Termites, the indicators of an ecosystem
The arrival of monsoon brings with it a much-needed respite from the heat of the summer. While rains are definitely welcome, there is someone who is not happy - the termites. When we hear the word 'termite', most of us are reminded of the irksome pests that eat away the wood in our houses, causing irreparable damage. But did you know that termites also act as indicators of the health of an ecosystem, and their mounds contain a host of information about the ecology of the region?
In a recent study published in the journal Ecosystems, a team of Indian and French researchers from the Indian Institute of Science (IISc), Bengaluru, and Université François Rabelais, France have tried to understand the factors that influence these termite mounds. With data from 579 termite mounds in the Bandipur Tiger Reserve, Karnataka, the team investigated the relationships between the abundance and distribution of termite mounds with the soil properties and the fragmentation of natural forests.
There are more than 3,000 species of termites in the world of which around 400 are found in Asia. In India, 26 species of those are considered as pests that bother us. Termites are detritivores that eat dead and decaying organic matter like logs of wood in a forest. They form an important link in the cycling of nutrients in the forests by breaking down wood and organic residues on the ground, which would otherwise take years to decay by microbes. "In the tropics, litter degradation and soil mixing are mainly performed by termites, especially in dry environments," says Dr Pascal Jouquet from IISc, the lead author of this study and who has also extensively studied termites in the forests of southern India.
Though there are studies that talk about the ecological role of termites, most of them refer to African termites, and the termites of Asia still largely remain understudied. "In African landscapes, termite mounds are called 'hotspots of fertility' or 'nutrient patches' and they increase plant and animal diversity in the ecosystem. What about Asia?" asks Pascal.
Factors that control the distribution and abundance of termite mounds in Asian ecosystems and their impact on nutrient cycling and soil dynamics at the ecosystem scale need to be well understood.
Termite mounds are commonly found in the forests of southern India. There are two types of mounds based on their shapes - lenticular and cathedral. Lenticular mounds are largely underground with a large dome-like shape, while cathedral mounds are tower-like structures. The
researchers looked at these two mounds in two dominant soil types - red soil (ferralsol) and black soil (vertisol). They also studied the differences between the mounds found inside the forests and on the highway margins close by. After studying 432 lenticular and 147 cathedral mounds, they estimated the physical and chemical properties, and the volume of soil, in each of these mounds based on their shape.
The findings of this study showed that lenticular and cathedral mounds were abundant in both types of habitats - forests and highway margins, and that their densities were not dependent on the soil type. However, although less conspicuous than cathedral mounds, this study shows the importance of lenticular mounds in terms of soil bioturbation since with about 13 mounds in a hectare, against two for cathedral, the volume of soil stored in lenticular mounds reaches between 27 to 47 m3 per hectare in the red and black soil, respectively.
Despite the large quantity of soil, the study finds a low impact of termites on the distribution of nutrients like carbon, nitrogen and phosphorus, at the ecosystem scale. This discovery upsets the belief that termite mounds are 'nutrient hotspots' but suggests an important role of termites on soil erosion at the watershed scale.
In conclusion, though many studies on African termites have claimed that termites are sensitive to destruction of habitat, the results of this study show that this may not be true for termites in India. The researchers did not see any difference in termite abundances in both habitats and soil types. Though the abundance of cathedral mounds were comparable to those found in Africa, the study found that the number of lenticular mounds 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 debunked several globally accepted theories about termites, possibly due to the bias in the location of study. It also highlights the need for more systematic studies on termites in the forests of southern India, a biodiversity hotspot. "Termite diversity and their symbiotic association with their fungus have been well studied but their impacts on soil dynamics, soil properties, erosion, soil fertility, carbon storage, water infiltration, etc. remains virtually unknown in Asia. This research tries to address some of these," remarks Pascal. The next time you spot a termite, perhaps it is time for you to stop and think about the host of information they carry - an incredible feat for an insect of that size!
(The author is with Gubbi Labs, a Bengaluru-based research collective)