Seed Dispersal Networks and Novel Ecosystem Functioning in Hawaii

Dr. Jeffrey Foster | Northern Arizona University



The Hawaiian Islands are both the extinction and invasive species capitals of the world. The result has been Hawaiian ecosystems fundamentally changed in form; that is, ecosystems replete with a mix of novel and native species. Most native Hawaiian plant species are bird-dispersed, yet no native avian dispersers remain in most Hawaiian ecosystems. Thus, ecosystem functioning will only be maintained by the handful of non-native invasive vertebrate dispersers that now reside on the islands, most of which are birds. In this context, research efforts must shift focus to non-native bird species (and potentially non-native rats) and the potential for these species to maintain native plant communities under current and predicted environmental conditions. To successfully manage and preserve Hawaiian terrestrial ecosystems, it is necessary to identify and characterize non-native invasive species (NIS) that are dispersers of desired plant species, determine their role in ecosystem function, and improve non-native plant management plans, while facilitating the recovery of native threatened, endangered, and at-risk plants.

The overarching objective of this project is to determine the effects of plant disperser traits, competition, predation, and landscape features on native and non-native plant dispersal and recruitment. This will be accomplished through the integration of field-based data collection, field experiments, and ecological modeling to describe and quantify seed dispersal in novel Hawaiian communities. Essential outcomes of the research include determining how well different species of non-native birds disperse native plant species across environments, whether non-native rat species have a cumulative positive (via seed dispersal) or negative (via predation on bird seed-dispersers and/or via seed predation) impact on communities, and creating predictive models to be used for management in novel environments and under future abiotic and biotic scenarios. The research is intended to provide the Department of Defense (DoD) and the scientific community with the essential tools for managing and maintaining native plant communities in Hawaii and other Pacific Islands.

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Technical Approach

Multi-species interactions are crucial to the maintenance of ecosystem structure and function. This is especially true for seed dispersal networks, where interactions among seed dispersers, plants, and predators influence the efficacy of seed dispersal and ultimately community structuring. Research on seed dispersal by birds has largely been restricted to individual species and focused on the identification of seeds in their diets and their role in plant dispersal. Thus, current research does not reflect the reality of multiple interacting native and non-native species (birds and rats), relative disperser effectiveness, and the capability of non-native dispersers to maintain native plant communities in severely altered ecosystems. This project will incorporate these interactions through the comprehensive examination of seed dispersal networks comprised of seven non-native invasive bird species, two common non-native invasive rat species, seven non-native invasive plant species, and eight ecologically important native plant species. Collection of field-based variables including species abundance, reproduction, predation, inter- and intra-specific competition, diet preferences, disperser behavior, gut passage times, and seed germination rates will be used to create and parameterize movement ecology models for assessing seed dispersal across heterogeneous landscapes. When integrated with high resolution vegetation and elevation data in a landscape modeling framework, these individually based movement ecology models can be used to estimate and predict how interactions within seed dispersal networks influence dispersal and recruitment probability of native and non-native plants.

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This project examines multiple seed dispersal networks comprised of interacting native and non-native plant and vertebrate species across several trophic levels and ecological contexts to develop predictive models for assessing recovery and maintenance of key ecological processes including dispersal, recruitment, and establishment of threatened, endangered, and at-risk plant species. These predictive models, capturing a range of elevation and precipitation gradients and utilizing generic bird (e.g., mass, life history, dietary) and plant (e.g., size, color, fruiting height) traits, are particularly useful as they can be applied to other similar Pacific Island habitats with different bird and plant species. Importantly, this work will provide DoD and adjacent resource managers with the tools to go beyond current NIS control and eradication efforts in Hawaii by providing meaningful predictive measures of native and non-native plant dispersal and establishment. In this context, the results will enable DoD to match environmental objectives with agency needs and to provide leadership on responses to global climate change and the recovery of native threatened, endangered, and at-risk plants in the Pacific Islands. (Anticipated Project Completion - 2018)

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Points of Contact

Principal Investigator

Dr. Jeffrey Foster

Northern Arizona University

Phone: 928-523-0694

Program Manager

Resource Conservation and Resiliency