As an indirect effect of consuming fruit, birds often transport plant seeds to locations distant from the original plants. This dispersal is critical for plants that cannot move their seeds without assistance. In the context of a community, the connections between birds and plants are analogous to social networks, with nodes representing plant species that are connected by the links (bird dispersal) between them. The arrival of invasive species can alter the connections between native species, disrupting these critical relationships. This project investigates how species invasions are altering the structure of seed dispersal networks in French Polynesia. Birds will be captured and fecal samples collected in order to characterize diet on two islands that vary in the degree of invasion by a fruit-bearing tree. Additionally, experiments with birds in aviaries will be used in order to discover how the abundance of an invasive species influences the dietary decisions of birds, and thus the role birds play in seed dispersal.
The control of invasive species is one of the most critical conservation issues facing resource managers globally. This project will inform invasive species control in French Polynesia through collaboration with local scientists and managers. The investigators provide data to two offices in the French Polynesian government. The project is also the first to gather systematic data on the status of a protected Fruit Dove, which is found on only a few islands in French Polynesia, providing information that is essential for conservation of this vulnerable species. Three French Polynesian and one American student will gain research experience while participating in field data collection, and one of the investigators is helping to develop curriculum and teaching in two classes of underprivileged 5th graders on the island of Moorea. The project is dedicated to developing close collaborative relationships with French Polynesian researchers, and provides tissue samples for the Moorea Biocode project, a program involving over 150 scientists from all over the world to DNA barcode every organism on the island of Moorea.
Species invasions are a particularly important threat to the biodiversity of islands ecosystems. Oceanic islands in the remote eastern Pacific contain some of Earth’s most vulnerable terrestrial ecosystems with large numbers of species that are have small restricted populations and rates of extinction that far exceed those of mainland systems. Introduced species in these novel communities often establish mutually beneficial relationships with other species, both native and introduced. Seed dispersal by birds is one such relationship that is critical for plant reproduction. When exotic species enter a community, they can disrupt seed dispersal relationships between native species causing cascading consequences for both plants and animals. There is a growing recognition that these changes cannot be fully understood without an approach which explicitly addresses interactions between species at the community level. This research uses the novel method of network analysis developed elsewhere to understand linkages between computers on the internet and between people in social networks to elucidate how the abundance of a highly invasive species influences the community-wide patterns of interaction between fruit-bearing plants and fruit-eating birds. The work is located on two biologically and geologically similar islands in French Polynesia that differ in the degree of invasion by Miconia calvescens, a highly aggressive fruit-bearing tree. The variation in abundance of this tree across sites provides an opportunity to investigate how the relative abundance of a single invasive species influences seed dispersal patterns at a community level. We have discovered that dispersal webs are smaller and less diverse on Tahiti which is much more highly invaded by Miconia than the nearby island of Moorea, indicating that the relative abundance of fruits in an environment is one important factor determining how and what birds consume. The implications of this research are that as ecosystems become more extensively invaded by fruit-bearing plants, we can expect that the impact of highly available fruiting resources is likely to cause shifts in the patterns of consumption of fruit by birds. These patterns may only be visible when entire communities of interacting partners are considered in concert, yet are critical to understanding how the regeneration of native plants will be affected in highly invaded ecosystems.
