bluuebunny/crossref_metadata_2025_split huggingface dataset:
The form of the curves: a direct evaluation of MacArthur & Wilson's classic theory
Authors: Manne Lisa L. , Pimm Stuart L. , Diamond Jared M. , Reed Timothy M. 
Published: March 2003

1. We calculate the yearly numbers of bird species immigrating to – and becoming extinct on – 13 small islands of the British Isles, using a long and relatively complete data record. 2. We estimate the size of the colonist pool for each island using four methods. 3. We assume that immigrations and extinctions are distributed binomially, and use a maximum likelihood method to fit concave immigration and extinction functions to the data, utilizing all four species pool estimates. 4. Extinction rates increase significantly and consistently with increasing numbers of breeding species on each island. For nine of the 13 islands the extinction functions are significantly concave. 5. Immigration rates decrease consistently with increasing numbers of breeding species on each island. Seven islands have significantly concave immigration functions. 6. Immigration rates and extinction rates decline consistently, but not significantly, with island distance and island size, respectively. The number of breeding species does not always reflect the number of species likely to have reached an island. Moreover, some species may choose not to breed when their chance of extinction is high. These factors, plus the modest range of island areas and distances in our database, reduce our chances of finding the theoretically predicted effects of area and distance on extinction and immigration rates.
Predator–prey relationships: arctic foxes and lemmings
Authors: Angerbjorn Anders , Tannerfeldt Magnus , Erlinge Sam 
Published: March 2003

1. The number of breeding dens and litter sizes of arctic foxesAlopex lagopuswere recorded and the diet of the foxes was analysed during a ship‐based expedition to 17 sites along the Siberian north coast. At the same time the cyclic dynamics of co‐existing lemming species were examined.2.The diet of arctic foxes was dominated by the Siberian lemmingLemmus sibiricus(on one site the Norwegian lemmingL. lemmus), followed by the collared lemmingDicrostonyx torquatus.3.The examinedLemmus sibiricuspopulations were in different phases of the lemming cycle as determined by age profiles and population densities.4.The numerical response of arctic foxes to varying densities ofLemmushad a time lag of 1 year, producing a pattern of limit cycles in lemming–arctic fox interactions. Arctic fox litter sizes showed no time lag, but a linear relation toLemmusdensities. We found no evidence for a numerical response to population density changes inDicrostonyx.5.The functional or dietary response of arctic foxes followed a type II curve forLemmus, but a type III response curve forDicrostonyx.6.Arctic foxes act as resident specialist forLemmusand may increase the amplitude and period of their population cycles. ForDicrostonyx, on the other hand, arctic foxes act as generalists which suggests a capacity to dampen oscillations.
Integrating nested spatial scales: implications for the coexistence of competitors on a patchy resource
Authors: Inouye Brian D. 
Published: March 2003

1.Intraspecific aggregation at a single spatial scale can promote the coexistence of competitors. This paper demonstrates how this same mechanism can be applied to the many systems that are patchy at two scales, with patches nested within ‘superpatches’.2.Data are presented from a field study showing that insects living in rotting fruits have aggregated distributions in the fruits under a single tree, and that the mean density and degree of aggregation varies significantly among trees. Observations in this system motivate the following models.3.A model of competition has been developed between two species which explicitly represents spatial variation at two scales. By integrating the probability distributions for each scale, the marginal distributions of competitors over all patches can be found and used to calculate coexistence criteria. This model assumes global movement of the competitors.4.Although spatial variation at a single scale may not be sufficient for coexistence, the total variation over all patches can allow coexistence. Variation in mean densities among superpatches and variation in the degree of aggregation among superpatches both promote coexistence, but act in different ways.5.A second model of competition between two species is described which incorporates the effects of limited movement among superpatches. Limited movement among superpatches generally promotes coexistence, and also leads to correlations among aggregation and the mean densities of competitors.
Trade‐offs between nutrient intake and faecal avoidance in herbivore foraging decisions: the effect of animal parasitic status, level of feeding motivation and sward nitrogen content
Authors: Hutchings M. R. , Kyriazakis I. , Gordon I. J. , Jackson F. 
Published: March 2003

