bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effects of species’ range sizes on the accuracy of distribution models: ecological phenomenon or statistical artefact?
Authors: McPHERSON JANA M. , JETZ WALTER , ROGERS DAVID J. 
Published: September 2004

Summary

Conservation scientists and resource managers increasingly employ empirical distribution models to aid decision‐making. However, such models are not equally reliable for all species, and range size can affect their performance. We examined to what extent this effect reflects statistical artefacts arising from the influence of range size on the sample size and sampling prevalence (proportion of samples representing species presence) of data used to train and test models.
Our analyses used both simulated data and empirical distribution models for 32 bird species endemic to South Africa, Lesotho and Swaziland. Models were built with either logistic regression or non‐linear discriminant analysis, and assessed with four measures of model accuracy: sensitivity, specificity, Cohen's kappa and the area under the curve (AUC) of receiver‐operating characteristic (ROC) plots. Environmental indices derived from Fourier‐processed satellite imagery served as predictors.
We first followed conventional modelling practice to illustrate how range size might influence model performance, when sampling prevalence reflects species’ natural prevalences. We then demonstrated that this influence is primarily artefactual. Statistical artefacts can arise during model assessment, because Cohen's kappa responds systematically to changes in prevalence. AUC, in contrast, is largely unaffected, and thus a more reliable measure of model performance. Statistical artefacts also arise during model fitting. Both logistic regression and discriminant analysis are sensitive to the sample size and sampling prevalence of training data. Both perform best when sample size is large and prevalence intermediate.
Synthesis and applications. Species’ ecological characteristics may influence the performance of distribution models. Statistical artefacts, however, can confound results in comparative studies seeking to identify these characteristics. To mitigate artefactual effects, we recommend careful reporting of sampling prevalence, AUC as the measure of accuracy, and fixed, intermediate levels of sampling prevalence in comparative studies.
Allee effects driven by predation
Authors: GASCOIGNE JOANNA C. , LIPCIUS ROMUALD N. 
Published: September 2004

Summary

In a population with Allee effects a positive relationship exists between fitness and population size or density. Allee effects may result in extinction thresholds and are therefore crucial in conservation and management. It has been shown theoretically that Allee effects can be driven by predation; however, there are few empirical data. Previous empirical work on Allee effects has emphasized that taxa with life‐history characteristics such as co‐operative breeding may be prone to such effects. Because predation is a general ecological mechanism, Allee effects may be more widespread than previously thought.
We used a series of simple heuristic models to develop a theoretical framework for understanding predation‐driven Allee effects as a function of predator functional and aggregative responses.
Predators can create an Allee effect if they have a type I (linear) or type II (saturating) functional response without a type III (sigmoid) aggregative response, or vice versa. In addition, predation must be the main driver of prey dynamics, and prey must have little spatial or temporal refuge from predation.
We highlighted several, mainly unrecognized, examples of predation‐driven Allee effects from the literature, the majority of which came from systems that had been perturbed by exploitation or introduced predators.
Synthesis and applications. Allee effects can arise from a general ecological process under a variety of different combinations of functional and aggregative responses. Allee effects may thus be present in a broad spectrum of different taxa with different types of life history, not only those taxa, such as broadcast spawners and co‐operative breeders, on which empirical work has focused thus far. Conservation biologists and managers working with heavily exploited or threatened populations, or attempting reintroductions, should be aware of the possibility of a threshold population size or density below which extinction is likely. These thresholds can occur regardless of species life history, if predation is a major source of mortality and spatial and temporal predation refuges are limited.
Implications of a zoned fishery management system for marine benthic communities
Authors: BLYTH ROBERT E. , KAISER MICHEL J. , EDWARDS‐JONES GARETH , HART PAUL J. B. 
Published: September 2004

Summary

The impacts of trawls and dredges on marine benthic habitats and communities have been studied extensively, but mostly at small scales and over short time periods. To investigate the large‐scale chronic impacts of towed fishing gears, zoned commercial fishery management systems allow comparison of habitats and communities between areas of seabed subjected to varying levels of towed‐gear use.
The Inshore Potting Agreement (IPA) was implemented in 1978 to restrict the use of towed gears in inshore areas that had traditionally been used by static‐gear (pot and net) fishers. We used scallop dredges to sample benthic communities at sites within and adjacent to the IPA area that had been subjected to four different commercial fishing regimes since the inception of the system. These were: (i) towed gears only, (ii) annual, seasonal towed‐gear use, (iii) temporary towed‐gear use but reverting to static‐gear use 18–24 months prior to sampling, and (iv) static gears only.
There were no significant differences in the total species richness or biomass of benthic communities between sites under regimes (i) and (ii). There was significantly greater total species richness and biomass of benthic communities at sites under regimes (iii) and (iv) than at sites under regimes (i) and (ii). The benthic community biomass under regime (iv) was significantly greater than under all other regimes.
The IPA has maintained benthic species that are important for the settlement and survival of others. The cessation of towed‐gear fishing for a period of greater than 2 years would be necessary for benthic communities in areas adjacent to the IPA to recover such that they were indistinguishable from areas where towed gears had not been used.
Synthesis and applications. Members of the fishing industry may object to the creation of permanent closed areas because harvestable stocks can move in space and time. This study indicates that zoned fishery management can allow some sectors of the fishing industry to retain access to fishery resources while protecting benthic species and habitats.
Electrocution alters the distribution and density of a top predator, the eagle owlBubo bubo
Authors: SERGIO FABRIZIO , MARCHESI LUIGI , PEDRINI PAOLO , FERRER MIGUEL , PENTERIANI VINCENZO 
Published: September 2004

