The decline of the natural ecosystem on the Ogasawara Islands caused by invasive species has been an important environmental problem and projects for eradicating invasive species are currently underway. Some invasive species have proliferated in the host environment and are affecting the material cycle in the ecosystem. If the invasive species were removed from the environment, the material cycle of the ecosystem may be altered and native species that should be protected may be negatively affected. After the introduction of invasive alien species, namely goats and rats, the vegetation declined on Nakoudojima Island, an island that belongs to the Ogasawara Islands. Therefore, in this study, a mathematical model was developed to simulate and analyze the ecosystem changes that occurred following the eradication of goats and rats. When only rats were eradicated, the island's vegetation changed to grassland but revegetation was delayed and the biomass of the native animal species did not recover significantly. When only goats were eradicated, the vegetation recovered and the biomass of the native animal species increased; however, the island became forested and many native herbaceous plant species became extinct. When goats and rats were eradicated simultaneously, the vegetation recovered and the biomass of the native animal species increased; however, the ecosystem became very unstable and two extreme results were obtained – the vegetation of the entire island changed to either forest or grassland. The results of this study suggest that instead of simply eradicating invasive species, it is necessary to monitor post-eradication changes in the ecosystem and take adaptive measures as required.
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