1.Three experiments were carried out to determine whether a trade‐off between the benefit of increased nitrogen content of swards and risks of parasitism exists in a grazing situation for sheep (Ovis ariesL.). The effect of level of feeding motivation and parasitic status on the grazing behaviour of sheep faced with this trade‐off was also investigated. Animals were presented with pairs of experimental swards (36 × 21 cm), which varied in nitrogen content (high = N+; low = N−) and level of contamination with faeces from sheep infected withOstertagia circumcincta(Ostertag) (20 g faeces per sward = F+; no faeces = F−), and allowed to graze for short periods. For this study, a ‘high parasite risk’ grazing strategy is defined as taking more bites from an N+F+ sward compared to an N−F− sward, when presented together as the trade‐off choice.2.Experiment 1 presented one choice (N+F− vs. N−F−) three times to 20 sheep divided into four animal treatment groups resulting from two levels of feeding motivation (high and moderate) and two parasitic states (parasitized byO. circumcinctaand non‐parasitized). Experiment 2 presented four choices (N+F+ vs. N−F− N+F+ vs. N−F+ ; N+F− vs. N−F− N+F− vs. N−F+) repeated three times to the same animals and treatments.3.Experiment 3 presented the above four choices three times each to 24 sheep in four animal treatment groups created from two parasitic states (parasitized byO. circumcinctaand non‐parasitized) and two immune states (immune toO. circumcinctaand naive).4.All animals selected the high nitrogen sward over the low nitrogen sward in experiment 1. When presented the trade‐off choice, animals with a high level of feeding motivation took greater parasitic risks, than moderately motivated animals in experiment 2. Both immune treatments took higher parasitic risks than both the naive treatments in experiment 3. Subclinical parasitism resulted in increased rejection of the N+F+ sward, reduced bite rates and grazing depths compared to non‐parasitized animals, thereby reducing further risk of parasitism in experiments 2 and 3. Non‐parasitized, moderately feeding motivated (control) animals in experiment 2 significantly rejected the N+F+ sward, adopting a low parasite risk strategy; non‐parasitized, naive (control) animals in experiment 3 adopted a similar grazing strategy. In each of the remaining three choices in both experiments one sward held a clear nitrogen or faecal benefit (absence of faeces) which was selected for by all treatments.5.Sheep are able to make complex grazing decisions involving nutrition and faecal avoidance and these decisions are affected by their physiological state. However, faeces aversion in sheep greatly outweighs their attraction toward high nitrogen swards.
Flexible niche partitioning via a foraging mode shift: a proposed mechanism for coexistence in stream‐dwelling charrs
Authors: Nakano Shigeru , Fausch Kurt D. , Kitano Satoshi 
Published: March 2003

