Abstract
New Zealand’s flora includes approximately 50% naturalised introduced flowering plant species and many have established in alpine and montane areas forming novel communities along with introduced pollinating insects. Indigenous New Zealand alpine and montane plant-pollinator communities are comprised of small, pale coloured flowers which rely on pollination services along with mainly unspecialised solitary pollinating insects. This unusual combination may make New Zealand alpine and montane plant-pollinator communities particularly vulnerable to changes in plant-pollinator network dynamics caused by the integration of non-native pollination mutualists. This is the only study known to date exploring the impact of introduced flowering species on native pollination networks in alpine and montane New Zealand.
Both native and introduced flowering species were assessed for attractiveness, floral rewards and accessibility to pollinators as well as temporal and spatial availability along an altitudinal gradient. Data based on over 338 hours of observations were used to analyse pollination networks and assess pollinator behaviour in a range of weather conditions. Additionally, experimental flower choice arrays were used to ascertain pollinator preferences for flowering species. The reproductive success of native flowering species in the presence of introduced flowering species was tested by measuring seed set.
Results showed that many introduced flowering species successfully integrated into native plant-pollinator networks. Some introduced flowering species augmented floral resources, filled temporal gaps in flowering and were highly connected into pollination networks, which may have been due to high quality and quantity of floral rewards. Despite this, some introduced flowers with specialised floral architecture excluded many native pollinators; these flowers were foraged on by introduced social bees creating compartments within pollination networks. Native flies and native solitary bees were important flower visitors and demonstrated differing behaviour with respect to flower choices and weather conditions. In 4/11 (36%) experimental flower choice arrays, introduced flowering species were preferred when compared with native flowering species by native pollinators. No native flowers were preferred in experimental choice arrays. However, seed set of native flowering species was found to be unaffected or increased by the presence of introduced flowering species.
Overall, introduced flowering species did not appear to have a detrimental effect on native flowering species or native pollinators in this study but provided additional community resources, and in one case facilitated pollination. Differing responses and behaviour of pollinating insect taxa highlight the importance of maintaining pollinator diversity for community resilience to climate change and other ecological perturbations. However, since results showed that introduced flowering species were preferred when compared with native flowering species in some contexts by native pollinators, introduced flowering species have the potential to affect the pollination of native flowering species if they increase in dominance in alpine and montane pollination communities. Effects are likely to be dependent on local neighbourhood flowering context as well as pollinating insect taxa present and could include facilitation of pollination of some native flowering species.