bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatially explicit, individual‐based, behavioural models of the annual cycle of two migratory goose populations
Authors: Pettifor R.A. , Caldow R.W.G. , Rowcliffe J.M. , Goss‐Custard J.D. , Black J.M. , Hodder K.H. , Houston A.I. , Lang A. , Webb J. 
Published: March 2003

1. Behaviour‐based models of animal population dynamics provide ecologists with a powerful tool for predicting the response of such populations to both natural and human‐induced environmental changes.2. We developed this approach by addressing two outstanding issues in the application of such models: the need to adopt a large‐scale spatially explicit approach, and the need to consider the year‐round dynamics of animal populations.3. Spatially explicit, year‐round, behaviour‐based models of two populations of arctic‐breeding geese, the Svalbard population of the barnacle gooseBranta leucopsisand the dark‐bellied race of the brent gooseBranta bernicla, were developed. Both populations have been the subject of serious conservation concern and are currently a source of increasing conflict with agricultural interests.4. There was generally good agreement between empirically derived and model‐generated density‐dependent functions, and of seasonal patterns of the distribution and movement of populations within and between sites, and of energy reserve levels within a population.5. Sensitivity analyses, however, highlighted the importance of accurate parameter estimation with respect to the predictions of such models, and the potential flaws in the predictions of existing models that have not adopted a spatially explicit approach when dealing with wide‐ranging migratory populations.6. The effect of the removal of a given area of habitat on both populations was predicted to vary depending upon the spatial configuration of the change. This further emphasizes the need for a spatially explicit approach.7. Both barnacle goose and brent goose populations were predicted to decline following habitat loss in their winter or spring‐staging sites. Simulations suggested that barnacle geese might be less vulnerable to winter habitat loss than brent geese. This reflected the relative strengths of the density‐dependence of productivity and winter mortality in the two models and provided a clear illustration of the need for a year‐round approach to animal population dynamics.8. We believe that these models, and this approach to understanding the population dynamics of long‐distance migrants, will be beneficial in attempting to answer the increasingly urgent and frequent requests to predict the response of such populations to environmental change.
The influence of the rice bug Leptocorisa oratorius on rice yield
Authors: Van Den Berg H. ,   SOEHARDI
Published: March 2003

Summary 1.

Leptocorisa oratorius, which feeds on the panicle of rice, is a major target for insecticide applications by farmers in Indonesia. The management of this insect has been insufficiently addressed because of unknown damage relationships in modern rice varieties. Hence, a study was conducted to assess the impact of L. oratorius on the yield of variety IR64. 2.
Sources of bias typically associated with studies on yield loss (spray effects, caging, plant compensation for damage) were avoided by studying the effect of differences in natural infestation levels of L. oratorius on rice yield at a large number of field sites. Several parameters, including the number of spikelets m−2 prior to panicle emergence (i.e. prior to attack by L. oratorius), were measured at each site to account for local conditions. The effect of these variables on yield was analysed in a statistical model. After removing non‐significant variables from the model, the effect unambiguously attributable to L. oratorius density was determined. 3.
The median density of L. oratorius in farmers' fields (pooled from panicle emergence until the milky stage of rice) was 0·10 adults hill−1 (i.e. 2·6 adults m−2) in the dry season (75 sites) and 0·14 adults hill−1 (3·5 adults m−2) in the wet season (94 sites). 4.
The analysis showed that L. oratorius populations caused no measurable reduction in yield of rice. If a linear relationship in the range of 2–10% yield loss for every added adult per hill was assumed, under the measured field populations of L. oratorius in East Java the median loss would have been in the range of 0·2–1·0% in the dry season of 1997 and 0·2–1·3% in the wet season of 1997/98. 5.
Additional field cage experiments were conducted to compare the susceptibility of different stages of rice development to L. oratorius attack and to study yield loss components. In field cages with a bug/panicle ratio substantially higher than observed in the field, L. oratorius reduced yield when feeding at peak flowering of rice, indicating that rice is most susceptible to L. oratorius attack at flowering. The presence of L. oratorius at peak flowering and at the peak milky stage, moreover, caused empty seed. There was, however, no indication that L. oratorius caused partially filled seed. Further study is needed of the possible mechanism by which the plant, under moderate attack from L. oratorius, redirects assimilates from damaged spikelets to those that would have gone unfilled. 6.
In conclusion, L. oratorius did not cause an important reduction in rice yield in this study, and we conclude that the application of insecticides targeted at L. oratorius is mostly unwarranted. Farmers need practical training on the biology of L. oratorius and its feeding on rice to appreciate why chemical control is generally not required.
Responses of male brushtail possums to sterile females: implications for biological control
Authors: Ji Weihong , Clout Mick N. , Sarre Stephen D. 
Published: March 2003

