bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of low‐level jet aircraft noise on the behaviour of nesting osprey
Authors: Trimper Perry G. , Standen Neil M. , Lye Leonard M. , Lemon David , Chubbs Tony E. , Humphries Gary W. 
Published: March 2003

1.  Nesting osprey Pandion haliaetus L. were exposed to controlled low‐level CF‐18 jet aircraft overflights along the Naskaupi River, Labrador, Canada, during 1995. Jet aircraft flew near five nests at distances ranging from 2·5 nautical miles (nm) to directly overhead at speeds of 400–440 knots. 2.  Maximum noise levels (L1) and other noise metrics were influenced by many factors including topography, distance, altitude, wind speed and direction. 3.  Based on 240 h of observations from blinds, we recorded osprey nest attendance and egg exposure during 139 individual overflights. Similar observations were completed at two control nests. Overflights as low as 30 m above ground occurred during incubation, nestling and prefledging only when observers were present. 4.  Osprey behaviour did not differ significantly (P = 0·126) between pre‐ and post‐overflight periods. Despite L1 values occasionally exceeding 100 decibels, adult osprey did not appear agitated or startled when overflown. 5.  Osprey were attentive to and occasionally flushed from nests when float planes, other osprey or raptors entered territories, and when observers were entering or exiting blinds.
The effect of local change in habitat quality on populations of migratory species
Authors: Sutherland William J. 
Published: March 2003

1. Habitat deterioration is a major problem world‐wide as a result of processes such as change in land use, introduced species, human disturbance and exploitation of food supplies. Many studies have shown that habitat change can have considerable effect on the numbers of individuals using a site. For migratory species, however, the consequences for the total population cannot be deduced from local studies. 2. For a migratory species, the change in total population size ΔN, as a consequence of habitat change in the wintering area, can be calculated from ΔN = LMγd′/(b′ + d′), where γ is the expected proportional change in the number of birds using a site as a result of the habitat change, L is the area affected, M is the density of individuals using the site prior to habitat change, b′ is the strength of the per capita density‐dependent breeding output, and d′ is the strength of the per capita density‐dependent winter mortality. Similarly the consequences of habitat change in the breeding area can be calculated from ΔN = LMγb′/(b′ + d′). 3. The same approach can be used for predicting the consequences of improvements in habitat quality. 4. A worked example is given to illustrate how this approach could be used to predict the consequences for the total population of changes in the food supply of oystercatchers within one estuary. 5. There is a need for more measures of γ, the expected proportional change in the number of birds using a site as a result of various forms of habitat deterioration, and the strengths of density dependence.
The impact of changing the season in which cereals are sown on the diversity of the weed flora in rotational fields in Denmark
Authors: Hald Anna Bodil 
Published: March 2003

1. Surveys have shown that there has been a dramatic decrease in the weed flora of fields under rotational cultivation during the last 30 years. This trend has been particularly noticeable in winter cereals, a crop of increasing importance in the landscape. 2. The weed flora of spring and winter cereals was compared in 19 unsprayed fields during a 5‐year study to test the hypothesis that cereal type exerts no effect on the flora or on the absolute and relative abundance of single species. 3. Plant and species densities, and accumulated species richness, were lower in winter than in spring cereals. 4. Floristic similarity was greater among spring cereal fields and between spring and winter cereals within the same fields than among winter cereal fields. 5. Species that occurred with unequal density in spring and winter cereals occurred at higher densities in the spring cereals; these species germinated mainly in the spring. However, for a few species the relative plant abundance was highest in winter cereals; these species were able to germinate both in the spring and autumn. 6. Some species – on the relative scale – occurred indifferently of season of sowing; all but one of these species were able to germinate both in the spring and autumn. 7. Plant species and taxa that are important food resources for arthropod herbivores occurred at greater densities in spring than in winter cereals and, in addition, occurred with the highest relative abundance in spring cereals. 8. Change in land use from spring to winter cereals involves not only an immediate reduction of more than 25% in the density of plants and species, but also a change and increased uncertainty in the composition of the weed flora. These findings may have serious implications for the ecology of wildlife in the agricultural landscape.
Conservation of arthropod diversity in montane wetlands: effect of altitude, habitat quality and habitat fragmentation on butterflies and grasshoppers
Authors: Wettstein Walter , Schmid Bernhard 
Published: March 2003

