TOEFL統合ライティング

📖 読解文章

The extinction of the dodo bird (Raphus cucullatus) in the late 17th century is often attributed solely to human overhunting by sailors and invasive species introduced by Europeans. However, recent ecological studies suggest that the dodo’s decline was primarily driven by a combination of natural factors, including volcanic activity, climate change, and competition from native species. First, geological evidence indicates that Mauritius, the dodo’s only habitat, experienced a series of volcanic eruptions between 1600 and 1700, which destroyed large areas of lowland forest, the dodo’s primary nesting and feeding grounds. Second, paleoclimate data show a significant cooling period, known as the Little Ice Age, which altered rainfall patterns and reduced the availability of fruits and seeds that constituted the dodo’s diet. Third, the dodo faced intense competition from endemic giant tortoises, which also relied on fallen fruit and ground vegetation, and whose populations were much larger, outcompeting the dodo for food resources. These natural pressures, rather than human actions, likely pushed the dodo to the brink of extinction, with human hunting merely delivering the final blow to an already vulnerable species.

🎧 リスニング講義

The professor challenges the reading’s argument that natural factors were the primary cause of dodo extinction. She contends that human activity was the decisive factor, and that the natural explanations are either exaggerated or unsupported. First, volcanic eruptions on Mauritius were not as widespread or destructive as the reading claims. Historical records and geological surveys show that eruptions were localized and occurred in uninhabited highland areas, leaving the lowland forests, where dodos lived, largely intact. Second, while the Little Ice Age did cause some cooling, Mauritius enjoys a tropical maritime climate, and the temperature drop was mild—only about 0.5°C. This minor change would not have significantly reduced fruit production, as modern ecological studies on similar island ecosystems show that such small temperature shifts have negligible effects on tropical plant productivity. Third, the reading overlooks that giant tortoises were already declining before human arrival due to natural cycles, and their populations were not large enough to outcompete dodos. In fact, dodos and tortoises co-existed for millennia, suggesting they had evolved to share resources. Instead, historical accounts document that sailors and rats decimated dodo nests and adults within decades of arrival, and the last confirmed sighting was in 1662, shortly after intensive hunting and deforestation for sugar plantations. Thus, human actions were the primary cause, not natural pressures.