Joanna K Carpenter, Janet M Wilmshurst, Kim R. McConkey, Julian P. Hume, Debra M. Wotton, Aaron B. Shiels, Olivia R. Burge, Don R. Drake
Many animals have gone extinct since humans first set foot on islands. Conservation biologists worry that the loss of these species and their interactions with other species could have severe consequences for the health and resilience of island ecosystems. Much research in this area has focused on the extinction of mutualist species on islands – species that positively benefit each other, such as birds that eat fruit and disperse a plant’s seeds, or insects that consume nectar and pollinate flowers – and whether introduced species might compensate for their loss by performing the same services. However, very little is known about the loss of ‘negative’ interactions between species on islands, such as animals eating seeds for food (seed predation), parasitism, or animals preying on other animal species, even though these interactions are also vital parts of an intact ecosystem.
Our paper focuses on seed-eating animals that originally lived on three island biodiversity hotspots: New Zealand, Hawai’i, and the Mascarenes. Each archipelago had native seed predators, ranging from tiny finches (Hawai’i), to huge flightless moa (New Zealand), the gizzards of which could contain several kilograms of stones to grind up their food.
Today, between 63 and 89% of these native seed predators are extinct. The seed predators that now live on these islands are mainly introduced rodents, pigs, gamebirds (such as quails), and other new bird species.
Our research shows that most of these introduced seed predators are very different to the original seed predators in terms of the size and proportion of seeds they eat, the amounts of seeds in their diets, and the way they destroy seeds. Because of this, the introduced seed predators are not replacing lost seed predation interactions, and instead are probably introducing entirely new impacts for plants. This could result in them gradually restructuring forest communities by, for example, preferentially eating certain plants’ seeds.
Our research demonstrates that ‘negative’ interactions were a crucial part of island communities, and therefore should be considered when restoring these unique systems.