153 research outputs found
Parameters behind "nonparametric" statistics: Kendall's tau,Somers' D and median differences
No full textSo-called "nonparametric" statistical methods are often in fact based on population parameters, which can be estimated (with confidence limits) using the corresponding sample statistics. This article reviews the uses of three such parameters, namely Kendall's tau, Somers' D and the Hodges-Lehmann median difference. Confidence intervals for these are demonstrated using the somersd package. It is argued that confidence limits for these parameters, and their differences,are more informative than the traditional practice of reporting only p-values. These three parameters are also important in defining other tests and parameters, such as the Wilcoxon test, the area under the receiver operating characteristic (ROC) curve, Harrell's C, and the Theil median slope. Copyright 2002 by Stata Corporation.confidence intervals, Gehan test, Harrell's C , Hodges-Lehmann median difference, Kendall's tau, nonparametric methods, rank correlation, rank-sum test, ROC area, Somers' D, Theil median slope, Wilcoxon test
The geometric mean of relative abundance indices : a biodiversity measure with a difference
No full textThis work is partly supported by the European Research CouncilThe 2010 Biodiversity Target of the Convention on Biological Diversity (CBD), set in 2002, which stated that there should be ‘a significant reduction of the current rate of biodiversity loss' by 2010, highlighted the need for informative and tractable metrics that can be used to evaluate change in biological diversity. While the subsequent Aichi 2020 targets are more wide-ranging, they also seek to reduce the rate of biodiversity loss. The geometric mean of relative abundance indices, G, is increasingly being used to examine trends in biological diversity and to assess whether biodiversity targets are being met. Here, we explore the mathematical and statistical properties of G that make it useful for judging temporal change in biological diversity, and we discuss its advantages and limitations relative to other measures. We demonstrate that the index reflects trends in both abundance and evenness, and that it is not prone to bias when detectability of individuals varies by species. We note that it allows data from different surveys to be combined to generate a composite index. However, the index exhibits high variance and unstable behaviour when rarely-recorded species are included in the analyses. Read More: http://www.esajournals.org/doi/abs/10.1890/ES11-00186.1Peer reviewe
Estimating bird abundance : making methods work
No full textIn many bird monitoring Surveys, no attempt is made to estimate bird densities or abundance. instead, counts of one form or another are made, and these are assumed to correlate with bird density. Unless complete Counts Oil Sample plots are feasible, this approach can easily lead to false conclusions, because detectability of birds varies by species, habitat, observer and many other factors. Trends in time of counts often reflect trends in detectability, rather than trends in abundance. Conclusions are further compromised when surveys are conducted at unrepresentative sites. We consider how to avoid these problems. We give a brief description of distance sampling methods, which allow detectability to be estimated. We consider strategies to ease their implementation, to enhance their reliability, to adapt the methods for difficult species, and to deal with circumstances in which representative sampling is problematic. We also consider some of the common problems encountered, and suggest solutions.Peer reviewe
Changing densities of generalist species underlie apparent homogenization of UK bird communities
No full textGeneralist species are becoming increasingly dominant in European bird communities. This has been taken as evidence of biotic homogenization, whereby generalist ‘winners’ systematically replace specialist ‘losers’. We test this pattern by relating changes in the average specialisation of UK bird communities to changes in the density of species with different degrees of habitat specialisation. Although we find the expected decline in community specialisation, this was driven by a combination of a strong increase in the density of the most generalist quartile of species and declines in the density of moderately generalist species. Contrary to expectation, specialist species increased slightly over the 18-year study period, but had little effect on the overall trend in community specialisation. Our results indicate that the apparent homogenization of UK bird communities is not driven by the replacement of specialists by generalists, but instead by the changing fortunes of generalist species
Evaluating the population-level impact of an invasive species, Ring-necked Parakeet Psittacula krameri, on native avifauna
No full textThe introduction of exotic species to ecosystems can have severe consequences for populations of native organisms, but logistical limitations and shortage of historical data often hinder attempts to quantify the ecological implications of such relationships. The establishment and rapid expansion of Ring-necked Parakeets Psittacula krameri in England therefore presents a rare opportunity to apply novel analytical methods to existing extensive national bird monitoring data from the UK Breeding Bird Survey for an invasive species. A previous study from Belgium suggests that Ring-necked Parakeets have the potential to reduce the abundance of Eurasian Nuthatch Sitta europaea through competition for nesting cavities. Our analysis provides no evidence for a significant impact through competition on Nuthatch populations or those of any other cavity-nesting species within the Parakeet's current range in the UK. However, we cannot exclude the possibility that competitive exclusion could be occurring at a minority of sites at which availability of nest cavities is limiting. This may yet have significant implications for future conflict if Parakeets continue to increase in numbers and range.</p
Searches for lepton number violating K+→π− (π0)e+e+ decays
No full textSearches for lepton number violating K+ -> pi(-)e(+)e(+) and K+ -> pi(-)pi(0)e(+)e(+) decays have been performed using the complete dataset collected by the NA62 experiment at CERN in 2016-2018. Upper limits of 5.3 x 10(-11 )and 8.5 x 10(-10) are obtained on the decay branching fractions at 90% confidence level. The former result improves by a factor of four over the previous best limit, while the latter result represents the first limit on the K+ -> pi(-)pi(0)e(+)e(+) decay rate. (C) 2022 The Author. Published by Elsevier B.V
Data from: Potential for coupling the monitoring of bush-crickets with established large-scale acoustic monitoring of bats
No full text1. Monitoring biodiversity over large spatial and temporal scales is crucial for assessing the impact of global changes and environmental mitigation measures. However, large-scale monitoring of invertebrates remains poorly developed despite the importance of these organisms in ecosystem functioning. Exciting possibilities applicable to professional and citizen science are offered by new recording techniques and methods of semi-automated species recognition based on sound detection. 2. Static broad-spectrum detectors deployed to record throughout whole nights have been recommended for standardised acoustic monitoring of bats, but they have the potential to also collect acoustic data for other species groups. Large-scale deployment of such systems is only viable when combined with robust automated species identification algorithms. Here we examine the potential of such a system for detecting, identifying and monitoring bush-crickets (Orthoptera of the family Tettigoniidae). We use incidental sound recordings generated by an extensive citizen science bat survey and recordings from intensive site surveys to test a semi-automated step-wise method with a classifier for assigning species identities. We assess species’ diel activity patterns to make recommendations for survey timing and interpretation of existing nocturnal datasets and consider the feasibility of determining site occupancy. 3. Of six species of bush-crickets, the species classifier achieved over 85% accuracy for three, speckled bush-cricket, dark bush-cricket and Roesel’s bush-cricket. It should be possible to automatically scan recordings for these species with minimal manual validation. Further refinement of the classifier is required for the three remaining species, in particular for the acoustically similar short-winged conehead and long-winged conehead. Diel activity patterns are species specific and it may be necessary to adjust the hours over which the detectors record to increase detection of key species, but this must be weighed against the costs in terms of increased memory and battery use and equipment security during daytime. 4. We conclude that with logistical support and centralised semi-automated species identification it is now possible for the public to contribute to large-scale acoustic monitoring of Orthoptera whilst recording bats. Further innovation of sound classifier algorithms is needed and would be aided by improved reference sound libraries from multiple locations spanning species’ ranges
Producing regional estimates of population size for common and widespread breeding birds from national monitoring data
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