The Effects Of Invasive Rats And Burrowing Seabirds On Seed And Seedling Communities With Focus On New Zealand Islands Item Type Thesis Authors Grant-Hoffman, Madeline N. Download date 26/09/2021 05:38:49 Link to Item http://hdl.handle.net/11122/8984 NOTE TO USERS Page(s) not included in the original manuscript are unavailable from the author or university. The manuscript was microfilmed as received 50=51 This reproduction is the best copy available. UMI THE EFFECTS OF INVASIVE RATS AND BURROWING SEABIRDS ON SEED AND SEEDLING COMMUNITIES WITH FOCUS ON NEW ZEALAND ISLANDS A Dissertation Presented to the Faculty of the University of Alaska Fairbanks in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY By Madeline N. Grant-Hoffman, B.S., M.S. Fairbanks, AK May 2009 UMI Number: 3374160 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI 3374160 Copyright 2009 by ProQuest LLC. All rights reserved. This edition of the work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 THE EFFECTS OF INVASIVE RATS AND BURROWING SEABIRDS ON SEED AND SEEDLING COMMUNITIES ON NEW ZEALAND ISLANDS By Madeline N. Grant-Hoffman RECOMMENDED: -su T ^ rh , C 2 Z Chair, Department of Biology & Wildlife APPROVED: Dean, College of Natural Sci§r^e”&"‘Mathematics k €an of the Graduate Schoc Date ABSTRACT Invasive rats (Rattus exulans, R. rattus, and R. norvegicus) affect vegetation directly through herbivory and indirectly through predation on burrowing seabirds (Procellariiformes: petrels, prions, shearwaters). These seabirds affect vegetation through allochthonous inputs and physical disturbance. I studied the direct impacts of rats on seedling communities on New Zealand islands with three different conditions regarding rats: islands where rats never invaded, islands where rats were present, and islands where rats were eradicated or where populations were low as a result of repeated eradications and reinvasions. I studied a subset of these islands to examine the indirect effects, through predation of burrowing seabirds, of invasive rats on seedlings. I also performed field, laboratory, and greenhouse experiments to determine the mechanisms driving observed patterns in seedling communities. Finally, through a literature review and laboratory trials with R. norvegicus I sought to find what plant species and plant parts invasive rats are exploiting and what characteristics may influence herbivorous consumption in rats. I found that both invasive rats and burrowing seabirds are driving factors for woody seedling communities on New Zealand islands. Woody seedling species richness and density are similar on islands with no history of rats and islands with current rat invasions. However, where rat populations have been historically high but are currently absent or low, seedling species richness is low and seedling densities are high. Low species richness on islands with a history of rats is due to selective consumption of both seeds and seedlings by rats. In addition, the presence of seabirds is associated with high species richness and density of seeds. However, at very high seabird densities, actual seedling richness and density are low due to extreme physical disturbance. Rats may prefer smaller, fleshy fruits and seeds to seedlings and other vegetative plant parts, but may be deterred from fruit or seed consumption by large size, hard seed coats, or plant chemical defenses. By understanding the separate effects of invasive rats and burrowing seabirds and the mechanisms driving these effects, island restoration efforts can be improved. TABLE OF CONTENTS Page SIGNATURE PAGE ............................................................................................................ i TITLE PA G E......................................................................................................................... ii ABSTRACT.......................................................................................................................... iii TABLTE OF CONTENTS ................................................................................................ v LIST OF FIGURES ............................................................................................................. x LIST OF TABLES............................................................................................................. xii CHAPTER 1: GENERAL INTRODUCTION ..... 1 LITERATURE CITED .......................................................................................................4 CHAPTER 2: INVASIVE RATS ALTER WOODY SEEDLING COMPOSITION ON SEABIRD-DOMINATED ISALNDS IN NEW ZEALAND ...............................7 ABSTRACT....................................................................................................................... 8 INTRODUCTION .......................................................................................................... 10 METHODS ...................................................................................................................... 16 Study area ...................................................................................................................... 16 Seedling counts and physical measurements............................................................ 16 Statistical analyses..................................................................... 18 Similarity and recovery of woody seedling communities .................................... 18 Woody plant species .......................................................................... 20 Microsite and biogeographical variables .............. 21 RESULTS ...................... 23 Similarity and recovery of woody seedling communities ........................................ 23 Woody plant species.......................... 26 Microsite and biogeographical variables ....................................... 27 DISCUSSION ....................................................................................................................29 Similarity and recovery of woody seedling communities ........................................ 29 Woody plant species.................... 31 Microsite and biogeographical variables .....................................................................33 ACKNOWLEDGEMENTS .............................. 35 LITURATURE CITED .................................. 36 FIGURE LEGENDS..........................................................................................................48 CHAPTER 3: INVASIVE RAT AND BURROWING SEABIRD EFFECTS ON SEEDS AND SEEDLINGS ON NEW ZEALAND ISLANDS ...............................53 ABSTRACT................................................... 54 INTRODUCTION ...................................... 55 METHODS .............................................................. 59 Study area .......................................... 59 Changes to the seed community ................................................................................... 60 Germination trials ........................................................................................................60 Seed traps ...................................................................................................................... 61 Reproductive material in the litter ..................................................... 62 Feeding trials................ 62 Viability tests for Pittosporum crassifolium .......................................................... 63 vii Changes to the seedling community ............................................................................ 64 Exclosure experiment........................................... 64 Statistical analyses..........................................................................................................65 Germination trials ........................................................................................................66 Seed traps ...................................................................................................................... 67 Reproductive material in the litter ............................................................................ 67 Feeding trials.................................................................................................................68 Exclosure experiment.................................................................................................. 68 RESULTS ........................................................................... 69 Changes to the seed community ................................................................................. 69 Germination trials ........................................................................................................69 Seed traps ...................................................................................................................... 70 Reproductive material in the litter ........................................................................... 70 Feeding trials.................................................................................................................71 Viability tests for Pittosporum