![]() The BBS is undertaken by the British Trust for Ornithology (BTO) and jointly funded by the BTO, the Joint Nature Conservation Committee and the Royal Society for the Protection of Birds. We use those estimates for farmland species to estimate temporal turnover in the British farmland bird community, and study how it varies spatially. ( 2014) fitted models to these data to allow estimation of abundance in any 1 km square on the British mainland for any species with adequate data. Sites are surveyed twice a year by volunteers walking along two parallel 1 km transect lines, and recording any adult birds detected. 2013) has been conducted annually since 1994 on a stratified random sample of 1 km squares. When we use species abundance distributions to measure turnover, turnover is evaluated by quantifying the rate at which individuals of one species are being replaced by individuals of another species. Measures based on the species abundance distribution or on species proportions are more informative and sensitive to biodiversity changes than measures based on presence/absence data. However, if available, it is more informative to use species abundance distributions to measure the compositional change over time (Magurran 2010). Traditionally, turnover usually refers to spatial turnover, and is usually measured from species presence–absence data (Rodrigues et al. Quantifying changes in species diversity over time or space provide valuable insights into understanding biodiversity trends. The relationship between richness and turnover is more complicated both negative and positive relationships between spatial turnover and richness have been observed in studies on spatial turnover using species–area relationships (Clarke and Lidgard 2000 Stevens and Willig 2002 Koleff et al. For example, one assemblage can have complete turnover (no species in common between two time points), but its evenness might stay the same (the species proportions might remain the same, even though they relate to different species for the two time points). There is no simple relationship between species turnover and other measures of diversity such as richness and evenness. Given species proportions, we propose four different families of turnover measure, all of which can be used to quantify either spatial or temporal change in diversity. Measuring turnover, whether spatial or temporal, is about assessing the changes between two species compositions, and such change is measured by dissimilarity, which is also referred to as differentiation, divergence or distance in different scientific fields, such as probability theory, mathematical geology and cluster analysis. Here, we concentrate on the dissimilarity of species composition. ( 2010) reviewed a number of indices used for measuring similarities between assemblages in the context of beta diversity. Beta diversity covers a broader range of objectives than the spatial turnover we discuss here. We refer to spatial turnover as the dissimilarity between pairs of locations that are neighbours, whereas beta diversity does not require this, and can be used to compare multiple assemblages. Thus, a region with high beta diversity has a diverse range of communities, perhaps reflecting a wide variety of habitats, while a region with low beta diversity has a relatively homogeneous community of species across the region. If we consider total diversity of a region (termed gamma diversity), we can partition it into alpha diversity, which measures average diversity at locations within the region, and beta diversity, which reflects spatial heterogeneity in diversity (Lande 1996). Spatial turnover is closely related to the concept of beta diversity. Although we focus on temporal turnover, these measures can also be used for quantifying spatial turnover between two neighbouring locations. We further study their properties in the context of measuring turnover, and provide transformation and modification for general applications. We propose families of turnover measures in this paper, and link some of them to the metrics summarized by Martín-Fernández et al. ![]() Thus, if a community is to exhibit zero turnover, then each species should represent a constant proportion of the community. ![]() This paper concentrates on temporal turnover, which we define as the change in species proportions over time, taking into account species identity. ![]() Maurer and McGill ( 2010) reviewed a large number of indices to measure species diversity, and gave a list of indices to measure different aspects of diversity, such as richness, evenness, dominance and rarity. Choice of measure depends both on the type of data available and on the questions being asked. Perhaps appropriately, there is a great diversity of measures for quantifying biodiversity (Pielou 1975 Krebs 1989 Magurran 2004).
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