Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

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Rhamnus, rats and rangitoto.


Rhamnus alaternus L. (evergreen buckthorn or rhamnus) is a major threat to native vegetation on Rangitoto, an extinct volcanic island off the Auckland waterfront. Possums (Trichosurus vulpecula, Kerr, 1792) and wallabies (Petrogale penicillata penicillata, Gray, 1827) have been eradicated from the island, and eradication of rats (Rattus spp.) is being considered. This study was initiated to gain information that might help that decision and in the continuing control of rhamnus. We measured the age of plants when they first bore fruit, the size of fruit and number and size of seeds in the fruit, and tested whether the seeds would pass unscathed through the digestive system of a Norway rat (Rattus norvegicus, Berkenhout, 1769). The youngest plants to bear fruits were mostly three years old. The fruit were comparable in size to those found in Israel, but bigger than those in the Balearic Islands, although there is probably considerable variation in fruit size across the species natural range. Few rats ate a few seeds, but no entire seeds were found in the rats' faeces.