CAREER: Using a multilayer plant-pollinator and fruit-frugivore network along a defaunation gradient to understand the combined influence of mutualisms on forest communities

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Plants require pollination and seed dispersal for regeneration, and many species rely on animals for both of these processes. Approximately 90% of plants are animal-pollinated, and 75-90% of tropical forest trees are animal-dispersed. However, research often focuses on these two interactions in isolation, even though global change drivers like invasive species, habitat degradation, and overharvesting have broad effects on animals. These effects could then cascade to affect pollination and dispersal of plants. This project identifies the plant-pollinator and plant-seed disperser interactions in native limestone forest of the Mariana Islands in the Western Pacific. The project will test whether joint consideration of pollination and seed dispersal improves predictions of which plant species are most dependent on animals and which animals are most critical. In addition, the research takes advantage of a defaunation gradient across the islands, ranging from a mostly intact animal community to an extremely degraded community. This gradient allows researcher to compare predicted impacts on plants of animal extinction to actual changes in plant communities. These results will be important for guiding conservation and restoration actions in areas where pollinator and disperser species are in decline. Finally, the lead researcher will build a mentoring network for Pacific Islander undergraduate and graduate students, high school teachers, and postgraduate technicians, develop a high school science module and after-school program in the Mariana Islands, and share scientific results with land managers in the Islands to inform management decisions. The project builds on the recent development of metabarcoding methods, which facilitate sampling of species interactions at the community-level, and multilayer species interaction network approaches, to identify the role of individual species across interaction types (i.e. pollination and seed dispersal). The research team will sample pollen from invertebrate and vertebrate pollinators and make observations of pollinator visitation to 15 common forest tree species on the islands of Saipan (fauna intact), Rota (partially defaunated), and Guam (defaunated) in the Western Pacific. The researchers will conduct a pollination experiment to determine how much each plant species depends on pollinators, and use stable isotopes to determine how much pollinators depend on plants. The plant-pollinator network will be compared to a fruit-frugivore network for the same forest communities compiled using previously collected data. Using these two networks, the researcher will compare species' roles across these two interaction types and identify changes along the defaunation gradient. Finally, both networks will be combined into a single multilayer network to identify patterns that emerge only when multiple interaction types are considered simultaneously. These results will advance understanding of the impact of population declines and extinctions on forest communities, and provide actionable recommendations for restoration in the Mariana Islands. This project is jointly funded by the Division of Environmental Biology/Population and Community Ecology program and the Established Program to Stimulate Competitive Research (EPSCoR).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.