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| A common approach for analysing geographical variation in biodiversity
involves using linear models to determine the rate at which species similarity
declines with geographical or environmental distance and comparing this rate
among regions, taxa or communities. Implicit in this approach areweakly justified
assumptions that the rate of species turnover remains constant along
gradients and that this rate can therefore serve as a means to compare ecological
systems. We use generalized dissimilarity modelling, a novel method that
accommodates variation in rates of species turnover along gradients and
between different gradients, to compare environmental and spatial controls
on the floras of two regions with contrasting evolutionary and climatic histories:
southwest Australia and northern Europe. We find stronger signals of
climate history in the northern European flora and demonstrate that variation
in rates of species turnover is persistent across regions, taxa and different
gradients. Such variation may represent an important but often overlooked
component of biodiversity that complicates comparisons of distance–decay
relationships and underscores the importance of using methods that
accommodate the curvilinear relationships expected when modelling beta
diversity. Determining how rates of species turnover vary along and between
gradients is relevant to understanding the sensitivity of ecological systems to
environmental change. | |
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