SummaryElectrocution has frequently been suggested as a cause of territory abandonment and eventual population decline of threatened species, but this has been rarely tested. We investigated the impact of electrocution in two eagle owlBubo bubopopulations located in the Italian Alps and Apennines and subject to different levels of electrocution risk (i.e. low and high risk). The eagle owl is one of the species most affected by electrocution, to the point of causing local conservation and economic concern. In a review of 25 studies, electrocution was frequently cited as the major cause of death and has progressively increased in the last three decades, independently from other causes of mortality.The impact of electrocution was tested by (i) comparing estimates of electrocution risk between currently occupied owl territories and infrequently occupied or abandoned territories; (ii) collecting information on the spatiotemporal frequency of electrocution incidents; (iii) measuring density, breeding success and post‐fledging survival for populations and territories subject to different electrocution risk.In the low‐risk population electrocution casualties varied spatiotemporally, peaking in the period of immature dispersal and at pylons that were good hunting perches. Furthermore, eagle owls over‐selected low‐altitude habitats, which forced them into close contact with power lines. However, nest‐site selection was independent of electrocution risk, although territories that were not occupied every year were nearer to power lines than stable territories.In contrast, in the high‐risk population, territories near to power lines, most of them at low altitude, were progressively abandoned during a 10‐year period, leading to a steeply declining, scattered, low‐density and increasingly high‐altitude population.Although there was no effect on long‐term breeding success, the presence of pylons within 200 m of the nest increased the likelihood of partial or complete brood loss in the post‐fledging period. We estimated that 17% of the fledged young were lost to electrocution.At the population level, density was negatively related to electrocution risk in eight Alpine study areas. However, comparison between the two regions suggested that electrocution impact may interact with other factors, such as resource availability.Synthesis and applications. Our results show how subtle anthropogenic disturbance may affect population breeding performance and quickly alter the gradient of environmental quality for an endangered bird, leading to potential population limitation. Conservation guidelines should prioritize the insulation of those pylons most likely to cause casualties (e.g. in good hunting habitat and close to nests), ensuring that all new lines are raptor safe.
Recovery of wild large herbivores following livestock decline in a tropical Indian wildlife reserve
Authors: MADHUSUDAN M. D. 
Published: September 2004

Summary

Resource competition is an important process governing the impact of livestock on native wild mammalian herbivores, an issue acknowledged to be of global conservation concern. Resource competition occurs between species when their resources (habitat and diet) overlap and are limiting. Yet the evidence that livestock compete with wild herbivores has remained weak because resource limitation is often difficult to demonstrate in the field.
This 2‐year field study at Bandipur National Park, India, examined livestock‐mediated resource limitation among five wild herbivore species: wild pig Sus scrofa, chital Axis axis, sambar Cervus unicolor, gaur Bos gaurus and Asian elephant Elephas maximus, by comparing their distribution and densities in adjoining livestock‐grazed and livestock‐free areas before, and after, a 49% decline in livestock density.
During 2001, mean densities of wild grazers, gaur (0·11 ha−1), chital (1·51 ha−1) and elephant (0·61 ha−1), were, respectively, 132, 11 and six times higher in the livestock‐free area than in the adjacent livestock‐grazed area. Densities of gaur, chital and elephant showed a sharp declining relationship with increasing livestock density, whereas no clear pattern was discernible with wild pig, a non‐ruminant generalist, and the sambar, a forest browser. Preferred plant biomass also fell sharply with increasing livestock density.
Following the decline in livestock density in the livestock‐grazed area in 2002, the densities of gaur, chital and elephant increased by a factor of 57, five and two in the same area, respectively, whereas no changes were seen in the densities of wild pig and sambar or in the preferred plant biomass. Except for a decline in elephant density, the livestock‐free area did not show changes in wild herbivore densities.
Given the considerable overlap in habitat and dietary preference/requirements between livestock and wild herbivores in the study area, it is suggested that the recovery of gaur, chital and elephant densities following the livestock decline represents their release from livestock‐mediated resource limitation.
Synthesis and applications. These results indicate that resource competition may be intense between wild herbivores and grazing livestock, and if left unchecked could trigger declines of wild herbivores, particularly grazing ruminants and bulk feeders. These results also suggest that, where possible, interventions to reduce livestock grazing may rapidly benefit wild herbivores that have been competitively suppressed. This has important implications for the management of livestock grazing in India's wildlife reserves.
Estimating population size by genotyping remotely plucked hair: the Eurasian badger
Authors: FRANTZ ALAIN C. , SCHAUL MICHEL , POPE LISA C. , FACK FRED , SCHLEY LAURENT , MULLER CLAUDE P. , ROPER TIMOTHY J. 
Published: September 2004

