Browsing by Author "Hubbell, Stephen P."
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- Spatial scaling of species abundance distributionsPublication . Borda-de-Água, Luís; Borges, Paulo A. V.; Hubbell, Stephen P.; Pereira, Henrique M.Species abundance distributions are an essential tool in describing the biodiversity of ecological communities. We now know that their shape changes as a function of the size of area sampled. Here we analyze the scaling properties of species abundance distributions by using the moments of the logarithmically transformed number of individuals. We find that the moments as a function of area size are well fitted by power laws and we use this pattern to estimate the species abundance distribution for areas larger than those sampled. To reconstruct the species abundance distribution from its moments, we use discrete Tchebichef polynomials. We exemplify the method with data on tree and shrub species from a 50 ha plot of tropical rain forest on Barro Colorado Island, Panama. We test the method within the 50 ha plot, and then we extrapolate the species abundance distribution for areas up to 5 km2. Our results project that for areas above 50 ha the species abundance distributions have a bimodal shape with a local maximum occurring for the singleton classes and that this maximum increases with sampled area size.
- Species accumulation curves and extreme value theoryPublication . Borda-de-Água, Luís; Alirezazadeh, Saeid; Neves, Manuela; Hubbell, Stephen P.; Borges, Paulo A. V.; Cardoso, Pedro; Dionísio, Francisco; Pereira, Henrique M.The species–area relationship (SAR) has been described as one of the few general patterns in ecology. Although there are many types of SAR, here we are concerned solely with the so-called species accumulation curve (SAC). The theoretical basis of this relationship is not well established. Here, we suggest that extreme value theory, also known as the statistics of extremes, provides a theoretical foundation for, as well as functions to fit, empirical species accumulation curves. Among the several procedures in extreme value theory, the appropriate way to deal with the species accumulation curve is the so-called block minima procedure. We first provide a brief description of this approach and the relevant formulas. We then illustrate the application of the block minima approach using data on tree species from a 50 ha plot in Barro Colorado Island, Panama. We conclude by discussing the extent to which the assumptions under which the extreme types theorem occurs are confirmed by the data. Although we recognize limitations to the present application of extreme value theory, we predict that it will provide fertile ground for future work on the theory of SARs and its application in the fields of ecology, biogeography and conservation.