Beyond beta: diversity partitioning reveals different underlying patterns in ant assemblages along two small scale gradients in a Brazilian neotropical forest

Beta diversity measures changes in species composition and, if partitioned, isolates the contributions of turnover and nestedness in such differences. High beta diversity values have been reported to ant assemblages found at the soil surface, tree canopy and underground soil layers. However, studies on ant assemblage at small-scale stratification have drawbacks regarding to sampling designs and on the searching of turnover and nestedness patterns contribution to overall beta diversity. We investigated how ant assemblage beta diversity changes along the epigaeic-hypogaeic and epigaeic-arboreal gradients in a Neotropical rainforest remnant and whether this change is driven by turnover or nestedness. We sampled ants at different depths/heights and calculated the Jaccard index between the ants sampled at these strata and the ones at the soil surface as an overall beta diversity measurement. Then, we partitioned the Jaccard index to account for turnover and nestedness separately. Overall beta diversity values did not significantly change, being consistently high along both gradients. Turnover's proportional contribution to beta diversity significantly increased with increasing height but did not significantly change with increasing depth. Turnover values were high throughout the subterranean gradient. This suggests that epigaeic ants better explore low heights than low depths. Our results revealed that the assemblages from both gradients are continuously different from the soil assemblage, that this difference is mainly due to turnover, and that turnover's importance increases along the epigaeic-arboreal gradient. These conclusions were only possible due to isolating the effects of turnover and nestedness, reinforcing the importance of doing so.