TOEFLスピーキング Task 3

The concept of "niche construction" refers to the process by which organisms actively modify their environment, thereby influencing their own evolution and that of other species. Unlike passive adaptation, niche construction highlights how organisms are not just products of natural selection but also agents that shape their habitats. For example, beavers building dams alter water flow, creating new ecosystems that affect the availability of resources for themselves and other organisms. This feedback loop can lead to evolutionary changes over generations.

Professor: Let's take a classic example from my research on coral reefs. In the Caribbean, the long-spined sea urchin (Diadema antillarum) grazes on algae that would otherwise overgrow and smother coral. By consuming algae, the urchin maintains clear space for coral larvae to settle and grow. This is niche construction because the urchin's feeding behavior physically modifies the reef environment, making it more suitable for corals. However, in the 1980s, a disease wiped out most of these urchins. Without them, algae flourished, covering reefs and preventing coral recruitment. Over time, the reef shifted from a coral-dominated to an algae-dominated system, affecting fish that depend on corals for shelter. This shows how a single species can engineer its habitat, and when it disappears, the entire ecosystem changes. The urchin's activity was not just adaptation; it actively built a niche that benefited multiple species.