bluuebunny/crossref_metadata_2025_split huggingface dataset:
How parasites divide resources: a test of the niche apportionment hypothesis
Authors: Mouillot David , George‐Nascimento Mario , Poulin Robert 
Published: August 2003

Summary

Modelling species abundance patterns, i.e. the distribution of relative abundance among species within the same community, has become a common framework in community ecology. To describe species abundance patterns several statistical models have been proposed, e.g. the log‐normal distribution, but these do not provide an ecological explanation of the underlying processes.
Tokeshi introduced (1990) and developed (1993, 1996, 1999) a series of niche‐orientated stochastic models to fit species abundance patterns. They suggest that abundance of species are proportional to the resources they apportion. Following this hypothesis, Tokeshi defined some processes in resource partitioning to explain species abundance patterns.
To study the rules which govern species assemblages, parasite communities present advantages because each host harbours a replicate community, the total niche is limited to the body of the host and demographic processes are usually similar for all parasite species in a community. Using five Tokeshi models, we searched for common rules structuring the parasite communities of six species of marine fish from the coast of Chile. The biovolume of each parasite species was preferred as a measure of its ‘abundance’ over actual numerical abundance, to account for the considerable variation in body size among parasite species.
The random assortment model, which suggests a lack of competition and interaction and independent apportionment of resources between species in the community, was fitted successfully to the parasite communities of three fish species for both means and variances of abundance ranks using a new Monte‐Carlo method.
These results are in accordance with current knowledge on parasite coexistence rules, i.e. that most parasite communities appear non‐saturated with species, with many empty niches and with interspecific competition not playing a major structuring role.
Age‐specific reproductive performance in red‐billed choughs Pyrrhocorax pyrrhocorax: patterns and processes in a natural population
Authors: Reid J. M. , Bignal E. M. , Bignal S. , McCracken D. I. , Monaghan P. 
Published: August 2003

Summary

Using data from a 20‐year study of individually marked red‐billed choughs, we examine how reproductive performance varies with age in male and female breeders, and investigate whether population‐level trends result from changes in individual performance and/or the phenotypic composition of the breeding population.
Across the population, mean clutch size, the probability of breeding successfully and the number of offspring fledged during successful attempts increased and then declined with female age. Male age did not explain a significant proportion of the residual variation.
All three measures of reproductive performance improved and then declined with age within individual females.
Females that died young laid relatively small clutches and fledged few offspring before death. Thus mean performance improved across young age classes partly because some poor breeders were absent from older age classes.
Females that ultimately reached the greatest ages had laid small clutches and fledged few offspring during their first few breeding attempts. Females that were more productive when they were young had relatively shorter lives. These data indicate a trade‐off between early reproduction and future survival in choughs, and suggest that individuals that reach old age are phenotypically distinct from an early stage in their breeding lives.
We emphasize that age‐specific changes in mean reproductive performance observed across wild populations are due to a complex interplay between improvement and senescence at the individual level, as well as changes in the phenotypic composition of the breeding population.
Is clutch size limited by incubation ability in northern lapwings?
Authors: Larsen Vegard A. , Lislevand Terje , Byrkjedal Ingvar 
Published: August 2003

Summary

The incubation‐limitation hypothesis states that clutch size in shorebirds is constrained by the ability to incubate more than four eggs successfully. In order to test predictions from this hypothesis, clutches of northern lapwings (Vanellus vanellus) were here experimentally increased and reduced by one egg at the onset of incubation. Parental behaviour, incubation time, hatching synchrony, egg viability, hatching success and body condition of hatchlings was compared with unmanipulated clutches.
Nest desertion and egg breakage was not observed in any of the experimental nests, showing that clutch enlargement did not alter the parental behaviour adversely.
There were no differences among the experimental groups in male and female attentiveness, but the total nest attentiveness was lower in reduced clutches than in the other clutch sizes; nor did the parents’ frequency of nest visits differ between clutch sizes.
Enlarged clutches were incubated longer than controls and reduced clutches. There were, however, no significant differences among clutch sizes in partial or total clutch predation rates. Hatchability of the eggs (proportion of eggs hatching of those present in nests at the end of incubation) was marginally lower in the enlarged clutches (92·5% vs. 100% in the two other groups).
Contrary to predicted, hatching success was highest in enlarged clutches. The numbers of hatched eggs calculated from Mayfield estimates of daily nest and egg survival rates were 0·93, 2·10 and 3·14 in three‐, four‐ and five‐egg clutches, respectively.
When controlling for egg volume, mean body mass of newly hatched chicks was lower in clutches with five eggs than in other nests.
We suggest that the lowered body condition of chicks could outweigh the benefits of laying five instead of four eggs in northern lapwings. Future studies of the selective mechanisms of clutch size in shorebirds should not only focus on the number of young that hatch, but also their quality.
Population stability in salmon species: effects of population size and female reproductive allocation
Authors: Einum Sigurd , Fleming Ian A. , Côté Isabelle M. , Reynolds John D. 
Published: August 2003

