bluuebunny/crossref_metadata_2025_split huggingface dataset:
Habitat loss, fragmentation and predator impact: spatial implications for prey conservation
Authors: Schneider Michael F. 
Published: March 2003

Summary

Because predators threaten the survival of endangered prey in many places, predator management is a widespread conservation tool. At the same time, the effects of predators on their prey are greatly influenced by landscape structure. Therefore, the management of landscapes could be an alternative to predator regulation.
A spatially explicit presence/absence model (a stochastic one‐layer cellular automaton) was used to investigate two different predator–prey systems that were subject to changes in the number and size of habitat patches in a model landscape.
The first scenario included grey‐sided voles Clethrionomysrufocanus, Norwegian lemmings Lemmus lemmus and small mustelids (stoats Mustelaerminea and weasels M. nivalis) interacting in a tundra landscape. In the second scenario, the effect of habitat perforation by human settlements with subsidized predators (house cats Felis silvestris catus) on the dynamics of lemmings (as surrogate for endangered prey) was studied.
Both the total area of lemming habitat and the degree of fragmentation were important determinants of the population size and persistence of lemmings. A qualitative change in the effect of fragmentation was observed when the area of lemming habitat decreased from 70% (positive effect) to 50% (negative effect). When lemming habitat covered 50% or less of the landscape, fragmentation had a negative effect on lemming population size and viability, even though habitat area did not decrease.
The spatial configuration of settlements as predator sources was important. A few evenly spaced predator sources had less negative effect on lemming populations than the same proportion of predator habitat that was randomly distributed, which in turn had less effect than many evenly spaced patches.
Including predator management in the model did not decrease the predators’ negative impact on the population size and persistence of the endangered prey when settlements occurred in many small patches.
It is concluded that predator management is not a viable strategy to combat the threat to the survival of endangered prey, but that careful planning of landscape pattern could compensate for negative predation effects. The location and size of patches of predator habitat should be optimized in order to minimize the negative effects of predators visiting adjacent areas of natural habitat.
The effects of disturbance on habitat use by black‐tailed godwits Limosa limosa
Authors: Gill Jennifer A. , Norris Ken , Sutherland William J. 
Published: March 2003

Summary

Human disturbance of wildlife is widely considered to be a serious conservation problem. However, despite many qualitative studies, little attempt has been made to assess whether human presence limits the number of animals that sites can support. This can be quantified by incorporating measures both of human presence and of resource distribution into analyses of population distribution. The effects of disturbance can then be measured from any reduction in resource use at disturbed sites, which in turn indicates any reduction in the number of animals supported.
Shorebirds are often considered highly susceptible to disturbance because of their very obvious flight responses to humans and because they use areas that are generally subject to high levels of human recreational use.
This study addressed the effect of human presence on the distribution of black‐tailed godwits Limosa limosa islandica on coastal areas in eastern England. We identified the prey types selected by godwits and related their depletion to different levels and types of human disturbance at a range of spatial scales.
Three methods of analysis are described: simple regressions of the effect of human activity on the number of godwits supported; multiple regression analyses of the effect of human presence and prey density on godwit numbers; and analyses of the effect of human presence on prey density at the end of the season. The latter method assumes that godwits are responsible for the majority of resource depletion. None of the analyses showed any effect of human presence on the number of godwits supported by the food supply at any of the spatial scales examined.
Many species may appear to avoid human presence but this may not reduce the number of animals supported in an area. Assessing the influence of disturbance on the relationship between animal distribution and resource distribution provides a means of assessing whether numbers are constrained by disturbance.
Effects of fungal pathogens on seeds of native and exotic plants: a test using congeneric pairs
Authors: Blaney C.S. , Kotanen P.M. 
Published: March 2003

SummaryIt has previously been hypothesized that low rates of attack by natural enemies may contribute to the invasiveness of exotic plants.We tested this hypothesis by investigating the influence of pathogens on survival during a critical life‐history stage: the seed bank. We used fungicide treatments to estimate the impacts of soil fungi on buried seeds of a taxonomically broad suite of congeneric natives and exotics, in both upland and wetland meadows.Seeds of both natives and exotics were recovered at lower rates in wetlands than in uplands. Fungicide addition reduced this difference by improving recovery in wetlands, indicating that the lower recovery was largely attributable to a higher level of fungal mortality. This suggests that fungal pathogens may contribute to the exclusion of upland species from wetlands.The effects of fungicide on the recovery of buried seeds did not differ between natives and exotics. Seeds of exotics were recovered at a higher rate than seeds of natives in uplands, but this effect was not attributable to fungal pathogens.Fungal seed pathogens may offer poor prospects for the management of most exotic species. The lack of consistent differences in the responses of natives vs. exotics to fungicide suggests few aliens owe their success to low seed pathogen loads, while impacts of seed‐pathogenic biocontrol agents on non‐target species would be frequent.
Changes in survival rates and population dynamics of greater snow geese over a 30‐year period: implications for hunting regulations
Authors: Menu Stéphane , Gauthier Gilles , Reed Austin 
Published: March 2003

