Did you know that termites are believed to be indicators of the health of an ecosystem? I know what you must be thinking: Termites? Those annoying pests that must be kept at bay with expensive chemicals? Absolutely! Termite nests, also called mounds, may contain a host of information about the ecology of a region.
Termites are cousins of cockroaches, and have been around since at least the time of the dinosaurs, if not earlier. Like honeybees, they live in large colonies with dedicated castes such as workers, soldiers, queens, and even kings. A little-known secret of the termite world: the termite queen can live to 30 years or more, making her the longest-lived insect on earth! Termites are detritivores – a fancy term for organisms that feed on dead and decaying organic matter. They perform an important function in the nutrient cycling in forests, by breaking down wood and organic residues on the ground. In the absence of these detritivores, it would take years for microbes to do the same thing.
There are more than 3000 species of termites in the world; with over 400 in Asia, and despite the important role they play, 26 of these species are considered pests in India. “In the tropics, litter degradation and soil mixing is mainly performed by termites, especially in dry environments” says Dr. Pascal Jouquet, the lead scientist of a research team, who has extensively studied termites in southern Indian forests.
A video of ants carrying termites away, as a source of food:
The team – comprising researchers from India and France – from the Indian Institute of Science, Bengaluru, tried to understand the factors that influence the occurrence of termite mounds. As a part of the study, they examined 579 termite mounds in the Bandipur Tiger Reserve in Karnataka, which falls within the Nilgiri Biosphere Reserve, now a UNESCO World Heritage Site. The researchers looked at the relationship between the abundance and distribution of termite mounds, and the soil properties and the fragmentation of natural forests.
“In African landscapes, termite mounds are called ‘hotspots of fertility’ or ‘nutrient patches’, and they increase plant and animal diversity in ecosystems. What about Asia?” Dr. Jouquet asks. Globally, existing knowledge on what factors control termite distribution and abundance in ecosystems, and how they impact nutrient cycling and soil dynamics at the ecosystem scale, is lacking. The ecological role of termites has been explored largely in the African context, and Asia remains understudied despite the common occurrence of termites in these parts.
Termite mounds commonly found in southern Indian forests are of two types: lenticular and cathedral. Lenticular mounds are largely underground with a large, dome-like shape, while cathedral mounds are above the ground, and are tall, tower-like structures. The researchers looked at the differences in these two mounds present in two dominant soil types – red soil (ferralsol) and black soil (vertisol), as well as differences between mounds found inside forests and on highway margins. They measured physical and chemical properties in 432 lenticular and 147 cathedral mounds, and estimated their soil volumes based on their shape.
Their findings showed that both lenticular and cathedral mounds were abundant in the two very different habitats – forests and highways margins, and that their densities were not dependent on soil type. This study shows that lenticular mounds, although less conspicuous than cathedral mounds, are important in terms of soil mixing, since the volume of soil stored in lenticular mounds reaches up to 27 and 47 m3 per hectare, in red and black soil respectively. Despite the large quantity of soil, this study finds a low impact of termites on nutrient (carbon, nitrogen and phosphorus) distribution at the ecosystem scale. This discovery upsets the possibility of termite mounds in southern India being ‘nutrient hotspots’, but suggests an important role of termites in soil erosion at the watershed scale.
In conclusion, although many studies in Africa have shown that termites are sensitive to the destruction of habitat and hence indicators of ecosystem health, this study in southern Indian forests could not substantiate that for termites in India. The researchers did not see any difference in termite abundances across two different habitats and soil types. Though the abundance of cathedral mounds was comparable to that found in Africa, the number of lenticular mounds in these forests was more than thrice that of cathedral mounds. It is also one of the few studies to show that the ability of termites to mix the soil is severely underestimated by not considering lenticular mounds.
This study has demonstrated the geographic bias in the existing knowledge about termites, and has challenged globally accepted theories about termites such as their role as indicators of ecosystem health, and their mounds acting as nutrient hotspots. It also highlights the need for more systematic studies on termites in southern Indian forests, which are biodiversity caches. “Termite diversity and their symbiotic association with their fungi have been well studied, but their impacts on soil dynamics, soil properties, erosion, soil fertility, carbon storage, water infiltration, etc. remain virtually unknown in Asia. This research tries to address some of these” remarks Dr. Jouquet.
About the research:
This project was carried out through multiple grants – mostly by the French, and in some measure by the Indian government – at the Indo-French Cell for Water Sciences. The study has been published in the journal ‘Ecosystems’ under the title “Abundance and Impact on Soil Properties of Cathedral and Lenticular Termite Mounds in Southern Indian Woodlands”. The article can be accessed at DOI: 10.1007/s10021-016-0060-5.
Authors of the published research:
Pascal Jouquet (the lead author), Etienne Airola, and Nabila Guilleux are researchers at the Institute of Ecology and Environmental Sciences, Institute of Research for Development (IRD) and the Indo-French Cell for Water Science (IFCWS), Civil engineering Department, Indian Institute of Science, Bengaluru. Ajay Harit and Jean Riotte are from the IFCWS. Ekta Chaudhary is a researcher at the Centre for Ecological Sciences, IISc. Séraphine Grellier is from the Université François Rabelais, Tours, France.