Planet of the ants

The ant colonies in the lush interiors of Corcovado National Park in Costa Rica play a key role in the fragile ecological balance of the forest.

June 05, 2010 07:57 pm | Updated 07:57 pm IST

Hard at work: Leaf-cutter ants on the forest floor. Photo: Divya Mudappa and  T.R. Shankar Raman

Hard at work: Leaf-cutter ants on the forest floor. Photo: Divya Mudappa and T.R. Shankar Raman

From out in the Pacific Ocean, not far from the Central American coast, one can look across a sweeping vista of blue water and white surf towards a forest-clad landscape. There one sees a range of low, rugged hills, clothed in dark and distant green. The forests on these hills are special. Here, in the great funnel of land linking the continents of North and South America, lies a Mesoamerican crucible of nature—the Corcovado National Park in Costa Rica.

For a visitor from the Asian tropics, the forests appear familiar and different, at once. There are tall trees, draped in large lianas or embraced by strangler figs, towering over verdant undergrowth. The heat and humidity are pervasive, bringing on torrents of perspiration. At first, there appears little to see, besides plants, but there are calls and songs of myriad birds, insects, and frogs all around. The forest bears the hallmarks of humid lowland tropical rainforest, in many ways similar to forests in Amazonia, equatorial Africa, or tropical Asia.

But on closer look, the differences are stark. The roaring of howler monkeys and the mystique of the elusive jaguar permeate these forests, not the presence of great apes and leopards as in Africa, or gibbons and clouded leopards as in Asia. One hears the swish of toucans and macaws in flight and the cries of colourful oropendolas and drab wood-creepers, rather than the whoosh of hornbill wings, and the songs of bulbuls and babblers. At night, kinkajous and opossums grace the trees, as pacas and armadillos forage on the forest floor. There are no civets and flying squirrels here, nor mouse deer and pangolin.

Small wonders

Also emblematic of these forests, and ubiquitous, are the ants. On the forest floor, busy lines of ants, millions upon millions of them, are at work. Like flag-bearers of solemn purpose, they carry cut leaves to their nests along long trails cleared by pincer and trampled by little feet. The convoys of leaf-cutter ant work by day and night to sustain their extraordinary society and sub-terranean fungal agriculture. Further on, another great line of ants is hunting—the army ants—and they have an astounding coterie of specialised birds that live off the prey flushed by the marauding swarms. Following the ants are ant-wrens and ant-shrikes, ant-birds and ant-pittas, and other birds. And punctuated throughout the forest is the handiwork of another ant—patches of ground bereft of seedlings under acacia trees. The acacia shelters ant colonies in swollen thorns and provides them special food on leafy platters. In return, the ants aggressively defend the tree from herbivores and maintain the space around free of competing plants.

The ants and the rainforest are intimately connected by ecology and evolution. Farmer or hunter, or thorn-dweller, the dark expanse of rainforest from earth to sky marks the contours of their world.

Biologists sometimes debate whether it is the large animals or the small that shape and structure the forest. Patient observation and research has shown that, in some ways, this is a false debate. When carnivores such as the jaguar and puma are driven extinct, the forest suffers a cascade of events, a vortex of ecosystem decay. Smaller animals, such as the agouti, a rodent, increase in abundance resulting in higher predation of tree seeds. The forest sans puma and jaguar and replete with agouti will eventually lose more species along with changes in forest regeneration and composition. When birds vital for seed dispersal, such as the fruit-eating toucans, manakins, and bellbirds disappear because of forest fragmentation and hunting, it is not merely their resplendent presence that the forest loses with their silent passing. And if one were to remove from this unique tapestry of life the little species, such as pollinating bees or the remarkable ants, the entire forest ecosystem would go into a tailspin of decay and alter unrecognisably from the ground up.

Not far beyond Corcovado lies a changing landscape. Hill slopes with the forests shaved off, like an unwanted stubble, now stand as open cattle pasture amidst fragments of forest and farms with banana, coffee, and, increasingly, the looming menace of oil-palm. Thin slivers of vegetation and second-growth connect the remnant forest patches—islands and bridges of rainforest amidst rustic bustle of farm and pasture. Leaf-cutter ants, adapted to feed on many plants that disturbance brings, increase in abundance, leading to new pressures on rainforest species. The army ants decline or disappear, and the ant-birds, with irrevocable fidelity, follow suit. The cascade of species loss and decay continues; there is hunting of wildlife, too.

Ray of hope

Across this vast, altered landscape are oases of rainforest revival. Pastures and degraded forest purchased by conservation groups and a few sensitive tourism operators are regenerating into secondary forest with tall trees graced by spider monkeys, trogons, and bromeliads. Driven by distant markets catering to conscientious consumers, many coffee and banana plantations are switching to more ecologically sustainable land-use practices certified by conservation groups such as Rainforest Alliance and the Smithsonian Institution. As yet, these oases are scattered and small.

Back in Corcovado, as a muggy afternoon turns into a golden evening, we watch as a high branch is chosen as a comfortable resting spot by a puma. Its presence sends a flock of a dozen toucans into tumult, but neither their loud cries nor the noisy passage of a herd of peccaries below disturbs the recumbent cat. The moment is telling. In an area that was partly farm and cattle pasture just over three decades ago, when the park was established, the rainforest with puma and peccary, toucan and tapir, army-ant and ant-bird, exemplifies the promise of ecosystem recovery.

Not far from here lies the land that is still changing. Seen from the air, or a high viewpoint, the people, busy at work in farms and forest edges, in pastures and on the streets of towns, are strangely like little ants.

The people and the land are intimately connected by culture and conscience. Farmer or hunter, or city-dweller, the transformed landscape from horizon to horizon marks the contours of their world.

T. R. Shankar Raman is with the Nature Conservation Foundation, Mysore (e-mail:

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