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Monday, December 5, 2011

Don’t be so quick to target invasive species


Invasive species can wreak havoc on an ecosystem.  A case in point is the notorious ship rat (Rattus rattus), which has been an unwelcome guest at every port visited by humans.  The North Island of New Zealand can thank the ship rat for the nearly complete elimination of all native vertebrates.  Unfortunately, many of the native plants relied on those vertebrates for pollination services.  But don’t worry, this story does have a happy ending.  A substitute pollinator has apparently taken over the duties vacated by the missing vertebrates.  That creature is… the ship rat.

David Pattermore and David Wilcove of Princeton University studied the pollination of three native New Zealand plants growing on North Island and in a nature reserve called Little Barrier Island.  Although the native vertebrate population had been depleted from North Island, it thrives in abundance on Little Barrier Island.  Surprisingly, the pollination rate for the plants was similar in the two areas. 

The primary pollinators on Little Barrier Island are the endemic birds and bats.  On North Island, that job is done by ship rats and by an introduced species of bird known as the silvereye.  Apparently, ship rats had replaced the very pollinators that they drove to extinction. 

This creates a tricky problem for conservationists trying to hold back the flood of invasion by non-native species.  Scourging ship rats from the North Island would do the native plants no favors.  After all, the plants don’t care whether it’s a rat or a bat that carries their pollen around.   The more that is understood about the current role of introduced species within an ecosystem, the better those locations can be managed.  At the very least, every effort must be made to reintroduce native pollinators before removing invaders.

You can see Pattermore’s explanation below.