The behavior that can end up being more harmful than helpful is:
a. iguanas and tortoises eat leaves, fruits, and flowers, relying on each other as important seasonal food sources.
While the interaction between iguanas and tortoises can provide some benefits, their feeding behavior can also lead to the overconsumption of plant resources, negatively impacting plant reproduction and survival. In contrast, the other options (b, c, and d) involve behaviors that specifically contribute to the reproductive success of plants, such as seed dispersal or pollination.