bluuebunny/crossref_metadata_2025_split huggingface dataset:
Population dynamics of the Indian meal moth: demographic stochasticity and delayed regulatory mechanisms
Authors: Bjørnstad Ottar N. , Begon Michael , Stenseth Nils ChR. , Falck Wilhelm , Sait Steven M. , Thompson David J. 
Published: March 2003

1.  Laboratory populations of the Indian meal moth [Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae)], undergo sustained periodic fluctuations in abundance. The period is just longer than the generation time. The fluctuations are accentuated in the presence of the P. interpunctella granulosis virus (PiGV). 2.  Time series spanning 8–10 generations from three replicate populations of the virus‐free (VF) system and three from the virus‐infected (VI) system are investigated using nonparametric autoregressive time series models. 3.  The dynamics are concluded to correspond to a third order process consistent with interactions in a three‐dimensional stage‐structured model for both systems. The functionally different interactive stages are believed to be the egg stage (preyed upon by larvae), small larvae (competing for resources and cannibalized by large larvae) and large larvae (competing for resources). 4.  The virus is seen as a modulator of the host vital rates more than an independent agent in a trophic host–pathogen interaction. The virus increases developmental time and decreases fecundity of the moths. 5.  A significantly nonlinear additive autoregressive model of order 3 appears to give a parsimonious description of the series. 6.  The demographic (birth and death) nature of the stochasticity inherent in the system is explicitly incorporated in the statistical model for the time series by assuming an overdispersed Poisson process. The variability around the skeleton is found to conform closely to this assumption. The demographic nature of the stochasticity cannot be fully understood on the basis of Gaussian (least‐squares) models on transformed (variance‐stabilized) data. 7.  Significant density dependencies are found at a 1‐week lag, a 2‐ to 3‐week lag and at a 6‐ to 7‐week lag. These are argued to be the signatures of within‐stage competition, between‐stage interactions and reproduction, respectively. Negative and statistically significant density dependence is apparent for the first two of these. No significant negative density dependence is apparent in the lag corresponding to reproduction. 8.  The fluctuations in both the VF and VI system appear to represent limit cycles or weakly dampened cycles clothed by Poisson demographic stochasticity. 9.  The enhanced cycles of the VI system are demonstrated to be consistent with a situation where the functional forms for the interactions are nearly the same as for the VF, but with delay structure shifted by just less than a week.
Non‐geographically based population structure of South Pacific sperm whales: dialects, fluke‐markings and genetics
Authors: Whitehead Hal , Dillon Mary , Dufault Susan , Weilgart Linda , Wright Jonathan 
Published: March 2003

1.  This study addresses the issue of structure in sperm whale (Physeter macrocephalus Linnaeus) populations and whether it is geographically based. 2.  During a survey around the South Pacific Ocean, we collected sloughed skin for genetic analyses, recorded coda vocalizations, and photographed fluke markings. 3.  Groups of female and immature sperm whales had characteristic mitochondrial haplotypes, coda repertoires, and fluke‐mark patterns, but there was no clear geographical structure in any of these attributes. 4.  However, similarities of coda repertoire and mitochondrial haplotype distribution were significantly correlated among pairs of groups in a manner that was not geographically based. There was also a significant canonical correlation coefficient between coda repertoire and fluke‐mark patterns. 5.  These results suggest that attributes (such as vocal repertoire and techniques of predator defence) which are acquired matrilineally, and probably culturally, are conserved during the fission and dispersal of groups.
Non‐interactive fish communities in the coastal streams of North‐western France
Authors: OBERDORFF THIERRY , HUGUENY BERNARD , COMPIN ARTHUR , BELKESSAM DJAMILA 
Published: March 2003

1.  Spatial patterns of freshwater fish species at regional and local scales were investigated to explore the possible role of interspecific interactions in influencing distribution and abundance within communities occupying coastal streams of North‐Western France. 2.  Nine sites from nine streams situated in the same biogeographical region were sampled annually over the 6‐year period from 1990 to 1995. 3.  Similar habitats (sites) with richer regional colonization pools exhibited proportionally richer local communities in terms of number of species, total density and total biomass of individuals. Furthermore, no negative relationships were found between density and biomass of each of the most common species and local species richness. 4.  Results of dynamic regression models (applied to the above‐mentioned species) suggest an absence of strong competition between all pairs of species. 5.  The evidence on lack of density compensation for species‐poor communities and absence of perceptible interspecific competition between species suggest that the communities studied are non‐interactive. 6.  Two main explanations can be advanced. First, the local abundance of species in the communities studied could be determined through differential responses to unpredictable environmental changes, rather than through biological interactions. Second, as a result of historical events, the communities studied are reduced in congeneric species which can limit, in turn, the influence of interspecific competition in structuring these communities. 7.  These results underline the strong influence of regional processes in shaping local riverine fish communities and minimize the possible influence of species interactions in governing these communities.
Local trophodynamics and the interaction of marine mammals and fisheries in the Benguela ecosystem
Authors: YODZIS PETER 
Published: March 2003