Summary1. Foraging behaviour, diet and interference competition were examined for two morphologically similar charrs,Salvelinus malma(Dolly Varden) andS. leucomaenis(white‐spotted charr), under varying food resource conditions over four summers in a Japanese mountain stream. Data were used to test predictions from a mechanistic model of resource partitioning developed from an earlier field experiment.2. The charrs adopted one of two distinct foraging modes, ambushing drifting invertebrates from relatively fixed foraging positions or actively searching for benthic prey over large areas. The proportion of benthos foragers increased markedly when drifting prey declined, and was much greater inS. malmathanS. leucomaeniswhen drift was lean, upholding predictions made from our earlier experiment.3. For drift foragers of both species, frequency of foraging attempts decreased as drift rate declined, and aggressive encounters increased. In contrast, for benthos foragers of both species the frequency of foraging attempts was essentially constant across the range of benthos biomass measured, and aggressive encounters remained low.4. Salvelinus leucomaenisate larger drifting prey thanS. malma, even though the former charr were smaller. In contrast,S. malmaforaged on benthic prey at a higher rate thanS. leucomaenis, although there was no difference in prey mass. Thus, the optimal point to shift to benthic foraging is at a higher drift threshold forS. malmathanS. leucomaenis, most probably due to differences in jaw morphology. Moreover, because dominance for favourable drift foraging positions was based on size alone,S. malmashifted to benthos foraging at a larger size thanS. leucomaenis, as predicted by a simple model.5. Charr consumed distinct prey types according to their foraging mode. Drift foragers primarily ate terrestrial invertebrates, whereas benthos foragers ate mainly chironomid larvae. Consequently, diet overlap was high when drift was abundant and both species were drift foragers, but declined as drift declined andS. malmashifted to benthos foraging. Therefore, species‐specific differences in foraging mode shifts across the resource gradient explained the flexible resource partitioning we observed, and probably account for the coexistence of these congeneric charrs in zones of sympatry in northern Japan.
The use of conspecific reproductive success for breeding habitat selection in a non‐colonial, hole‐nesting species, the collared flycatcher
Authors: Doligez Blandine , Danchin Etienne , Clobert Jean , Gustafsson Lars 
Published: March 2003

Summary 1. Breeding habitat quality strongly affects fitness. Therefore, individuals are likely to select their breeding habitat after gathering information on quality of potential breeding patches. In the study reported in this paper, we investigated whether local reproductive success of conspecifics in a patch (patch reproductive success, PRS) could be used to assess habitat quality and make dispersal decisions in a non colonial, hole‐nesting, passerine bird, the collared flycatcher (Ficedula albicollis). 2. Assumptions for such a breeding habitat selection mechanism were met: the habitat patches were of different quality, as measured by PRS, with relative quality varying between years, and PRS was autocorrelated in time. 3. As in many other species, breeding dispersal was related in both sexes to individual reproductive success before dispersal: unsuccessful individuals were more likely to disperse than successful ones. 4. Additively, PRS influenced both breeding and natal dispersal. This effect depended on sex. Dispersal was negatively related to PRS in females, and positively in males with low competitive ability (juvenile and unsuccessful adult males). 5. Breeding dispersal was positively related to flycatcher density in males, but negatively in females. Moreover, when included in the analyses, laying date of the previous breeding attempt (which should be correlated with competitive ability) replaced the effect of PRS in adult males. 6. The observed patterns can be explained by PRS (or another variable correlated with PRS) being used to assess different components of habitat quality in each sex, in relation to intraspecific competition pressure. We suggest that males of low competitive ability may either use PRS to assess the level of expected intraspecific competition the following year, and choose to disperse from high PRS woodlands, or be forced to disperse when PRS is high because of strong competition. Females might use PRS to assess the expected reproductive output if breeding in the patch the following year.
Host diet affects extinctions and colonizations in a parasitoid metapopulation
Authors: Van Nouhuys Saskya , Hanski Ilkka 
Published: March 2003

Summary1. In the Åland islands of SW Finland, the parasitoidCotesia melitaearum(Wilkonson) is a specialist on the Glanville fritillary butterfly,Melitaea cinxia(L.),which uses two host plants,Plantago lanceolata(L.) andVeronica spicata(L.).2. Extensive survey data on the butterfly and parasitoid populations collected in 1994–97 were used to examine possible associations of parasitoid colonizations and extinctions, with host population isolation, host population size, and host diet (plant species).3. The likelihoods of parasitoid colonization and host patch occupancy were found to increase with decreasing isolation from other parasitoid populations, increasing host population size and an increasing fraction of host larvae onV. spicata. The likelihood of parasitoid population extinction increased with decreasing host population size and decreasing fraction of hosts onV. spicata.The pattern of association was exceptional in one area of high‐density parasitoid populations as well as during a year of many extinctions but few colonizations.4. Among host populations occupied byC. melitaearum, the fraction of host larval groups parasitized was higher in host populations using the more rare host plant,V. spicata. If host larval groups were present on both host plant species within one host population, then the larval groups onV. spicatawere more likely to be parasitized.5. The large‐scale population dynamics of the parasitoid wasp are influenced by the distribution of the two host plants of the butterfly, by host‐plant‐dependent parasitoid behaviour and by host butterfly oviposition preference.6. Possible explanations for the apparent superiority ofV. spicataforC. melitaearumas the host butterfly's host plant are discussed. These include host larval group size, larval web structure, plant spatial aggregation, plant chemistry, and host larval physiology and phenology.
Sublethal infection and the population dynamics of host–microparasite interactions
Authors: Boots Michael , Norman Rachel 
Published: March 2003