SummaryIn recent decades, the populations of several goose species have increased dramatically and are severely impacting on their habitat. We examined the relative contribution of reproduction and mortality to changes in the dynamics of the entire North American population of greater snow geeseAnser caerulescens atlanticusfrom 1970 to 1998.The total population increased 10‐fold over this period, with two phases of rapid population growth in 1970–74 and 1984–98 separated by an intervening period of stagnation. The reproductive rate was estimated from age ratios in the autumn, survival from ring recoveries, and harvest rates from hunter surveys.Variations in population growth could not be explained by changes in reproduction, which was similar across the three periods (overall mean 26 ± 3% young in the autumn flock) with no evidence of density‐dependence.Adult survival did not differ between the two periods of rapid population growth (0·84 ± 0·04 during 1970–74 vs. 0·80 ± 0·04 during 1990–96), thus providing no evidence of density‐dependence effects either. The survival rates of young could only be estimated during 1990–96, when they varied greatly (mean 0·36 ± 0·12, annual range 0·11–0·48).Adult harvest rates were much higher during the period of no population growth (0·11 ± 0·01%) than before (0·04 ± 0·01%) or after (0·06 ± 0·01%). The increased harvest starting in 1975 was due to the re‐opening of the US hunting season. Thus, reduced survival due to increased hunting mortality apparently caused the stagnation of growth between 1975 and 1983.We conclude that hunting mortality has had the most impact on recent population dynamics in the greater snow goose and, in the absence of density‐dependent effects, hunting could be used to limit the growth of this population.
Comparative foraging and nutrition of horses and cattle in European wetlands
Authors: Menard Catherine , Duncan Patrick , Fleurance Geraldine , Georges Jean‐Yves , Lila Marc 
Published: March 2003

Summary

Equids are generalist herbivores that co‐exist with bovids of similar body size in many ecosystems. There are two major hypotheses to explain their co‐existence, but few comparative data are available to test them. The first postulates that the very different functioning of their digestive tracts leads to fundamentally different patterns of use of grasses of different fibre contents. The second postulates resource partitioning through the use of different plant species. As domestic horses and cattle are used widely in Europe for the management of conservation areas, particularly in wetlands, a good knowledge of their foraging behaviour and comparative nutrition is necessary.
In this paper we describe resource‐use by horses and cattle in complementary studies in two French wetlands. Horses used marshes intensively during the warmer seasons; both species used grasslands intensively throughout the year; cattle used forbs and shrubs much more than horses. Niche breadth was similar and overlap was high (Kulczinski’s index 0·58–0·77). Horses spent much more time feeding on short grass than cattle. These results from the two sites indicate strong potential for competition.
Comparative daily food intake, measured in the field during this study for the first time, was 63% higher in horses (144 gDM kg W−0·75 day−1) than in cattle (88 gDM kg W−0·75 day−1). Digestibility of the cattle diets was a little higher, but daily intake of digestible dry matter (i.e. nutrient extraction) in all seasons was considerably higher in horses (78 gDM kg W−0·75 day−1) than in cattle (51 gDM kg W−0·75 day−1). When food is limiting, horses should outcompete cattle in habitats dominated by grasses because their functional response is steeper; under these circumstances cattle will require an ecological refuge for survival during winter, woodland or shrubland with abundant dicotyledons.
Horses are a good tool for plant management because they remove more vegetation per unit body weight than cattle, and use the most productive plant communities and plant species (especially graminoids) to a greater extent. They feed closer to the ground, and maintain a mosaic of patches of short and tall grass that contributes to structural diversity at this scale. Cattle use broadleaved plants to a greater extent than horses, and can reduce the rate of encroachment by certain woody species.
Nest‐site limitation and density dependence of reproductive output in the common goldeneyeBucephala clangula: implications for the management of cavity‐nesting birds
Authors: Pöysä H. , Pöysä S. 
Published: March 2003

