bluuebunny/crossref_metadata_2025_split huggingface dataset:
Survival costs of chick rearing in black‐legged kittiwakes
Authors: Golet Gregory H. , Irons David B. , Estes James A. 
Published: March 2003

1. We tested for costs of chick rearing in the black‐legged kittiwake Rissa tridactyla (Linnaeus) by removing entire clutches from 149 of 405 randomly selected nests, in which one or both mates was colour‐banded. After the manipulation, we monitored adult nest attendance and body condition at unmanipulated and manipulated nests, and measured the survival and fecundity of these adults the following year. 2. Late in the chick‐rearing period, adults from unmanipulated nests (i.e. with chicks) went on significantly longer foraging trips, and were significantly lighter for their size, than adults from manipulated nests (i.e. without chicks). 3. Adults from unmanipulated nests also survived to the following nesting season at a significantly lower rate than those from the manipulated nests (0·898 vs. 0·953), suggesting that attempting to raise chicks can reduce life expectancy by 55%. 4. There was a tendency for adults from nests that were unmanipulated in year one to have lower reproductive success in year two, primarily because of reduced fledging success, and a higher incidence of non‐breeding. 5. These findings suggest that mass loss in kittiwakes during chick rearing may not be adaptive. Raising chicks can lead to reproductive costs, and the causal mechanism appears to be a reduction in body condition. 6. We compare our results with previous brood (or clutch) size manipulation experiments that have measured adult body condition, survival and/or future fecundity. Although the empirical evidence suggests that long‐lived species are more likely to experience survival costs than short‐lived species, we believe the opposite may be true. We suggest that shifting the experimental protocol of cost of reproduction studies from brood enlargements (an approach taken in most prior studies) to brood reductions will provide more accurate quantifications of naturally occurring costs. 7. The cost of reproduction is one mechanism proposed to explain the reduced survival rates reported for kittiwake populations in the North Atlantic relative to those in the North Pacific ocean. Oceanographic data, however, suggest that lower food availability may limit survival of kittiwakes in the North Atlantic where a deeper mixed layer and reduced primary production combine to make conditions less favourable for this seabird during the winter months.
Population dynamics of apparent competition in a host–parasitoid assemblage
Authors: BONSALL MICHAEL B. , HASSELL MICHAEL P. 
Published: March 2003

Summary

The population dynamics of two moth species, Plodia interpunctella (Hübner) and Ephestia kuehniella Zeller in the presence of their shared parasitoid, Venturia canescens (Gravenhorst), were studied in well replicated time series experiments.
Moths were prevented from competing for resources and could therefore only interact via the shared parasitoid. This study examines the consequences of apparent competition on the population dynamics of a simple laboratory insect assemblage.
Ephestia kuehniella suffers severly in the presence of the shared parasitoid. In all eight replicates, this moth species is eliminated. Time series analysis reveals that the E. kuehniella populations show divergent oscillations.
Plodia interpunctella and V. canescens populations show persistent populations. Time series analysis reveals that there is a delayed density dependence acting on these populations and the dynamics are either stable equilibrium or damped oscillations.
Repeated‐measures analysis of the strength of the indirect interaction reveals that the effects of apparent competition before E. kuehniella is lost are amensal. The indirect interaction between E. kuehniella and P. interpunctella is [–, 0] rather than [–, –].
The spatial structure of populations
Authors: Thomas Chris D. , Kunin William E. 
Published: March 2003

1. Studies of the spatio‐temporal dynamics and structure of populations have identified many categories of population type. However, recognized categories intergrade, making it difficult to assign empirical population systems to single categories. 2. We suggest that most population categories can be arranged along two axes that combine per capita birth (B), death (D), emigration (E) and immigration (I) rates. The ‘Compensation Axis’ describes the source‐sink component of population structure, with source populations exporting individuals (B > D, E > I) and sinks and pseudosinks consuming individuals (B < D, E < I). The ‘Mobility Axis’ describes the involvement of a local population in regional (I + E) rather than local (B + D) processes, running from separate populations, through metapopulations, to patchy populations. 3. Each sample area within a spatially structured population system can potentially be assigned to a position along each of these axes, with individual sample areas weighted by local population size. The positions of these sample areas and their relative weightings allow the relative importance of different types of process to be judged. A worked exampled is provided, using the butterfly Hesperia comma. This approach shifts the emphasis from pattern (categories that real population systems do not fit) onto process. 4. In many systems, continuous variation in habitat quality and demographic parameters make clear distinctions between ‘habitat’ and ‘non‐habitat’ difficult to sustain. In such cases, we advocate the use of a spatial grid system, with effects of patch size and isolation combined into a single, weighted distance function (neighbourhood). 5. The relative importance of different processes depends on the spatial scale at which the system is observed. This again emphasizes the value of a process‐based approach.
The equilibrium assumption in estimating the parameters of metapopulation models
Authors: Moilanen Atte 
Published: March 2003

