Mutualistic interactions between ants and plants are common in the tropics. Many ant-plants have structures that house ants, and feed them, and in turn the ants protect the plants from herbivory. Ant-plant mutualisms provide excellent examples of niche construction, as ants modify their environments to benefit the host plant which then provides more resources for the ants. The dynamic relation between the ant and plant partners has interesting consequences for the growth and life history of colonies. As an ant colony grows larger, like any organism, it uses more resources. But as a plant-ant mutualist colony grows longer, it creates more resources by promoting the growth of the plant and thus more nest sites and food for the ants. Ant-plant mutualisms thus make unique ecological and evolutionary contributions to tropical diversity. http://www.stanford.edu/%7Edmgordon/