Pollination performance and vulnerability to pollination breakdown of sixteen native shrub species from New Zealand.

Abstract

The reproductive biology of 16 native shrub species was studied in 34 populations to identify breeding systems, pollen limitation, local abundance, and population age structures. Seven of the study species are hermaphroditic, seven dioecious, and two gynodioecious. One of the 18 hermaphrodite populations (Alseuosmia macrophylla at Mamaku Plateau) had high levels of self-incompatibility and pollen limitation and mutualism failure was evident. In the gender-dimorphic taxa, two populations (Coprosma spathulata from Hakarimata and Cyathodes juniperina from Pukemokemoke) had high levels of pollen limitation and insect-pollinated species consistently ranked higher in a vulnerability assessment compared with wind-pollinated species. There was no significant relationship between natural fruit set and the distance to the nearest conspecific pollen in any of the study populations. Seedling recruitment was variable but evident in 32 of the 34 study populations and appeared to be related to availability of suitable habitat. The species we studied occur mostly on forest edges where they rely on disturbed soil and high light conditions for establishment, and edges may be important for successful reproduction of some native plants, especially shrubs. We have demonstrated that plants with self-incompatibility mechanisms and pollinator specialisation are at greater risk from pollen limitation and mutualism failure than self-compatible or generalist species.