1. The patterns of arthropod diversity were investigated in 24 montane wetlands in Switzerland. These differed in altitude, management regime (cattle‐grazing vs. mowing), vegetation structure (index combining vegetation height and density) and degree of habitat fragmentation. 2. The general arthropod diversity was determined by net sampling at 10 sampling points per site. The diversity of grasshoppers and butterflies was measured by counting species richness at the site and species density (species richness per unit area) on transects. The species richness of grasshoppers and butterflies was found to be more sensitive to the geographical attributes of the site whereas species density was more affected by the habitat quality. 3. Grasshopper diversity decreased within the observed altitudinal range (800–1400 m) and was higher at grazed sites, whereas butterfly diversity was higher at mown sites. Arthropod diversity but not abundance of arthropods was positively related to the vegetation structure. 4. The species richness of butterflies was negatively influenced by the degree of habitat fragmentation: both the size of habitat as well as the area of wetland habitats within 4 km were related positively to the number of specialist wetland butterflies. 5. Late mowing as well as low‐density cattle‐grazing are appropriate management actions to maintain arthropod diversity in montane wetlands. In order to establish site‐specific management plans, the biology of the present target species as well as the historical context should be considered. 6. We suggest that the best protection for the species examined in this study would be a network of wetland sites managed using a variety of traditional, non‐intensive methods. This can only be achieved by coordinated planning of conservation measures among sites.
Virus‐vectored immunocontraception to control feral cats on islands: a mathematical model
Authors: Courchamp Franck , Cornell Stephen J. 
Published: March 2003

Summary1. Feral catsFelis catusintroduced onto oceanic islands pose a major ecological threat to endemic vertebrates, but their control is difficult. Immunocontraception has not been considered previously as a method for their control or eradication, and therefore we used a modelling approach to assess whether virus‐vectored immunocontraception (VVIC) might be effective.2. We compared the relative efficiency of cat control/eradication using immunocontraception and three different disseminating techniques, i.e. baits, genetically modified viral vectors, or both. We accounted for several forms of dynamic compensation likely to arise in a population with artificially reduced fertility.3. We conclude that, under the assumptions of our model, immunocontraception can control or eradicate feral cats on oceanic islands. VVIC was found to be a more efficient dissemination technique than baits, but an integrated method involving viral‐infected baits was the most likely to lead to eradication.4. We advocate field trials of this VVIC technique, when available, under island conditions where any risks to non‐target fauna would be minimal.
Sea otter population dynamics and the ExxonValdez oil spill: disentangling the confounding effects
Authors: Garshelis David L. , Johnson Charles B. 
Published: March 2003

Summary

Oil that spilled after the grounding of the Exxon Valdez in 1989 killed large numbers of sea otters in western Prince William Sound, Alaska, USA. However, our boat‐based counts of sea otters during 1990–96 at oiled sites were as high or higher than boat‐based counts in the same area in the early 1980s.
Another study reported a significant decline in sea otter numbers after the spill, but our reanalysis of that data produced results very similar to ours. Counts of otters were higher than pre‐spill counts in the oiled area; the only detectable decline was in the northern part of the sound, outside the area of oiling.
We suggest that otter numbers in the western sound may have been increasing during the late 1980s, masking the loss due to the spill. Direct evidence for such an increase is lacking because no counts were conducted during this period. However, for several years after the spill pup production was higher than normal, which, if characteristic of the period immediately pre‐spill, could have spurred a population increase.
Heightened pup production may have been caused by increased food supplies: after the spill, otters obtained more and larger clams per dive and spent less time feeding per day than in the early 1980s.
We postulate that in the early 1980s clams were still recovering from the uplift caused by the 1964 earthquake, which resulted in massive clam mortality and habitat change in the western sound. Lingering effects of previous catastrophic events, like the earthquake and even 19th‐century fur harvests, have hampered attempts to assess the impacts of the oil spill on sea otter population dynamics. The effects of uncontrolled and unreplicated environmental incidents, even major disasters, may be difficult to assess because of confounding factors.
The effect of dairy farming on barn swallowHirundo rusticaabundance, distribution and reproduction
Authors: Møller Anders Pape 
Published: March 2003

