Mutualism seems particularly important in the tropics.
There are no obligate ant-plant mutualisms north of 14 degrees latitude. There are no nectar eating or fruit eating bats north of 32-33 degrees. There are no orchid bees north of 24 degrees. Numbers of plant species with extrafloral nectaries, places which produce decline rapidly north of 24 degrees. Slight perturbations in conditions or population numbers and one species or the other could become extinct.