1.  A method for finding the consequences of long‐term generalized press perturbations in multispecies ecological communities, with relatively modest requirements for data, is explicated. The approach uses energetic and allometric reasoning to set some parameter values for which data are not available. The remaining unknown parameters are treated as random variables, enabling the calculation of probability distributions for the outcomes that are of interest. 2.  The method is used to investigate the effect of a cull of fur seals on fisheries in the Benguela ecosystem, using a 29‐species foodweb for that system. In the case of Cape fur seals treated here, it is found that a cull of seals is more likely to be detrimental to total yields from all exploited species than it is to be beneficial. 3.  The influence of weak links on the effects of a cull is investigated. Using both consumption by each species and consumption of each species to define link strength, a clear threshold in link strength is found, indicating that 44% of all links could be deleted from the foodweb without affecting the predictions significantly. Even using a criterion based on consumption by each species alone (conventional dietary proportion data), about the same number of links can be deleted without seriously affecting the predictions of the model. This is a very helpful (and encouraging) result for the design of an observational protocol for systematic efforts to gather data for multispecies modelling.
Sampling effort, regression method, and the shape and slope of size–abundance relations
Authors: Griffiths David 
Published: March 2003

1. Despite a substantial body of work there remains much disagreement about the form of the relationship between organism abundance and body size. In an attempt at resolving these disagreements the shape and slope of samples from simulated and real abundance–mass distributions were assessed by ordinary least squares regression (OLS) and the reduced major axis method (RMA). 2. It is suggested that the data gathered by ecologists to assess these relationships are usually truncated in respect of density. Under these conditions RMA gives slope estimates which are consistently closer to the true slopes than OLS regression. 3. The triangular relationships reported by some workers are found over smaller mass and abundance ranges than linear relations. Scatter in slope estimates is much greater and positive slopes more common at small sample sizes and sample ranges. These results support the notion that inadequate and truncated sampling is responsible for much of the disagreement reported in the literature. 4. The results strongly support the notion that density declines with increasing body mass in a broad, linear band with a slope around −1. However there is some evidence to suggest that this overall relation results from a series of component relations with slopes which differ from the overall slope.
Distribution ofCrassiphiala bulboglossa, a parasitic worm, in shoaling fish
Authors: Krause Jens , Ruxton Graeme D. , Godin Jean‐Guy J. 
Published: March 2003

1. The distribution of transmittable parasites in group‐living host species has been investigated in a number of studies. However, little is known about the distribution of parasites with indirect life cycles in this context. This study investigates the relationship between parasitism and shoal composition by looking at the distribution ofCrassiphiala bulboglossa(Haitsma), a trematode worm which uses fish as an intermediate host, within and between fish shoals in a lake. In particular, tests aimed at establishing whether the parasite distribution was affected by parasite‐assortative shoaling behaviour, host group size, host habitat characteristics, and other factors (such as species identity and body length) that potentially covary with parasite infection.2.Overall, 34 fish shoals were caught. For each shoal member, the fish species was identified, its standard body length measured and its parasites (C. bulboglossa) counted. Three habitat characteristics were also recorded for each shoal: water depth and distances to shore and to vegetation.3.Crassiphiala bulboglossaprevalence and load varied with fish species. Only 6% of the golden shiners [Notemigonus crysoleucas(Mitchill)] were parasitized, whereas 24% of the killifish (Fundulus diaphanus(Lesueur)] and 98% of the white suckers [Catostomus commersoni(Lacépède)] were infected. Infected shiners and killifish had very low parasite loads, whereas suckers were heavily parasitized. Parasite prevalence within shoals was not correlated with the average body lengths of killifish and shiners in shoals (sample size was too small for testing in suckers).4.Killifish shoals showed parasite prevalences significantly different from those expected under a null hypothesis that assumes assortment of fish between shoals by size and species but not by parasitism. In shiners and suckers, no evidence for non‐random distribution of parasites among shoals was found, which may have been because of lack of statistical power.5.Parasite prevalence was related to the number of conspecifics in a shoal for shiners but not for killifish.6.There was no significant relationship between parasite prevalence and habitat characteristics in shiners and killifish.
Increasing returns in the life history of Columbian ground squirrels
Authors: Dobson F. Stephen , Risch Thomas S. , Murie Jan O. 
Published: March 2003

