, Volume 163, Issue 2, pp 449–460

Invasive rats alter woody seedling composition on seabird-dominated islands in New Zealand

  • Madeline N. Grant-Hoffman
  • Christa P. Mulder
  • Peter J. Bellingham
Community ecology - Original Paper

DOI: 10.1007/s00442-009-1523-6

Cite this article as:
Grant-Hoffman, M.N., Mulder, C.P. & Bellingham, P.J. Oecologia (2010) 163: 449. doi:10.1007/s00442-009-1523-6


Invasive rats (Rattus rattus, R. norvegicus, R. exulans) have large impacts on island habitats through both direct and indirect effects on plants. Rats affect vegetation by extirpating burrowing seabirds through consumption of eggs, chicks, and adults. These seabirds serve as ecosystem engineers, affecting plant communities by burying and trampling seeds and seedlings, and by altering microclimate. Rats also directly affect plant communities by consuming seeds and seedlings. We studied the direct and indirect impacts of rats on the seedlings of woody plants on 21 islands in northern New Zealand. We compared seedling densities and richness on islands which differed in status with respect to rats: nine islands where rats never invaded, seven islands where rats were present at the time of our study, and five islands where rats were either eradicated or where populations were likely to be small as a result of repeated eradications and re-invasions. In addition, we compared plots from a subset of the 21 islands with different burrow densities to examine the effects of burrowing seabirds on plants while controlling for other factors that differ between islands. We categorized plant communities by species composition and seedling density in a cluster analysis. We found that burrow densities explained more variation in seedling communities than rat status. In areas with high seabird burrow density seedling densities were low, especially for the smallest seedlings. Species richness and diversity of seedlings, but not seedling density, were most influenced by changes in microclimate induced by seabirds. Islands where rats had been eradicated or that had low rat populations had the lowest diversity and richness of seedlings (and adults), but the highest seedling density. Seedling communities on these islands were dominated by Pseudopanax lessonii and Coprosma macrocarpa. This indicates lasting effects of rats that may prevent islands from returning to pre-invasion states.


Rattus rattusRattus norvegicusEcosystem engineerSeedling communityPredator eradication

Supplementary material

442_2009_1523_MOESM1_ESM.doc (46 kb)
(Doc 47 kb)

Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • Madeline N. Grant-Hoffman
    • 1
    • 4
  • Christa P. Mulder
    • 1
    • 2
  • Peter J. Bellingham
    • 3
  1. 1.Department of Biology and WildlifeUniversity of Alaska FairbanksFairbanksUSA
  2. 2.Institute of Arctic BiologyUniversity of Alaska FairbanksFairbanksUSA
  3. 3.Landcare ResearchLincolnNew Zealand
  4. 4.National Landscape Conservation System, Grand Junction Field OfficeBureau of Land Management ColoradoGrand JunctionUSA