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Exotic Species Help Ecosystems

Exotic animals are generally considered to be a major threat to native species, but scientists in New Zealand have found some positives.

Prof Jason Tylianakis of the University of Canterbury says exotic species may fill ecological gaps in their new home, such as those left by native species that have become extinct.

Tylianakis has been examining the role of exotic birds in dispersing the seeds of native New Zealand trees and shrubs. “Many fruiting plants require birds to carry their seeds to new locations and drive the persistence and recovery of native forests,” he says.

Tylianakis studied the network of feeding interactions between different species of plants and birds in the North and South islands, and found that the intermediate body and beak size of exotic birds allowed them to feed on a great variety of different fruits. This allowed the birds to disperse the seeds of plant species that were not eaten by native birds at any given location, and helped to stabilise seed dispersal across a whole range of plants.

“Native fruit-eaters have developed strong affinities for or against consumption of native fruit species, making our native communities vulnerable to loss of key bird species,” says Dr Daniel Stouffer of the University of Canterbury. “However, the exotic species are more than happy to make equal use of all the fruits available, thereby spreading their benefit more widely.”