Summary Hole‐nesting birds are frequently faced with a shortage of suitable nest sites in regions of intensive forest management. Nest boxes are sometimes provided to alleviate nest‐site limitation in cavity‐nesting waterfowl and are also recommended for several rare and endangered species. However, the impacts on effective breeding numbers and breeding success have rarely been considered, particularly in instances where density dependence might operate. We experimentally manipulated nest sites to assess limits on the population size of a secondary cavity‐nesting species, the common goldeneyeBucephala clangula, living on freshwater lakes. We also examined density dependence in their reproductive output. Breeding pairs were counted in experimental and control areas over a 12‐year period; for 4 years (1988–91) before nest box addition (1992–94 in the experimental area) and for 5 years (1995–99) afterwards. Broods were counted each year between 1988 and 1999 to study reproductive output. Mean number of pairs per lake increased after the addition of nest boxes in the experimental area but not in the control area. However, neither the mean number of broods per lake nor the mean number of fledged birds per lake increased significantly in the experimental area. When the whole period of 1988–99 was considered and data pooled from all the lakes, the numbers of broods and fledged birds showed negative density dependence of reproductive output. Our results indicate that nest sites limit the population size of breeding common goldeneye, but show also that density‐dependent factors operate to limit reproductive output. The possibility that density dependence may negate management actions directed at increasing breeding numbers in cavity‐nesting waterfowl should be considered carefully before taking these actions. This also applies to nest box provisioning programmes aiming to manage populations of endangered species.
Biological control of cactus weeds: implications of hybridization between control agent biotypes
Authors: Hoffmann J. H. , Impson F. A. C. , Volchansky C. R. 
Published: March 2003

Summary

Results of recent research on Dactylopius opuntiae, a biological control agent for cactus weeds (Opuntia spp.) in South Africa and elsewhere, challenge the maxim that genetic diversity of agents necessarily enhances the chances of success in biological weed control.
Two biotypes of D. opuntiae, each specific to a different Opuntia species, interbred freely, at least under insectary conditions. We therefore carried out cross‐breeding experiments to determine the viability and host‐preferences of progeny produced by these crosses.
Unlike their parents, F1 hybrids were not species‐specific, developing equally well on either of the parental hosts, Opuntia ficus‐indica and Opuntia stricta. The situation was more complex in F2 back‐crosses between hybrids and in crosses between parent strains and hybrids because male cochineal insects contributed only maternally inherited genes to their progeny, due to their unusual haploid‐diploid (lecanoid) mechanism of sex determination. Some F2 combinations produced cohorts of progeny that were either entirely true‐bred (i.e. host‐specific) or entirely hybrid (i.e. not host‐specific) genotypes, while other combinations produced groups of siblings with some individuals (theoretically half) that were true‐bred genotypes and the balance were hybrid genotypes.
The lack of host‐specificity of hybrids should enhance overall biological control of the target species directly, because hybrids attack both host‐plants, and indirectly, because hybrid nymphs have greater chances of finding a suitable host‐during passive dispersal. However, this advantage will be negated when F2 crosses produce host‐specific nymphs on host‐plants that are incompatible for their survival.
These findings show that only pure strains of D. opuntiae should be released in monocultures of the target weeds. More generally, they caution that the possible consequences of mixing genotypes of a biological control agent species should be investigated before different provenances are amalgamated to enhance genetic diversity.
Effects of experimental irrigation and drought on the composition and diversity of soil fauna in a coniferous stand
Authors: Lindberg Niklas , Engtsson Jan B. , Persson Tryggve 
Published: March 2003

SummaryThe effects of experimental long‐term summer drought and irrigation on soil fauna were studied in a Norway spruce stand in south‐western Sweden. The treatments, carried out over 8 and 10 years respectively, were chosen to simulate two scenarios of climate change, involving drier and wetter summers.Different microarthropod communities developed in the different treatments. The abundances of enchytraeids, mesostigmatid mites and macroarthropod predators were all lowest in the drought plots. Drought decreased and irrigation increased the abundance and diversity of Oribatida. Drought decreased the abundance of Collembola.The dominance structure of Oribatida and Collembola also changed, but less markedly. Drought affected community composition of both groups more than irrigation.The study confirms that soil microarthropods can be useful environmental indicators, but their responses did not support the widely held view that deviations from a log‐normal dominance structure indicates a stressed community.The results also indicate that a drier climate with summer drought will lead to the local extinction of some soil animal species in this region.
Effects of extremely low frequency magnetic fields on pain thresholds in mice: roles of melatonin and opioids
Authors: Jeong J. H. , Choi K. B. , Yi B. C. , Chun C. H. , Sung K.‐Y. , Sung J.‐Y. , Gimm Y.‐M. , Huh I. H. , Sohn U. D. 
Published: March 2003

