Academic Reading — Test 186

Reading passage

THE ECOLOGICAL FUNCTION OF TERMITE MOUNDS IN TROPICAL SAVANNAS A. Across the savannas of Africa, Australia and South America, the landscape is frequently punctuated by earthen towers that rise a metre or more above the surrounding grassland. These structures, built by colonies of termites over periods that can exceed half a century, are far more than insect dwellings. Ecologists who have studied savanna systems in detail now regard termite mounds as foundational features of the habitat, shaping the distribution of plants, water and other animals across enormous areas. A single mound may house several million individual termites, organised into castes that perform distinct tasks: workers forage and build, soldiers defend the colony, and a reproductive pair, the queen and king, sustain the population for years. The mound itself is not merely a shelter but a finely tuned environmental control system, regulating temperature and humidity for the fungus gardens and brood chambers that lie beneath its surface. B. One of the most significant roles of termite mounds is their influence on soil composition. As termites tunnel through the earth in search of food, they transport mineral-rich subsoil upward and deposit it near the surface, mixing it with saliva and faecal matter to construct their galleries. This process concentrates nutrients such as calcium, phosphorus and nitrogen in and around the mound at levels considerably higher than those found in the surrounding flat terrain. Over time, rainfall washes some of these nutrients outward, creating a halo of enriched soil that can extend many metres beyond the mound's base. Botanists have long observed that vegetation growing near termite mounds tends to be denser and more nutritious than vegetation elsewhere on the savanna, a pattern that has earned these structures the informal title of "fertility islands." C. The physical architecture of the mound also alters the local hydrology in ways that benefit the broader ecosystem. Termite tunnels, which can extend several metres into the ground, increase the porosity of the soil, allowing rainwater to infiltrate more readily instead of running off the surface. This improved drainage reduces erosion during the heavy downpours typical of the wet season and helps recharge groundwater that sustains plant roots through the long dry months. In several studies of savanna grasslands, soil adjacent to active mounds has been found to retain moisture noticeably longer than soil in open grass-dominated areas, a difference that becomes critical when rainfall is scarce. Because of this capacity to store water, mound clusters are sometimes described as natural reservoirs that buffer the ecosystem against drought. D. The distinctive vegetation patterns associated with termite mounds also generate habitat diversity that supports a remarkable range of other species. Because the soil near a mound is richer and the drainage superior, trees and shrubs often establish themselves on or beside mounds even in areas where the wider grassland supports few woody plants. These small clusters of trees, sometimes called mound-thickets, offer shade, nesting sites and food resources unavailable on the open plain. Researchers working in East African savannas have documented birds, reptiles and small mammals that depend disproportionately on these mound-associated thickets for shelter, while larger herbivores such as antelope are frequently observed grazing on the nutrient-rich grasses that ring a mound. Termite mounds, once abandoned by their original builders, are also commonly colonised by other animals, including aardvarks and various burrowing rodents, which excavate the soft soil to create dens. E. Termite mounds further influence the spatial pattern of vegetation at a landscape scale. In several regions, mounds are distributed with surprising regularity, spaced roughly evenly across the terrain rather than clustered randomly. This regularity, scientists suggest, arises because young colonies must establish themselves at a sufficient distance from existing mounds to avoid competition for resources and territorial conflict with neighbouring colonies. The resulting grid-like arrangement of fertile patches creates a mosaic of differing soil and vegetation conditions across the savanna, which in turn diversifies the niches available to other organisms. Some researchers argue that this patterning plays a stabilising role during periods of environmental stress, since the network of mounds maintains pockets of productive habitat even when surrounding grassland is degraded by overgrazing or fire. F. Despite their ecological importance, termite mounds and the colonies within them remain vulnerable to disturbance from agricultural expansion and changing rainfall patterns linked to climate change. When mounds are destroyed to clear land for cultivation, the loss extends beyond the termites themselves: the nutrient cycling, water infiltration and habitat provision associated with the mound disappear as well, and recovery of these functions can take decades given the slow rate at which colonies mature. Conservation biologists increasingly argue that termite mounds should be regarded as keystone structures, comparable in ecological significance to large trees or watering holes, and that their preservation ought to be incorporated explicitly into land management strategies for savanna regions. As research continues to reveal the extent of their influence, termite mounds are gaining recognition not as incidental features of the savanna landscape but as active engineers of its ecology.