1. We examined positive associations and trade‐offs of maternal and reproductive traits in a population of Columbian ground squirrels, Spermophilus columbianus. 2. Structural size, body condition, mother's personal allocation to body mass during reproduction, and timing of littering were estimated for live‐trapped reproductive females that were observed during an 8‐year period, and were compared to litter mass, litter size, and average pup mass using path analyses. 3. Mothers exhibited age‐structured traits that influenced reproductive patterns. Yearling mothers were significantly smaller, bred later, and had smaller litters than older females. Mothers that gained more body mass during reproduction and older mothers in good body condition that were structurally large had larger litters. 4. Early seasonal timing of littering was an important positive influence on successful reproduction by older mothers only in early breeding seasons and in years when conditions for reproduction were good for all females. 5. The number of offspring that survived to 1 year of age was most strongly associated with litter mass and litter size; date of breeding was of secondary influence, with earlier litters exhibiting greater success. 6. In general, mothers that gained the most in body mass during reproduction were concurrently more successful in weaning large litters (perhaps due to better quality of foraging habitat). 7. In addition to expected reproductive trade‐offs, reproduction by Columbian ground squirrels exhibited positive associations of life‐history traits that may reflect evolutionary increasing returns.
Dispersal in a metapopulation of the bush cricket,Metrioptera bicolor(Orthoptera: Tettigoniidae)
Authors: Kindvall Oskar 
Published: March 2003

1. I present a stochastic simulation model that describes individual movements ofMetrioptera bicolorPhilippi in a heterogeneous landscape, consisting of patches of suitable habitat surrounded by a matrix of unprofitable habitats. Although the model is parameterized with information about daily movement behaviour, it can generate spatially explicit predictions about inter‐patch dispersal rates for much longer periods, e.g. one generation.2.Long‐term dispersal experiments were conducted to evaluate model predictions. Patch‐specific emigration rates and the total distance moved by individuals could be predicted with satisfactory precision. Because of the stochastic nature of the model, it failed to predict which recipient patches emigrating individuals actually chose in a particular situation.3.Spatially explicit simulations of the movement model were made for the whole natural distribution area ofM. bicolor. The results suggest that emigration rates are negatively correlated with patch size. Local populations occurring on small patches may be more prone to extinction than those on large patches, by losing more emigrants than are compensated for by immigration.
Consequences of maternal size for reproductive expenditure and pupping success of grey seals at North Rona, Scotland
Authors: Pomeroy P. P. , Fedak M. A. , Rothery P. , Anderson S. 
Published: March 2003

1. The reproductive performance of individually marked mothers aged between 4 and 36 years breeding at the established grey seal colony of North Rona, Scotland was studied. Natality rate was between 0·805 and 0·975 for these females during 1979–95 and 57% of females produced 74% of the pups born. Mothers pupped successfully on N. Rona after absences of up to 5 years. 2. The average maternal postpartum mass (MPPM) of mothers was 190 ± 23 (SD) kg, larger than had been recorded from this colony previously. Although annual mean MPPM increased during the study, there were increases and decreases in individuals’ MPPM between years. 3. Pup mass at birth and pup growth rate were related to MPPM and date of parturition. No evidence of differential postpartum expenditure in the sexes was found. Relative pup birth mass decreased with MPPM but relative pup weaning mass remained constant over the range of MPPM. 4. Maternal mass expenditure during lactation averaged 39% of MPPM, and the consequences for MPPM in the year following either high or low relative expenditure were inversely related to relative expenditure in the first year. However, mothers increased their mass after skipping breeding in a year. 5. General Linear Models and REML analyses indicated that expenditures were significantly different between mothers when other variables and factors had been taken into account. In general, maternal expenditure was greater for animals of larger masses and duration of lactation, but corrected maternal expenditure of longer individuals was less than expected. Pup mass at weaning was influenced by mother's identity and year and there was evidence that individual mothers which were longer for their weight raised smaller pups. 6. The life history consequences of reproductive expenditure in any year appeared in subsequent breeding patterns. The cost of breeding for larger animals and larger expenditures was indicated by lower pupping success rates in years following births and skipped breeding years.
Asymmetric competition between two tit species: a reciprocal removal experiment
Authors: Torok JÁnos , TÓth LÁszló 
Published: March 2003

1. In a 5‐year field experiment, competition for food was tested between great tit (Parus major L.) and blue tit (P. caeruleus L.), two common hole‐nesters in Central Europe. Experimental (‘allopatric’) populations of both species were created during the breeding seasons by preventing the nesting or egg laying of one of the competing species. 2. An asymmetric relationship was found between the two tits; blue tits were more successful in the competitive interaction. Detectable effects were found only in nestling condition. Great tits raised lighter nestlings when breeding sympatrically with blue tits. 3. A possible mechanism is suggested that could be responsible for the different competitive abilities of the two species; blue tits are more effective in utilizing the most abundant size categories of caterpillar food supply than great tits.
Synchrony, scale and temporal dynamics of rock partridge (Alectoris graeca saxatilis) populations in the Dolomites
Authors: Cattadori Isabella. M. , Hudson Peter. J. , Merler Stefano , Rizzoli Annapaola 
Published: March 2003

