Control of a native and introduced foundation species by marine and terrestrial enemies

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Overview: The morphology and structure of foundation species, such as trees and coral reefs, are strongly influenced by the animals that inhabit them. Since foundation species form the integral structure of habitats, changes caused by animals can elicit cascading effects to the rest of the ecosystem. Red mangroves are a critical foundation species that thrives in the ecotone between land and sea; thus, they are affected by a suite of marine and terrestrial herbivores and structure-modifying species. Damage by these species modifies growth and fecundity and is responsible for the complex architecture mangroves exhibit. When a foundation species is introduced without their natural enemies (such as herbivores, structure modifiers) they may experience enhanced growth, fecundity, and survivorship. This release from their enemies may explain why some invaders succeed in a new range. Red mangroves (Rhizophora mangle) were introduced to Hawaii from their native range (Caribbean) over a century ago. Here they exhibit rapid growth, high fecundity, and few enemies appear to control them. These mangroves convert native habitats (e.g. sand-flats, ponds) into dense thickets causing substantial changes to Hawaiian ecosystems. In this study, the fellow will (1) quantify the relative effects of different marine and terrestrial guilds in affecting growth, fecundity, and architecture of an important foundation species and (2) test a widely cited mechanism for successful invasions (Enemy Release Hypothesis). This project will use manipulative and natural experiments replicated across broad geographic ranges where mangroves are native (Caribbean) and introduced (Hawaiian Islands). The proposed sponsors, Celia Smith (University of Hawaii Manoa) and Mark Torchin (Smithsonian), will provide complementary training for the fellow and access to the logistical framework necessary to complete this project (e.g. Smithsonian field stations in Florida, Belize, and Panama). Intellectual Merit: Results from this project will broaden understanding of how habitat engineering and herbivory alters foundation species and community ecology and reveal the importance of natural enemies in controlling growth and architecture of introduced species. This project will determine how different multi-species assemblages alter the architecture of a foundation species between native and introduced ranges. This study will also answer other important questions such as: how do terrestrial species mediate habitat quality and quantity for marine species? And what is the relative importance of marine vs. terrestrial species in determining growth and architecture in foundation species in an ecotone? Finally, this study will test an important mechanism underpinning successful biological invasions. Broader Impacts: This project will broaden the participation of students from under-represented groups by integrating students directly in the research plan. Students of diverse backgrounds (79.2% non-Caucasian descent at University of Hawaii) will receive research training from seminar courses taught by the fellow. Select students will assist the fellow on international research trips and in Hawaii to participate in data collections. The fellow will also work within the former GK-12 framework of University of Hawaii to develop inquiry based curriculum for K-6 classes. The fellow will disseminate curriculum and research findings through online resources (STRI Bioinformatics website), scientific conferences, and through academic publications. Results from this project will inform management of introduced species and restoration efforts by revealing where managers could devote pest control efforts.