bluuebunny/crossref_metadata_2025_split huggingface dataset:
Colonization rates and distances of a host butterfly and two specific parasitoids in a fragmented landscape
Authors: Van Nouhuys Saskya , Hanski Ilkka 
Published: March 2003

SummaryWe describe the pattern of colonization of suitable, but currently empty, habitat by a host butterfly and two specialist parasitoids living in a highly fragmented landscape.Using survey data collected over 8 years, field sampling and small‐scale experiments we show that the ability of the Glanville fritillary butterfly (Melitaea cinxia) to colonize new habitat is intermediate between that of its two larval primary parasitoids.The butterfly forms a classic metapopulation, which the parasitoidHyposoter horticolaexperiences as a single patchily distributed host population because of its high rate of dispersal and long colonization distances. In contrast, most of the local butterfly populations are presently inaccessible to the parasitoidCotesia melitaearum,which has a limited dispersal range and therefore persists only in tightly clustered networks of host populations.At the regional scale, the butterfly may escapeC. melitaearumby colonizing empty habitat, but host dispersal does not limit parasitism byH. horticola,which consequently must be limited by local interaction.The parasitoidH. horticolamostly avoids direct competition withC. melitaearumbecause the majority ofH. horticolapopulations are outside the range of dispersal by currentC. melitaearumpopulations. In contrast, allC. melitaearumpopulations experience competition withH. horticola.
The consequences of disrupted dispersal in fragmented red‐cockaded woodpeckerPicoides borealispopulations
Authors: Schiegg Karin , Walters Jeffrey R. , Priddy Jeffery A. 
Published: March 2003

SummaryHabitat fragmentation may adversely affect animal populations through several mechanisms. However, little is known about how the impacts of some of these mechanisms are manifested in altered dynamics of wild populations.We used a spatially explicit individual‐based simulation model to examine the potential effects of disrupted dispersal due to fragmentation on the population dynamics of the endangered, co‐operatively breeding, red‐cockaded woodpeckerPicoides borealis.We simulated population dynamics as a function of population size and spatial aggregation of territories. Dispersal success (but not mortality or fecundity) was an emergent property of model runs. In the model all female and some male fledglings dispersed in straight lines in random directions, and the remaining males stayed on their natal territories as helpers and competed for breeding vacancies in their immediate neighbourhood.Population trend was tied to the higher dispersal success of both males and females in larger and less fragmented populations. Helpers were more successful than dispersing males. Male breeder recruitment depended entirely on helpers when populations were small (25 or 100 territories).Declining populations were characterized by high emigration rates and both failure and delay in female recruitment. The large numbers of unpaired males resulted in lowered reproductive output at the population level and in the loss of territories. Populations of 25 territories were stable when territories were highly aggregated, despite high emigration rates. These results closely match empirical observations.A number of co‐operatively breeding species are endangered. The unusual dispersal behaviour of helpers may make such species sensitive to habitat fragmentation but also resilient to reductions in population size when territories are aggregated. Small populations of co‐operative breeders may have considerable conservation value as a source of genetic diversity.
Stability and complexity in microcosm communities
Authors: Fox Jeremy W. , McGrady‐Steed Jill 
Published: March 2003

Summary

Theory predicts that communities comprising many species connected randomly by strong interactions are unlikely to exhibit stable, feasible equilibria (i.e. positive equilibria to which all species will return following perturbation), making the observed complexity of natural communities very surprising. This prediction has never been tested experimentally in speciose communities.
We tested this prediction using long‐term data from experimental communities of bacteria, protists and small metazoans in laboratory microcosms. Initial communities varied in species richness ( S
), composition and connectance (
C ; the fraction of possible interspecific interactions that are actually realized).
Many initial communities lost species to extinction (unstable and/or infeasible communities), but population densities and species compositions subsequently stabilized.
We used logistic regression to describe the probability that an initial community would be stable and feasible as a function of complexity [( SC
)
1/2 ]. Probability of a stable, feasible equilibrium declined with complexity, as predicted by theory.
We also found that communities converged in connectance over time, so that at the end of the experiment connectance was independent of species richness. Monte Carlo simulations indicated that this result was highly improbable if extinctions occurred at random with respect to connectedness. Connectance is also independent of species richness in well‐resolved natural food webs, a pattern usually ascribed to phylogenetic and/or physiological constraints on diet breadth. However, such constraints cannot explain our results. Trophic interactions causing non‐random extinctions may provide a novel explanation for patterns in the connectance and species richness of whole food webs.
Individual variation in prey selection by sea otters: patterns, causes and implications
Authors: Estes J. A. , Riedman M. L. , Staedler M. M. , Tinker M. T. , Lyon B. E. 
Published: March 2003

