bluuebunny/crossref_metadata_2025_split huggingface dataset:
A test for a regime shift
Authors: SOLOW ANDREW R. , BEET ANDREW R. 
Published: April 2005

AbstractThis note describes a formal statistical approach to testing for a regime shift based on population time series for a system of interacting species or groups. Under this approach, a regime shift is said to occur if the system switches abruptly from varying around one locally stable steady state to varying around another. This allows the problem to be formulated as testing for a changepoint in a vector autoregressive process. The test is illustrated using data from the North Sea covering the period 1963–97.
Differential effects of landscape and management on diversity and density of ground‐dwelling farmland spiders
Authors: SCHMIDT MARTIN H. , ROSCHEWITZ INDRA , THIES CARSTEN , TSCHARNTKE TEJA 
Published: April 2005

Summary

The distribution and abundance of animals are influenced by factors at both local and wider landscape scales. Natural enemies of pests in arable fields often immigrate from the surrounding landscape, and are also influenced by local management practices. Thus, landscape diversification and farming methods may both enhance farmland biodiversity, but their relative roles and possible interactions have been little explored.
The relationships of ground‐dwelling spiders (Araneae) to landscape features and to organic agriculture were studied in 12 pairs of organic vs. conventional fields of winter wheat Triticum aestivum along a gradient of landscape complexity.
High percentages of non‐crop habitats in the landscape increased local species richness of spiders from 12 to 20 species, irrespective of local management. This indicates that larger species pools are sustained in complex landscapes, where there is higher availability of refuge and overwintering habitats.
Organic agriculture did not increase the number of spider species, but enhanced spider density by 62%. Additionally, spider density was positively related to the percentage of non‐crop habitats in the surrounding landscape, but only in conventional fields.
Synthesis and applications. The species richness of ground‐dwelling spiders in crop fields was linked to large‐scale landscape complexity, while spider densities responded to local management practices. Organic agriculture benefits farmland spiders and augments the numbers of predatory spiders, thereby contributing to pest control. However, measures to conserve species richness must also take landscape‐scale factors into account. Complex landscapes including perennial non‐crop habitats should be preserved or restored to achieve high levels of spider diversity.
Why high seed densities within buried mesh bags may overestimate depletion rates of soil seed banks
Authors: VAN MOURIK TOM A. , STOMPH TJEERD J. , MURDOCH ALISTAIR J. 
Published: April 2005

Summary

Estimates of seed bank depletion rates are essential for modelling and management of plant populations. The seed bag burial method is often used to measure seed mortality in the soil. However, the density of seeds within seed bags is higher than densities in natural seed banks, which may elevate levels of pathogens and influence seed mortality. The aim of this study was to quantify the effects of fungi and seed density within buried mesh bags on the mortality of seeds. Striga hermonthica was chosen as the study species because it has been widely studied but different methods for measuring seed mortality in the soil have yielded contradictory estimates.
Seed bags were buried in soil and exhumed at regular time intervals to monitor mortality of the seeds in three field experiments during two rainy seasons. The effect of fungal activity on seed mortality was evaluated in a fungi exclusion experiment. Differences in seed‐to‐seed interaction were obtained by using two and four densities within the seed bags in consecutive years. Densities were created by mixing 1000 seeds with 0, 10, 100 or 1000 g of coarse sand.
The mortality rate was significantly lower when fungi were excluded, indicating the possible role of pathogenic fungi.
Decreasing the density of seeds in bags significantly reduced seed mortality, most probably because of decreased seed‐to‐seed contamination by pathogenic fungi.
Synthesis and applications. Models of plant populations in general and annual weeds in particular often use values from the literature for seed bank depletion rates. These depletion rates have often been estimated by the seed bag burial method, yet seed density within seed bags may be unrealistically high. Consequently, estimates of seed mortality rates may be too high because of an overestimation of the effects of soil or seed‐borne pathogens. Species that have been classified from such studies as having short‐lived seed banks may need to be re‐assessed using realistic densities either within seed bags or otherwise. Similarly, models of seed bank dynamics based on such overestimated depletion rates may lead to incorrect conclusions regarding the seed banks and, perhaps, the management of weeds and rare species.
The history and geography of diversification within the butterfly genus Lycaeides in North America
Authors: NICE CHRIS C. , ANTHONY NICOLA , GELEMBIUK GREG , RATERMAN DENISE , FFRENCH‐CONSTANT RICHARD 
Published: April 2005

