Effect of native and alien vertebrate frugivores on seed viability and germination patterns of Rubia fruticosa (Rubiaceae) in the eastern Canary Islands

Summary 1. This study shows the first results obtained concerning the relative importance and effect on the seeds of a particular plant species, Rubia fruticosa Ait. (Rubiaceae), of passage through the digestive tube of the three main groups of vertebrate seed dispersers: native reptiles and birds, and alien mammals. 2. Native birds and reptiles dispersed a high proportion of undamaged seeds of R. fruticosa . 3. In contrast, seeds defecated by the two alien mammals showed significantly greater proportions of damaged seeds. Seed viability was much higher for reptiles and birds than for mammals, which was consistent with germination results. 4. Ingested seeds had a significantly thinner coat than uningested control seeds. Seeds that had passed through native dispersers had a significantly thicker coat than those passed through one of the alien mammals (the squirrel). 5. Considering both quantitative and qualitative components of seed dispersal, we conclude that native reptiles and birds are the most important seed dispersers in this multidisperser system.