SummaryRecent changes in agricultural practice have been hypothesized to affect the abundance and reproductive success of farmland birds. The influence of dairy farming on barn swallowsHirundo rusticawas investigated by comparison of their abundance, phenotype and reproduction on the same farms before and immediately after dairy farming ceased, while a control sample of farms without change in farming practice in the same years was used to check for temporal changes unrelated to farming practice.The abundance of barn swallows decreased significantly when dairy farming ceased, with an average reduction of 48%, while there was no significant difference in the sample of control farms. This was mainly due to a decrease in the abundance of yearling immigrants. The abundance of insect food measured with sweep nets decreased significantly in the absence of cattle, while there was no significant change in the sample of control farms.The mean phenotypes of adult barn swallows breeding on the same farms with and without dairy farming did not differ significantly for any of the 16 variables measured (11 morphological variables, body mass, parasite load, haematocrit, leucocyte counts, and arrival date), nor were there any significant differences recorded in the sample of control farms.The mean phenotypes of barn swallow nestlings on the same farms with and without dairy farming differed for tarsus length, body mass, haematocrit, leucocyte concentration and T‐cell mediated immune response, with nestlings being of poorer quality in the absence of cattle. There was no significant differences recorded in the sample of control farms.Start of reproduction was not delayed in the absence of cattle, but size of first clutches was reduced by the absence of cattle. The frequency of second clutches decreased in the absence of cattle, and laying of second clutches was also delayed. Hatching, fledging and breeding success did not differ between the two types of farming practice. This led to an overall reduction in annual reproductive success in the absence of cattle. None of these significant differences was recorded in the sample of control farms.These observations suggest that termination of dairy farming reduces local population size, reproductive success and the quality of offspring produced. There is little evidence of the distribution of phenotypes of adult barn swallows being affected by the presence of cattle.
Simulating the long‐term dynamics of slug populations: a process‐based modelling approach for pest control
Authors: Shirley Mark D.F. , Rushton Stephen P. , Young Andrew G. , Port Gordon R. 
Published: March 2003

Summary

An individual‐based simulation model was developed to investigate the long‐term dynamics of slug populations using the field slug Deroceras reticulatum as the test species.
The model consisted of two components: a model to provide meteorological data and simulate crop growth; and a model to simulate slug life histories. The patterns of slug population dynamics produced by the model matched the characteristic bivoltine life cycle of D. reticulatum observed in field studies.
A sensitivity analysis showed that the output of the model was significantly influenced by soil moisture, air temperature and leaf area index. These three environmental factors relate directly to important features in the biology of slugs. Of the life‐history variables used as inputs to the model, growth rate, environmental mortality and the mortality of sexually mature slugs had a significant effect on the population dynamics predicted by the model.
The model output was compared with the observed dynamics of slug populations collected in the field. Predicted slug dynamics and observed slug numbers showed a high degree of fidelity.
The simulation model was used to investigate the effects of varying the timing of control methods used to combat slug damage to crops. This result suggested that there is a ‘window of opportunity’, immediately post‐harvest, when slug control is likely to have a significant effect on both the current slug population and the slug numbers in the following spring.
Modelling approaches that link crop growth and population dynamics of pests have potential in assessing their agricultural impacts and in evaluating alternative strategies for their management.
Relationships between biomass and plant species richness in arid‐zone grazing lands
Authors: Oba Gufu , Vetaas Ole R. , Stenseth Nils C. 
Published: March 2003

Summary

The relationship between biomass and species richness in temperate vegetation has been described as a hump‐back response model. The hump‐back model predicts that herbaceous species richness is highest at an intermediate level of biomass. However, this has not been investigated in arid‐zone grazing lands.
We tested the hump‐back prediction in an arid tropical grazing region in northern Kenya where a seasonal grazing exclosure system is practised. We compared vegetation structure, species richness and composition on an open range and exclosures at five sites to elucidate the potential mechanisms behind variation in species richness.
More biomass was accumulated within seasonal exclosures than in continuously grazed areas. Species richness in exclosure plots varied from 5·3 to 8·3 species m−2, while that in open plots varied from 5·1 to 7·5 species m−2. A pair‐wise test showed no difference in two of the five sites with respect to both total and herbaceous species richness.
The primary floristic gradient illuminated through ordination was related to biomass, while the secondary gradient was related to species richness. The exclosure plots had more abundant species, especially compared with open plots, which had more rare and occasional species. A total of 37 herbaceous species was recorded; 22% were indifferent to grazing, 30% grazing intolerant and 48% promoted by grazing.
The relationship between biomass and herbaceous species richness showed (i) no trend within the exclosures (maximum biomass 800 g m−2); (ii) a positive trend in the open grazing land (maximum of 500 g m−2); and a hump‐back pattern when (i) and (ii) were analysed together. Optimum richness corresponded to a biomass level of 400–500 g m−2. Species richness declined with increase in age of exclosures.
We confirmed that species richness will decline when biomass exceeds 500 g m−2, as predicted by the hump‐back model, even in arid grazing lands. Seasonal grazing exclosures may increase species richness to a certain level, but the decline in species richness with age of exclosures indicates that long‐term exclusion of grazing may not necessarily increase species richness in arid‐zone grazing lands.
Exploring spatial vegetation dynamics using logistic regression and a multinomial logit model
Authors: Augustin Nicole H. , Cummins Roger P. , French Donald D. 
Published: March 2003

