bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rodent post‐dispersal seed predation in deciduous woodland: predator response to absolute and relative abundance of prey
Authors: Hulme Philip. E.. , Hunt Melanie. K.. 
Published: March 2003

1. The response of post‐dispersal seed predators to changes in the absolute and relative abundance of seeds of two tree species: ash (Fraxinus excelsior) and wych elm (Ulmus glabra) was studied in seminatural woodland in County Durham, UK. 2. Analysis examined two components of seed predation: seed encounter (the probability of at least one seed being removed) and seed exploitation (the proportion of seeds removed once encountered). Exclosure studies identified small mammals, particularly the woodmouse (Apodemus sylvaticus) as the principal post‐dispersal seed predators and revealed a marked preference (almost four‐fold difference in encounter) for seeds of Ulmus over Fraxinus. 3. For both Fraxinus and Ulmus, a linear regression model described the relationship between seed density and the number of seeds removed by rodents more successfully than non‐linear models. These relationships were maintained whether the species were presented singly or together with neither the slopes of Fraxinus or Ulmus changing significantly. These results indicate that, over the range of seed densities used, rodents consumed a constant proportion of seeds irrespective of seed density or frequency. The high rates of exploitation for Ulmus seeds suggests the slope of the relationship primarily reflects rates of encounter, whereas for Fraxinus it is a result of both low encounter and exploitation. 4. Linear regression identified seed removal by rodents to be frequency‐independent both over the woodland as a whole and within each of six micro‐habitats. This appeared to be a result of the marked preference for Ulmus over Fraxinus which was not reversed even when Ulmus was rare. Frequency‐dependent seed predation by rodents is predicted to be most likely when both prey have similar low palatabilities. 5. When encountered by rodents, patches of Ulmus seeds were exploited almost completely, irrespective of seed density or frequency which suggests rodents have the potential to cause local extinction of Ulmus seed populations. In contrast, the lower rates of encounter and exploitation of Fraxinus seeds implies ample opportunities for prey escape.
Numerical and functional responses in generalist predators: hen harriers and peregrines on Scottish grouse moors
Authors: Redpath Stephen M. , Thirgood Simon J. 
Published: March 2003

Summary 1. The functional and numerical responses of two generalist raptors (hen harrier and peregrine) were studied on one moor for 6 years and on five other moors for 5 years. 2. Neither species showed numerical responses to grouse abundance. Harrier densities were highest in areas and years where their small prey (meadow pipits and small mammals) were most abundant. Peregrine densities were highest on southern study moors, probably in association with high abundance of racing pigeons. 3. For harriers preying on grouse chicks, the available data fitted a sigmoidal or type III functional response. Peregrines showed a type II response to adult grouse densities around eyries. 4. The proportion of grouse chicks taken by harriers was estimated to have been highest at densities of 67 chicks km–2 (equivalent to a mean of about 12 broods km–2). The proportion of adult grouse taken by peregrines appeared to be inversely density dependent, such that an increasing proportion of grouse was taken at grouse densities below 20 km–2. 5. In the absence of persecution, the impact of harriers on grouse populations is most likely to be greatest on moors where alternative prey and thus harriers are abundant. The question of whether harriers may dampen grouse population cycles at low grouse density is discussed.
A fixed energetic ceiling to parental effort in the great tit?
Authors: Tinbergen J. M. , Verhulst S. 
Published: March 2003

