Species richness

About: Species richness is a(n) research topic. Over the lifetime, 61672 publication(s) have been published within this topic receiving 2183796 citation(s).

Species assemblages and indicator species:the need for a flexible asymmetrical approach

Abstract: This paper presents a new and simple method to find indicator species and species assemblages characterizing groups of sites The novelty of our approach lies in the way we combine a species relative abundance with its relative frequency of occurrence in the various groups of sites This index is maximum when all individuals of a species are found in a single group of sites and when the species occurs in all sites of that group; it is a symmetric indicator The statistical significance of the species indicator values is evaluated using a randomization procedure Contrary to TWINSPAN, our indicator index for a given species is independent of the other species relative abundances, and there is no need to use pseudospecies The new method identifies indicator species for typologies of species releves obtained by any hierarchical or nonhierarchical classification procedure; its use is independent of the classification method Because indicator species give ecological meaning to groups of sites, this method provides criteria to compare typologies, to identify where to stop dividing clusters into subsets, and to point out the main levels in a hierarchical classification of sites Species can be grouped on the basis of their indicator values for each clustering level, the heterogeneous nature of species assemblages observed in any one site being well preserved Such assemblages are usually a mixture of eurytopic (higher level) and stenotopic species (characteristic of lower level clusters) The species assemblage approach demonstrates the importance of the ''sampled patch size,'' ie, the diversity of sampled ecological combinations, when we compare the frequencies of core and satellite species A new way to present species-site tables, accounting for the hierarchical relationships among species, is proposed A large data set of carabid beetle distributions in open habitats of Belgium is used as a case study to illustrate the new method

Quantifying biodiversity: procedures and pitfalls in the measurement and comparison of species richness

Abstract: Species richness is a fundamental measurement of community and regional diversity, and it underlies many ecological models and conservation strategies. In spite of its importance, ecologists have not always appreciated the effects of abundance and sampling effort on richness measures and comparisons. We survey a series of common pitfalls in quantifying and comparing taxon richness. These pitfalls can be largely avoided by using accumulation and rarefaction curves, which may be based on either individuals or samples. These taxon sampling curves contain the basic information for valid richness comparisons, including category‐subcategory ratios (species-to-genus and species-toindividual ratios). Rarefaction methods ‐ both sample-based and individual-based ‐ allow for meaningful standardization and comparison of datasets. Standardizing data sets by area or sampling effort may produce very different results compared to standardizing by number of individuals collected, and it is not always clear which measure of diversity is more appropriate. Asymptotic richness estimators provide lower-bound estimates for taxon-rich groups such as tropical arthropods, in which observed richness rarely reaches an asymptote, despite intensive sampling. Recent examples of diversity studies of tropical trees, stream invertebrates, and herbaceous plants emphasize the importance of carefully quantifying species richness using taxon sampling curves.

Estimating Terrestrial Biodiversity through Extrapolation

Abstract: Both the magnitude and the urgency of the task of assessing global biodiversity require that we make the most of what we know through the use of estimation and extrapolation. Likewise, future biodiversity inventories need to be designed around the use of effective sampling and estimation procedures, especially for 'hyperdiverse' groups of terrestrial organisms, such as arthropods, nematodes, fungi, and microorganisms. The challenge of estimating patterns of species richness from samples can be separated into (i) the problem of estimating local species richness, and (ii) the problem of estimating the distinctness, or complementarity, of species assemblages. These concepts apply on a wide range of spatial, temporal, and functional scales. Local richness can be estimated by extrapolating species accumulation curves, fitting parametric distributions of relative abundance, or using non-parametric techniques based on the distribution of individuals among species or of species among samples. We present several of these methods and examine their effectiveness for an example data set. We present a simple measure of complementarity, with some biogeographic examples, and outline the difficult problem of estimating complementarity from samples. Finally, we discuss the importance of using 'reference' sites (or sub-sites) to assess the true richness and composition of species assemblages, to measure ecologically significant ratios between unrelated taxa, to measure taxon/sub-taxon (hierarchical) ratios, and to 'calibrate' standardized sampling methods. This information can then be applied to the rapid, approximate assessment of species richness and faunal or floral composition at 'comparative' sites.

The maintenance of species-richness in plant communities: the importance of the regeneration niche

Abstract: SUMMARY 1According to ‘Gause's hypothesis’ a corollary of the process of evolution by natural selection is that in a community at equilibrium every species must occupy a different niche. Many botanists have found this idea improbable because they have ignored the processes of regeneration in plant communities. 2Most plant communities are longer-lived than their constituent individual plants. When an individual dies, it may or may not be replaced by an individual of the same species. It is this replacement stage which is all-important to the argument presented. 3Several mechanisms not involving regeneration also contribute to the maintenance of species-richness: (a). differences in life-form coupled with the inability of larger plants to exhaust or cut off all resources, also the development of dependence-relationships, (b) differences in phenology coupled with tolerance of suppression, (c) fluctuations in the environment coupled with relatively small differences in competitive ability between many species, (d) the ability of certain species-pairs to form stable mixtures because of a balance of intraspecific competition against interspecific competition, (e) the production of substances more toxic to the producer-species than to the other species, (f) differences in the primary limiting mineral nutrients or pore-sizes in the soil for neighbouring plants of different soecies, and (g) differences in the competitive abilities of species dependent on their physiological age coupled with the uneven-age structure of many populations. 4The mechanisms listed above do not go far to explain the indefinite persistence in mixture of the many species in the most species-rich communities known. 5In contrast there seem to be almost limitless possibilities for differences between species in their requirements for regeneration, i.e. the replacement of the individual plants of one generation by those of the next. This idea is illustrated for tree species and it is emphasized that foresters were the first by a wide margin to appreciate its importance. 6The processes involved in the successful invasion of a gap by a given plant species and some characters of the gap that may be important are summarized in Table 2. 7The definition of a plant's niche requires recognition of four components: (a) the habitat niche, (b) the life-form niche, (c) the phenological niche, and (d) the regeneration niche. 8A brief account is given of the patterns of regeneration in different kinds of plant community to provide a background for studies of differentiation in the regeneration niche. 9All stages in the regeneration-cycle are potentially important and examples of differentiation between species are given for each of the following stages: (a) Production of viable seed (including the sub-stages of flowering, pollination and seed-set), (b) dispersal, in space and time, (c) germination, (d) establishment, and (e) further development of the immature plant. 10In the concluding discussion emphasis is placed on the following themes: (a) the kinds of work needed in future to prove or disprove that differentiation in the regeneration niche is the major explanation of the maintenance of species-richness in plant communities, (b) the relation of the present thesis to published ideas on the origin of phenological spread, (c) the relevance of the present thesis to the discussion on the presence of continua in vegetation, (d) the co-incidence of the present thesis and the emerging ideas of evolutionists about differentiation of angiosperm taxa, and (e) the importance of regeneration-studies for conservation.