1 We studied the effects of extremely low frequency (ELF, 60 Hz) magnetic fields (MFs) on pain thresholds using the hot plate test. The implication of opioid and benzodiazepine system in the MFs‐induced alteration of pain thresholds was also studied. 2 There was an increase at night time and a decrease at daytime of pain thresholds in normal mice. Exposure of MFs (24 h, 20 gauss (G)) inhibited the increase of pain thresholds at night time and even produced hyperalgesia at daytime. 3 The increase of pain thresholds induced by melatonin at daytime was inhibited by exposure to MFs (24 h, 20 G) or opioid antagonist naloxone. The MFs and naloxone synergically inhibited hypoalgesia produced by melatonin. The hyperalgesia at daytime after MFs exposure was potentiated by the benzodiazepine agonist, diazepam, and inhibited by the benzodiazepine antagonist, flumazenil. There was no significant difference in all rotarod performance we tested. 4 From these results, it is suggested that exposure to MFs inhibits the increase of pain thresholds at night time and produces hyperalgesia at daytime with the involvement of opioid and benzodiazepine systems.
Snails of the genusPachnodus(Mollusca; Gastropoda; Enidae): their origins and evolution
Authors: Gerlach Justin 
Published: March 2003

SummaryAimThe phylogeny of the enid land‐snail genusPachnoduswas determined in order to provide information on biogeographical patterns within the granitic Seychelles islands.LocationThe genusPachnodusis endemic to the granitic islands of Seychelles (Mahé, Silhouette, Praslin, La Digue and Fregate).MethodsPhylogeny was determined using a cladistic analysis of nineteen shell and soft‐body anatomy characters. The outgroup used was the central‐east African genusCerastus.ResultsThe proposed phylogeny indicates that the genus divided into two distinct subgenera early in its history. Subsequent speciation occurred in parallel in the two subgenera, resulting in several islands supporting at least two distinct species representing the two subgenera.Main conclusionsThe pattern of speciation is largely explicable by vicariance as a result of sea‐level rises, followed by habitat specialisation and further speciation. The pattern is in contrast to previously published scenarios for other taxa in the islands and indicates significant differences between evolutionary and habitat factors in the biogeography of the Seychelles fauna
Biodiversity and pollen analysis: modern pollen studies and the recent history of a floodplain woodland in S. W. Ireland
Authors: Brown A. G. 
Published: March 2003

SummaryOne of the problems with biodiversity for palynologists is that their samples come from an unbounded area and source area varies with both pollen/spore type and vegetation type. There have been two broad approaches to the problem of inferring diversity from pollen/spore samples; firstly the use of pollen type richness as a proxy for species richness, and secondly the ‘identification’ of past vegetation communities aided by ecological inference and historical or modern data concerning species affinities and typical diversity. The estimation of biodiversity from pollen analysis depends upon the pollen count, taxonomic precision, source strength for individual types and dispersal/transport of pollen from source areas to the site. A transect of surface pollen samples is used here to test the effect of a vegetation boundary on pollen/spore diversity and compare the pollen/spore diversity with the species richness of the woodland. Palynological richness (at a constant count sum) does, to some extent, reflect changing local vegetation along the transect. Type count curves also reflect the changes in vegetation type along the transect due to the partial influence of species richness on pollen/spore richness. This study suggests that depending upon the woodland composition, the woodland may not entirely drown‐out the pollen signal of the surrounding vegetation, and that a small woodland may be more representative (as a sampling site) of the valley floor diversity than a raised mire. The surface transect is also used in the interpretation of Medieval pollen levels from The Gearagh.
Mountain Park area: a plant refugium in the Canadian Rocky Mountains?
Authors: Strong W. L 
Published: March 2003

SummaryAimThe purpose of this study was to evaluate evidence related to the occurrence of a hypothesized Wisconsinan glacial refugium along the eastern slopes of the Rocky Mountains in western Canada.LocationThe study area was located ≈60 km south of Hinton, Alberta. The area of interest occurred within the vicinity of the abandoned early 1900s coal mining town known as Mountain Park (52°55 N, 117°16 W).MethodsContemporary botanical, palynological, and geomorphic information for the Mountain Park and surrounding area was compiled. For comparative purposes, vascular and nonvascular floristic lists were developed from available literature for five national parks along the Canadian cordilleran. All species were classified according to their phytogeographical affiliations.ResultsThe available data suggested that most of the Mountain Park area was glaciated during the Wisconsinan, except possibly at high elevations (> 2075–2255 m above sea level). Palynological evidence from the surrounding area indicated that coniferous forest developed in the area after 11,400 yearsBP. If vegetation did exist in the Mountain Park area before 11,400 yearsBP, it would probably have been tundra. The known Mountain Park area flora (554 species) contained only one vascular and six nonvascular species with an exclusively arctic‐alpine affiliation. A comparison of Mountain Park flora with five other locations indicated that vascular species were more strongly associated with areas further south. No significant statistical difference (Chi‐square Goodness of Fit,P< 0.05 level) was found among the nonvascular floras.Main conclusionsLate Wisconsinan and postglacial migrations were considered to be stronger ecological possibilities for explaining the current vascular flora of the Mountain Park area thanin situsurvival. Some nonvascular species may have survived in high elevation nunatak areas during glaciation. These circumstances were probably similar to more interior Rocky Mountain locations which are known to have been glaciated during the Wisconsinan.