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Restoring Function to a Novel Ecosystem in the Presence of One of the World's Most Destructive Invasive Species
Dr. Haldre Rogers | Rice University
Species invasions are threatening ecosystems worldwide. They not only simplify and change communities, creating novel ecosystems, but also threaten important ecological processes that maintain these systems. Island ecosystems are at particular risk of losing ecological function due to invasive species because of their isolated evolutionary history. The Department of Defense (DoD) is responsible for management of extensive areas of land, including land on Pacific islands that are novel ecosystems caused by species invasions and challenge DoD’s mission to “sustain the long-term ecological integrity of the resource base and the ecosystem services they provide.” The return of highly degraded systems to their original state may not be financially feasible or even technically possible, but these ecosystems still have tremendous value. Managing them to maximize that value requires an understanding of how these systems function, and how they can serve the DoD mission. DoD is mandated to maintain habitat for threatened and endangered species, regardless of the state of the system. In highly degraded systems, such as the island of Guam where virtually all native birds have been extirpated and the cause of species loss and species endangerment (the brown treesnake [Boiga borealis]) is still present, managers may need to work to recover function without attempting to replicate the original ecosystem.
This research will focus on a critical ecological process in tropical systems—and likely the furthest reaching ecological casualty of the brown treesnake invasion on Guam—animal-mediated seed dispersal. The objective of the project is to assess if and how seed dispersal could be returned to Guam’s forests. The aim is to first understand how dispersal services have been disrupted, then identify the role that native and non-native species could play in restoring seed dispersal despite the continued presence of brown treesnakes. Researchers will investigate the limitations of different restoration options and develop a “User’s Guide” for managers so they may weigh the advantages and disadvantages of each approach.
The research will be conducted in karst limestone forest—the primary forest type used by native, fruit-eating birds and bats—and in degraded forest on Guam, as well as on the nearby islands of Saipan and Rota, which have relatively intact frugivore communities. The project team has identified four steps to the process of restoring function to Guam’s forests. First, the team will determine how loss of frugivores has impacted ecological function in Guam’s forests and identify the consequences for long-term forest health. To do this, the team will investigate the impact of disperser loss on the 21 most common fleshy-fruited forest tree species and on forest regeneration in degraded habitat, followed by modeling what these forests may look like in the future. Second, the team will determine the ecological role of frugivorous species that may be used to restore ecological function, including native species (both extant and extirpated from Guam) and existing non-native species. The team will use foraging observations and fecal analyses on Saipan and Guam to determine which tree species are dispersed by which frugivore and, along with germination trials, the relative importance of each frugivore species. Using telemetry, the team will determine movement patterns for the various species to predict the area over which an individual could potentially provide dispersal services and whether species move seeds to degraded forest. Third, the team will address challenges that might be faced when attempting to re-establish avian frugivores or expand the range of existing frugivores on Guam and evaluate the benefits and dangers of using extant non-native species to restore ecological function. Fourth, the team will identify candidate frugivore assemblages based upon the results from the studies described above and then use conservation planning tools to identify spatially explicit snake control strategies that would maximize the function provided by the disperser assemblage.
The results of this project will provide resource managers with DoD and other agencies on Guam important insight on the long-term consequences associated with the loss of seed dispersers, and guidance in the possible options for recovering ecological function in Guam’s forests. The modeling efforts will inform decisions on where to strategically situate planned and anticipated snake fences. Although the research will be directly applicable to the resource managers in the Mariana Islands, the overall strategy will be a useful guide for management of any highly degraded land, providing a roadmap for restoring ecological function in other novel ecosystems. (Anticipated Project Completion - 2020)