Comparative effects of native frugivores and introduced rodents on seed germination in New-Caledonian rainforest plants

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Native frugivores play an important role in native plant community dynamics by participating in seed dispersal. Today many island forests are invaded by introduced omnivores, such as rats, but their role in dispersing native plants is still little known. Here, we evaluated whether native seeds from New-Caledonian rainforests can germinate after passing through an invasive rat digestive tract and compared seed germinability and germination time between seeds ingested by invasive rats and native frugivores. We offered native fruits of Ficus racemigera and Freycinetia sulcata to the rats Rattus rattus and R. exulans, three flying foxes Pteropus spp. and the pigeon Ducula goliath. Our results showed that seeds can germinate after passing through an invasive rat digestive tract, and suggest that rats can disperse seeds of both plant species. However, invasive rats may be less efficient than native frugivores, as more seeds were destroyed when passing through rat digestive tracts than through native frugivores, and because germinability was lower and germination time was longer for seeds passing through invasive rats than through native frugivores. The reduced efficiency of rats may result from their generalized diet, the structure of their digestive tract, and/or their feeding behavior. In New-Caledonian rainforests, dispersal services on both plant species are likely well fulfilled by flying foxes and Ducula pigeons, but rats do not seem to be as efficient dispersers. Consequently, management measures to protect native frugivores should help to conserve seed dispersal services.