Final answer:
The type of ecological interaction where saguaro cacti are pollinated by lesser long-nosed bats is known as mutualism, a symbiotic relationship benefiting both species.
Step-by-step explanation:
The ecological interaction that best fits the description of saguaro cacti being pollinated by lesser long-nosed bats looking for food in saguaro blossoms is mutualism. In mutualism, both species benefit from the interaction. The bats are attracted to the flowers by their white color and strong fragrance, which are adaptations of the plants to nocturnal pollination. These flowers open at night and are structured to allow the bats to access their nectar, resulting in the bat getting food and the cactus being pollinated. Both the bat and the cactus are partners in a symbiotic relationship, which has co-evolved over time to become increasingly effective. The lesser long-nosed bat contributes to the reproduction of the saguaro cactus by transferring pollen from one flower to another, while it gains sustenance from the nectar provided by the flowers.