Summary 1. A large group of parasites, including many of the larval pathogens of insects, cause an infection from which infectious hosts are unable to recover. In addition, a proportion of those individuals that do not develop the lethal disease on exposure to the parasite may still be harmed by it. 2. We examined the role of these sublethal effects on host‐population dynamics. Specifically we considered the case where there are three distinct classes of individuals: (i) susceptibles; (ii) infected and infectious individuals that will not reproduce and cannot recover; and (iii) sublethally infected individuals. 3. Parasites with sublethal effects are less likely to persist and control their host population. This is a consequence of the sublethally infected individuals not being infective. Less intuitively, the sublethal infection is highly destabilizing, increasing the risk of cyclic behaviour in host–parasite population densities. 4. Because sublethal infection acts as a destabilizing force in these host–parasite interactions, parasites with pronounced sublethal effects may be less effective as classical biological control agents.
Intermittent breeding in the short‐tailed shearwaterPuffinus tenuirostris
Authors: Bradley J. S. , Wooller R. D. , Skira I. J. 
Published: March 2003

1. At one colony of short‐tailed shearwaters in Bass Strait, Australia, all birds breeding have been recorded individually each year for over 50 years. Among individuals known to be alive and to have bred before, 14% of each sex were not present at their breeding colony, on average, in any one year.2. A further 15% of males and 13% of females (a significant difference), known to have bred before, were present but not associated with an egg in any one year.3. Intermittent breeding was associated with pair bond breakdown and with a reduced ability to raise offspring, even when years of absence were allowed for.4. The frequency of attendance, laying and successful rearing of progeny to fledging increased with age in the early years of breeding. However, this was followed by a decrease, except in the case of laying frequency, which continued to increase throughout life.5. Our analysis indicated that intermittent breeding in short‐tailed shearwaters did not result from individuals implementing trade‐offs between the effort required for breeding success and their breeding life span. Rather, we suggest that individuals of higher quality are able to breed more frequently than others without any compensatory reduction in either their annual breeding success or their overall breeding life span.
The effect of landscape composition on colonization success, growth rate and dispersal in introduced bush‐crickets Metrioptera roeseli
Authors: Berggren Å. , Carlson A. , Kindvall O. 
Published: March 2003

Summary

Fragmentation and habitat loss affects both existing and introduced populations. Small habitat areas may have harsher biotic and abiotic conditions, as well as restricting population sizes. Loss of connectivity reduces the opportunities for individuals to move between patches to rescue populations or to re‐colonize patches. Knowledge of how landscape composition affects the introduced populations is therefore essential for successful management and future re‐introductions.
To study the effect of landscape composition and structure on the success of colonization, population growth and dispersal distances, we introduced Roesel’s bush‐crickets Metrioptera roeseli to 70 habitat islands in areas previously unoccupied by the species. The introduction sites differed in habitat area and connectivity. The population survival and dispersal were then studied for 5 years after initial introductions.
In addition to results showing the importance of suitable habitat for population persistence, connectivity in form of linear landscape elements and nodes was also crucial. Linear landscape elements and/or nodes were important for colonization success, growth and dispersal. Linear landscape elements and nodes also reduced the negative effects of unsuitable habitat (matrix) and isolation from suitable habitat and on the populations.
These results stress the importance of connectivity in the landscape for population survival and establishment. Consideration of this should be taken into account in both management and re‐introductions of bush‐crickets and other invertebrates with similar population characteristics and behaviour.
Patterns of reproductive effort and success in birds: path analyses of long‐term data from European ducks
Authors: Blums Peter , Clark Robert G. , Mednis Aivars 
Published: March 2003

