A null model assuming a linear decline in species assemblage similarity with distance was able to match observed patterns in turnover in many cases. It was most successful in predicting turnover along high variation transects and for mammals. In many cases, species turnover was predicted from the simple assumption of consistent decline in the similarity between sites with increasing distance irrespective of the gradient in environmental variability. However, important differences occurred between taxonomic groups and gradients of low vs high variation. These differences suggest that protecting a few species rich sites in regions of low variability may capture a substantial proportion of regional diversity for highly mobile groups with large range sizes, although this wouldn’t be the case for less vagile and more geographically restricted species. Regions with high variation in NPP require a greater number of reserves owing to strong and consistent turnover irrespective of taxonomic group. Understanding the factors that drive spatial patterns in biodiversity is fundamental to developing effective conservation strategies. The relationships between net primary productivity (NPP) and species richness are well documented in the literature, yet the influence of spatial variation in productivity on species turnover has received relatively little attention. The aims of this study were to: i) compare patterns in species turnover among different taxonomic groups occupying spatial gradients that encompassed low variation in NPP and high variation in productivity; and ii) contrast these patterns with those produced by null models. We examined species turnover for birds, mammals and butterflies along replicate transects of approximately 1000 km split into 10 sampling sites. Six transects encompassed spatial gradients with little variation in NPP and six transects encompassed gradients with high variation in NPP. We calculated three representative indices of turnover and plotted these against distance between sampling sites to determine the decline in similarity among species assemblages with distance. Computer simulations were used to generate random (null) species distributions along transects based on simple ‘random distribution models’. These models assumed no differences between species and a consistent decline in species assemblage similarity with distance. Species turnover was greatest along transects with high variation in NPP, especially for birds. Significant turnover for mammals and butterflies was also recorded along many low variation transects. Birds and butterflies exhibited the lowest turnover overall – mammals had high turnover in almost all transects. Patterns in turnover varied depending on the index used. The index emphasising continuity in species composition always recorded the greatest turnover compared to indices representing differences in species identities or richness.
|Title of host publication||Focus on biodiversity research|
|Place of Publication||New York, USA|
|Publisher||Nova Science Publishers|
|Number of pages||20|
|Publication status||Published - 2007|