Progress in understanding pollination systems in New Zealand

Abstract

Pollination in New Zealand, an isolated oceanic archipelago in the Southern Hemisphere, has previously been characterised as having low rates of self‐incompatibility and a lack of specialised pollination, as well as little pollinator dependence. These features have been interpreted as supportive of “Baker's Rule”, which suggests that long‐distance colonisation selects for breeding systems that do not require biparental mating. However, we show that recent studies of the angiosperm flora reveal sexual systems (sexual dimorphism, self‐incompatibility, monoecy, dichogamy, and herkogamy) that usually involve a dependence on pollen vectors. The level of self‐incompatibility in the flora, though still poorly known, should be regarded as moderate rather than unusually low (about 36% of hermaphrodite populations tested are strongly or partially self‐incompatible), though many more species remain to be tested. As found elsewhere, incompatibility is higher in the trees and shrubs (around 80%) compared with herbs (21%). Moreover, high rates of autonomous selfing have been demonstrated empirically in only 21% of the self‐compatible species, demonstrating that they are not regular selfers. The pollinator dependence that these features impose makes much of the flora vulnerable to declines in pollinator service. Pollination systems in New Zealand have been characterised as unspecialised, imprecise entomophilous systems that correspond to the predominance of small white or pale flowers with dish or bowl shapes. We use a two‐tiered conceptual framework incorporating a coarse‐scale blossom class analysis and a finer scale syndrome concept analysis to assess the level of specialisation in plant‐pollinator relationships of New Zealand. Within each of the syndromes is a continuum of blossom classes: open‐, directed‐, and closed‐access. Highly specialised systems are found in closed‐access blossoms but they are not common in New Zealand (e.g., Solanum, Carmichaelia, orchids, and mistletoes). Large directed‐access blossoms are primarily associated with bird pollination but certain small entomophilous blossoms, called “knob” blossoms (Pseudopanax, Geniostoma), are also important for perching birds and may be considered ornithophilous. Bats and lizards play a minor role in pollination. Moth pollination is not well studied and may reveal cryptic specialisation based on scent. The majority of pollination systems in New Zealand correspond to the “small bee syndrome”, which is a generalised bee‐pollinated system common elsewhere and includes visits from flies and other diverse insects. Naturalised exotic bees may have both positive and negative effects on indigenous pollination systems and could play a significant role in invasive mutualisms in which some weeds are specialised to their services. Future research in New Zealand pollination and breeding systems needs to focus on endangered mutualisms, particularly in birds; on invasive mutualisms, particularly for offshore islands; and on community analyses that evaluate exotic‐indigenous interactions and the potential for specialisation in the poorly known insect pollination systems.