1. The construction of a predictive metapopulation model includes three steps: the choice of factors affecting metapopulation dynamics, the choice of model structure, and finally parameter estimation and model testing. 2. Unless the assumption is made that the metapopulation is at stochastic quasi‐equilibrium and unless the method of parameter estimation of model parameters uses that assumption, estimates from a limited amount of data will usually predict a trend in metapopulation size. 3. This implicit estimation of a trend occurs because extinction‐colonization stochasticity, possibly amplified by regional stochasticity, leads to unequal numbers of observed extinction and colonization events during a short study period. 4. Metapopulation models, such as those based on the logistic regression model, that rely on observed population turnover events in parameter estimation are sensitive to the implicit estimation of a trend. 5. A new parameter estimation method, based on Monte Carlo inference for statistically implicit models, allows an explicit decision about whether metapopulation quasi‐stability is assumed or not.6. Our confidence in metapopulation model parameter estimates that have been produced from only a few years of data is decreased by the need to know before parameter estimation whether the metapopulation is in quasi‐stable state or not.7. The choice of whether metapopulation stability is assumed or not in parameter estimation should be done consciously. Typical data sets cover only a few years and rarely allow a statistical test of a possible trend. While making the decision about stability one should consider any information about the landscape history and species and metapopulation characteristics.
Density–distribution relationships in British butterflies. II. An assessment of mechanisms
Authors: Cowley M. J. R. , Thomas C. D. , Wilson R. J. , León‐Cortés J. L. , Gutiérrez D. , Bulman C. R. 
Published: March 2003

Summary The interspecific density–distribution relationship is a general and robust pattern that has been described as a rule in community ecology. Many theoretically plausible causes of the relationship have been described, but it is still disputed which factor(s) are most important. Using data on the densities and distributions of butterflies and their host plants collected in a 35‐km2area of north Wales, and data on butterfly mobility, niche breadth, habitat breadth and distance from range margins, we examined five of the principal explanatory mechanisms. We found that several variables were significantly correlated with density or distribution. Habitat breadth, mobility and distance from range margin had significant positive effects on butterfly distribution. Host‐plant density was significantly positively related to butterfly density; mobility was significantly negatively related to density. Despite these results, we could not unambiguously demonstrate that one hypothesis (or several interacting hypotheses) generated density–distribution correlations. The most conclusive evidence was that statistical patterns of distribution (aggregation models) underpinned the positive density–distribution relationship seen amongst the more mobile butterflies. The results provided evidence against the metapopulation dynamic explanation, and were equivocal with respect to the contributions of range position, niche breadth and resource availability. An alternative approach was to explore deviations from the underlying relationship between density and distribution, rather than concentrating on the correlation itself. This approach wasmuchmore successful: we demonstrated that species that occurred at high densities relative to their distributions used aggregated resources and were relatively sedentary; whereas those that occurred at low densities relative to their distributions used less aggregated resources, and were more mobile. Mobile species had less aggregated distributions than did relatively sedentary species. Given that the interspecific density–distribution pattern appears to be almost ubiquitous and that the proposed explanations are not mutually exclusive, faster progress may be made by examining deviations from the pattern than from further analysis of the pattern itself.
Food limitation explains most clutch size variation in the Nazca booby
Authors: Clifford L. D. , Anderson D. J. 
Published: March 2003

Summary Natural selection is expected to optimize clutch size, but intrapopulation variation is maintained in many bird species. The Nazca booby provides a simple system in which to investigate clutch size evolution because clutch size and brood size are decoupled due to obligate siblicide. The indirect effect of brood size on clutch size evolution can therefore be eliminated. In Nazca boobies, second eggs provide insurance against the failure of the first egg or early death of the first hatchling, but approximately half of all females lay only one egg. We tested the hypothesis that one‐egg clutches result from food limitation by providing female Nazca boobies with supplemental food. A higher proportion of supplemented females produced two‐egg clutches than did control females. Supplemented females produced larger second‐laid eggs than did control females, but not first‐laid eggs. Laying date and laying interval were not affected. Comparisons of clutch size and egg volume between years indicated that the supplemental feeding experiment was not conducted in a year with a poor natural food supply. Thus supplemented females produced larger clutch sizes despite apparently normal natural food levels. This experiment nearly completes our understanding of clutch size variation in the Nazca booby, and indicates that food limitation and the costs of egg‐laying should be considered carefully in studies of clutch size evolution.
Using individual‐based simulations to test the Levins metapopulation paradigm
Authors: Keeling Matt J. 
Published: March 2003