SummaryThis study presents statistical methodology that uses spatial explanatory variables to improve simpler estimates of transition probabilities from categorical data, such as vegetation type, that have been recorded as classified cells (pixels) in a grid or lattice at different times.A specific application is to examine successions in semi‐natural vegetation in north‐east Scotland. Questions related to these data include: Do transition probabilities of a pixel depend on the size of a patch of vegetation (polygon) and pixel location within the polygon? Do stable areas remain stable? Does the proximity of certain vegetation types influence transitions?We selected spatial variables that were likely to be important in this application, where short‐range vegetative spread was thought to be an important factor.The multinomial logit model is used to estimate the transition probabilities as a function of explanatory variables, including location, neighbourhood information and other factors recorded at the start of the transition period. This model allowed the testing of different assumptions about the dynamics of underlying processes leading to transitions.When the number of categories, for example vegetation types, observed is large in comparison to the sample size, estimates of transition probabilities can be unreliable. We show that using change of category within the time period as the response in a logistic regression can still provide insight to the underlying dynamics of change in such a case.The methods are illustrated with some Scottish vegetation classification data with pixels of size 5 × 5 m covering a square of area 0·25 km2. Two contrasting squares were investigated: the first was upland moorland grazed by sheep and the second was a lowland area with more varied vegetation and low intensity grazing by cattle.In both squares there are strong spatial trends, and the neighbourhood of a pixel affected its transition. Prediction misclassification rates estimated from different models were compared using K‐fold cross‐validation. The multinomial model, including position in the square and number of neighbouring pixels in the same category as the pixel modelled, reduced the misclassification rate compared with the model without spatial explanatory variables.The improved estimates of transition probabilities could be incorporated into Markov models used in simulation studies to predict future vegetation changes under different management strategies.
Breeding bird species diversity in the Negev: effects of scrub fragmentation by planted forests
Authors: Shochat Eyal , Abramsky Zvika , Pinshow Berry 
Published: March 2003

Summary

Afforestation of the Northern Negev, Israel, from 1956 resulted in patches of primarily coniferous trees that fragmented large scrubland areas. This alteration in landscape pattern was followed by immigration of mediterranean bird species to the Negev.
We counted breeding birds, and measured various environmental variables in scrubland and planted forest patches, to test whether bird assemblages were random subsets of the regional species pool, and whether area or habitat structure was the major correlate with species abundance and distribution.
Of 22 bird species recorded, only three appeared in both scrub and forest, showing that these two habitats were occupied by different species assemblages. In both habitats, species richness increased with area at a rate greater than that expected by random sampling. In the scrub this increase was related to area per se, while in the forest it was related to habitat diversity in terms of stand age and tree type.
The density of forest species was unaffected by area, but specialist scrubland species declined as area decreased. We suggest that edge effects might reduce species abundance in small scrubland patches.
Nested subset analysis indicated that, at the community level, species composition was not random. However, at the species level, the distribution of three forest‐dwelling species appeared as random, as it was associated with habitat rather than with patch size.
Our results indicate that increased diversity of breeding birds in the Northern Negev will require scrub patches larger than 50 ha among the increasingly forested landscape. In contrast, increasing forest area would hardly increase species diversity in the whole landscape. Future forest management regimes should also aim to increase habitat diversity by adding foliage layers, especially in the understorey. Exotic coniferous forests support fewer species than deciduous forests in mediterranean zones around the world. The suggested management regime may improve such forests as habitat for species‐rich bird communities.
The effects of induced sterility on the territorial behaviour and survival of foxes
Authors: Saunders Glen , McIlroy John , Berghout Mani , Kay Barry , Gifford Eddie , Perry Rob , Van De Ven Remy 
Published: March 2003

Summary

This paper reports on the behavioural effects of surgical sterilization when used to simulate immunocontraception in free‐ranging female foxes Vulpes vulpes.
During 3 years of trapping, 348 male and female foxes were fitted with transmitters in two treatment (females sterilized) and two untreated areas.
Radio‐tracking indicated that sterile and fertile vixens maintained similar‐sized territories during the breeding season, but that sterile females were possibly more likely to share their territories with each other.
There were no consistent differences in survival or dispersal between sterile and fertile females.
Outcomes from the study suggest that immunocontraception in free‐living foxes is feasible.