Summary 1.  Increasingly immunocontraception is being considered as a potential method for the biological control of mammalian pests. Although several studies have investigated or modelled its demographic consequences, there have been few studies of the possible effects of the presence of sterile females on local males. 2.
In New Zealand, the brushtail possum Trichosurus vulpecula is an important mammalian pest, for which immunocontraception has been proposed as a control method. 3.  We surgically sterilized female brushtail possums in two populations to study the potential effects of immunocontraception on body condition and local sex ratios. 4.  Large numbers of leucocytes (indicating oestrus) were present in the reproductive tracts of sterile female possums several weeks after most control (non‐sterile) females were pregnant and had ceased mating activity. This indicates that the sterilization of females prolonged the mating season of local possums. 5.  The body condition of males was significantly poorer in the presence of sterilized females in the winter post‐mating period following the treatment. In contrast, the body condition of females showed no change following the sterilization treatment, either during the autumn mating period or in the winter post‐mating period. 6.  More adult male possums were recorded at both study sites after the sterilization treatment, resulting in a change to the originally female‐biased sex ratio. This may have been caused by the prolonged presence of oestrous females attracting males from surrounding areas. 7.  The implications of our results for the control of possums by sexually transmitted immunocontraception are twofold. First, the reduced body condition of males in the presence of sterilized females might result in increased male mortality. Secondly, the attraction of males from surrounding areas to those containing sterilized females might facilitate the local spread of an immunocontraceptive agent. 8.  We advocate further assessments of the effects of sterilization and/or immunocontraception on the population demography, individual condition and survival of pest animals.
Habitat associations and breeding success of yellowhammers on lowland farmland
Authors: Bradbury Richard B. , Kyrkos Antonios , Morris Antony J. , Clark Stéphanie C. , Perkins Allan J. , Wilson Jeremy D. 
Published: March 2003

1. Yellowhammers began to decline on British lowland farmland in the late 1980s and losses are presently 10% per year. This study examined variation in the habitat selection and breeding success of yellowhammers, allowing an evaluation of whether Britain's yellowhammer decline might have been caused by recent changes in agriculture. 2. Yellowhammer territories were associated with hedgerows, vegetated ditches and wide uncultivated grassy margins around fields. Pasture and silage leys were avoided. Nests were built among herbaceous vegetation in ditches or in the shrubby vegetation of hedgerows. 3. Breeding started slightly earlier on organic farms than on intensively managed farms, but no measure of breeding success differed between farm types. Predation was the cause of most (64%) nest failures. A maximum of three breeding attempts (two successful) was observed per pair, with a mean clutch size of 3·3, a Mayfield nest success rate of 0·46, and 2·6 nestlings fledged per successful brood. These data, together with published estimates of adult yellowhammer survival and of post‐fledging survival among other passerines, suggest that breeding productivity is too low to maintain a stable population. 4. The removal of hedgerows or abandonment of hedge management, filling or clearing of ditches, intensification of grassland management and cropping or grazing right up to the field edge, are all likely to have adversely affected yellowhammers on lowland farmland in southern England. Policy reforms that redirect subsidy support to environmentally beneficial management of field margin habitats and retention of winter‐feeding sites such as stubbles should assist in restoring populations of breeding yellowhammers on lowland farmland. 5. Our data expand further the array of farmland bird species for which interactions between agricultural change and population change are increasingly understood.
The ecological challenge of immunocontraception: editor's introduction
Authors: Barlow N.D. 
Published: March 2003

Summary 1.  The problems of vertebrate pests are greater now than ever before, with vertebrate control constrained by problems of humaneness, scale and environmental impact. However, immunocontraception involves a conceptually ideal solution. Although not intrinsically novel, its delivery in baits or by a self‐spreading vector and its effectiveness in pest control, are now the focus of growing international interest. 2.  Major ecological questions correspond to the two forms of delivery: baits and vectors. First, given an effective immunocontraceptive, inserted into a bait and eaten by a pest, would the resulting level of sterilization in the population effectively suppress densities? Secondly, given that the immunocontraceptive agent can be inserted into a microparasitic or macroparasitic infective vector, would the modified vector persist at sufficient prevalence in the host population, and hence suppress densities to the required extent? 3.  The papers published in this Special Profile focus on behaviour following sterilization or they model the likely impact of viral‐vectored immunocontraception. They highlight advantages and disadvantages of immunocontraception and some general, novel and specific issues. These include the possibility of behaviourally mediated population responses to fertility control; the possible advantages of a mixed baiting and vector strategy; the competitiveness of a modified vector; the appropriateness of immunocontraception for controlling invasive vertebrates on islands; and the need for a ‘pay‐off’ methodology for assessing genetic modifications against alternatives. 4.  The findings offer significant benefits for management and policy: they will inform decisions on whether to pursue immunocontraception as a control option, and they provide evidence about efficacy and risk in applications to release genetically modified vectors. 5.  Although many of the problems in developing immunocontraception technology are biotechnological, questions about the effectiveness of immunocontraceptive pest control are ultimately in the domain of ecologists.
The seasonal abundance of blowflies infesting drying fish in south‐west India
Authors: Wall R. , Howard J.J. , Bindu J. 
Published: March 2003

