Lower Ant Diversity on Earth Mounds in a Semi-Arid Brazilian Ecosystem: Natural or a Sign of Degradation?

Abstract

Natural earth mounds in many ecosystems harbor higher biodiversity than surroundings because they provide greater habitat heterogeneity. However, in the semi-arid Caatinga ecosystem of NE Brazil, natural mounds have much less vegetation and leaf litter with lower biodiversity as compared to the surrounding lowlands. The following hypotheses were tested: (i) low vegetation cover on the mounds results from highly compacted and leached soils as compared to adjacent lowlands and (ii) low vegetation cover reduce ant populations and diversity because of limited foraging and nesting resources. This study was carried out in four mound fields. At each mound field, 30 sampling were taken using pitfall traps.The high resistance of the mound soil to root penetration and low soil pH were the main reason for the difference in ant diversity between mound and adjacent lowlands. Adjacent lowlands were found to have twice as many ant individuals as the mounds along with higher ant species richness and diversity. These results suggest that environmental degradation in the Caatinga led to deforestation and thus compaction and leaching of soil mounds.