SummarySize is a basic attribute of any population but it is often difficult to estimate, especially if the species under investigation is rare or cryptic. For example, there is currently no cheap and robust way of estimating the abundance of the European badgerMeles meles, despite the species’ role as an agricultural pest and carrier of bovine tuberculosis.We tested the reliability and accuracy of estimating badger abundance by genotyping DNA extracted from remotely plucked hair. We assessed the accuracy of our methodology by estimating local abundance by direct observation. Hair samples were collected near five target setts using a baited barbed wire enclosure or (at one sett) barbed wire suspended over a clearly visible badger run. All the hairs found on a barb were included in the extraction.Of the 113 samples collected over a 6‐month period, 105 gave rise to amplifiable DNA and originated from single animals. Through comparison with reliable reference genotypes of captured badgers, we showed that amplifiable DNA, including extracts obtained from single guard hairs, produced accurate profiles in a single round of amplifications.Direct observation of the target setts suggested that a minimum of 13 badgers was present in the study area. Analysis of the 105 usable samples provided a baseline estimate of 15 animals.To test the practical use of hair trapping to estimate population size, hair samples were collected daily during a 3‐week period. The 66 usable samples obtained originated from 14 of the 15 known badgers. Estimates of true abundance were generated using rarefaction analyses, the least biased of which produced an abundance estimate of 14·23, corresponding well with the number of genetic profiles obtained over the 6‐month period. The results allowed comparisons of theoretical predictions and empirical data relating to rarefaction analyses.Synthesis and applications.DNA extracted from remotely plucked badger hair could form the basis of a potentially cost‐effective, reliable and widely applicable method of estimating badger abundance. Hair trapping may offer a feasible method of estimating population size in a range of species even when the species are rare or patchily distributed.
Diclofenac poisoning as a cause of vulture population declines across the Indian subcontinent
Authors: GREEN RHYS E. , NEWTON IAN , SHULTZ SUSANNE , CUNNINGHAM ANDREW A. , GILBERT MARTIN , PAIN DEBORAH J. , PRAKASH VIBHU 
Published: September 2004

Summary

Rapid population declines of the vultures Gyps bengalensis, Gyps indicus and Gyps tenuirostris have recently been observed in India and Pakistan, continuing at least up to 2003. Surveys indicate annual rates of decline of 22–50% for G. bengalensis and G. indicus during 2000–03. Previous studies in Pakistan have shown that the non‐steroidal anti‐inflammatory drug diclofenac causes renal failure and is lethal to G. bengalensis when it feeds on the carcass of a domestic animal that received a normal veterinary dose shortly before death. In Pakistan, diclofenac poisoning was found to be by far the most frequent cause of death.
A simulation model of vulture demography, described in this paper, demonstrated that the observed rates of population decline could be caused by contamination with a lethal level of diclofenac in a small proportion (between 1 : 130 and 1 : 760) of ungulate carcasses available to vultures.
Proportions of adult and subadult vultures found dead or dying in the wild that had signs of diclofenac poisoning were similar to the proportions of deaths expected from the model if the observed population decline was due entirely to diclofenac poisoning. The proportion of the excess mortality required to cause the observed population declines that could be attributable to diclofenac was estimated to be between 71% and 100%, depending on model assumptions. However, across all or most of the plausible range of assumed values for adult survival, the upper 95% confidence limit for the proportion of excess mortality due to diclofenac was 100%. Hence, available data are consistent with diclofenac poisoning being at least the major cause, and possibly the only cause, of rapid population declines of Gyps vultures across the Indian subcontinent.
Synthesis and applications. We recommend that urgent action is taken in the range states of the three currently threatened vulture species to prevent the exposure of vultures to livestock carcasses contaminated with diclofenac. Research is also needed to identify alternative drugs that are effective in livestock and safe for vultures. Efforts should also be made to raise awareness, among veterinarians, pharmacists, livestock owners and the general public, of the problem of diclofenac contamination and the availability of safe alternatives. Captive holding and breeding of vultures until diclofenac is controlled is recommended as a precaution to ensure the long‐term survival of the threatened species and to provide a stock of birds for future reintroduction programmes.
Modelling the impacts of atmospheric nitrogen deposition on Calluna‐dominated ecosystems in the UK
Authors: TERRY A. C. , ASHMORE M. R. , POWER S. A. , ALLCHIN E. A. , HEIL G. W. 
Published: September 2004