Summary

We tested ecological hypotheses about timing of breeding and reproductive effort in birds, by analysing > 15‐year data sets for individually marked females in three species of Latvian ducks (northern shoveler, tufted duck, common pochard).
Duckling survival and recruitment declined with advancing hatch date in pochard and tufted duck, after controlling for effects of female age and other factors with path analysis, a novel finding which indicates that fitness advantages associated with early hatching extended beyond the prefledging period. Logistic regression analysis suggested further that individual duckling prefledging survival was moderate in the earliest phase of the breeding season, greatest in mid‐season and lowest later on.
However, selection acting against early hatched ducklings was surpassed by strong directional selection favouring recruitment of the earliest hatching females. The absolute and relative numbers of female recruits produced by a breeding female declined sharply with advancing hatch date in all species.
Unlike previous studies, an hypothesized intraspecific trade‐off between duckling mass and brood size was detected, being very robust in two of three species.
Unexpectedly, female age effects on recruitment were manifested only indirectly by several pathways, the most important being the earlier hatching dates of older females. Size‐adjusted body mass (i.e. condition index) was positively related to reproductive success, and was 2–8‐fold more influential than female size (indexed by wing length).
Overall, fecundity‐independent variables (e.g. hatching date, weather, indices of duckling production and habitat quality) generally had 2–10 times greater influence on recruitment rates than did fecundity‐dependent variables such as female size or condition, duckling mass and brood size, suggesting a critical role for external environmental factors vs. individual female‐specific traits in the recruitment process.
Model complexity and population predictions. The alpine marmot as a case study
Authors: Stephens Philip A. , Frey‐roos Fredy , Arnold Walter , Sutherland Wlliam J. 
Published: March 2003

SummaryDuring the past 15 years, models have been used increasingly in predictive population ecology. Matrix models used for predicting the fates of populations are often extremely basic, ignoring density dependence, spatial scale and behaviour, and often based on one sex only. We tested the importance of some of these omissions for model realism, by comparing the performance of a variety of population models of varying levels of complexity.Detailed data from more than 13 years of behavioural and demographic research on a population of alpine marmotsMarmota marmotain Berchtesgaden National Park, southern Germany, were used to parameterize four different population models. The models ranged from a simple population‐based matrix model, to a spatially explicit behaviour‐based model.The performance of the models was judged by their ability to predict basic population dynamics under equilibrium conditions. Only a spatially explicit individual‐based model ignoring optimal behaviour predicted dynamics significantly different to those observed in the field, highlighting the importance of considering realistic patterns of behaviour in spatially explicit models.Using realistic levels of environmental and demographic stochasticity, variance in population growth rates predicted by all models was high, even within the range of population densities experienced in the field. This emphasizes the difficulty of using population‐level field data to determine overall patterns of density dependence for use in population models.All models were also used to predict potential density‐dependent effects on alpine marmot population growth. In this regard, the models differed greatly. It was concluded that the simplest matrix model was adequate for making predictions regarding population sizes or densities under equilibrium conditions, but that for predictions requiring an understanding of transient dynamics only the behavioural model would be adequate.An emergent feature of this study of alpine marmot population dynamics was the prediction of a demographic Allee effect with a profound influence on population dynamics across a very broad range of population sizes. Three mechanisms were identified as underlying this Allee effect: stochastic skews in sex ratio and demographic composition at low population sizes; less efficient social thermoregulation during hibernation in small groups; and difficulties with mate finding during dispersal, even at relatively high population sizes.