SummaryLongitudinal records of prey selection by 10 adult female sea otters on the Monterey Peninsula, California, from 1983 to 1990 demonstrate extreme inter‐individual variation in diet. Variation in prey availability cannot explain these differences as the data were obtained from a common spatial‐temporal area.Individual dietary patterns persisted throughout our study, thus indicating that they are life‐long characteristics.Individual dietary patterns in sea otters appear to be transmitted along matrilines, probably by way of learning during the period of mother–young association.Efficient utilization of different prey types probably requires radically different sensory/motor skills, each of which is difficult to acquire and all of which may exceed the learning and performance capacities of any single individual. This would explain the absence of generalists and inertia against switching, but not the existence of alternative specialists.Such individual variation might arise in a constant environment from frequency‐dependent effects, whereby the relative benefit of a given prey specialization depends on the number of other individuals utilizing that prey. Additionally, many of the sea otter's prey fluctuate substantially in abundance through time. This temporal variation, in conjunction with matrilineal transmission of foraging skills, may act to mediate the temporal dynamics of prey specializations.Regardless of the exact cause, such extreme individual variation in diet has broad ramifications for population and community ecology.The published literature indicates that similar patterns occur in many other species.
Preliminary estimates of fallen dead wood and standing dead trees in managed and unmanaged forests in Britain
Authors: Kirby K.J. , Reid C.M. , Thomas R.C. , Goldsmith F.B. 
Published: March 2003

1.  The amount of dead wood, particularly as fallen dead wood and standing dead trees, in British forests is attracting attention from forest managers as part of their interest in increasing biodiversity within forests managed for timber. Existing levels of dead wood in managed and unmanaged forests were assessed to provide a basis for what might be considered high or low amounts of dead wood under present conditions. 2.  Estimates of fallen dead wood, derived from line‐intersect sampling, were collated for 63 sites (87 stands) in Britain. The values obtained ranged from virtually zero in recently cut coppice to 60–140 m3 ha−1 in stands largely undisturbed over at least the last 80 years. The highest values (from unmanaged stands) overlap with estimates for the volumes of fallen logs in old‐growth broadleaved forests in North America and continental Europe. Forests currently managed for timber had less than 20 m3 ha−1 of fallen logs. 3.  In unmanaged stands, localized accumulation of fallen material was often associated with exceptional events such as the 1976 drought or the 1987 great storm. Following the 1987 storm the amounts of fallen dead wood in unmanaged forests in eastern England appear to have doubled from about 10 m3 ha−1 to 23 m3 ha−1. 4.  Large standing dead trees (snags), > 40 cm diameter, were rarely recorded in the forests surveyed because most forests in Britain have been cut over at least once this century and any large timber removed. 5.  The following, based on the range of values found in this survey, are proposed as provisional benchmarks for amounts of dead wood in British broadleaved forests: low <20 m3 ha−1 fallen dead wood, 0–10 snags ha−1 (all below 10 cm diameter); medium 20–40 m3 ha−1 fallen dead wood, 11–50 snags ha−1 (of which some are more than 10 cm diameter); high >40 m3 ha−1 fallen dead wood, more than 50 snags ha−1 (of which some are more than 40 cm diameter). 6.  Further work on assessing the dead wood resource in British forests is needed.
Long‐term population studies and the development of an integrated management programme for control of Opuntia stricta in Kruger National Park, South Africa
Authors: Hoffmann J.H. , Moran V.C. , Zeller D.A. 
Published: March 2003

