Birds and mammals vital for plant survival

Research has shown that the loss of native birds and bats from New Zealand ecosystems can have serious consequences for the survival of native plant species.

Dr David Pattemore, a scientist at Plant & Food Research, has undertaken research on the pollination of native New Zealand plants. His research shows that birds and mammals play a critical role in ensuring native plants are pollinated, with implications for the ongoing viability of plant populations.

Dr Pattemore’s research, undertaken as part of his PhD study at Princeton University, compared pollination of native plants at sites in the upper North Island to pollination on Little Barrier Island - the only site where all native bird and bat pollinators still occur. The research focused on the pollination of three native plants – Pohutukawa (Metrosideros excelsa), Rewarera (Knightia excelsa) and a hebe species (Veronica macrocarpa) – and found that on Little Barrier Island, pollination of these plants relied on the presence of native birds and the Short-tailed bat. Outside of Little Barrier Island, levels of pollination for Rewarera and the hebe species were maintained, but there was a decline in pollination for Pohutukawa. In the absence of native birds and mammals, these levels of pollination were maintained by the presence of the recently arrived silvereye and the invasive ship rat.

“Birds, bats and other mammals feed on the nectar from flowers, but until recently little was understood about the importance of this activity in assisting plant pollination,” says Dr Pattemore. “The loss of native vertebrate species, such as birds and bats, has a major effect on our ecosystems. However, for some plants, introduced species are able to partially compensate for the loss of native pollinators.

“This research has outlined the importance of native pollinators, particularly of the endangered Short-tailed bat, in ensuring the health of our plant populations. The contribution of silvereyes and rats has probably disguised the critical importance of native birds and bats by maintaining pollination where it would otherwise have been severely reduced. However, these new species can never fully replace our native species, and, especially in the case of the rat, their negative impacts mean that it is still a priority to control or eradicate these invasive species where possible.”

“The clear implication is that the restoration of native forest systems cannot be considered to be complete until native bird and bat populations have been re-established,” states Dr Pattemore. “However, this restoration process must consider critical ecosystem functions, such as pollination, in managing invasive species to ensure a healthy forest environment is maintained. If not, the loss of all bird and mammal pollinators in our forest could have serious consequences.”

Dr Pattemore’s research is published in the Proceedings of the Royal Society B journal and it was funded by the High Meadows Foundation, the Todd Foundation for Excellence, Princeton University and Auckland Regional Council. Dr Pattemore was a Fulbright New Zealand/MoRST award recipient.

Videos summarising the findings of this paper can be found at www.youtube.com/plantandfood.