Approximation of density functions by orthogonal series with grouped data

Summary Letg(x) andf(x) be continuous density function on (a, b) and let {ϕ_j} be a complete orthonormal sequence of functions onL ₂(g), which is the set of squared integrable functions weighted byg on (a, b). Suppose that over (a, b). Given a grouped sample of sizen fromf(x), the paper investigates the asymptotic properties of the restricted maximum likelihood estimator of density, obtained by setting all but the firstm of the ϑ_j’s equal to0. Practical suggestions are given for performing estimation via the use of Fourier and Legendre polynomial series. Research partially supported by: CNR grant, n. 93. 00837. CT10.     

Estimating the Size of Street-Dwelling Populations Using Mark-Resighting Counts

Mark-resighting constitutes an advanced technology for estimating animal abundance. Joint hypergeometric maximum likelihood, Minta-Mangel and Bowden estimators are usually adopted with mark-resighting data. In presence of any tendency of animals to aggregate into groups, the Bowden estimator is the sole reliable method, providing that marks are quite evenly distributed among groups. In some cetacean surveys, marking disturbances are avoided through natural marking. Natural marking with Bowden criterion is used to estimate the abundance of street-dwelling populations. The marked individuals are persons identified and recorded in the initial part of the survey and recognizable in subsequent occasions. A simulation helps determine the performance of the Bowden estimator under a wide set of situations, taking into account key features of street-dwelling populations. When marked individuals are evenly distributed among groups, the strategy is efficient.     

Empirical investigation about statistical properties of abundance estimates based on line-intercept and network sampling of tracks

Line-intercept sampling (Becker, 1991) and network sampling (Becker et al., 1998) seem to be the most appropriate procedures for estimating animal abundance in a study area on the basis of tracks. The purpose of this paper is to investigate the statistical properties of these alternative procedures by constructing confidence intervals for abundance and comparing the interval performances in terms of width and coverage.     

A two-phase sampling strategy for large-scale forest carbon budgets

The estimation of forest carbon sources and sinks is an important issue in forest inventories. For monitoring forest carbon budgets, a two-phase strategy is proposed. In the first phase, N points are thrown onto the study region by means of unaligned systematic sampling and then classified as forest or non-forest on the basis of aerial information. In the second phase, a sample of n points of those classified as forest is achieved by means of a sampling scheme with selection probabilities proportional to the sizes of an auxiliary variable. Subsequently, circular plots of adequate size are centred in the n selected points and visited in order to quantify the carbon amount within. Unbiased estimators of the forest area size as well as of the overall amount of carbon in that area and a conservative estimator of their variance–covariance matrix are derived. The strategy is applied to estimate carbon budgets in the forests of Trentino (North Italy).     

Urban biodiversity hotspots are not related to the structure of green spaces: a case study of tenebrionid beetles from Rome,Italy

At global and regional scales, area prioritisation is frequently done by the identification of hotspots based on species extinction risk. The logic of the hotspot identification has never been used in urban contexts. In this paper, the tenebrionid beetles (Coleoptera Tenebrionidae) of urban Rome were studied as an exercise to show how the hotspot approach can be profitably used in an urban area to identify priority areas for biodiversity conservation. For this, tenebrionid species from 16 green spaces were scored according to their vulnerability on the basis of their geographical distribution, habitat specificity and abundance. Species vulnerability scores were then used to calculate two indices of area prioritisation (the Biodiversity Conservation Concern and the Biodiversity Conservation Weight) for each green space. Values of these indices were correlated with site characteristics and compared with those obtained from other, more natural contexts. Except for distance to other sites, no significant correlation was found between conservation values and site characteristics, which indicates that the conservation importance of green spaces cannot be predicted on the basis of their geographical characteristics, but must be established on the basis of the species that they actually host. The importance of urban green spaces for biodiversity conservation may be questioned because of the large presence of ubiquitous and alien species in urban areas. Conservation values obtained for tenebrionids of green spaces in Rome are similar to those of various animal groups in more natural contexts and hence highlight the actual importance of green areas for insect biodiversity conservation.     

Influence of urbanization on the avian species-area relationship: insights from the breeding birds of Rome

Urban Ecosystems - The species-area relationship (SAR) is one of the most investigated patterns in ecology and conservation biology, yet there is no study testing how different levels of...