The impacts of tropical mound-building social insects on soil properties vary between taxa and with anthropogenic habitat change

Abstract

Ants and termites reach high abundances in the tropics and substantially affect the environment through a range of their activities. Because of foraging and decomposition of organic matter at their nesting sites, these locations show fundamentally altered soil properties compared to the adjacent soil. However, such changes are typically studied only within one species or taxon and in one habitat type. Consequently, it is not clear how these effects vary across different taxa and in relation to anthropogenic habitat change. In this study we assess the impacts of different mound-building taxa across a gradient of tropical habitat change in SE Asia comprising primary forest, logged forest and oil palm plantation. To do this we analysed chemical soil properties of mounds of multiple taxa of social insects, with some taxa spanning the full habitat change gradient, and where taxa differ in their mound construction type. Our results show that soils in mounds and adjacent soils have consistently different properties. However, these patterns differ both between social insect taxa and across habitat types. Specifically, mounds of soil-feeding termites Dicuspiditermes spp. were substantially enriched in basic soil nutrients such as C, N, P, especially in oil palm, while mounds of the leaf litter-feeding termite Macrotermes gilvus were depleted. Ant mounds did not show a clear pattern. This indicates that different social insect taxa in a particular habitat affect soil properties in differing ways, and furthermore that such impacts can change when a habitat is anthropogenically altered. Our research highlights the importance of termites for driving the heterogeneity of soil properties and nutrient redistribution across tropical landscapes.