1.  A cactus, Opuntia stricta, has invaded almost 16 000 ha of conserved, natural habitatand has become a major weed problem in Kruger National Park (KNP), South Africa. 2.  The main objectives in the control of O. stricta are to reduce the density of the weed and to curb long‐range dispersal of seeds by preventing young plants from reaching the size (28 cladodes) at which they start to produce fruits. 3.  Herbicides have failed to provide satisfactory control of O. stricta because the weed infestations are replenished from seeds in the soil and from small plants that are overlooked during spraying. 4.  A phycitid moth, Cactoblastis cactorum, was released in KNP during 1988 in an attempt to control O. stricta biologically. 5.  Population counts of the biological control agent and of the weed over a 5‐year period showed that, even though C. cactorum has not provided complete control of O. stricta in KNP, the moderate levels of larval damage have stunted the growth of O. stricta and have considerably extended the time that the young plants take to reach sexual maturity. 6.  Comparisons of modelled (i.e. with no C. cactorum) and actual populations of O. stricta showed that C. cactorum is making a substantial contribution to the control of O. stricta in residual infestations of the weed that have been treated with herbicides. 7.  The need for long‐term evaluation studies in biological weed control is demon strated by the development of an integrated management programme for effective control of O. stricta.
Experimental refuges for migratory waterfowl in Danish wetlands. I. Baseline assessment of the disturbance effects of recreational activities
Authors: Madsen Jesper 
Published: March 2003

1. Potential human sources of disturbance, including fishing, sailing, windsurfing and different types of waterfowl hunting, are described and their effects on autumn‐staging waterbirds, including mute swan, wigeon and coot, were examined at a coastal wetland in Denmark from 1985 to 1988. 2. Bird and human distributions were superimposed on the distribution of submerged vegetation and water depths to identify the extent of spatial overlap; likewise, seasonal and diurnal temporal overlap in bird abundance, and human activities were defined. Behavioural and distributional reactions of waterbirds to different human activities, in terms of escape distances, disruption of activity patterns and redistribution, were assessed to establish their relative effects. 3. Sailing and windsurfing showed little spatial overlap, and fishing partial spatial overlap with bird distributions; these activities almost ceased before the peak in autumn bird numbers. Hunting showed a high degree of spatial and temporal overlap with bird presence. 4. Birds responded to windsurfing at greatest distances, whereas hunting (especially from mobile punts) caused the longest disruptions to activities of waterfowl. In terms of behaviour and redistribution, wigeon was more affected by shooting than was mute swan or coot. One or two mobile shooting punts reduced wigeon numbers, whereas numbers were unaffected by the presence of up to 4–6 stationary punts; fishing boats had no effect on wigeon abundance. 5. Hunting, especially shooting from mobile punts, was identified as the most disturbing human activity in relation to staging waterfowl in this area. Similar results and conclusions were reached in another comparable study area. The results have implications for refuge designs and zoning of disturbing recreational activities.
Experimental refuges for migratory waterfowl in Danish wetlands. II. Tests of hunting disturbance effects
Authors: Madsen Jesper 
Published: March 2003

