A következő címkéjű bejegyzések mutatása: Beta diversity. Összes bejegyzés megjelenítése
A következő címkéjű bejegyzések mutatása: Beta diversity. Összes bejegyzés megjelenítése

2013. október 28., hétfő

Halme et al. (2013) Biological Conservation

Panu Halme, Péter Ódor, Morten Christensen, Andrej Piltaver, Mirjam Veerkamp, Ruben Walleyn, Irén Siller, Jacob Heilmann-Clausen (2013): The effects of habitat degradation on metacommunity structure of wood-inhabiting fungi in European beech forests. Biological Conservation 168: 24–30. http://dx.doi.org/10.1016/j.biocon.2013.08.034


Abstract
Intensive forest management creates habitat degradation by reducing the variation of forest stands in general, and by removing old trees and dead wood in particular. Non-intervention forest reserves are commonly believed to be the most efficient tool to counteract the negative effects on biodiversity, but actual knowledge of the conservation efficiency is limited, especially for recent reserves. The structure of ecological communities is often described with measures of nestedness, beta diversity and similarity between communities. We studied whether these measures differ among forest reserves with different management histories. For this purpose, we used a large data set of wood-inhabiting fungi collected from dead beech trees in European beech-dominated forest reserves. The structure of fungal assemblages showed high beta diversity, while nestedness and similarity was low. During the decomposition process of trees beta diversity between the communities occupying different trees increased in natural, but not in previously managed sites. Effects of management and decay process on nestedness were complex. We argue that the detected differences most likely reflect historical effects which have extirpated specialized species from the local species pools in managed sites, and resulted in more homogeneous communities in managed sites. It is alarming that community structure is affected the most in the latest decay stages where the decay process turns the dead wood into litter, and which is thus the interface between the wood decay and the litter-decaying ecosystem. The effects of simplified communities in late decay stages on soil biodiversity should be studied.


Keywords
Beta diversity, Decay stage, Forest management, Nestedness, SDR simplex, Similarity

2013. január 3., csütörtök

Schmera & Podani (2013) Ecological Indicators

Dénes Schmera, János Podani (2013): Components of beta diversity in hierarchical sampling designs: A new approach. Ecological Indicators 26: 126–136. http://dx.doi.org/10.1016/j.ecolind.2012.10.029


Abstract
Diversity partitioning has been generally used to estimate the contribution of different levels of sampling hierarchy to landscape diversity. However, beta diversity values derived by partitioning strongly depend on focus and sample size and the partitioning is inadequate to express the contribution of landscape elements to community variation. Pairwise dissimilarities are also frequently used to express community turnover, but related approaches capture only limited aspects of it, especially for hierarchical sampling designs. To avoid these shortcomings, we suggest a procedure which quantifies the role of different levels of sampling hierarchy (relative beta diversity) and the share of landscape elements in the corresponding relative beta diversity (contribution value). Our novel method uses pairwise dissimilarities and is based on partitioning a dissimilarity matrix of sampling units. It is suitable to testing various null hypotheses via permutation techniques as demonstrated by artificial and actual data. The method is a valuable tool in ecology because it complements existing approaches while providing a unique way to understand community diversity in space.


Highlights
► A method quantifying different aspects of community variation is proposed. ► We demonstrated its utility by examining artificial and actual data sets. ► Significance tests are possible via randomization models. ► It complements existing approaches to measure community variation.



Keywords
Beta diversity, Diversity partitioning, Hierarchy theory, Scale concept, Turnover

2012. november 5., hétfő

Sólymos & Lele (2012) Global Ecology and Biogeography


Abstract
Aim: We conducted a meta-analysis of species–area relationships (SARs) by combining several data sets and important covariates such as types of islands, taxonomic groups, latitude and spatial extent, in a hierarchical model framework to study global pattern and local variation in SARs and its consequences for prediction.
Location: One thousand nine hundred and eighteen islands from 94 SAR studies from around the world.
Methods: We developed a generalization of the power-law SAR model, the HSARX model, which allows: (1) the inclusion of multiple focal parameters (intercept, slope, within-study variance), (2) use of multiple effect modifiers based on a collection of SAR studies, and (3) modelling of the between- and within-study variability.
Results: The global pattern in the SAR was the average of local SARs and had wide confidence intervals. The global SAR slope was 0.228 with 90% confidence limits of 0.059 and 0.412. The intercept, slope and within-study variability of local SARs showed great heterogeneity as a result of the interaction of modifying covariates. Confidence intervals for these SAR parameters were narrower when other covariates in addition to area were accounted for, thus increasing the accuracy of the predictions for species richness. The significant effect of latitude and the interaction of latitude, taxa and island type on the SAR slope indicated that the ‘typical’ latitudinal diversity gradient can be reversed in isolated systems.
Main conclusions: The power-law relationship underlying the HSARX model provides a good fit for non-nested SARs across vastly different spatial scales by taking into account other covariates. The HSARX framework allows researchers to explore the complex interactions among SAR parameters and modifying variables, to explicitly study the scale dependence, and to make robust predictions on multiple levels (island, study, global) with associated prediction intervals. From a prediction perspective, it is not the global pattern but the local variation that matters.

Keywords
Beta diversity, data cloning, empirical Bayes, hierarchical model, islands, latitudinal diversity gradient, maximum likelihood, prediction, prognosis, species–area relationship