From genetic neighbourhood to local community: Estimating a key parameter of the Unified Neutral Theory of Biodiversity
Issues related to the size and nature of what is termed a ''local community'' in a continuous metacommunity under unified neutral theory are explored. Developments in the parallel field of neutral genetics theory allow the size of genetic neighbourhoods in the context of isolation by distance processes to be calculated. These suggest a way to estimate the geographical size of an equivalent form of local community in ecology. It is derived from the estimated spatial autocorrelation value at zero geographical distance and this is obtained using the distribution of the relative frequencies of species in field samples separated by varying geographical distance. A data set of 62000 beetles collected for other purposes, and consisting of beetle samples collected by fogging 52 trees in Nothofagus spp. forest and 24 trees in Araucaria forest distributed in southern Chile were used to demonstrate the proposed methods. Local communities had estimated effective community sizes (Je) of ~12000 individuals in each forest type for predators and ~30000 for phytophages/xylophage beetle communities. These numbers can be used in available software to estimate the number of species and the distribution of specimens between species in a local community. The geographical size of a local community can be used in other ways. Firstly, because it is related to the distance moved between birth and breeding, it provides information on the geographical scale of community processes; it gives a measure of the scales over which speedy recolonization is possible and scales over which breaks in the habitat cannot be easily crossed. Secondly, replicate samples geographically separated by less than the area of a local community are not independent, but pseudoreplicate measures of the characteristics of the metacommunity.