Jo Carpenter with a kakapo, a native seed predator endemic to New Zealand. Credit: Theo Thompson
Jo Carpenter with a kakapo, a native seed predator endemic to New Zealand. Credit: Theo Thompson

Dr. Jo Carpenter, a postdoctoral researcher at Manaaki Whenua – Landcare Research discusses with us her recently accepted article, “The forgotten fauna: native vertebrate seed predators on islands”, as well as her favourite part about being an ecologist and conservationist.

What’s your paper about?

Hawaiian palila, a critically endangered seed predator that specialises on seeds of Sophora chrysophylla. Credit: Jack Jeffrey Photography.
Hawaiian palila, a critically endangered seed predator that specialises on seeds of Sophora chrysophylla. Credit: Jack Jeffrey Photography.

Our paper highlights the original vertebrate seed predators that occurred on three iconic archipelagos (New Zealand, Hawaii, and the Mascarenes), and assesses whether new introduced seed predators are likely to be functionally compensating for the loss of the original seed predators. We found that each island group once supported between 19 and 24 species of avian seed predators, but now between 63 and 89% of those species are extinct. These islands now predominantly contain introduced seed predators, such as rats, pigs, and quails. Although there were several examples where the introduced seed predators were functionally similar to the extinct seed predators, most introduced species are functionally different to the extinct species, and therefore may be introducing novel seed predation pressures for island plants.      

What is the background behind your paper?

Island ecosystems have suffered many extinctions in recent centuries, and with these species extinctions comes the loss of interactions between species. Sometimes, the loss of these interactions can have cascading impacts for ecosystems. For that reason, there has been a flurry of fascinating research examining the loss of mutualistic interactions on islands (in particular pollination and seed dispersal), and whether new introduced species might be able to compensate for the loss of the original endemic mutualists, by carrying out the same functions. But very few studies have investigated the loss of insular antagonistic interactions – like seed predation, herbivory, or parasitism – even though these interactions were also an intrinsic and important part of these ecosystems.

Does this article raise any new research questions?

Santalum paniculatum seeds destroyed by rats in Hawaii. Credit: Don Drake.
Santalum paniculatum seeds destroyed by rats in Hawaii. Credit: Don Drake.

Yes! We are hoping that this paper can act as a springboard for more detailed, system-specific research into the loss of seed predation interactions on islands. For example, we focused on vertebrate seed predators in our paper, but we know that invertebrate seed predators can also be extremely important – it would be fascinating to know more about how invertebrate seed predator faunas have changed over time. Another valuable research avenue would be to understand how contemporary seed predation interacts with all the other ecological changes that island plant communities have suffered, such as lost seed dispersal and pollination. We hypothesize in our paper that large-seeded species may be particularly at risk, as they appear to be vulnerable to seed predation by introduced seed predators (such as rats), while simultaneously being more likely to undergo dispersal failure due to the disproportionate loss of large-gaped frugivores on islands. 

Why is it important?

Many of the species that have been introduced to islands are seed predators, but with the exception of rats and to some extent pigs, we know very little about their impacts, and how their impacts compare to those of lost native seed predators. Seed predation can have a huge influence on plant community structure and successional pathways, so understanding how these interactions have changed on islands over time is really important for understanding the pressures shaping insular plant communities today.

Did you have any problems setting up the experiment/gathering your data?

Painting showing the extinct broad-billed parrot, a seed predator from the Mascarenes. Credit: Julian Hume
Painting showing the extinct broad-billed parrot, a seed predator from the Mascarenes. Credit: Julian Hume

I think gathering data for extinct species is always going to be fraught with difficulties! Luckily, in New Zealand at least we have an incredible fossil record which allows some deeper inferences into what extinct species were up to. For example, people have found over 150 coprolites (subfossilied faeces) belonging to moa species (extinct flightless birds ranging in size from 15 to 200 kg). From these coprolites, palaeoecologists have reconstructed a remarkably comprehensive picture of moa diets, which helps to elucidate their roles as both seed predators and dispersers. 

Were you surprised by anything when working on it?

I was a little shocked at the magnitude of extinctions that had taken place across the vertebrate seed predator faunas. We obviously expected that there would have been quite a few losses, but we discovered that only 12 species are still extant, out of the original 62 species that were found across the three island groups. And of those 12 extant species, most are functionally extinct across most of their native range.

What are you currently working on?

I’m working on a medley of diverse research projects at the moment, ranging from investigating ship rat abundance across elevational gradients, to collaborating with Maori (the indigenous people of New Zealand) to evaluate how they can re-establish cultural keystone species in their forests. The overarching goal is to be able to predict rat dynamics across all of New Zealand’s forest types so that we can make the most effective conservation interventions to save our native bird species.

What’s your current position?

I’m currently a post-doctoral researcher at Manaaki Whenua – Landcare Research, a Crown Research Institute in New Zealand.

What project/article are you most proud of?

For my PhD, I carried out a study examining seed dispersal of a New Zealand tree called hinau, which has a mysterious dispersal syndrome where its fruits drop to the ground when they are ripe. I found that most hinau fruits were being dispersed by an unlikely candidate: the New Zealand weka, an endemic flightless rail. Weka are threatened, but they are also somewhat maligned in New Zealand conservation circles because they are an omnivorous bird which sometimes preys on other threatened species. I discovered that weka are an important yet underestimated seed disperser for several plant species, as they hoover up lots of fruit from the forest floor, and move surprisingly large distances for a flightless bird. As weka are frequently excluded from restoration projects, I hope this research will help to create a more nuanced view of this charming yet controversial species.

What is the best thing about being an ecologist?

Spending time in wild, remote places that most people never get to see. I think it’s definitely the days where I’m cruising around doing fieldwork in a stunning landscape that I feel like I surely have the best job in the world!

Read the paper in full here.