Summary

Levins metapopulations have become a standard tool for modelling spatially heterogeneous populations. The acceptance of these models by ecologists may be attributed to their simple structure and their use of presence–absence data.
Using structured‐metapopulations, which possess stochastic dynamics at the local subpopulation level, the extinction and subsequent recolonization rates can be calculated and compared to those of the classical Levins model.
Single‐species metapopulations conform to the Levins ideal, validating the widespread use of this conceptual model. However, multispecies systems are shown to deviate in a consistent manner. This deviation, which is explained in terms of a correlation between patch occupancy and average population levels of the species, can be used to identify the signature of enemy–victim interactions.
Longevity of kings and queens and first time of production of fertile progeny in dampwood termite (Isoptera; Termopsidae; Zootermopsis) colonies with different reproductive structures
Authors: Thorne Barbara L. , Breisch Nancy L. , Haverty Michael I. 
Published: March 2003

Summary

We report age‐specific survivorship of founding kings and queens and colony age of first production of fertile progeny (alates) of two cohorts, containing 52 and 42 complete colonies, respectively, in the primitive dampwood termite Zootermopsis nevadensis ssp. nevadensis.
Longevity of kings and queens was determined and compared in various experimental manipulations of reproductive structure of incipient colonies (removal of king or queen or both vs. unmanipulated pairs as controls) performed one year after pairing. Life span of reproductives was also evaluated in circumstances of interactions between young colonies, a treatment inspired by field observations of natural nest spacing and intraspecific competition between young dampwood termite colonies.
In our first experimental series, founding pairs survived 2–7 years (x̄ = 4·5 ± 0·3 SE) after pairing. Kings lived significantly longer (x̄ = 4·7 ± 0·3 years after pairing; range 2·2–7·3 years) in treatments initiated as pairs than when left as the remaining founder in the queen removal treatment (x̄ = 3·2 ± 0·6 years after pairing; range 1·5–5·3 years), even though one or more female replacement reproductives differentiated within several months after queen loss. Queen life span in the absence of kings averaged 4·9 ± 0·4 years (range 3·6–6·3 years) after pairing, not significantly different from the life span of queens living with kings. There was no significant difference between king and queen life spans in non‐interaction treatments in our first experiment. Results from the second experimental series (35 colonies) are presented to date.
Survival of pairs until death of one mate was significantly shorter in interaction treatments compared with control colonies, suggesting that intraspecific competition between young colonies may create opportunities for replacement reproductives.
The first alates were produced between 1·8 and 6·5 years after pairing in our first experimental series, and between 2·4 and 5 years, to date, in the second experiment.
Ecological and evolutionary correlates of long life span in social insect reproductives and other animals are discussed.
Long‐term recolonization patterns of ants in Western Australian rehabilitated bauxite mines with reference to their use as indicators of restoration success
Authors: Majer J.D. , Nichols O.G. 
Published: March 2003

1.  The return of invertebrate animals to rehabilitated mine pits is desirable for the re‐establishment of ecosystem functioning. A long‐term ant monitoring programme is reported over 14 years in a jarrah Eucalyptus marginata forest control plot and in three bauxite mine pits, one of which had been left unvegetated, one planted with marri trees E. calophylla and the other seeded with mixed native plant species. 2.  The results confirm published findings for the first 2 years of the succession that seeding with mixed species results in a more rapid attainment of a forest‐like ant fauna, although in the last 6 years of the study the ant fauna of the planted plot had become more similar to that of the seeded plot. 3.  Changes in the nature of the ant fauna are described and it is concluded that although composition has substantially converged on that of the forest by the end of the study, differences still persist. 4.  Research on vegetation, spiders and ants in bauxite mined areas which have been rehabilitated using more recent technology suggest that these differences will lessen with time and with the introduction of improved rehabilitation prescriptions. 5.  An additional aim of the study was to validate the chronosequence approach to studying ecosystem recovery following disturbances such as mining. It is concluded that long‐term studies provide important information that is missed by the chronosequence approach. Ideally, rapid‐feedback chronosequence approaches should be augmented by long‐term case studies.
Effects of delayed hay removal on the nutrient balance of roadside plant communities
Authors: Schaffers A. P. , Vesseur M. C. , Sýkora K. V. 
Published: March 2003

