Home About us Contact
|
Home About us Contact | ||
|
|
||
Simpson Diversity (simpson + diversity)
Selected AbstractsInterpreting and estimating measures of community phylogenetic structuringJOURNAL OF ECOLOGY, Issue 5 2008Olivier J. Hardy Summary 1To characterize the spatial phylogenetic structure of communities, Hardy & Senterre (2007) (J. Ecol., 95, 493,506) partition Gini,Simpson diversity and its generalization, Rao's entropy, defining IST and PST as the proportion of diversity expressed among sites. 2Interpreting IST as a measure of ,differentiation' between sites is inadequate because low values are actually compatible with high differentiation (low species sharing) in species rich communities. To avoid an inadequate use of IST, for example in conservation biology, we offer a more literal interpretation: IST expresses the ,local species identity excess'. Similarly, PST expresses the ,local phylogenetic similarity excess'. 3Villéger & Mouillot (2008) (J. Ecol., 96, 845,848, this issue) argue that the equations of Hardy & Senterre (2007) to compute diversity are inadequate when sites differ in size, and they provide new expressions weighting sites by their sizes. We argue that whether sites must be weighted equally or not depends on the question being asked. Moreover, actual size and sample size must be distinguished, the latter being important for defining estimators. 4Synthesis. The formulations given by Hardy & Senterre (2007) and by Villéger & Mouillot (2008) are both correct in the specific contexts we detail. [source] Characterizing the phylogenetic structure of communities by an additive partitioning of phylogenetic diversityJOURNAL OF ECOLOGY, Issue 3 2007OLIVIER J. HARDY Summary 1Analysing the phylogenetic structure of natural communities may illuminate the processes governing the assembly and coexistence of species in ecological communities. 2Unifying previous works, we present a statistical framework to quantify the phylogenetic structure of communities in terms of average divergence time between pairs of individuals or species, sampled from different sites. This framework allows an additive partitioning of the phylogenetic signal into alpha (within-site) and beta (among-site) components, and is closely linked to Simpson diversity. It unifies the treatment of intraspecific (genetic) and interspecific diversity, leading to the definition of differentiation coefficients among community samples (e.g. IST, PST) analogous to classical population genetics coefficients expressing differentiation among populations (e.g. FST, NST). 3Two coefficients which express community differentiation among sites from species identity (IST) or species phylogeny (PST) require abundance data (number of individuals per species per site), and estimators that are unbiased with respect to sample size are given. Another coefficient (,ST) expresses the gain of the mean phylogenetic distance between species found in different sites compared with species found within sites, and requires only incidence data (presence/absence of each species in each site). 4We present tests based on phylogenetic tree randomizations to detect community phylogenetic clustering (PST > IST or ,ST > 0) or phylogenetic overdispersion (PST < IST or ,ST < 0). In addition, we propose a novel approach to detect phylogenetic clustering or overdispersion in different clades or at different evolutionary time depths using partial randomizations. 5IST, PST or ,ST can also be used as distances between community samples and regressed on ecological or geographical distances, allowing us to investigate the factors responsible for the phylogenetic signal and the critical scales at which it appears. 6We illustrate the approach on forest tree communities in Equatorial Guinea, where a phylogenetic clustering signal was probably due to phylogenetically conserved adaptations to the elevation gradient and was mostly contributed to by ancient clade subdivisions. 7The approach presented should find applications for comparing quantitatively phylogenetic patterns of different communities, of similar communities in different regions or continents, or of populations (within species) vs. communities (among species). [source] Woody Encroachment Removal from Midwestern Oak Savannas Alters Understory Diversity across Space and TimeRESTORATION ECOLOGY, Issue 1 2010Lars A. Brudvig Recovering biodiversity is a common goal during restoration; however, for many ecosystems, it is not well understood how restoration influences species diversity across space and time. I examined understory species diversity and composition after woody encroachment removal in a large-scale savanna restoration experiment in central Iowa, United States. Over a 4-year time series, restoration had profound effects across space and time, increasing richness at local and site-level scales. Restoration sites had increased , (within sample) Simpson's diversity and , and , (site level) species richness relative to control sites, although , and , (among sample) Simpson's diversity, , richness, and , species evenness were not affected. Changes in richness were driven by graminoids at the , and , scales and woody species (and some evidence for forbs) at the , scale. Interestingly, indicator species analysis revealed that at least some species from all functional groups were promoted by restoration, although no species were significant indicators of pre-treatment or control sites. Both savanna and nonsavanna species were indicators of restored sites. Restoration promoted exotic species at both scales, although species with spring phenologies were unaffected. Woody encroachment removal may be a means to promote species establishment in savannas; however, in this study, it resulted in establishment and proliferation of native and exotic and savanna and nonsavanna species. Future work might consider reintroduction of key savanna species to supplement those that have established. Work like this demonstrates the utility of restoration experiments for conducting research on large- and multiscale processes, such as species diversity. [source] Relationship Between Aboveground Biomass and Multiple Measures of Biodiversity in Subtropical Forest of Puerto RicoBIOTROPICA, Issue 3 2010Heather D. Vance-Chalcraft ABSTRACT Anthropogenic activities have accelerated the rate of global loss of biodiversity, making it more important than ever to understand the structure of biodiversity hotspots. One current focus is the relationship between species richness and aboveground biomass (AGB) in a variety of ecosystems. Nonetheless, species diversity, evenness, rarity, or dominance represent other critical attributes of biodiversity and may have associations with AGB that are markedly different than that of species richness. Using data from large trees in four environmentally similar sites in the Luquillo Experimental Forest of Puerto Rico, we determined the shape and strength of relationships between each of five measures of biodiversity (i.e., species richness, Simpson's diversity, Simpson's evenness, rarity, and dominance) and AGB. We quantified these measures of biodiversity using either proportional biomass or proportional abundance as weighting factors. Three of the four sites had a unimodal relationship between species richness and AGB, with only the most mature site evincing a positive, linear relationship. The differences between the mature site and the other sites, as well as the differences between our richness,AGB relationships and those found at other forest sites, highlight the crucial role that prior land use and severe storms have on this forest community. Although the shape and strength of relationships differed greatly among measures of biodiversity and among sites, the strongest relationships within each site were always those involving richness or evenness. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp [source] | ||||||||||