1. In most situations that have been studied, the creation of refuge areas for migratory waterfowl has generally increased the number of waterfowl using a site. However, experimental evidence to show that the increases were caused by reduced disturbance and not by confounding factors, e.g. improvement of habitat quality of the sites or general population increases, is generally lacking. 2. In two Danish coastal wetlands, waterfowl hunting was the most critical source of disturbance to autumn‐staging waterfowl (Madsen 1998). To test whether hunting disturbance displaced birds from sites, experimental refuge areas were established, with hunting‐free areas manipulated annually during a 4‐year period, followed by permanent refuge establishments, monitored for a further 4 years. 3. In both areas, experiments showed that quarry geese and dabbling ducks redistributed according to the position of the hunting‐free areas, whereas protected species did not. In quarry geese, there was a 6–8‐fold increase in numbers from before to after the experiments; in quarry dabbling ducks there was a 4–50‐fold increase. Dabbling ducks extended the staging period into the winter. Protected waterfowl as well as goldeneye and coot (both quarry species) did not redistribute; their numbers either fluctuated or increased (2 to > 50 fold). 4. In quarry geese and dabbling ducks, changes in food supplies (of the herbivorous species), intensities of recreational activities outside the refuge areas, weather or overall population sizes could not explain the increases. In protected species, as well as goldeneye and coot, trends in local numbers were in accordance with overall population trends for some species; in others, the rate of increase in local numbers was higher than in overall population size. 5. In both areas, species richness increased from before to after the experiments. This was most pronounced in one of the areas where the refuge included shallow‐watered areas in association with salt marshes. 6. It is concluded that prior to experiments, waterfowl hunting caused a displacement of quarry species, resulting in a species‐poor waterfowl community. Refuge creation is an efficient management tool to improve the conservation value and biodiversity of wetlands of importance to waterfowl.
Improving grasslands: the influence of soil moisture and nitrogen fertilization on the establishment of seedlings
Authors: Haugland Espen , Froud‐Williams Robert J. 
Published: March 2003

1. In order to investigate the factors influencing the establishment of seedlings in permanent grassland, the influence of soil moisture and nitrogen fertilization on competition between established plants of Lolium perenne and seedlings of Phleum pratense or Trifolium pratense was studied in two experiments under greenhouse conditions using the ‘split‐box’‐technique. 2. There was no difference in the production of plant dry matter of P. pratense or T. pratense between 30% volumetric soil water content (−0·005 MPa) and 22% (−0·04 MPa), but 15% soil moisture (−0·33 MPa) reduced plant growth. L. perenne yields were linearly reduced by reduced soil moisture content. 3. Shoot competition from L. perenne reduced the plant dry matter yield of P. pratense and T. pratense more than did root competition in these experiments. When shoot competition was present, differences between moisture contents were not detected, indicating that light was probably the limiting resource under such conditions. No significant interaction between root competition and soil moisture was observed for plant weight. 4. Root competition was not prevented even though sufficient water and nitrogen were supplied. This indicated either that some other growth factor was limiting or the plants competed for resources at the root hair level even though sufficient resources were supplied at the pot or field scale. Therefore, in the situation of direct drilling of species during grassland renovation, it may be difficult to alleviate competition by adequate provision of water and nitrogen.
Do wood‐pigeons avoid pesticide‐treated cereal seed?
Authors: MKay H. V. , Prosser P. J. , Hart A. D. M. , Langton S. D. , Jones A. , MCoy C. , Chandler‐Morris S. A. , Pascual J. A. 
Published: March 2003

1. Pesticides applied to seeds before sowing may present a high risk to seed‐eating birds. Some of these chemicals are highly toxic but are avoided by captive birds in laboratory tests. However, evidence for birds avoiding them in the field is lacking. The objective of this study is to investigate avoidance and other factors affecting risk of poisoning, using the model of wood‐pigeons Columba palumbus L. feeding on winter‐drilled cereal seed treated with the organophosphorus insecticide fonofos. 2. Wood‐pigeons feeding on arable fields in Cambridgeshire, UK, were counted once or twice per week over four winters from 1992 to 1996. In autumn, newly drilled cereal fields are shown to be preferred to alternative crops such as stubble and ploughed fields and root crops. In spring, newly drilled cereal fields are sometimes preferred to older cereal fields, stubble, ploughed fields and drilled onions. 3. Fewer fields drilled with fonofos‐treated cereal seed were used by wood‐pigeons than untreated (without fonofos) fields for the first week after drilling only. The extent of the avoidance reaction was related to the concentration of fonofos on the seed left exposed on field surfaces. 4. The concentration of fonofos on newly drilled seed exposed on field surfaces (mean of 241 mg kg–1) was much lower than expected from the approved application rate (1080 mg kg–1). Residues decayed linearly at a rate of 2% per day after drilling and varied widely between fields. 5. The density of seed left exposed after drilling also varied widely between fields, being greater on headlands (field edges) than the main field and declining at a rate of 2% per day after drilling. 6. Of 61 wood‐pigeons shot within the study area over three winters, 26 had been feeding on cereal seed and of these, six contained fonofos residues at levels similar to poisoned birds submitted to the MAFF Wildlife Incident Investigation Scheme. 7. In conclusion, fonofos‐treated cereal seed may be partially avoided in the wild. Avoidance fails to prevent poisoning under some (rare) conditions, possibly when seed density, concentrations of fonofos and levels of hunger are all above average. The implications for risk assessment are discussed.
A strategy for minimizing waterfowl deaths on toxic waterbodies
Authors: Read J. L. 
Published: March 2003

