Current rates of fruit removal and seed dispersal in NewﾠZealand fleshy-fruited mountain plants
- School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch 8140, NewﾠZealand
The New Zealand mountain flora is rich in fleshy-fruited species but many terrestrial frugivorous birds are extinct or declining, potentially putting seed dispersal mutualisms at risk. To determine whether fruits are currently being removed by animals, we measured removal rates of eight fleshy-fruited mountain plant species from five families over two fruiting seasons, at two sites in inland Canterbury. We compared fruit removal rates within cages (no animal access to fruits), on unmanipulated plants (open-access to fruits by all animals), and within lizard-only cages (large mesh). For the eight species, unmanipulated fruit removal rates were generally high, with overall percent fruit removal by the end of autumn ranging from 67% to 99% (mean 81%) in open-access treatments. Effects of cage treatments were significant for seven of the eight species, with 58–75% removal (mean 62%) in lizard-only treatments and 23–79% (mean 40%) in animal-exclusion cages. The largest difference in fruit removal between open-access and cage treatments was for the montane shrub Aristotelia fruticosa (98% vs 5% respectively) and the smallest was for Coprosma petriei (81% vs 65%, cage treatment effect non-significant). On average, fruit removal inside lizard-access cages was just over half of that on open-access plants, suggesting that lizards can move many fruits. Delays in fruit removal are unimportant provided that most fruits are removed before they rot, and levels of final fruit removal seen in this study provide no evidence for large-scale dispersal failure despite changes to the disperser fauna.