Summary 1. To elucidate the links between avian brood size, parental effort and parental investment, we measured daily energy expenditure (DEEfem), condition (residuals of mass on tarsus) and feeding rate in female great tits Parus major L. rearing broods in which the number of young was either reduced, unmanipulated or enlarged. 2. Female condition was negatively correlated with manipulation when measured at the nestling age of 8 days (measured during the day), which suggests a shift in allocation from self‐feeding to chick‐feeding. However, there was no detectable manipulation effect on condition measured at the nestling age of 12 days (measured during the night). Either female condition was only affected by manipulation in the early nestling phase or the females adjusted their diurnal mass trajectory in response to brood size manipulation. More detailed data are required to verify this point. There were no indications of a fitness cost associated with the condition during the day, but condition at night was positively related to winter survival. Since manipulation only affected condition during the day, there was no link between manipulation and winter survival. 3. The duration of the working day was not affected by manipulation and female feeding rate tended to flatten off with manipulated brood size. Similarly, brood reduction resulted in a lower DEEfem, whilst brood enlargement had no effect. This suggests that females worked at an energetic ceiling when rearing an unmanipulated brood. However, the level of this ‘ceiling’ in DEEfem was not fixed: it differed between years. This leads us to conclude that the observed ceiling was imposed by extrinsic factors (e.g. available foraging time) and not by an intrinsic factor such as maximum energy assimilation rate. We hypothesize that time limitation was the cause for the observed ceiling in energy expenditure and that the annual variation in the level of this ceiling was due to annual variation in ambient temperature. 4. A cost of reproduction was previously demonstrated in this population: brood enlargement caused a reduction in the incidence of second clutches. However, since DEEfem did not differ between control and enlarged broods, we judge it unlikely that daily energy expenditure is a general predictor for parental investment.
Factors affecting maternal care in an income breeder, the European roe deer
Authors: Andersen Reidar , Gaillard Jean‐Michel , Linnell John D. C. , Duncan Patrick 
Published: March 2003

1. Maternal care is a major component of demographic tactics in mammals. In ungulates most work has been done on capital breeders (e.g. bighorn sheep), which rely heavily on body reserves to raise their young. Roe deer, in contrast, are close to the income breeder end of the capital–income breeder continuum, and show high levels of maternal care.2. The aim of this study was to explore the factors determining the level of maternal care in roe deer, in particular the effects of maternal body weight, mother's parity, litter size and year of birth on the amount of prenatal care (i.e. the average mass of an offspring multiplied by the number of offspring) and postnatal care (i.e. the average growth rate of the offspring multiplied by their number). The study was carried out on a captive population of roe deer fedad libitum, and in a wild population.3. In both populations prenatal care increased with increasing maternal body weight. In the population fedad libitumthis effect was found in light females only (< 22 kg); in the wild population the positive relationship between maternal body weight and prenatal care was entirely accounted for by variation in litter size (i.e. heaviest females produced larger litters) and density (i.e. females were lightest in years with high population density). Parity did not affect prenatal care.4. In 14 females fedad libitumthere was no relationship between postnatal care and maternal body weight. Multiparous females had higher levels of postnatal care. In contrast, 20 wild females showed a positive relationship between postnatal care and maternal body weight, and only litter size affected the level of postnatal care.5. Even after accounting for the confounding effects of maternal body weight, parity, litter size and population density, we found no trade‐off between pre‐ and postnatal care in any of the two populations. The conditions under which the pattern of maternal care could impose trade‐offs that affect the individual offspring are discussed.
Mechanisms of population regulation in the fire antSolenopsis invicta: an experimental study
Authors: Adams Eldridge S. , Tschinkel Walter R. 
Published: March 2003

