Legacy of loss: seed dispersal by kererū and flightless birds in New Zealand.
| dc.contributor.author | Carpenter, Joanna K. | |
| dc.date.accessioned | 2019-05-20T20:09:19Z | |
| dc.date.available | 2019-05-20T20:09:19Z | |
| dc.date.issued | 2019 | en |
| dc.description.abstract | The New Zealand avifauna has experienced dramatic losses since human arrival. I investigated how these declines and extinctions have affected seed dispersal. My first aim was to assess the current state of kererū (New Zealand pigeon, Hemiphaga novaeseelandiae) populations, by measuring trends in kererū detections and dispersal quantity of six plant species at Pelorus over three decades. Kererū detections declined significantly over the period, but there was no overall worsening in dispersal quantity. This is probably because kererū numbers did not change significantly during the autumn fruiting season, and other birds contributed to the dispersal of smaller-seeded species. Secondly, I assessed whether the extinction of moa (Dinornithiformes), New Zealand’s largest herbivores, created a ‘gap’ in the dispersal of large seeds. I compared the seed remains found in 152 moa coprolites and 23 subfossil moa gizzards. While large seeds were present in 48% of moa gizzards, the coprolites had an extremely finely ground consistency and contained no seeds larger than 3.3 mm. Since the powerful grinding in moa gizzards meant large seeds were predated, not dispersed, moa extinction has not reduced dispersal (except for some herbs and shrubs whose small seeds reached coprolites intact). Thirdly, I investigated the role of an extant flightless bird, the weka (Gallirallus australis), in the dispersal of hīnau (Elaeocarpus dentatus). I measured hīnau dispersal from the canopy and the ground at two mainland New Zealand sites and two island bird sanctuary sites. I found that canopy fruit handling rates were low even on islands, which suggests that hīnau may be adapted for ground-based dispersal by flightless birds. Ground-based dispersal of hīnau was low on the mainland (4% seeds dispersed) compared to islands (76% dispersed), due to low frugivore numbers on the mainland. Weka conducted the majority of dispersal on islands. Fourthly, I assessed the seed dispersal effectiveness of weka. I estimated the seed retention times of weka for hīnau and miro (Prumnopitys ferruginea), using PIT-tagged seeds. Weka had the longest avian seed retention times ever recorded (means of 38.5 hours for miro and 125.2 for hīnau). I obtained high-resolution weka movement data by GPS tagging 39 birds over three sites, then combined movement and seed retention time data in a mechanistic model to assess how far weka disperse hīnau and miro seeds. Weka dispersed 93-97% of seeds away from the parent canopy, with 1% of seeds dispersed >1 km. My findings demonstrate that unexpected bird species are providing important seed dispersal services, and that New Zealand seed dispersal networks may therefore be less resilient to frugivore loss than they initially appear. Fortunately, the key flightless avian disperser identified in my results is still extant, meaning that restoration of this ecosystem service is possible. | en |
| dc.identifier.uri | http://hdl.handle.net/10092/16731 | |
| dc.identifier.uri | http://dx.doi.org/10.26021/7154 | |
| dc.language | English | |
| dc.language.iso | en | |
| dc.publisher | University of Canterbury | en |
| dc.rights | All Rights Reserved | en |
| dc.rights.uri | https://canterbury.libguides.com/rights/theses | en |
| dc.title | Legacy of loss: seed dispersal by kererū and flightless birds in New Zealand. | en |
| dc.type | Theses / Dissertations | en |
| thesis.degree.discipline | Ecology | en |
| thesis.degree.grantor | University of Canterbury | en |
| thesis.degree.level | Doctoral | en |
| thesis.degree.name | Doctor of Philosophy | en |
| uc.bibnumber | 2733410 | |
| uc.college | Faculty of Science | en |