AbstractThe Lycaeides butterfly species complex in North America consists of two nominal, morphologically defined species. These butterflies are ecologically diverse and appear to be distributed as a geographically complex mosaic of locally differentiated populations that may be undergoing adaptive radiation. We asked whether patterns of molecular genetic variation within the species complex are congruent with currently recognized morphological species and whether the distribution of molecular variation is consistent with the hypothesis that Pleistocene climate changes contributed to the process of differentiation within the genus. Variation in the form of the genitalia from 726 males from 59 populations clearly distinguishes both species with only six populations containing morphologically intermediate or ambiguous individuals. However, partitioning of molecular variance in a 236 bp section of the mitochondrial AT‐rich region from 628 individuals (57 populations) surveyed using single strand conformation polymorphism analysis (SSCP) indicates that only 26% of the total genetic variation is distributed along nominal species boundaries as defined by morphology. Instead, three phylogeographical groups were detected, represented by three major haplotype clades, which account for 90% of the total genetic variance. Pleistocene glaciations appear to have fostered divergence during glacial maxima, while postglacial range expansions created opportunities for gene exchange and reticulation along suture zones between geographical groups. Data presented here allow us to make inferences about the history of the species complex. However, evidence of ancestral polymorphism and reticulation limit our ability to define species boundaries based on mitochondrial DNA sequence variation.
Postglacial colonization of the Tibetan plateau inferred from the matrilineal genetic structure of the endemic red‐necked snow finch, Pyrgilauda ruficollis
Authors: QU YAN HUA , ERICSON PER G. P. , LEI FU MIN , LI SHOU HSIEN 
Published: April 2005

AbstractMost phylogeographical studies of postglacial colonization focus on high latitude locations in the Northern Hemisphere. Here, we studied the phylogeographical structure of the red‐necked snow finch Pyrgilauda ruficollis, an endemic species of the Tibetan plateau. We analysed 879 base pairs (bp) of the mitochondrial cytochrome b gene and 529 bp of the control region in 41 birds from four regional groups separated by mountain ranges. We detected 34 haplotypes, 31 of which occurred in a single individual and only three of which were shared among sampling sites within regional groups or among regional groups. Haplotype diversity was high (h = 0.94); nucleotide diversity was low (ð = 0.00415) and genetic differentiation was virtually non‐existent. Analyses of mismatch distributions and geographically nested clades yielded results consistent with contiguous range expansion, and the expansion times were estimated as 0.07–0.19 million years ago (Ma). Our results suggest that P. ruficollis colonized the Tibetan plateau after the extensive glacial period (0.5–0.175 Ma), expanding from the eastern margin towards the inner plateau. Thus, in contrast to many of the postglacial phylogeographical structures known at high latitudes, this colonization occurred without matrilineal population structuring. This might be due to the short glacial cycles typical of the Tibetan plateau, adaptation of P. ruficollis to cold conditions, or refugia and colonized habitat being semicontinuous and thus promoting population mixing.
Genetic variability and phylogeography of the invasive zebra mussel,Dreissena polymorpha(Pallas)
Authors: ASTANEI IULIAN , GOSLING ELIZABETH , WILSON JIM , POWELL EITHNE 
Published: April 2005

AbstractThe zebra mussel,Dreissena polymorpha(Pallas), a bivalve species originally native to the Black and Caspian seas, has invaded Ireland in the last decade. Five microsatellite loci were used to investigate genetic diversity and population structure in 10 populations across Europe (Ireland, UK, the Netherlands and Romania) and the Great Lakes (Lake Ontario and Lake St Clair). Levels of allelic diversity and mean expected heterozygosity were high for all populations (mean number of alleles/locus andHEwere 10–15.2 and 0.79–0.89, respectively). High levels of polymorphism observed in Irish populations suggest that the Irish founder population(s) were large and/or several introductions took place after foundation. Significant deficits of heterozygotes were recorded for all populations, and null alleles were the most probable factor contributing to these deficits. Pairwise comparisons using Fisher exact tests andFSTvalues revealed little genetic differentiation between Irish populations. The UK sample was not significantly differentiated from the Irish samples, most probably reflecting an English origin for Irish zebra mussels. No significant differentiation was detected between the two Great Lakes populations. Our data support a northwest rather than a central or east European source for North American zebra mussels.
The effects of habitat fragmentation on the social kin structure and mating system of the agile antechinus, Antechinus agilis
Authors: BANKS S. C. , WARD S. J. , LINDENMAYER D. B. , FINLAYSON G. R. , LAWSON S. J. , TAYLOR A. C. 
Published: April 2005