SummaryWe tested for density‐dependent regulation of biomass in a population of the fire antSolenopsis invictaand examined the mechanisms of population recovery following replicated colony removals. All colonies were killed within the core area (1018 m2) of six plots, while six additional plots served as undisturbed controls. Over the next 5 years, colonies were mapped several times per year and the biomass of each colony was estimated from the volume of the nest‐mound. The average biomass and density of colonies within the removal areas gradually converged on those of control plots and were no longer detectably different after two years. Thereafter, ant biomass on experimental and control plots showed nearly identical seasonal and yearly fluctuations.Territories of colonies surrounding the removal areas rapidly expanded following the deaths of neighbours, while average territory size on control plots showed little short‐term change. Significantly more new colonies were established within core areas of experimental plots than within core areas of control plots during the first year following removals. The per‐colony probability of movement and the net influx of colony biomass were significantly higher in central regions of the experimental plots than in control plots during the first year. The directions of colony movements were clustered towards the centres of experimental plots in the first 2 years, but did not show significant directional trends on control plots. In all 5 years of the study, annual mortality rates were lower for larger colonies, but the size‐specific risk of mortality was not significantly affected by the experimental removal of competitors. The growth rates of colonies, adjusted for initial size, were significantly higher in central regions of experimental plots than in control plots during the first two years of the study. In all years, colony growth rates declined with increasing colony size. These results indicate that populations ofS. invictaare regulated by competition among neighbouring colonies. Due to large intraspecific variation in colony size, the dynamics of ant populations are described more accurately by measures of total ant biomass than by colony density alone.
Post‐fledging care, philopatry and recruitment in brown thornbills
Authors: Green David J. , Cockburn Andrew 
Published: March 2003

Summary We describe patterns of post‐fledging care, dispersal and recruitment in four cohorts of brown thornbillsAcanthiza pusilla. We examine what factors influence post‐fledging survival and determine how post‐fledging care and the timing of dispersal influence the probability of recruitment in this small, pair breeding, Australian passerine. Fledgling thornbills were dependent on their parents for approximately 6 weeks. Male fledglings were more likely than female fledglings to survive until independence. For both sexes, the probability of reaching independence increased as nestling weight increased and was higher for nestlings that fledged later in the season. The timing of dispersal by juvenile thornbills was bimodal. Juveniles either dispersed by the end of the breeding season or remained on their natal territory into the autumn and winter. Juveniles that delayed dispersal were four times more likely to recruit into the local breeding population than juveniles that dispersed early. Delayed dispersal was advantageous because individuals that remained on their natal territory suffered little mortality and tended to disperse only when a local vacancy was available. Consequently, the risk of mortality associated with obtaining a breeding vacancy using this dispersal strategy was low. Males, the more philopatric sex, were far more likely than females to delay dispersal. Despite the apparent advantages of prolonged natal philopatry, however, only 54% of pairs that raised male fledglings to independence had sons that postponed dispersal, and most of these philopatric sons gained vacancies before their parents bred again. Consequently, few sons have the opportunity to help their parents. Constraints on delayed dispersal therefore appear to play a major role in the evolution of pair‐breeding in the brown thornbill.
Life‐history strategies in parasitoid wasps: a comparative analysis of ‘ovigeny’
Authors: Jervis Mark A. , Heimpel George E. , Ferns Peter N. , Harvey Jeffrey A. , Kidd Neil A. C. 
Published: March 2003

Summary Ecologists concerned with life‐history strategies of parasitoid wasps have recently focused on interspecific variation in the fraction of the maximum potential lifetime egg complement that is mature when the female emerges into the environment. Species that have all of this complement mature upon emergence are termed ‘pro‐ovigenic’, while those that do not are termed ‘synovigenic’. We document and quantify the diversity of egg maturation patterns among 638 species of parasitoid wasps from 28 families. We test a series of hypotheses concerning variation in ‘ovigeny’ and likely life‐history correlates by devising a quantitative index – the proportion of the maximum potential lifetime complement that is mature upon female emergence. Synovigeny, which we define as emerging with at least some immature eggs, was found to be by far the predominant egg maturation pattern (98·12% of species). Even allowing for some taxonomic bias in our sample of species, pro‐ovigeny is rare among parasitoid wasps. There is strong evidence for a predicted continuum in ovigeny index among parasitoid wasps, from pro‐ovigenic (ovigeny index = 1) to extremely synovigenic species (ovigeny index = 0). As predicted, synovigenic species are longer‐lived than pro‐ovigenic ones, and ovigeny index and life span are negatively correlated across parasitoid taxa, suggesting a life span cost of concentrating reproductive effort early in adult life. There is equivocal evidence that host feeding (i.e. consumption of host haemolymph and/or tissues by adult wasps) is confined to synovigenic parasitoid wasps. It is also not certain from our analyses whether host feeding is associated with a relatively low ovigeny index. As predicted, egg resorption capability is concentrated among producers of yolk‐rich eggs. Also, the hypothesis that it is associated with a tendency towards a low ovigeny index is supported. Parasitoid species that produce yolk‐rich eggs also exhibit a lower ovigeny index than species that produce yolk‐deficient eggs. Ovigeny index appears to be linked to parasitoid development mode (koinobiosis–idiobiosis). We conclude that ‘ovigeny’ is a concept applicable to insects generally.
The effects of dispersal mode on the spatial distribution patterns of intertidal molluscs
Authors: Johnson M. P. , Allcock A. L. , Pye S. E. , Chambers S. J. , Fitton D. M. 
Published: March 2003

