Jonas Kuppler, Maren K. Höfers, Wolfgang Trutschnig, Arne C. Bathke, Jesse A. Eiben, Curtis C. Daehler and Robert R. Junker
The fascinating landscapes of the Hawaiian Islands harbor unique ecosystems with plants and animals that can be found nowhere else in the world. Over the last centuries, thousands of so-called exotic species (i.e. species that do not naturally occur in an area) have been introduced to and spread throughout the islands. These exotic species can severely disturb native communities and cause the displacement of native species due to their ability to rapidly and efficiently exploit a broad spectrum of resources. In case of flower-visiting animals, resource use and its overlap between species is often estimated based on the number of (shared) plant species. However, whether a flower visitor is able to exploit a plant resource is delimited by floral traits such as morphological barriers, a specific color or scent, and not by the species identity.
In this study, we introduce a novel approach to estimate the range of resources used by an animal and their overlap in resource use with other species, based on the morphology and scent of flowers the animal exploits. This approach provides a more precise and mechanistic understanding of species’ resource requirements than using plant species identity only. In the Hawaii Volcanoes National Park, we measured the floral morphology and scent of a large number of native and exotic plant species and recorded flower-visitor interactions. Our results show that exotics were able to utilize a broader range of resources, which was additionally exemplified by the absence of native flower visitors on exotic plant species. Especially, exotic species utilize a broader range of different smelling flowers. Further, exotic species shared less of their resource with natives than the other way around.
The differences in resource use and overlap of native and exotic flower visitors suggests a potential advantage in resource exploitation of the latter, potentially explaining their success in Hawaiian ecosystems. Predicted range expansion of exotic plant and animal species may further increase competition for, and reduce the availability of, resources for native animals. This may lead to further declines of native species and increasing threats for Hawaiian ecosystems.
Photo caption: Top: Landscape Hawai’i Volcanoes National Park. Middle: Native Hylaeus bees visiting a flower of Metrosideros polymorpha. Bottom: Native Himatione sanguinea visiting flowers of Sophora chrysophylla. Photocredit: Robert R. Junker (top, middle) & Jonas Kuppler (bottom)