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Non-native species not the bad guys in a changing eco-system

Non-native species not the bad guys in a changing eco-system

April 17, 2014

University of Canterbury researchers are investigating some positive features of animals being introduced to New Zealand.

Exotic animals are generally considered to be a major threat to native species in New Zealand and worldwide.

Despite numerous examples of invasive species harming ecosystems, exotic species may actually be able to fill ecological gaps in their new home, such as those left by native species that have gone extinct.

Professor Jason Tylianakis says this is one of the first examples of exotic species filling the roles left by declining natives across a whole range of species.

"A collaborative research project between scientists at the University of Canterbury and University of Oviedo, Spain, has examined 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.

"New Zealand fruit-feeding birds have historically suffered a strong decline of native birds but they have also gained new fruit-eaters in the form of introduced European birds such as blackbirds and song thrushes."

The Canterbury researchers studied the network of feeding interactions between different species of plants and birds in the North and South Islands. They 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 seeds of plant species that were not frequently eaten by native birds at any given location and helped to stabilise seed dispersal across a whole range of plants.

Without introduced species, many native plants would not have their fruits eaten and their seeds would simply fall to the ground below the tree.

Another Canterbury researcher Dr Daniel Stouffer says exotic species were less discriminating in their fruit consumption patterns.

"Native fruit-eaters have developed strong affinities for or against consumption of particular native fruit species making our native communities vulnerable to loss of key bird species. On the contrary, the exotic species were more than happy to make equal use of all the fruits available, thereby spreading their benefit more widely."

Professor Tylianakis says people often consider invasions by non-native species as always being harmful.

"However, many of our native species have already gone extinct and sometimes we need new species to fill their role. Although they often do harm, we can’t always assume that non-native species are the bad guys in our constantly-changing ecosystems,” Professor Tylianakis says.


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