SummaryAs many species of marine benthic invertebrates have a limited capacity for movement as adults, dispersal mode is often considered as a determinant of geographical ranges, genetic structure and evolutionary history. Species that reproduce without a larval stage can only disperse by floating or rafting. It is proposed that the colonization processes associated with such direct developing species result in spatial distributions that show relatively greater fine scale patchiness than the distributions of species with a larval dispersal stage. This hypothesis was tested by collecting molluscs at different spatial scales in the Isle of Man.Spatial distribution patterns supported the predictions based on dispersal mode. Estimated variance components for species with larval dispersal suggested that the majority of the spatial variation was associated with variation between shores. In comparison, there was relatively more variability within shores for abundance counts of species with direct development.Multivariate analyses reflected the univariate results. An assemblage of direct developers provided a better discrimination between sites (100 m separation) but the group of species with larval dispersal gave a clearer separation of shores (separated by several km).The fine scale spatial structure of direct developing species was reflected in higher average species diversity within quadrats. Species richness also reflected dispersal mode, with a higher fraction of the regional species pool present for direct developers in comparison to species with larval dispersal. This may reflect the improved local persistence of taxa that avoid the larval dispersal stage.
Mechanisms of functional response and resource exploitation in browsing roe deer
Authors: Illius Andrew W. , Duncan Patrick , Richard Caroline , Mesochina Pascal 
Published: March 2003

Summary

The functional responses of roe deer were examined using 11 plant species. A technique to discriminate between encounter‐ and handling‐limited processes was used, and it can be concluded that the functional response applicable to patch browsing by roe deer is governed not by the rate of encounter but by the rate of oral processing.
The large differences between plant species were due to variations in both parameters of the functional response: h
, the time lost in biting, and
R
max , the maximum processing rate. Removing the thorns from three of the species affected these parameters differently, according to the size and density of thorns.
Animals took larger bites from larger patches (branches), and bite mass declined as patch exploitation progressed, implying that animals were selecting the larger items to eat first. It was demonstrated experimentally that depletion of the larger bites does occur first, and it was concluded that prey selection is an important component of herbivore foraging behaviour.
The gain curves for deer feeding on the different plant species are calculated as being virtually linear. Patch depression did not, in general, occur because increasing bite rate compensated for declining bite mass. Our mechanistic approach is contrasted with other approaches to describing the gain curve in the literature.
A priori and empirical grounds are presented for rejecting the hypothesis that resource exploitation by browsing mammals is governed by optimal patch use. Diet optimization, involving a trade‐off between diet quality and quantity, offers a better explanation of herbivore foraging behaviour.
Predator–prey cycles in an aquatic microcosm: testing hypotheses of mechanism
Authors: Shertzer Kyle W. , Ellner Stephen P. , Fussmann Gregor F. , Hairston Nelson G. 
Published: March 2003

