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Introduction ‘Diversity’ is a concept that features prominently in a variety of disparate disciplines (Stirling 2007 ). Yet it is almost impossible to find a precise definition. In the nineties, Stirling ( 1998 ), following
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In two arid/semiarid regions, we studied diversity of algae in lakes and pools with salinity ranging from 0.1‰ up to 39‰ In plankton and periphyton of 34 lakes in northern Kazakhstan, we found 252 species belonging to 113 genera of 8 algal divisions. In 24 pools with experimental salinity ranges in the Negev desert of Israel, we recorded 86 species from 47 genera of 6 algal divisions. The dominant groups of both arid regions are represented by widespread species of diatoms, green algae, and cyanobacteria in similar proportions. Alkaliphiles among the indicators of acidification and betamesosaprobionts among the indicators of saprobity prominently prevail in both regions. The indices of saprobity in lakes (1.48–2.7) and in pools (0.75–2.18) reflect a low-trophic loading. Oligohalobes-indifferents are most common in both arid regions. Cluster analysis based on data containing 420 species revealed 9 clusters, of which the highly diverse communities of low mineralized lakes and pools and the low diversity communities of highly-mineralized lakes and pools are separated at the highest dissimilarity level. CCA analysis revealed correlation of the algal species diversity preferences with salinity level in lakes in Kazakhstan and in pools of Israel, which are more impacted by arid factors. These results point to mineralization being the most important variable defining the diversity levels irrespective of the type and location of reservoirs in the arid regions.
The multidimensional character and inherent conflict with categorisation of interdisciplinarity makes its mapping and evaluation a challenging task. We propose a conceptual framework that aims to capture interdisciplinarity in the wider sense of knowledge integration, by exploring the concepts of diversity and coherence. Disciplinary diversity indicators are developed to describe the heterogeneity of a bibliometric set viewed from predefined categories, i.e. using a top-down approach that locates the set on the global map of science. Network coherence indicators are constructed to measure the intensity of similarity relations within a bibliometric set, i.e. using a bottom-up approach, which reveals the structural consistency of the publications network. We carry out case studies on individual articles in bionanoscience to illustrate how these two perspectives identify different aspects of interdisciplinarity: disciplinary diversity indicates the large-scale breadth of the knowledge base of a publication; network coherence reflects the novelty of its knowledge integration. We suggest that the combination of these two approaches may be useful for comparative studies of emergent scientific and technological fields, where new and controversial categorisations are accompanied by equally contested claims of novelty and interdisciplinarity.
There is a recent proposal to apply convex hulls to the measurement of habitat filtering, trophic diversity and functional richness. Although this approach has successful applications, some conceptual difficulties with the interpretation of results should not be overlooked. The basic assumption that trait convergence and the associated deflation of the convex hull is a result of environmental (habitat) filtering does not always hold, because 1) some traits may converge as a result of competition as well, and 2) environmental factors, such as disturbance, may lead to divergence, rather than convergence for certain characters. There is neither evidence nor theoretical proof that increasing correlations between traits and reduction in trait combinations are always caused by habitat filtering, especially when individual trait tranges are unchanged. Diversity measurements in terms of convex hull volumes may be misleading because zero or near zero values may results no matter how wide the individual trait ranges are. For these reasons, applications of convex hulls cannot be viewed uncritically, and considerable care must be taken even if the method is used in combination with other techniques.
The relationship between species diversity and ecosystem functions has generated considerable debate among ecologists. Ecosystem functions (e.g. productivity, nutrient retention) are often positively correlated with species richness in experimental plant assemblages, but little or no correlation exists in natural communities.We examined the effects of species richness on productivity and available soil nitrate by experimentally manipulating richness using random draws from a pool of ten perennial grasses. Species richness had no significant effect on aboveground productivity or soil nitrate availability, suggesting that functional diversity may be more important than species richness in determining ecosystem functions. The relationship between diversity and ecosystem functions may also depend on resource limitation. A positive relationship is expected when below-ground resources are limiting, but the relationship is expected to weaken when below-ground resource supply rates are higher and competition for light becomes more important. Further experiments are required to determine the mechanisms underlying diversity-productivity relationships.