SummaryPopulation stability (i.e. level of temporal variation in population abundance) is linked commonly to levels of environmental disturbances. However, populations may also differ in their propensity to dampen or amplify the effects of exogenous forces. Here time‐series of population estimates were used to test for such differences among 104 populations of six salmon species.At the species level, Atlantic (Salmo salarL.), chinook (Oncorhynchus tshawytschaWalbaum) and coho salmon (O. kisutchW) were less variable than sockeye (O. nerkaW) and pink salmon (O. gorbuschaW). Chum salmon (O. ketaW) was more similar to sockeye and pink salmon. These differences may be related in part to differences in body size, and hence susceptibility to adverse environmental conditions, at the time when they migrate to the sea or lakes.At the population level no effect of fecundity on variability was found, in contrast to findings for marine fishes, nor of egg size. Whereas substantial differences in the temporal stability of environmental factors among geographically close populations may over‐ride any effects of fecundity or egg size in fresh water, this is less likely in the marine environment where spatial autocorrelations of environmental variability are more pronounced.Variation in population sizes was related positively to the duration of time‐series when using standard deviations of ln‐transformed population estimates, and also when using linearly detrended population variation, suggesting non‐linear long‐term abundance trends in salmon populations that extend beyond the 7‐year period of the shortest time‐series.When controlling for differences among species, stability increased with increasing population size, and it is hypothesized that this is due to large populations having a more complex spatial and genetic structure than small populations due to wider spatial distribution. The effects of population size on stability, as well as differences in stability among species, suggest that population‐ and organism‐specific characteristics may interact with exogenous forces to shape salmon population dynamics.
Mass provisioning to different‐sex eggs within the laying sequence: consequences for adjustment of reproductive effort in a sexually dimorphic bird
Authors: Blanco Guillermo , Martínez‐Padilla Jesús , Serrano David , Dávila José A. , Viñuela Javier 
Published: August 2003

Summary

In birds, the potential maternal ability to adjust resource allocation to different eggs in the clutch might have a major effect on the survival expectancies of particular nestlings or entire broods. We assessed whether sexually size‐dimorphic Eurasian kestrels Falco tinnunculus (Linnaeus) are able to adjust their reproductive effort by adopting different strategies of egg mass provisioning according to egg sex and laying order.
Initial eggs bearing male embryos were heavier than initial eggs bearing female embryos, but no differences in egg mass associated to sex were detected for eggs laid subsequently. Furthermore, in clutches started with a male egg, egg mass declined in subsequent eggs, while in clutches started by a female egg the opposite trend in within‐clutch egg‐mass variation was found. This suggests differential deposition of resources invested in initial eggs of different sex leading to saved or depleted resources for subsequent eggs.
Daughters from initial eggs hatched earlier than sons from initial eggs, which may enhance survival of smaller siblings hatched later. These contrasting strategies of egg provisioning and hatching patterns depending on the sex of the first‐laid egg were associated, respectively, with marked mass hierarchies and a lack of mass hierarchies at fledgling in broods initiated with eggs bearing sons and daughters.
Parental kestrels may allocate reproductive effort by promoting favouritism towards early hatched chicks or by avoiding any favouritism by producing siblings of each sex with similar mass. This may be achieved depending on the female ability both to identify egg sex and to partially reabsorb or differentially allocate resources to eggs accordingly to adjust reproductive investment. This may be a key mechanism to control sibling competition in birds with sexual dimorphism in mass.
Effect of experimentally altered food abundance on fat reserves of wintering birds
Authors: Rogers Christopher M. , Heath‐Coss Rejeana 
Published: August 2003

