The Impact of Non-Native Predators on Pollinators and Native Plant Reproduction in a Hawaiian Dryland Ecosystem

Dr. Christina Liang | USDA Forest Service



Oceanic islands are well known for their high endemism and unique biological diversity, which make them particularly susceptible to disturbances such as non-native species invasions. Such invasions can disrupt pollination services and result in negative impacts on native plant reproduction and genetic diversity. Non-native invasive predators (NIP) consume animal pollinators and, by doing so, reduce pollinator populations and possibly eliminate entire pollinator guilds. Loss of pollination services due to NIP is likely an important, although poorly understood, factor in both native plant conservation and management of long-term sustainability of native island ecosystems. This project will determine the impacts of NIP on native and non-native pollinators and pollinator services for at-risk as well as common native plant species in an invaded Hawaiian tropical dryland ecosystem. Specific objectives are to: (1) identify current pollinators and pollination effectiveness for focal plant species; (2) examine the diets of study site NIP (rodents, ants, and yellowjackets); and (3) apply common NIP control techniques to experimentally determine their effectiveness at reducing NIP populations and NIP impacts on pollination and native plant reproduction.

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Technical Approach

This project will combine field observation, experimental manipulation, and laboratory analysis to examine interactions between native plants, pollinators (native and non-native), and NIP. This combined approach will provide a comprehensive understanding of current pollination services in invaded landscapes. The work will take place in the Pōhakuloa Training Area (PTA) on the island of Hawaiʻi. The team will first combine field observations, pollination experiments, and surveys of pollinators and predators to assess existing pollination of wild individuals of the focal plants. Second, genetic testing of NIP gut contents will be used to develop dietary component lists for each NIP species in the study area. Third, independent and combined experimental removals of each NIP using common predator controls in replicated study plots will be performed. During 30 months of continuous NIP control, the team will evaluate pollination effectiveness for experimental plant individuals and examine densities of predators, pollinators, and other components of the arthropod community within the study sites. Finally, the team will assess the resilience of pollination processes over three to six months following cessation of NIP control treatments.

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By targeting an essential ecosystem service, this project will provide critical understanding for the management of native plants, including threatened and endangered species, within Department of Defense (DoD) holdings on invaded lands. Results will have relevance at the local scale by quantifying pollination effectiveness for focal plant species at PTA, assisting PTA managers and other local land managers with management of at-risk species under their jurisdiction. At the broader, Hawaiʻi-wide scale, the results will assess frequently utilized NIP control methods and identify predators that exert particularly strong impacts on pollination. At the Pacific region and global scales, the results will form the basis of a User’s Guide enabling land managers (including DoD managers on a diversity of islands) to evaluate pollination of native plant species, select appropriate management strategies for NIP, and determine when to intervene with active conservation methods such as hand-pollination for at-risk species. (Anticipated Project Completion - 2018)

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Points of Contact

Principal Investigator

Dr. Christina Liang

USDA Forest Service

Phone: 808-854-2650

Fax: 808-933-8120

Program Manager

Resource Conservation and Resiliency