1. Mass losses and nutrient losses from fresh roadside cuttings were studied in the field during a 6‐week period. Large amounts (over 50%) appear to be lost from the cuttings. The losses were positively related to initial nutrient concentrations during this short‐term study. Mass and nitrogen losses were best explained by the initial C:N ratio, phosphorus and potassium losses by the initial phosphorus concentration. 2. For potassium the losses were particularly large (up to 90%). For this element only, the observed relationship between loss rate and initial chemical composition could not be established significantly. It is concluded that potassium is mainly lost by leaching whereas the major nitrogen, phosphorus and mass losses are most probably caused by rapid microbial decomposition of readily soluble substances. 3. Using existing data on chemical composition of other roadside cuttings, nutrient losses after different hay removal delay times were modelled for different plant communities. All or most of the losses were assumed to return to the soil system. 4. When soil impoverishment is aimed for, cuttings should be removed within 1 or 2 weeks in most plant communities. If removal is delayed longer, the amounts of nutrients removed will often fall below the annual atmospheric input. In plant communities where annual above‐ground production of nitrogen and phosphorus are lower than the annual atmospheric deposition already, rapid removal of the cuttings may be the only way to maintain at least potassium at a limiting level. 5. The main effect of hay‐making on the soil nutrient status most likely consists of a reduction of the potassium availability, at least on sandy soils with a low cation exchange capacity and provided there is little delay in hay removal.
Response of soybean to attack by stemfly Melanagromyza sojae in farmers' fields in Indonesia
Authors: VAN DEN BERG H. , SHEPARD B. M. , NASIKIN  
Published: March 2003

Summary

To determine the effect of Melanagromyza sojae, a common pith‐boring agromyzid fly, on soybean under field conditions in Indonesia, physiologically mature plants from 70 farmers' field sites were uprooted. Plant parameters and exit holes in the stem (created by M. sojae prior to pupation) were recorded.
Melanagromyza sojae was present at all sites and infested 84% of the plants. Farmers' applications of insecticides had no influence on the infestation level by M. sojae. Most exit holes occurred above the cotyledons.
Exit holes in the hypocotyl (i.e. the stem section below the cotyledons), indicative of early attack, were associated with a decrease in the number of seeds per plant, stem diameter and plant height. This suggests that early attack adversely affects plant development. Exit holes above the hypocotyl, indicative of attack later in the season, were associated with an increase in plant parameters, suggesting that late attack occurred in response to the plant's size or vigour.
Multiple regression was conducted to evaluate the influence of infestation on seed production. Separate models were used to analyse early and late attack. For late attack, the plant variables ‘stem diameter’ and ‘plant height’ were added to the regression.
Early attack caused less than 2% yield loss on a per‐plant basis. Possible compensation by neighbouring plants was not considered. Later attack did not reduce yield. Therefore measures to control M. sojae would have been unwarranted.
Infestation had no effect on the 100‐seed weight, confirming that the number of seeds per plant reliably predicted yield.
Testing large‐scale hypotheses using surveys: the effects of land use on the habitats, invertebrates and birds of Himalayan rivers
Authors: Manel S. , Buckton S.T. , Ormerod S.J. 
Published: March 2003

1. Piecemeal changes in land use might have cumulative effects on regional biodiversity. However, this hypothesis is difficult to test experimentally at the scales involved, so alternative approaches are required. Here, we illustrate some of the strengths and weaknesses of surveys for evaluating the effects of land use on rivers and river birds over a large area of the Himalayan mountains.2. We surveyed 180 streams and their catchments in north‐west India and Nepal in 1994–96. We then used analysis of covariance (ancova), multiple linear regression and multiple logistic regression to assess how stream habitat structure, stream chemistry, aquatic invertebrate abundance and the occurrence of river birds were affected by land use after accounting for altitudinal pattern.3. Streams draining terraced catchments differed significantly in habitat structure from other streams. They had more physical modifications, wider channels, fewer cascades, finer substrata and simpler riparian vegetation with fewer trees. We detected no clear effects of land use on stream chemistry, but terracing was accompanied by significantly increased abundances of benthic dipterans, ephemeropterans and total aquatic invertebrates.4. River bird occurrence was best explained by altitude, and secondarily by habitat structure. Some of the habitat features influenced by terracing significantly affected birds both positively (grey wagtailMotacilla cinerea) and negatively (little forktailEnicurus scouleri, river chatChaimarrornis leucocephalus, brown dipperCinclus pallasii, plumbeous redstartRhyacornis fuliginosus). However, only in the grey wagtail did the presence of terracingper seaffect occurrence unequivocally; effects on other species were either small or confounded by altitude.5. We cannot refute the hypothesis that catchment land use affects Himalayan river ecology, but our data on the regional consequences for river birds were equivocal. We suggest that large‐scale surveys, although providing one of the few pragmatic methods of assessing large anthropogenic effects on ecosystems, will need careful design to factor out potential confounds if they are to be used to test hypotheses robustly. They should also be supported where possible with process studies, intervention studies and model applications to independent data.