AbstractHabitat fragmentation is one of the major contributors to the loss of biodiversity worldwide. However, relatively little is known about its more immediate impacts on within‐patch population processes such as social structure and mating systems, whose alteration may play an important role in extinction risk. We investigated the impacts of habitat fragmentation due to the establishment of an exotic softwood plantation on the social kin structure and breeding system of the Australian marsupial carnivore, Antechinus agilis. Restricted dispersal by males in fragmented habitat resulted in elevated relatedness among potential mates in populations in fragments, potentially increasing the risk of inbreeding. Antechinus agilis nests communally in tree hollows; these nests are important points for social contact between males and females in the mating season. In response to elevated relatedness among potential mates in fragmented habitat, A. agilis significantly avoided sharing nests with opposite‐sex relatives in large fragment sites (but not in small ones, possibly due to limited nest locations and small population sizes). Because opposite‐sex individuals shared nests randomly with respect to relatedness in unfragmented habitat, we interpreted the phenomenon in fragmented habitat as a precursor to inbreeding avoidance via mate choice. Despite evidence that female A. agilis at high inbreeding risk selected relatively unrelated mates, there was no overall increased avoidance of related mates by females in fragmented habitats compared to unfragmented habitats. Simulations indicated that only dispersal, and not nonrandom mating, contributed to inbreeding avoidance in either habitat context. However, habitat fragmentation did influence the mating system in that the degree of multiple paternity was reduced due to the reduction in population sizes and population connectivity. This, in turn, reduced the number of males available to females in the breeding season. This suggests that in addition to the obvious impacts of reduced recruitment, patch recolonization and increased genetic drift, the isolation of populations in habitat patches may cause changes in breeding behaviour that contribute to the negative impacts of habitat fragmentation.
Multiple paternity in a natural population of a salamander with long‐term sperm storage
Authors: ADAMS ERIKA M. , JONES ADAM G. , ARNOLD STEVAN J. 
Published: April 2005

AbstractSperm competition appears to be an important aspect of any mating system in which individual female organisms mate with multiple males and store sperm. Postcopulatory sexual selection may be particularly important in species that store sperm throughout long breeding seasons, because the lengthy storage period may permit extensive interactions among rival sperm. Few studies have addressed the potential for sperm competition in species exhibiting prolonged sperm storage. We used microsatellite markers to examine offspring paternity in field‐collected clutches of the Ocoee salamander (Desmognathus ocoee), a species in which female organisms store sperm for up to 9 months prior to fertilization. We found that 96% of clutches were sired by multiple males, but that the majority of females used sperm from only two or three males to fertilize their eggs. The high rate of multiple mating by females suggests that sperm competition is an important aspect of this mating system. Comparison of our data with those of other parentage studies in salamanders and newts reveals that multiple mating may be common in urodele amphibians. Nevertheless, the number of males siring offspring per clutch in D. ocoee did not differ appreciably from that in other species of urodeles with shorter storage periods.
Habitat specialization and adaptive phenotypic divergence of anuran populations
Authors: VAN BUSKIRK J. , ARIOLI M. 
Published: April 2005

AbstractWe tested for adaptive population structure in the frog Rana temporaria by rearing tadpoles from 23 populations in a common garden experiment, with and without larval dragonfly predators. The goal was to compare tadpole phenotypes with the habitats of their source ponds. The choice of traits and habitat variables was guided by prior information about phenotypic function. There were large differences among populations in life history, behaviour, morphological shape, and the predator‐induced plasticities in most of these. Body size and behaviour were correlated with predation risk in the source pond, in agreement with adaptive population divergence. Tadpoles from large sunny ponds were morphologically distinct from those inhabiting small woodland ponds, although here an adaptive explanation was unclear. There was no evidence that plasticity evolves in populations exposed to more variable environments. Much among‐population variation in phenotype and plasticity was not associated with habitat, perhaps reflecting rapid changes in wetland habitats.
Macroevolutionary trends in the Dinosauria: Cope's rule
Authors: HONE D. W. E. , KEESEY T. M. , PISANI D. , PURVIS A. 
Published: April 2005

AbstractCope's rule is the tendency for body size to increase over time along a lineage. A set of 65 phylogenetically independent comparisons, between earlier and later genera, show that Cope's rule applied in dinosaurs: later genera were on average about 25% longer than the related earlier genera to which they were compared. The tendency for size to increase was not restricted to a particular clade within the group, nor to a particular time within its history. Small lineages were more likely to increase in size, and large lineages more likely to decrease: this pattern may indicate an intermediate optimum body size, but can also be explained as an artefact of data error. The rate of size increase estimated from the phylogenetic comparisons is significantly higher than the rate seen across the fauna as a whole. This difference could indicate that within‐lineage selection for larger size was opposed by clade selection favouring smaller size, but data limitations mean that alternative explanations (which we discuss) cannot be excluded. We discuss ways of unlocking the full potential usefulness of phylogenies for studying the dynamics of evolutionary trends.
The benefits of polyandry in the free‐spawning polychaete Galeolaria caespitosa
Authors: MARSHALL D. J. , EVANS J. P. 
Published: April 2005