Summary

Blowfly infestation of sun‐drying fish is a major economic problem in many developing countries of Asia, Africa and the Pacific. To consider the ecology of infestation, adult and larval blowfly populations were monitored between 27 October 1997 and 27 April 1999 at a fish landing and drying site, approximately 5 km north of Calicut, in Kerala state on the coast of south‐west India.
During the 548‐day sampling period, a total of 96 953 adult Diptera was collected from 16 sticky targets, placed inside and outside eight fish‐storage sheds. Of these, 91 912 (95%) were Chrysomya megacephala, 3719 (4%) were other Calliphoridae and 1322 (1%) were other species, largely Sarcophagidae.
The population of C. megacephala showed pronounced seasonal fluctuations in response to climate, particularly relative humidity. Significantly shorter‐frequency fluctuations within fish‐processing sheds were also evident, the periodicity of which corresponded approximately to C. megacephala generation cycles. Spatial variation in C. megacephala abundance was evident within the site, higher populations occurring closest to the beach and numbers declining with distance inland.
The pattern of drying fish infestation by C. megacephala broadly followed changes in the density of adult flies and the seasonal change in weather, with peaks during the monsoon and troughs in the dry hot periods. High relative humidity played a significant but secondary role in increasing infestation.
Quantification of the relationship between larval infestation and percentage fish loss suggests that, given the infestation levels observed, between 10% and 60% post‐harvest wet weight losses would be expected in the monsoon period, depending on the species of fish landed.
The study emphasizes the importance of developing a clear understanding of the basic ecology and spatial and temporal dynamics of an insect pest, prior to the design or implementation of any pest management programme.
Can grazing response of herbaceous plants be predicted from simple vegetative traits?
Authors: Díaz Sandra , Noy‐Meir Imanuel , Cabido Marcelo 
Published: March 2003

Summary

Range management is based on the response of plant species and communities to grazing intensity. The identification of easily measured plant functional traits that consistently predict grazing response in a wide spectrum of rangelands would be a major advance.
Sets of species from temperate subhumid upland grasslands of Argentina and Israel, grazed by cattle, were analysed to find out whether: (i) plants with contrasting grazing responses differed in terms of easily measured vegetative and life‐history traits; (ii) their grazing response could be predicted from those traits; (iii) these patterns differed between the two countries. Leaf mass, area, specific area (SLA) and toughness were measured on 83 Argentine and 19 Israeli species. Species were classified by grazing response (grazing‐susceptible or grazing‐resistant) and plant height (< or > 40 cm) as well as by life history (annual or perennial) and taxonomy (monocotyledon or dicotyledon).
Similar plant traits were associated with a specific response to grazing in both Argentina and Israel. Grazing‐resistant species were shorter in height, and had smaller, more tender, leaves, with higher SLA than grazing‐susceptible species. Grazing resistance was associated with both avoidance traits (small height and leaf size) and tolerance traits (high SLA). Leaf toughness did not contribute to grazing resistance and may be related to selection for canopy dominance.
Plant height was the best single predictor of grazing response, followed by leaf mass. The best prediction of species grazing response was achieved by combining plant height, life history and leaf mass. SLA was a comparatively poor predictor of grazing response.
The ranges of plant traits, and some correlation patterns between them, differed markedly between species sets from Argentina and Israel. However, the significant relationships between plant traits and grazing response were maintained.
The results of this exploratory study suggest that prediction of grazing responses on the basis of easily measured plant traits is feasible and consistent between similar grazing systems in different regions. The results challenge the precept that intense cattle grazing necessarily favours species with tough, unpalatable, leaves.
Recovery of bird populations after clearfelling of tall open eucalypt forest in Western Australia
Authors: Williams M.R. , Abbott I. , Liddelow G.L. , Vellios C. , Wheeler I.B. , Mellican A.E. 
Published: March 2003

