Abstract
Species abundance distributions (SAD) are central to the description of diversity and have played a major role in the development of theories of biodiversity and biogeography. However, most work on species abundance distributions has focused on one single spatial scale. Here we used data on arthropods to test predictions obtained with computer simulations on whether dispersal ability influences the rate of change of SADs as a function of sample size. To characterize the change of the shape of the SADs we use the moments of the distributions: the skewness and the raw moments. In agreement with computer simulations, low dispersal ability species generate a hump for intermediate abundance classes earlier than the distributions of high dispersal ability species. Importantly, when plotted as function of sample size, the raw moments of the SADs of arthropods have a power law pattern similar to that observed for the SAD of tropical tree species, thus we conjecture that this might be a general pattern in ecology. The existence of this pattern allows us to extrapolate the moments and thus reconstruct the SAD for larger sample sizes using a procedure borrowed from the field of image analysis based on scaled discrete Tchebichef moments and polynomials.
Highlights
The number of species and their relative abundance are important components of species diversity and community structure[1,2,3]
The aims of this paper are threefold: (i) to test whether a pattern concerning the different scaling of the species abundance distribution (SAD) as a function of area of high- and low-dispersal ability species predicted by computer simulations holds for an island arthropod assemblage; (ii) to extrapolate the SAD to large spatial scales, hitherto not obtained, and to identify how the relative abundance of arthropods scales as a function of area or sample size; and (iii) to test whether the pattern for the raw moments previously identified for hyper-diverse tropical tree species communities[5] applies to less diverse island arthropod assemblages and gathering evidence on whether this may be a general pattern and motivate researchers to assess whether other datasets on other taxa yield similar results
For high dispersal ability species (Fig. 3a,c), when the number of transects increases the number of singletons keeps increasing, some peaks start appearing for intermediate abundance classes
Summary
The number of species and their relative abundance are important components of species diversity and community structure[1,2,3]. For very large sample sizes the two distributions are again similar, because for both communities of high and low dispersal ability species, new species are mainly rare ones; intermediate or large abundance species have already been identified As we will see, our empirical data only describe the transitions in the distributions for small sample sizes obtained with the simulations, that is, the change from monotonically decreasing functions to functions with a maximum developing for intermediate abundance classes
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