Summary

Current models of adaptive fat regulation make opposing predictions concerning the effect of increased winter food supply on size of the avian winter fat reserve. To distinguish between models, food supply was varied experimentally in nature and two measures of size of the fat reserve were taken at food‐supplemented sites and non‐supplemented sites.
In two winters, most of the seven species sampled showed slightly higher visible subcutaneous fat class at supplemented than at non‐supplemented sites; treatment and species factors were statistically significant. Body mass corrected for wing length showed a similar if non‐significant trend.
A parallel dispersal study of birds colour‐banded at non‐supplemented sites showed that these birds did not move 0·8 or 1·5 km to use supplemental food at private feeding stations in the study areas. In addition, accipiter hawk attack rate did not differ between supplemented and non‐supplemented sites.
These results are consistent with a model of adaptive fat regulation (based on between‐day environmental variability caused by severe weather events) that predicts an increase in the winter fat reserve at increased food supply. Other published studies, all from the north temperate zone, showed the same pattern.
The present results are inconsistent with a second model (based on within‐day foraging interruption) which predicts a decrease in the fat reserve under increased food supply. However, a set of published studies, all from tropical regions or regions with mild maritime climate, showed the decrease at higher food predicted by the second but not the first model.
Models of adaptive fat regulation in small birds are therefore limited in their predictive power, perhaps because they are developed for environments that differ in the time scale of environmental stochasticity. New studies are needed that explore further the complexities of environment‐specific adaptive fat models, e.g. a winter feeding experiment in a tropical bird species.
Differential body condition regulation by males and females in response to experimental manipulations of brood size and parental effort in the blue‐footed booby
Authors: Velando Alberto , Alonso‐Alvarez Carlos 
Published: August 2003

SummaryIn long‐lived species, such as seabirds, the allocation of resources between self‐maintenance and reproduction is of particular interest because only a small reduction in adult survival may have a large negative effect on lifetime reproductive success. There is much debate about whether seabirds have a fixed or flexible level of investment in their current reproduction, and it has been proposed that parents can regulate the risk of an increase in mortality under the control of a mass threshold.Body mass change as response to experimental manipulations of parental effort was examined in blue‐footed boobies (Sula nebouxiiMine‐Edwards), a sexually size‐dimorphic seabird, with females approximately 31% heavier than males.First, paternal effort was manipulated by trimming the flight feathers and thereby handicapping males during the chick‐rearing period. Mass remained stable in handicapped males, while there was a reduction of female body mass as response to the handicapped partner. The handicapping of males had a significant effect on chick mass.Secondly, an experiment was made by enlarging and decreasing broods of two chicks to three and one during the first week after hatching. Body mass of females, but not males, was lower in enlarged broods, and body mass of males, but not females, was higher in the reduced broods when the chicks were 45 days old. Chick body masses were lower among enlarged broods than among reduced and control broods.Overall, these and other results revealed that blue‐footed boobies have a sex‐specific body mass regulation. Males had a fixed body mass at the end of experiments; they were working at some physiological maximum or were unwilling to pay the cost in terms of future survival, when the effort demanded was increased. Females performed a flexible effort and were working with a buffer of nutritional reserves that they used when necessary. Below a critical level, females preferentially allocated resources to the maintenance of their body condition at the expense of investment in current reproduction.
The effect of weather on lesser kestrel breeding success: can climate change explain historical population declines?
Authors: Rodríguez Carlos , Bustamante Javier 
Published: August 2003

Summary

We model the effect of annual weather conditions on lesser kestrel Falco naumanni breeding success in South‐western Spain. Models indicate that rainfall is a good predictor of breeding success and has in general a positive effect on reproduction.
Rainfall and temperature in spring, during the courtship period, influence colony occupancy rate. Mean minimum temperatures have a positive effect on nest occupation while the relationship between occupation and rainfall is curvilinear with an optimum around 84 mm.
Nest success rate is influenced positively by rainfall in winter and negatively by rainfall during the nestling period.
The mean number of chicks per successful nest is positively influenced by rainfall during the winter, arrival, courtship, and incubation periods. Rainfall during these periods explains 35% of the variance in this breeding parameter.
Nestling body condition is affected positively by rainfall during the courtship and incubation periods.
Models that consider the amount of rainfall at each colony in periods defined by the breeding phenology of the lesser kestrel outperform those based on total annual rainfall or on winter NAO‐index.
Although rainfall in spring has declined significantly since 1966, retrospective predictions of lesser kestrel population growth rate at our colonies indicate that the effect of climate change on breeding success cannot be held responsible for the historical population decline.
Occupancy as a measure of territory quality
Authors: Sergio Fabrizio , Newton Ian 
Published: August 2003