Summary

Fussmann et al. (2000
) presented a simple mechanistic model to explore predator–prey dynamics of a rotifer species feeding on green algae. Predictions were tested against experimental data from a chemostat system housing the planktonic rotifer
Brachionus calyciflorus
and the green alga
Chlorella vulgaris .
The model accurately predicted qualitative behaviour of the system (extinction, equilibria and limit cycles), but poorly described features of population cycles such as the period and predator–prey phase relationship. These discrepancies indicate that the model lacked some biological mechanism(s) crucial to population cycles.
Here candidate hypotheses for the ‘missing biology’ are quantified as modifications to the existing model and are evaluated for consistency with the chemostat data. The hypotheses are: (1) viability of eggs produced by rotifers increases with food concentration, (2) nutritional value of algae increases with nitrogen availability, (3) algal physiological state varies with the accumulation of toxins in the chemostat and (4) algae evolve in response to predation.
Only Hypothesis 4 is compatible with empirical observations and thus may provide important insight into how prey evolution affects predator–prey dynamics.
Interactions between weaver ants Oecophylla smaragdina, homopterans, trees and lianas in an Australian rain forest canopy
Authors: Blüthgen Nico , Fiedler Konrad 
Published: March 2003

Summary

Tritrophic interactions between the weaver ant Oecophylla smaragdina (Fabricius) (Hymenoptera: Formicidae), plants and honeydew‐producing trophobionts (Hemiptera: Sternorrhyncha and Auchenorrhyncha, Lepidoptera: Lycaenidae) were studied in a rain forest canopy in Northern Queensland, Australia.
Most commonly attended trophobionts by O. smaragdina
at this study site were Coccidae (
Coccus
sp.,
Milviscutulus
sp.) and Membracidae (
Sextius
sp.), followed by
Toxoptera aurantii
(Aphidae),
Planococcus citri
(Pseudococcidae),
Icerya
sp. (Margarodidae), an unidentified species of Eriococcidae,
Austrotartessus
sp. (Cicadellidae), and lycaenid butterfly larvae (
Anthene seltuttus
,
Arhopala centaurus group).
Most trophobionts were highly polyphagous, and trees and lianas from many plant species and families acted as homopteran hosts. However, lianas were found to play a key role. First, the majority (68%) of aggregation sites was found on lianas, especially on the legumes Entada phaseoloides
and
Caesalpinia traceyi
, and secondly, per capita ant visitation rate (
VR
) at coccoids was significantly higher on lianas compared to trees. In total,
VR to homopterans was 64% higher on lianas.
Sites of ant–homopteran aggregations were regularly replaced by new locations on fresh plant growth. The mean longevity of nests of this polydomous ant species was 131 days, of individual aggregation sites with membracids 54 days and with coccoids 130 days.
Our results suggest that plant‐specific differences in suitability for honeydew production (especially the availability of lianas) and the availability of preferred trophobionts have a strong influence on the vigour of Oecophylla colonies.
Predation by Eurasian sparrowhawks produces density‐dependent mortality of wintering redshanks
Authors: Whitfield D. Philip 
Published: March 2003

Summary

This study examined annual differences in redshank Tringa totanus winter mortality caused by predation by Eurasian sparrowhawks Accipiter nisus over an 11‐year period at a rocky shore in south‐east Scotland.
Redshank numbers at the beginning of a winter showed no trend over the study period and winter mortality rates also showed no temporal trend. Mean winter mortality through predation by sparrowhawks was 30·6% for juveniles and 5·6% for adults.
The study demonstrated density‐dependent winter mortality in both juvenile and adult redshanks due to predation by sparrowhawks. Wind speed was also positively associated with juvenile winter mortality but had a weaker influence on adult mortality. This apparent influence of wind speed on juvenile mortality was not confirmed by correlations between monthly juvenile mortality and weather variables (minimum temperature, rainfall and wind speed).
Density‐dependent functions differed between adult and juvenile redshanks, consistent with differences in the competitiveness of the two age classes. It is suggested that individual differences in vulnerability to predation arose through differences in individual susceptibility to density‐dependent competition during foraging. Companion studies indicated that as bird density increased more birds were forced to spend more time feeding in an area where risk of predation was high.