Biomedical subjects

Carlo Ricotta

Publications and source records attributed to Carlo Ricotta.

6 recordsLinked to original sources

PubMed2006

Towards a unifying approach to diversity measures: bridging the gap between the Shannon entropy and Rao's quadratic index.

The diversity of a species assemblage has been studied extensively for many decades in relation to its possible connection with ecosystem functioning and organization. In this view most diversity measures, such as Shannon's entropy, rely upon information theory as a basis for the quantification of diversity. Also, traditional diversity measures are computed using species relative abundances and cannot account for the ecological differences between species. Rao first proposed a diversity index, termed quadratic diversity (Q) that incorporates both species relative abundances and pairwise distances between species. Quadratic diversity is traditionally defined as the expected distance between two randomly selected individuals. In this paper, we show that quadratic diversity can be interpreted as the expected conflict among the species of a given assemblage. From this unusual interpretation, it naturally follows that Rao's Q can be related to the Shannon entropy through a generalized version of the Tsallis parametric entropy.

Animals↗

PubMed2005

Through the jungle of biological diversity.

Biological diversity would apparently seem the most intuitive and easily studied of all the ecological concepts. However, in practice biodiversity has suffered from great number of definitions that vary with the specific needs of the different researchers, thus making it extremely confusing as an ecological concept. In this paper, I shortly review the concept of biodiversity showing that there exists a substantial ambiguity among ecologists as far as biodiversity conceptualization and evaluation is concerned. I conclude that, due to this major disagreement on its very nature, biodiversity may be defined simply as a set of multivariate summary statistics for quantifying different characteristics of community structure.

Animals↗

PubMed2003

On parametric evenness measures.

The degree to which abundances are divided equitably among community species or evenness is a basic property of any biological community. Several evenness indices have thus far been proposed in ecological literature. However, despite its vast potential applicability in ecological research, none seems to be generally preferred. Furthermore, only very few parametric evenness families have thus far been proposed. While traditional evenness indices supply point descriptions of community evenness, according to a parametric evenness family E(alpha), there is a continuum of possible evenness measures that differ in their sensitivity to changes in the relative abundances of dominant and rare species as a function of the parameter alpha. In this review, I first summarize the basic requirements that a parametric evenness measure should meet to adequately behave in ecological studies. Next, I discuss the major drawbacks of these requirements and propose some alternative solutions.

Animals↗

PubMed2003

Additive partition of parametric information and its associated beta-diversity measure.

A desirable property of a diversity index is strict concavity. This implies that the pooled diversity of a given community sample is greater than or equal to but not less than the weighted mean of the diversity values of the constituting plots. For a strict concave diversity index, such as species richness S, Shannon's entropy H or Simpson's index 1-D, the pooled diversity of a given community sample can be partitioned into two non-negative, additive components: average within-plot diversity and between-plot diversity. As a result, species diversity can be summarized at various scales measuring all diversity components in the same units. Conversely, violation of strict concavity would imply the non-interpretable result of a negative diversity among community plots. In this paper, I apply this additive partition model generally adopted for traditional diversity measures to Aczél and Daróczy's generalized entropy of type alpha. In this way, a parametric measure of beta-diversity is derived as the ratio between the pooled sample diversity and the average within-plot diversity that represents the parametric analogue of Whittaker's beta-diversity for data on species relative abundances.

Biomass↗

PubMed2003

Parametric scaling from species relative abundances to absolute abundances in the computation of biological diversity: a first proposal using Shannon's entropy.

Traditional diversity measures such as the Shannon entropy are generally computed from the species' relative abundance vector of a given community to the exclusion of species' absolute abundances. In this paper, I first mention some examples where the total information content associated with a given community may be more adequate than Shannon's average information content for a better understanding of ecosystem functioning. Next, I propose a parametric measure of statistical information that contains both Shannon's entropy and total information content as special cases of this more general function.

Biodiversity↗

PubMedDate not supplied

Parametric scaling from species to growth-form diversity: an interesting analogy with multifractal functions.

We propose a measure of divergence from species to life-form diversity aimed at summarizing the ecological similarity among different plant communities without losing information on traditional taxonomic diversity. First, species and life-form relative abundances within a given plant community are determined. Next, using Rényi's generalized entropy, the diversity profiles of the analyzed community are computed both from species and life-form relative abundances. Finally, the speed of decrease from species to life-form diversity is obtained by combining the outcome of both profiles. Interestingly, the proposed measure shows some formal analogies with multifractal functions developed in statistical physics for the analysis of spatial patterns. As an application for demonstration, a small data set from a plant community sampled in the archaeological site of Paestum (southern Italy) is used.

Fractals↗