Summary

Increasing concern over the sustainable management of forested landscapes and the extent of forest clearance world‐wide has led to a growing interest in the impacts of logging and associated habitat disturbance on biodiversity.
We conducted an experimental study of the impact of clearfelling on birds of the karri Eucalyptus diversicolor forest in south‐west Western Australia over a 17‐year period, and a retrospective study of both clearfelled and naturally regenerated karri stands aged from 0 to 146 years.
One‐third of species still had significantly reduced abundance 14 years after disturbance ceased, although all affected species made limited use of regenerating forest.
Multivariate analysis of changes in bird community structure showed that the effects of disturbance were still evident 14 years after clearfelling. Clearfelling may also have produced some temporary changes in community structure in adjacent unlogged forest.
Species richness and total abundance of birds declined by 58% and 96%, respectively, in the first year after clearfelling, and 14 years after logging were still 17% and 55% below levels in adjacent undisturbed forest. During this early successional phase both measures increased as a simple function of stand age. Species richness of regrowth reached that of old‐growth at 30–50 years and total abundance of all bird species in regrowth was similar to that of old‐growth after approximately 70 years.
Several bird species offer potential as indicators of the ecological sustainability of karri forest management. These species nest in large hollows in standing live trees (two cockatoo species) or have been slow to recolonize immature regrowth karri forests (six species).
Post‐hoc power analysis showed that even the long‐term and intensive sampling employed in this study failed to detect declines in abundance of less than 80–90% for most bird species. For many uncommon species, trying to estimate changes in abundance is problematic and likely to require replication which is difficult to achieve in field situations where logged and unlogged forests are compared. Despite this, the present study identified some key impacts of forest clearfelling on bird communities, with implications both for the consequences of clearfelling of forests and the criteria for sustainable forest management.
Evaluating presence–absence models in ecology: the need to account for prevalence
Authors: Manel Stéphanie , Williams H. Ceri , Ormerod S.J. 
Published: March 2003

Summary

Models for predicting the distribution of organisms from environmental data are widespread in ecology and conservation biology. Their performance is invariably evaluated from the percentage success at predicting occurrence at test locations.
Using logistic regression with real data from 34 families of aquatic invertebrates in 180 Himalayan streams, we illustrate how this widespread measure of predictive accuracy is affected systematically by the prevalence (i.e. the frequency of occurrence) of the target organism. Many evaluations of presence–absence models by ecologists are inherently misleading.
With the same invertebrate models, we examined alternative performance measures used in remote sensing and medical diagnostics. We particularly explored receiver‐operating characteristic (ROC) plots, from which were derived (i) the area under each curve (AUC), considered an effective indicator of model performance independent of the threshold probability at which the presence of the target organism is accepted, and (ii) optimized probability thresholds that maximize the percentage of true absences and presences that are correctly identified. We also evaluated Cohen's kappa, a measure of the proportion of all possible cases of presence or absence that are predicted correctly after accounting for chance effects.
AUC measures from ROC plots were independent of prevalence, but highly significantly correlated with the much more easily computed kappa. Moreover, when applied in predictive mode to test data, models with thresholds optimized by ROC erroneously overestimated true occurrence among scarcer organisms, often those of greatest conservation interest. We advocate caution in using ROC methods to optimize thresholds required for real prediction.
Our strongest recommendation is that ecologists reduce their reliance on prediction success as a performance measure in presence–absence modelling. Cohen's kappa provides a simple, effective, standardized and appropriate statistic for evaluating or comparing presence–absence models, even those based on different statistical algorithms. None of the performance measures we examined tests the statistical significance of predictive accuracy, and we identify this as a priority area for research and development.
Using satellite telemetry to define spatial population structure in polar bears in the Norwegian and western Russian Arctic
Authors: Mauritzen Mette , Derocher Andrew E. , Wiig Øystein , Belikov Stanislav E. , Boltunov Andrei N. , Hansen Edmond , Garner Gerald W. 
Published: March 2003

Summary

Animal populations, defined by geographical areas within a species’ distribution where population dynamics are largely regulated by births and deaths rather than by migration from surrounding areas, may be the correct unit for wildlife management. However, in heterogeneous landscapes varying habitat quality may yield subpopulations with distinct patterns in resource use and demography significant to the dynamics of populations.
To define the spatial population structure of polar bears Ursus maritimus in the Norwegian and western Russian Arctic, and to assess the existence of a shared population between the two countries, we analysed satellite telemetry data obtained from 105 female polar bears over 12 years.
Using both cluster analyses and home‐range estimation methods, we identified five population units inhabiting areas with different sea‐ice characteristics and prey availability.
The continuous distribution of polar bear positions indicated that the different subpopulations formed one continuous polar bear population in the Norwegian and western Russian Arctic. Hence, Norway and Russia have a shared management responsibility.
The spatial population structure identified will provide a guide for evaluating geographical patterns in polar bear ecology, the dynamics of polar bear–seal relationships and the effects of habitat alteration due to climate change. The work illustrates the importance of defining population borders and subpopulation structure in understanding the dynamics and management of larger animals.