Summary

The increased deposition of nitrogen (N) from the atmosphere over the last century has been associated in Europe with changes in species composition, including replacement of characteristic ericaceous shrubs such as Calluna vulgaris by grasses in heathlands and moorlands. However, these changes may also be associated with changes in management practices and environmental stresses, which may interact with changes in N deposition. Policies have now been implemented to reduce N deposition, but whether, and over what time scale, changes in vegetation composition will be reversed is uncertain.
A model was developed to simulate competitive growth between Calluna vulgaris and the grass species Deschampsia flexuosa and Molinia caerulea, driven by light and N availability. The model was parameterized for application to UK heath and moorland systems, and tested using a synthesis of data from 10 years of three field manipulation experiments in the UK. New routines to simulate management (burning, mowing, sheep grazing) were incorporated, and the model included a stochastic treatment of heather beetle Lochmaea suturalis responses. The effects of increases and decreases in N deposition over a period of 250 years were simulated under different management regimes.
Model runs demonstrated that changes in species composition in response to step changes in N deposition may occur over several decades and management cycles. The simulations showed a strong effect of management intensity, and in particular litter removal, in modifying the long‐term impact of N deposition: recovery of Calluna dominance in lowland heaths was predicted within two to three decades of a decrease in N deposition under high‐intensity management, but over five decades under low‐intensity management. The timing of outbreaks of heather beetles, which were modelled stochastically, also had a strong effect on the balance between Calluna and grass species. Sensitivity analysis demonstrated the importance of mineralization rates, and Calluna growth rates and mortality rates, in influencing model outcomes, and also demonstrated significant interactions between these three factors and the probability of heather beetle outbreaks.
Synthesis and applications. Using a simulation model of competition between heather and grasses for light and N, scenarios were run for 250 years. Nitrogen deposition above 30 kg ha year−1 initially increased Calluna biomass, consistent with field experiments, but after several decades led to grass dominance rather than heather dominance. The effect of N deposition depended on grazing pressure and the degree of litter removal through mowing, burning or sod‐cutting. The benefits of policies to reduce N deposition, in terms of restoring heather dominance, may only be realized after several decades, and active site management may be needed to capture the full benefits of such policies.
Integrative measures of consumption rates in salmon: expansion and application of a trace element approach
Authors: KENNEDY BRIAN P. , KLAUE BJOERN , BLUM JOEL D. , FOLT CAROL L. 
Published: September 2004

Summary

Establishing reliable estimates of consumption is necessary for understanding the physiology, bioenergetics and trophic relationships of organisms. For fish, the inability to measure consumption directly prevents a mechanistic understanding of habitat–foraging relationships. Building upon established models for 137caesium (Cs) mass balance in fish, we used natural abundances of a stable geologically derived isotope of Cs to estimate consumption rates over the first growing season for Atlantic salmon Salmo salar and to derive a general model that provides integrative estimates of consumption rates for individuals of all sizes.
To test the reliability of the trace metal approach we (i) performed a sensitivity analysis of model parameters and (ii) parameterized the model with site‐specific data, including gut contents, Cs concentrations of invertebrate prey and assimilation rates.
We applied the method in two sites to make the first in situ determinations of consumption rates of individual age‐0 salmon at post‐larval and fry stages, for fish as small as 0·1 g. Consumption estimates were most responsive to changes in three parameters: Cs body burdens, Cs concentration in prey items and assimilation efficiency, all of which could be measured with high precision using inductively coupled plasma mass spectrometry.
The assimilation efficiency of Cs measured on field‐caught age‐0 salmon was approximately 60%. Consumption rates at 2 weeks post‐stocking were highly variable in both sites, ranging from no detectable consumption to 8·5% fresh weight (fw) day−1. By the end of the growing season, consumption rates were less variable (2–4% fw day−1).
Synthesis and applications. This study is the first to demonstrate that background levels of geologically derived Cs can be used to estimate consumption rates of fish. Our results show that extremely low consumption rates during the first 6 weeks of life correspond closely with the critical survival period in other fish populations, and suggest a mechanism for a hypothesized survival bottleneck at this time. The results implicate the importance of early season habitat availability when considering management priorities of fish. Additionally, our use of stable Cs at natural abundance concentrations permits the global application of this trace element approach for estimating consumption rates of fish as well as other organisms. This general approach can be adopted for conservation and management settings in which it is necessary to identify suitable foraging habitat of a species or to quantify the relationship between consumption and growth.