RASP

(Rats and Seabirds Project)

Mulder Lab, University of Alaska Fairbanks

Background

Questions

Participants

Support

Links

Background:

Islands off the coast of New Zealand have experienced several waves of invasion by rats, including Pacific rats (kiore, Rattus exulans), Norway rats (Rattus norvegicus) and ship rats (Rattus rattus). In addition to devastating native bird, reptile, and large invertebrate populations, rats are likely to have affected the soils and vegetation of islands. As eradication of rats from islands becomes a common management tool, questions regarding effects of rats (and of their removal) on ecosystem functioning become particularly important for planning island restoration.

In this project we are comparing vegetation and ecosystem processes on three types of islands off the coast of New Zealand:

1) Islands that have never been invaded by rats;

2) Islands that currently have rats;

3) Islands that have had rats in the past, but where they have been eradicated.

Questions:

1) How do rats alter vegetation processes directly? Possible effects include:

· seed, fruit and seedling predation

· seed dispersal

· consumption of herbivores

· transmission of disease between plants

2) How do rats alter soil and vegetation processes indirectly, by reducing seabird populations?

Most of the islands support or used to support large nesting seabird populations. The presence of rats greatly reduces seabird populations (often eliminating them altogether).

Seabirds are expected to have several large effects:

· Seabirds feed at sea during the day, and bring nutrients of marine origin (particularly P) to the land when they return at night to their burrows. This changes nutrients available to plants and microbes.

· They burrow into the soil, disturbing it, mixing in litter, and dislodging seedlings (see image on left).

· They crash through the trees, which may damage or dislodge leaves.

3) How well do vegetation and soils recover following rat eradication?

Recovery from some effects of rats may be fairly fast (e.g. seedling presence of species for which rats consume seeds). Others, particularly soil characteristics, may depend on recolonization by seabirds.

Participants and their interests:

This project is a collaboration between three different institutions: the University of Alaska Fairbanks (UAF), Landcare Research of New Zealand (Landcare), and the New Zealand Department of Conservation (DoC).

Christa Mulder is investigating seedling densities, and herbivory and pathogen levels on trees. (Here she demonstrates how to ease into the “walrus wiggle” necessary to negotiate the very heavily burrowed surface.)

Mel Durrett is a Ph.D. student in the Mulder lab. Her thesis focuses on spatial and temporal variation in nutrient effects (from seabird guano) on plants.

Nikki Grant-Hoffman is a Ph.D. student in the Mulder lab. Her thesis focuses on seed and seedling dynamics under different rat histories.

David Wardle is investigating soil characteristics, including soil structure, nutrient content, and changes in decomposer communities.

Peter Bellingham is investigating forest composition and effects of soils on growth rates of different tree species.

Tad Fukami (University of Hawai’i) studies diversity of fungal organisms in decomposing Melicytus ramiflorus, a common shrub / short tree species.

Dave Towns is examining invertebrate diversity in litter.

Karen Boot provides logistical and field technical support.

(She is also the expert at digging big holes to collect soil samples.)

Support:

Many of the islands we work on are owned or managed by local iwi and hapu (Māori tribes). We are grateful for the support of and permission to work on the islands received from: Ngati Hako, Ngati Hei, Ngati Mnuhiri, Ngati Paoa, Ngati Puu, Ngati Rehua, and Ngati Wai. Without their support this work would not be possible. We also thank John Callum, Bryce Rope, and the Neureter family for permission to work on their privately owned islands.

Financial support is provided by the National Science Foundation (US), the Marsden Foundation (Royal Society of New Zealand), the Department of Conservation (New Zealand), and the Japan Society for the Promotion of Science.

For questions about this project, please contact Christa Mulder at ffcpm2@uaf.edu .

Links:

· The RASP webpage at Landcare: click here

· New Zealand offshore islands, click here.

· The Institute of Arctic Biology at the University of Alaska: click here.

· The Mulder lab: click here.