Final answer:
The relationship between the Monarch butterfly and milkweed plants is mutualism, where both species benefit from the interaction.
Step-by-step explanation:
The relationship described in the question is mutualism. Mutualism is a type of symbiotic relationship in which both species involved benefit from the interaction.
In the case of the Monarch butterfly and milkweed plants, the butterfly obtains nectar from the flower while incidentally picking up pollen on its leg. When the butterfly visits other milkweed plants, it transfers the pollen, aiding in cross-pollination. This benefits the butterfly by providing food and benefits the milkweed plants by facilitating reproduction through pollination.
Other examples of mutualistic relationships include bees pollinating plants and obtaining nectar in return, and bats pollinating flowers while feeding on nectar.