托福口语 Task 3

In biology, the concept of 'mutualism' refers to a symbiotic relationship between two species where both organisms benefit from the interaction. This is distinct from parasitism, where one benefits at the expense of the other, or commensalism, where one benefits while the other is unaffected. Mutualism often involves the exchange of resources, such as food, shelter, or protection. A classic example is the relationship between certain plants and their insect pollinators, where plants provide nectar and insects help with reproduction. However, mutualism can also involve more complex services, such as protection from predators.

Professor: Now, let's look at a specific case of mutualism that might surprise you. Consider the acacia tree and the ants that live on it. The acacia tree provides the ants with shelter in its hollow thorns and food in the form of nectar secreted at the base of its leaves. In return, the ants aggressively defend the tree against herbivores. They attack any insect or larger animal that tries to eat the leaves, and they also clear away competing plants that might overshadow the acacia. Without the ants, the acacia tree would suffer from heavy leaf loss and reduced growth. The ants, in turn, rely entirely on the tree for their survival—they can't live elsewhere. So, both species benefit: the tree gets protection, and the ants get food and a home. This is a textbook example of mutualism.