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Tufts University

Publication Date

Spring 2005

Program Name

Ecuador: Comparative Ecology and Conservation

Abstract

The biological world is under attack. All across the world in every continent and sub-continent biological diversity is rapidly decreasing (Wilson, 1999). As the human population continues to exponentially increase, especially in Third World countries where biological diversity reaches its peak, countless diverse biological habitats are threatened by accelerating human consumption and the growing needs of growing human populations. In Ecuador, only 1% of the original tropical forest remains, as a result of the accelerating need of viable agricultural tracts for Ecuador’s relatively poor farmers, as well as the unsustainable harvest of valuable hardwood tree species endemic to Ecuador’s primary forest (Jatun Sacha, 2001). Known as biological “hot spots” certain biologically diverse ecosystems in Ecuador have been classified as being particularly threatened habitats which contain thousands of rare endemic plants and animals. The need to protect the very little natural primary forest habitats left is a great responsibility left to those who passionately care about the world’s dwindling biological diversity and are trying to preserve important biological hotspots while providing for the world’s growing populations. With this in mind Jatun Sacha, an Ecuadorian environmental organization, purchased large tracts of threatened primary forest as a result of an evaluation by Conservation International’s Rapid Assessment Program which concluded that the tropical pre-montane primary forest in northwestern Ecuador was an extreme biological hotspot which needed immediate management and conservation attention (Jatun Sacha, 2001). The purchased reserve, known as the Bilsa Biological Reserve, now covers 3000 hectares of extremely biologically diverse primary forest and secondary forest which has grown back over areas greatly affected and damaged by human involvement. One of the most important missions of the Reserve is active reforestation of the 20% of the reserve that contains secondary forest, with biologically and economically valuable hardwood primary forest tree species many of which are very rare, endemic and threatened (Jatun Sacha, 2001). The Reserve is currently using 26 primary forest species chosen by relative rarity and endemism, but also by the possible use of such trees as an economic resource for the local people, providing an incentive to protect the threatened primary forest instead of unsustainably cutting it down for additional pasturelands (Aurelia, 2005). As well, the Reserve is looking into the future by choosing tree species which have the potential to play important roles in carbon sequestration, providing another economic incentive to protect the forest. The seeds of the selected trees to be reforested are either purchased or collected from existing stands of primary forest within the reserve (Aurelia, 2005). The seeds are then grown in seedbeds within the reserve and then planted in reforestation lines in different areas of the reserve. The seedbeds are typically monocultures of the selected tree species, while the reforestation lines are planted with many different and diverse tree species to reproduce the same incredible floral diversity within the natural primary forest ecosystem. One of the major threats to reforestation efforts is voracious herbivores who recklessly attack the seedbeds, which are especially vulnerable to pest infiltration as a monoculture. As well the plants within the reforestation lines themselves often seriously damaged or killed, slowing down and preventing the successful transformation of secondary forest to primary forest. The most serious herbivorous threat to the active reforestation taking place within the Bilsa Biological Reserve is the activity of leaf-cutter ants (Aurelia, 2005). Especially within the seedbeds, these pests can defoliate entire trees overnight and reduce a viable crop of reforestation sprouts to dead stems in the blink of an eye. Other studies conducted at the Bilsa Biological Reserve have found dozens of nests near seedbeds and reforestation lines, and the unrelenting harvesting of affected seedlings and young trees by multiple leaf-cutter ant colonies is witnessed throughout the year, to the chagrin of the dedicated volunteers and employees within the reserve who have worked tirelessly to bring back the primary forest to the extensive secondary forest tracts (Beloqui, 2001). Leaf-cutter ants are a disturbance adapted species (Beloqui, 2001). They especially thrive in canopy gaps within primary forest, as well as ecologically disturbed secondary forest, which generally involves the same disturbance adapted floral vegetative resources. The recent widespread ecological destruction especially in biologically diverse ecosystems like that which exists at Bilsa Biological Station has witnessed a drastic increase in the pest problems presented by leaf-cutter ants Atta sp. and Acromyrmex sp. due to the expansion of their preferred habitats, namely ecologically disturbed forest and secondary forest (Beloqui, 2001). The leaf-cutter ants are unique among ants in that they collect pieces of leaves to bring back to their home nest, which are then used to grow symbiotic fungi (Beloqui, 2001). While certain species cut grasses, the vast majority of leaf-cutter ants prefer dicotyleden plants. A mature nest can contain several million workers who forage along well-groomed trails emanating from the host nest. Young leaves at the top are especially targeted, due to their high sugar content, while the ants work their way down the targeted plant (Beloqui, 2001). Introduced exotic species have been known to be especially selected, as well as fruit trees such as citrus, leading to the abandonment of fruit agriculture by many South American farmers. Understanding the precise nature of the herbivorous threats presented by foraging leaf-cutter ants to the ongoing reforestation efforts being conducted at Bilsa Biological Reserve is essential to understanding leaf-cutter ants and possible solutions to the ecological destruction caused by such devastating pests. This study looks at the relative activity of leaf-cutter ants in untouched secondary forest as well as reforested secondary forest to determine the precise nature of the herbivorous threat presented by foraging leaf-cutter ants with respect to the ongoing reforestation efforts within the Bilsa Biological Reserve in northwestern Ecuador. Due to the observed activity of leaf-cutter ants within the reserve it was expected that the activity of the leaf-cutter ants would be relatively higher in reforestation lines and seedbeds, due to the vulnerable monoculture of young leaves available within seedbeds, and the general lack of natural ecological interaction between primary forest species and leaf-cutter ants leading to the easy exploitation of such introduced tree species within secondary forests by foraging leaf-cutter ants.

Disciplines

Entomology | Natural Resources and Conservation

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