1. Harvesting records of rock partridge (Alectoris graeca saxatilis) were examined first to identify the presence of cycles in a species with a southern European distribution and then to examine synchrony between populations at a range of scales. 2. Hunting records from 1965 to 1994 were obtained from 210 hunting areas and analysed at three spatial scales: subpopulation, population and metapopulation. Rock partridge exhibited cyclic fluctuations in about 40% of the time series with a period of 4–7 years. The results did not change with spatial scale. The density‐dependent structure of the populations showed that most populations exhibited damped oscillations. 3. The proportion of populations that were in synchrony increased with scale from the population to metapopulation level. There was no decline in synchrony with distance but a large variation between populations irrespective of distance. 4. The populations clustered into dry and wet habitats, with those in the dry habitat being more cyclic. We suggest the lack of spatial synchrony with distance but greater synchrony within habitats may reflect the influence of stochastic events operating on populations with different density dependence structures.
Rabbits killing birds: modelling the hyperpredation process
Authors: Courchamp Franck , Langlais Michel , Sugihara George 
Published: March 2003

1. Introduced rabbits are known to have catastrophic effects on oceanic islands, either by direct destruction of the vegetative cover, or by the resulting disturbance of indigenous vertebrates. 2. Another dramatic effect, less well known, but potentially of major importance, is the hyperpredation process. This process, related to apparent competition, predicts that an introduced prey species, well adapted to high predation pressure, could induce the extinction of an indigenous prey, through the sudden increased population size of an introduced predator. In many island ecosystems, the simultaneous presence of introduced feral cats and rabbits is thus potentially a further threat for small vertebrates endemic of these islands. 3. Through a mathematical model, we tested this hypothesis, using a tri‐trophic system comprising an indigenous prey (birds), an introduced prey (rabbits) and an introduced predator (cats), and we demonstrated the theoretical existence of the hyperpredation process. 4. In addition, the numerical analysis of the model allowed a quantification of this process. It shows that the conditions required for an indigenous species to cope with the hyperpredation process imply very high intrinsic growth rates and/or carrying capacity, as well as behavioural anti‐predator response to the introduced predator. Since these conditions are unlikely to be met, this process is a further potential threat to most indigenous vertebrate prey. 5. Finally, our model shows that, although it can be induced by both types of adaptation together or alone, behavioural adaptations alone are more powerful in generating the hyperpredation process, than are life history traits adaptations.
Spatial dynamics of predation by carabid beetles on slugs
Authors: Bohan David A. , Bohan Anna C. , Glen David M. , Symondson William O. C. , Wiltshire Christopher W. , Hughes Louise 
Published: March 2003

Summary 1. An explicitly spatial sampling approach was employed to test the null hypothesis that the predation on slugs by the carabid beetle Pterostichus melanarius (Illiger) was opportunistic. 2. The beetles and slugs were sampled across a nested series of grids of sampling points, in a field of winter wheat during June and July 1997. 3. The spatial distribution of all slugs in June was found to change with the scale of the sampling grid, from random on the 0.25 m scale, through aggregation at 1 m, to random at 4 m. At the highest scale of 16 m, the slugs were significantly spatially aggregated. 4. The distribution of beetles in June was also spatially dynamic, with randomness observed at the 4 m and 8 m scales. At 16 m, significant aggregation was observed. 5. The dynamic distributions of slugs and beetles, at 16 m, were found not to be associated with, and thus were not determined by, soil or crop factors. 6. Comparison of slug and beetle populations showed, however, that the distributions at 16 m were dynamically associated with each other. In June where there were many slugs there were also many carabids, whilst in July where there were many carabids there were few slugs. 7. Approximately 11% of the beetles sampled across the 16 m grid in June and July were found to have ingested slug protein, following intensive enzyme‐linked immunosorbent assay (ELISA) testing. 8. The spatial distribution of these slug‐positive beetles was significantly associated with the distribution of the larger slug classes, over 25 mg. Where there were many large slugs in June there were many slug‐positive beetles. Conversely, in July few large slugs were found where there were many slug‐positive beetles. 9. Parametric analysis revealed that these changes in the large slug class, at each sampling point between June and July (growth), were negatively related to the local numbers of slug‐positive beetles, and that growth declined as the local numbers of beetles increased. 10. These findings suggest that predation was not opportunistic, but direct and dynamic, falsifying the null hypothesis. Moreover, this predation elicited significant changes in the spatial distribution and local density of the slugs, in a manner that may be termed spatially density dependent.