Quantifying seed dispersal of matai (Prumnopitys taxifolia)
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
In New Zealand’s highly modified environment, it is unclear how ecological services function within modified habitats and with an altered suite of mutualists and predators. I used matai (Prumnopitys taxifolia) to investigate the status of dispersal including the range of native and introduced species involved, and to test the feasibility of using microsatellites (repetitive regions of DNA) to identify maternal origin of seeds and therefore measure dispersal. I isolated ten microsatellite loci, five of which were polymorphic. Across 20 adult matai on Banks Peninsula, none shared a multi-locus genotype across these five loci; this suggests that these loci will be sufficiently variable to allow the individual identification required for parentage analysis. Although logistic problems prevented full testing of the system, preliminary results suggest that these microsatellites will allow identification of the maternal parent of seeds genotyped from their seed coat. Seed traps and ground plots throughout forest fragments on the Port Hills found varying levels of insect (0–19%) and rodent (0–1.5%) pre-dispersal predation over two years; despite this, 19–55% of seeds caught beneath female matai trees had been consumed and excreted by a bird. The majority of seeds (98%) were caught within 55 m of the nearest female matai tree, with a maximum distance of 130 m, indicating dispersal was occurring within these sites. Through observations on fruiting trees, I found four bird species regularly visited and fed on matai fruits; native kereru (Hemiphaga novaeseelandiae) and bellbird (Anthornis melanura), and exotic blackbird (Turdus merula) and song thrush (T. philomelos). As expected, kereru performed the majority of feeding visits (50%), but surprisingly the two introduced species combined contributed 22% of the feeding visits. I argue that the prevailing methods for measuring avian frugivory systematically under-estimate the contribution made by introduced birds. This finding is important as Turdus species are abundant and widespread in New Zealand. Finally, I examined whether feral pigs (Sus scrofa) disperse seeds of matai. Both captive and wild pigs consumed matai seeds and excreted a proportion of these intact; germination rates of these seeds (57–68%) were comparable to hand-cleaned seeds (64%). This is the first demonstration of feral pigs dispersing the seeds of a New Zealand native plant. Large mammals such as pigs may provide long distance dispersal of fleshy-fruited species, which will be particularly important in today’s highly fragmented forests. Further dispersal research should consider the effects of these introduced avian and mammalian dispersers if we are to understand how ecological services are functioning amidst our modified environments.