Rainy season decreases ground-dwelling ant richness, but increases the difference in species composition in a tropical relictual mountain forest.

The structure of biological communities is strongly driven by climatic conditions (e.g. seasonality) and local factors (e.g. habitat structure). In particular, seasonality affects local communities by altering resource availability and their frequency over seasons, limiting the establishment of many taxa locally. Simultaneously, local conditions (e.g. canopy height), alter the availability of nesting and foraging sites, leading to changes in local patterns of diversity. We hypothesize that rainfall decreases ground-dwelling ant richness and increases species turnover, because the heterogeneity of resources decreases with rainfall affecting ant species activity. Moreover, canopy height should enhance ant richness and beta diversity. Our sampling method involved four primary linear transects, each spaced 100 m apart. Within this framework, we established a grid of 16 collection points for pitfall-trap installation, spaced 200 m from each other while maintaining a minimum distance of 50 m from any forest border. An analysis of covariance was conducted, examining the influence of seasonal variation (dry versus rainy periods) and canopy height (CH) on ant richness and beta diversity components (turnover and nestedness). This 12-month study was conducted in a tropical relictual mountain forest in Northeastern Brazil. Our results partially supported our hypothesis, showing that an increase in rainfall led to a decrease in ant species richness and an increase in the difference in species composition (nestedness) between seasons. Additionally, CH was found to decrease species richness, total beta diversity, and turnover, with no discernible impact on nestedness. In conclusion, our results suggest that seasonal changes and canopy height might play crucial roles in shaping ant community assembly and foraging activities in tropical forest enclaves within the Caatinga biome. [ABSTRACT FROM AUTHOR]