that most studies do not show a high degree of concordance between observed and predicted species richness patterns, particularly in 2‐D. Additionally, spatial patterns of variation in range size and species turnover do not unequivocally support mid‐domain models. Thus, the models do not adequately describe observed species richness gradients and thus fail to explain them.Although mid‐domain models have served a useful purpose in drawing attention to the need to clarify the null expectation in the study of species richness gradients, their use appears to be severely limited by difficulties associated with the treatment of ranges, boundary definitions and a lack of clarity regarding the extent to which the observed data should be used to generate the null patterns.
Early Maternal Changes Contributing to the Formation of the Chorioallantoic and Yolk Sac Placentas in Rat: a Morphological Study
Authors: Kaloğlu C. , Gürsoy E. , Onarlioğlu B. 
Published: July 2003

SummaryIn order to determine the maternal changes contributing to the formation of the chorioallantoic and yolk‐sac placentas, rat gestation sites were examined by light and electron microscopy on days 7 through 10 of pregnancy.On day 7, the implantation chamber showed different compartments and contained the blastocyst in the antimesometrial chamber. The epithelial lining of the implantation chamber disappeared at the antimesometrial chamber, transformed into disintegrated cells in the mesometrial chamber, and showed signs of the programmed cell death in the decidual crypt. On day 8, the mesometrial chamber lumen contained red blood cells and it was continuous with subepithelial sinusoids. The endothelial cells lining the mesometrial sinusoids also showed some characteristics of the sprouting type angiogenesis such as hypertrophy and cell proliferation. While the yolk‐sac placental circulation was more obvious with participation of the giant trophoblasts at the antimesometrial pole of the conceptus on day 9, the antimesometrial cells showed autophagic degeneration after the formation of the chorioallantoic placenta on day 10. The contribution of the regional cell death and angiogenesis to form both of the two placentas are discussed.