1. AgResearch, Lincoln Science Centre; Private Bag 4749 Christchurch 8140 New Zealand
2. Soil and Physical Sciences; Faculty of Agriculture and Life Sciences; Lincoln University; P.O. Box 84 Lincoln 7647 Christchurch New Zealand
3. Department of Zoology; University of Otago; P.O. Box 56 Dunedin 9054 New Zealand
4. National Institute of Water and Atmospheric Research; P.O. Box 8602, 10 Kyle Street Riccarton Christchurch 8011 New Zealand