The Effects of Rodents on Ground Dwelling Arthropods in the Waitakere Ranges A thesis submitted to the Auckland University of Technology in fulfilment of the Degree Master of Philosophy Peter A. King January 2007 TABLE OF CONTENTS ATTESTATION …………………………….…………….…….………………….…....8 ACKNOWLEDGEMENTS………………………………………………………….……9 ABSTRACT ……………………...……………………….……….………….……....…11 1 INTRODUCTION.............................................................................................................. 13 1.1 GONDWANALAND ORIGINS OF NEW ZEALAND’S ARTHROPODS.............. 14 1.2 IMPACTS OF HUMAN COLONISATION............................................................... 17 1.3 ARTHROPODS IN THE DIETS OF INTRODUCED PREDATORS....................... 19 1.4 IMPACT OF INTRODUCED PREDATORS ON NATIVE VERTEBRATES ......... 22 1.5 EFFECTS OF PREDATORS ON NATIVE ARTHROPODS.................................... 24 1.5.1 Research on Offshore Islands .......................................................................24 1.5.2 Research on the Mainland ............................................................................29 1.6 IMPACT OF HABITAT STRUCTURE ON ARTHROPOD POPULATIONS......... 32 1.7 ARTHROPODS AS INDICATORS OF ENVIRONMENTAL CHANGE................ 33 1.8 SUMMARY ................................................................................................................ 35 1.9 AIMS OF THIS RESEARCH ..................................................................................... 36 2 METHODS .........................................................................................................................38 2.1 INTRODUCTION....................................................................................................... 38 2.2 SITE DESCRIPTIONS................................................................................................ 39 2.2.1 Treatment Sites............................................................................................42 2.2.2 Control Sites ...............................................................................................45 2.3 ASSESSMENT OF SITE CHARACTERISTICS....................................................... 48 2.3.1 Vegetation Parameters .................................................................................48 2.3.2 Physical Parameters .....................................................................................48 2.3.3 Ground Cover..............................................................................................49 2.4 WEATHER MEASUREMENTS................................................................................ 50 2.4.1 Temperature ................................................................................................50 2.4.2 Rainfall.......................................................................................................50 2.5 POSSUM AND RODENT CONTROL AT THE TREATMENT SITES (LTFERP). 50 2.6 RODENT MONITORING .......................................................................................... 51 2.6.1 Previous Research........................................................................................51 2.6.2 This Study...................................................................................................55 2.7 POSSUM CONTROL IN THE WAITAKERE RANGES.......................................... 55 2.8 POSSUM MONITORING .......................................................................................... 56 2.8.1 Previous Research........................................................................................56 2.8.2 This Study...................................................................................................56 2.9 ARTHROPOD MONITORING.................................................................................. 57 2.9.1 Pitfall Traps ................................................................................................61 2.9.2 Sampling Regime ........................................................................................64 2.10 STATISTICAL ANALYSIS OF DATA..................................................................... 66 2.10.1 Ground Cover..............................................................................................66 2.10.2 Rat Tracking ...............................................................................................66 2 2.10.3 Pitfall Trap Samples.....................................................................................67 3 RESULTS............................................................................................................................ 68 3.1 KANUKA FOREST.................................................................................................... 68 3.1.1 Study Site Physical Characteristics ...............................................................68 3.1.2 Vegetation Assessment ................................................................................68 3.1.3 Rodent Monitoring ......................................................................................70 3.1.4 Ground Weta...............................................................................................73 3.1.5 Cave Weta...................................................................................................78 3.1.6 Carabid Beetles ...........................................................................................82 3.1.7 Prowling Spiders .........................................................................................87 3.1.8 Kanuka Forest Results Summary ..................................................................91 3.2 PODOCARP-BROADLEAF FOREST....................................................................... 95 3.2.1 Study Site Physical Characteristics ...............................................................95 3.2.2 Vegetation Monitoring .................................................................................95 3.2.3 Rodent Monitoring ......................................................................................97 3.2.4 Ground Weta...............................................................................................99 3.2.5 Cave Weta...................................................................................................99 3.2.6 Carabid Beetles .........................................................................................101 3.2.7 Prowling Spiders .......................................................................................103 3.2.8 Podocarp-Broadleaf Results Summary ........................................................105 3.3 TARAIRE FOREST.................................................................................................. 107 3.3.1 Study Site Physical Characteristics .............................................................107 3.3.2 Vegetation Assessment ..............................................................................107 3.3.3 Rodent Monitoring ....................................................................................109 3.3.4 Ground Weta.............................................................................................112 3.3.5 Cave Weta.................................................................................................112 3.3.6 Carabid Beetles .........................................................................................114 3.3.7 Prowling Spiders .......................................................................................117 3.3.8 Taraire Results Summary ...........................................................................119 3.4 OVERVIEW OF ARTHROPOD ABUNDANCE AT TREATMENT SITES ......... 121 3.5 POSSUM MONITORING ........................................................................................ 122 3.5.1 At the LTFERP .........................................................................................122 3.5.2 At the Control Sites ...................................................................................123 3.5.3 Possum Footprints on Rodent Tracking Cards used in 2005–06 at the Control Sites ...123 3.6 WEATHER MONITORING..................................................................................... 124 3.6.1 Rainfall Data .............................................................................................124 3.6.2 Temperature Data ......................................................................................124 4 DISCUSSION ................................................................................................................... 126 4.1 INTRODUCTION..................................................................................................... 126 4.2 RODENT MONITORING ........................................................................................ 127 4.3 IMPACT OF RODENTS ON ARTHROPODS ........................................................ 130 4.3.1 On Ground Weta .......................................................................................130 4.3.2 On Cave Weta ...........................................................................................132 4.3.3 On Carabid Beetles ....................................................................................133 4.3.4 On Prowling Spiders..................................................................................135 3 4.4 ARTHROPODS IN TARAIRE FOREST ................................................................. 136 4.4.1 The