SummaryTerritory quality may affect individual fitness and contribute to density‐dependent reproduction, with repercussions on population regulation. We investigated the probable causes and population consequences of spatio‐temporal variations in territory quality, measured by occupancy, in eight black kiteMilvus migransBoddaert populations, one of them studied for 10 years (Lake Lugano) and the rest for 4–5 years.Over a period of years, the occupation rate of territories varied from a random pattern. Some territories were preferred while others were avoided. On return from migration, males and females settled earlier on high‐occupancy territories.The positive association between territory occupancy and breeding performance held in all years of study at Lake Lugano, and in six of seven tested populations. As a result, high‐occupancy territories contributed most of the young produced by each population.The occupation rate of the overall 225 territories was related positively to food availability and negatively to mortality risk, measured as proximity to the nearest eagle owlBubo buboLinnaeus nest.At the population level, spatial variation in mean occupancy was positively correlated with spatial variation in mean productivity, suggesting that mean occupancy could be used as a measure of overall habitat quality and population performance.In the Lake Lugano area, a higher proportion of low quality territories was occupied in years of higher density and annual productivity was related negatively to its coefficient of variation. However, annual productivity was not related significantly to the proportion of low quality territories occupied, so support for the theory of site‐dependent population regulation was only partial.In a review of 22 studies of territory occupancy in 17 species, occupancy always deviated from a random pattern in species in which it was tested and was always correlated with productivity and/or with some other measure of territory quality. Our results confirm the importance of prioritizing conservation of high quality territories. Occupancy may be a reliable method of quality assessment, especially for populations in which not all territories are always occupied, or for species in which checking occupancy is easier than finding nests.
Nutrient exchanges between marine and terrestrial ecosystems: the case of the Galapagos sea lion Zalophus wollebaecki
Authors: Fariña J. M. , Salazar S. , Wallem K. P. , Witman J. D. , Ellis J. C. 
Published: August 2003

Summary

The movement of materials and organisms between ecosystems is a common process in nature.
In the present study we investigate the hypothesis that the transport of nutrients by low‐mobility species and their effect on terrestrial ecosystems depends on habitat topography. Specifically, we hypothesized that the influence of a marine organism with low mobility on terrestrial environments would be spatially restricted.
To address this hypothesis we analysed the distribution (both geographical and local scales) of Galapagos sea lion colonies, and quantified the spatial extent of their influence on terrestrial ecosystems (soil and plants).
Our results showed that the influence of Z. wollebaecki on Galapagos terrestrial habitats is restricted to shorelines with low elevations, but that it is it is geographically ubiquitous across the Archipelago.
Our study demonstrated that Z. wollebaecki is an effective vector for the transport of marine nutrients to terrestrial ecosystems. Transported nutrients occur in high concentrations in the soils and are used by shoreline plants. These effects are spatially restricted to the areas where seals occur and the most parsimonious explanatory variable for these patterns is the islands’ topography (or elevation).
The Prudhoe Cognitive Function Test, a scale to assess cognitive function in adults with Down's syndrome: inter‐rater and test–retest reliability
Authors: Margallo‐Lana M. L. , Moore P. B. , Tyrer S. P. , Dawson H. , Jenkins K. , Kay D. W. K. 
Published: August 2003

AbstractBackground The Prudhoe Cognitive Function Test (PCFT) was designed to measure cognitive function in subjects with all degrees of intellectual disability (ID) and to be administered by non‐specialist raters. The aim of the present study was to measure the test–retest and inter‐rater reliability of the PCFT.Methods Three raters, one a specialist and two non‐specialists, administered the PCFT to 14 subjects with Down's syndrome on two occasions separated by 4 weeks.Results The intra‐class correlation coefficients (ICCs) between the rater pairs (n = 3) were 0.99, 0.99 and 0.98 (P < 0.01). Floor effects were recorded for two items. The ICC for test–retest reliability was 0.99 (P < 0.01).Conclusions The PCFT is a highly reliable instrument when used by either specialist or non‐specialist raters. It has excellent temporal stability.
Impulsiveness as a factor in sexual offending by people with mild intellectual disability
Authors: Parry C. J. , Lindsay W. R. 
Published: August 2003

AbstractBackground  It has been suggested that sexual offending by people with intellectual disability (ID) results from a pattern of impulsive behaviour that is consistent with psychosocial disadvantage, rather than sexual deviancy. This study aimed to explore this hypothesis by assessing levels of impulsiveness in sexual offenders, non‐sexual offenders and non‐offenders with mild ID.Method  Impulsiveness was assessed using a modified version of the Barratt Impulsiveness Scale (11th edition). Total impulsivity scores were compared between sexual offenders, non‐sexual offenders and non‐offenders, all with mild ID.Results  There was a significant difference in the levels of impulsiveness between sexual offenders and non‐sexual offenders with ID (t = 2.83, P < 0.01). The sexual offenders were less impulsive than non‐sexual offenders.Conclusions  This study did not support the hypothesis that sexual offending by people with ID is better explained by impulsive behaviour rather than sexual deviancy. It supports recent findings that among the general population, sexual offenders are less impulsive than controls and violent offenders.