1.A deterrent was used in conjunction with engineering and management techniques to discourage nomadic waterfowl from landing and remaining on toxic waterbodies.2.Four behavioural traits of nomadic waterfowl were exploited in the development of the deterrent: nocturnal movements, attraction to reflective surfaces, fear of diurnal predators, and naivety to local conditions and deterrents.3.A rotating, intermittent beacon directed at a shallow angle across the water surface effectively discouraged most waterfowl. This beacon was floating and solar‐powered and built to be acid resistant.4.A series of deterrents, with gas‐powered sonic guns and provision of clean alternative waterbodies nearby, significantly lessened the likelihood of waterfowl injury or mortality on toxic waterbodies.
Clearcutting and burning of northern spruce‐fir forests: implications for small mammal communities
Authors: Sullivan Thomas P. , Lautenschlager R. A. , Wagner Robert G. 
Published: March 2003

1.This study was designed to test the hypotheses that (i) abundance and related demographic parameters of small mammal populations would decline after clearcutting of northern spruce‐fir forest, and (ii) prescribed burning, following clearcutting, an approach to emulating natural disturbance, would enhance the species richness and diversity of the small mammal community relative to unharvested and clearcut forests.2.Intensive live‐trapping of small mammal populations was conducted in replicated forest (uncut), clearcut and clearcut‐burned sites from 1988 to 1992 in west‐central British Columbia, Canada.3.Mean abundance of southern red‐backed volesClethrionomys gapperiwas significantly higher on forest sites (11·74 ha–1) than on clearcut (0·60 ha–1) or clearcut‐burned (0·02 ha–1) sites. Mean numbers of deer micePeromyscus maniculatuswere significantly higher on the clearcut‐burned sites (16·88 ha–1) than on forest sites (9·04 ha–1). Demographic parameters of reproduction, survival and body weight of deer mice were similar across all sites.4.The long‐tailed voleMicrotus longicaudushad a strong annual fluctuation in abundance, particularly on clearcut sites (14·04 ha–1), where there were significantly more animals than on either forest (1·53 ha–1) or clearcut‐burned (2·67 ha–1) sites. Meadow volesM. pennsylvanicuswere relatively uncommon but occurred more often on clearcut and clearcut‐burned sites than on forest sites.5.The north‐western chipmunkTamias amoenusoccurred at significantly higher numbers on clearcut (4·16 ha–1) and clearcut‐burned (3·88 ha–1) sites than on forest sites, where it was rarely captured. ShrewsSorexspp. were at similar numbers across forest, clearcut and clearcut‐burned sites. WeaselsMustelaspp. were captured more often on clearcut and clearcut‐burned sites than on forest sites. A rare species, the western jumping mouseZapus princeps, was captured on clearcut and clearcut‐burned sites only.6.Mean species richness of small mammals was significantly higher on clearcut sites (3·51) than on forest (2·73) or clearcut‐burned (2·72) sites. Species diversity was similar over all sites. Although species composition was altered by clearcutting, abundance of all species, exceptC. gapperi, was the same or higher than that in uncut forest.7.Prescribed burning of clearcuts may not be necessary to mimic natural disturbance regimes. Clearcutting of northern spruce‐fir forest may provide diverse habitats for small mammals through different stages of succession (along with old growth forest) much as wildfires formerly did.