Why is the southern cassowary considered a keystone species?

Answer 1

Cassowaries are considered a keystone species. They play an important role in the ecology of the rainforest and bushland areas where they live, as they are vital in dispersing seeds in their native forests.

They are frugivores which feed on the fruit of up to 238 different species of plants. Because they are able to eat larger fruits, they can therefore can disperse large rainforest fruits after the seeds have passed through their digestive system, which is gentle enough to allow the seeds to remain viable. The cassowary has a wide range, so is also the only long distance means for dispersing large seeded fruits. The seeds are excreted into a pile of the cassowary's own dung, meaning the seeds have their own ready-made pile of fertiliser. The smell of the dung even helps to deter seed-eating predators such as the white-tailed rat. Of the hundreds of fruit-bearing species on which the cassowary feeds, between 70 and 100 of them appear to rely completely on the cassowary for dispersal.