AbstractIn many species, females are thought to benefit from polyandry due to the reduced risks of fertilization by genetically incompatible sperm. However, few studies that have reported such benefits have directly attributed variation in female reproductive success to the interacting effects of males and females at fertilization. In this paper, we determine whether male × female interactions influence fertilization in vitro in the free‐spawning, sessile polychaete Galeolaria caespitosa. Furthermore, we determined whether polyandry results in direct fertilization benefits for females by experimentally manipulating the number of males contributing towards staged spawning events. To test for male × female interaction effects we performed an initial experiment that crossed seven males with six females (in all 42 combinations), enabling us to assess fertilization rates for each specific male–female pairing and attribute variation in fertilization success to males, females and their interaction. This initial experiment revealed a strong interaction between males and females at fertilization, confirming that certain male–female combinations were more compatible than others. A second experiment tested the hypothesis that polyandry enhances female reproductive success by exposing each female's eggs to either a single male's sperm (monandry) or the sperm from three males simultaneously (polyandry). We performed this second experiment at two ecologically relevant sperm concentrations. This latter experiment revealed a strong fertilization benefit of polyandry, independent of the effects of sperm concentration (which were also significant). We suggest that these direct fertilization gains arising from polyandry will constitute an important source of selection on females to mate multiply in nature.
Hybridization and invasiveness in the freshwater snail Melanoides tuberculata: hybrid vigour is more important than increase in genetic variance
Authors: FACON B. , JARNE P. , POINTIER J. P. , DAVID P. 
Published: April 2005

AbstractMany invasive taxa are hybrids, but how hybridization boosts the invasive process remains poorly known. We address this question in the clonal freshwater snail Melanoides tuberculata from Martinique, using three parental and two hybrid lines. We combine an extensive field survey (1990–2003) and a quantitative genetic experiment to show that hybrid lines have outcompeted their parents in natural habitats, and that this increased invasiveness co‐occurred with pronounced shifts in life‐history traits, such as growth, fecundity and juvenile size. Given the little time between hybrid creation and sampling, and the moderate standing genetic variance for life‐history traits in hybrids, we show that some of the observed trait changes between parents and hybrids were unlikely to arise only by continuous selection. We therefore suggest that a large part of hybrid advantage stems from immediate heterosis upon hybridization.
Duration and Severity of Clinical Signs as Prognostic Indicators in 30 Dogs with Thoracolumbar Disk Disease After Surgical Decompression
Authors: Kazakos G. , Polizopoulou Z. S. , Patsikas M. N. , Tsimopoulos G. , Roubies N. , Dessiris A. 
Published: April 2005

SummaryThe objective of this study was to evaluate the duration and severity of neurological dysfunction as prognostic indicators for the final outcome in 30 dogs with thoracolumbar intervertebral disk disease, treated surgically with hemilaminectomy without concurrent prophylactic fenestration. The lesion localization was assessed comparing plain radiographic, myelographic and surgical findings and success rates were evaluated during case follow‐up. Evidence of a single disk extrusion existed in 17 dogs on survey spinal radiographs, while myelography revealed definite spinal cord compression in 28 cases and was inconclusive in the remaining two cases. Case follow‐up continued for a period ranging from 3 months to 2 years post‐operatively, depending on the degree of neurological dysfunction on presentation and owner compliance. The severity of clinical signs and the interval elapsing prior to decompressive surgery did not correlate with the case outcome, with 12 of 20 dogs (60%) that exhibited the most pronounced neurological dysfunction (paraplegia with or without analgesia) regaining voluntary motor function during the follow‐up period. Recurrences proven to be disk‐related did not occur in any dog throughout the post‐surgical observation period. It was concluded that the time elapsing from loss of motor function and the severity of clinical signs is not an objective method to predict the case outcome.
Conserving biodiversity under climate change: the rear edge matters
Authors: Hampe Arndt , Petit Rémy J. 
Published: April 2005

AbstractModern climate change is producing poleward range shifts of numerous taxa, communities and ecosystems worldwide. The response of species to changing environments is likely to be determined largely by population responses at range margins. In contrast to the expanding edge, the low‐latitude limit (rear edge) of species ranges remains understudied, and the critical importance of rear edge populations as long‐term stores of species’ genetic diversity and foci of speciation has been little acknowledged. We review recent findings from the fossil record, phylogeography and ecology to illustrate that rear edge populations are often disproportionately important for the survival and evolution of biota. Their ecological features, dynamics and conservation requirements differ from those of populations in other parts of the range, and some commonly recommended conservation practices might therefore be of little use or even counterproductive for rear edge populations.