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Without birds, a New Zealand shrub suffers

A shoot of Rhabdothamnus solandri showing the bird-pollinated flower and hairy leaves.
[Dave Kelly, University of Canterbury]

Species of birds around the world have slowly been disappearing, and some researchers are worried that many plant species could disappear as well if pollinating birds are no longer around to spread their seeds. Until now, though, researchers have had no proof that such a breakdown between plants and animals is happening.

In a Science report this week, researchers describe how they used the country of New Zealand and three small islands off its coast to test that theory and find the proof they've been looking for. In the end, Sandra Anderson and colleagues say that the disappearance of pollinating birds from New Zealand's mainland has also reduced the number of Rhabdothamnus solandri bushes in the region.

This discovery demonstrates what can happen when the interactions between two species, like birds and bushes, break down because of human impacts. In the future, the researchers' findings might be used to strengthen biodiversity conservation efforts.

A male stitchbird (or hihi) on Tiritiri Matangi Island. This important pollinator vanished off the North Island with the arrival of mammalian predators 140 years ago, but persists on nearby islands. Where stitchbirds and bellbirds survive, the pollination mutualism still works well.
[Dave Kelly, University of Canterbury]

Since 1870, when mammalian predators arrived in New Zealand, the country has lost two out of three of its pollinating bird species, according to the researchers. On three offshore islands, however, humans and other predators are rare and all three species of pollinating birds still live in peace.

For years, Anderson and her team studied the pollinating birds on the islands and on the mainland. They analyzed how pollination and the spread of seeds from various plants were affected in both places. They even planted additional R. solandri seeds on New Zealand's mainland to see what would happen.

The researchers found that pollination of R. solandri bushes has become extremely limited on the mainland, but not on the islands. The plants' seed production on the mainland was also reduced by 84 percent compared to the island rates. Anderson and colleagues say that the islands have many more younger plants, compared to New Zealand's mainland as well.

And what about the seeds the researchers planted? Five years later, most of them had not been able to develop past seedlings an observation that means pollen and seeds are severely limited on the mainland.

These researchers say that since all of these changes have taken place very slowly over years and even decades similar effects could be going on unreported around the world right now. It will take much more research to determine exactly how these interactions between various plant and animal species affect the world around us.


This research appears in the 03 February 2011 issue of Science Express.