The Shape of Species Abundance Distributions Across Spatial Scales

Species abundance distributions (SADs) describe community structure and are a key component of biodiversity theory research. Although different have been proposed to represent SADs at scales, systematic empirical assessment how SAD shape varies across wide scale gradients is lacking. Here, we examined 11 large-scale datasets for range taxa used maximum likelihood methods compare the fit logseries, lognormal, multimodal (i.e., with multiple modes abundance) models gradient spanning several orders magnitude. Overall, there was higher prevalence multimodality larger spatial extents, whereas logseries exclusively selected as best smaller areas. For many communities largest extent (either lognormal or multimodal) conserved gradient, despite steep declines in area taxonomic diversity sampled. Additionally, affected by species richness, but did not detect effect total number individuals. Our results reveal clear departures from predictions two major macroecological theories shape. Specifically, neither Neutral Theory Biodiversity (NTB) nor Maximum Entropy Ecology (METE) able accommodate variability encountered. This highlighted inadequacy distribution contrary NTB, METE expectation scales. Importantly, accounts SADs. We suggest our underpinned both inter- intraspecific aggregation patterns, highlighting importance determinants patterns. Critical developments remain incorporating scale, ecological heterogeneity patterns determining