Threats from alien plant species in the Galápagos Islands.
Changes in the number of alien plant species on the Galapagos Islands and in the number which have become naturalized or invasive since records were first published are reviewed. The results indicated that there are now 438 introduced species representing 45% of the total flora; 2.5% of the alien species and 5.6% of the naturalized alien species, are aggressive and represent a threat to indigenous ecosystems. The invasive species are identified as Psidium guajava [guavas], Rubus niveus, Cinchona succirubra [C. pubescens], Lantana camara, Kalanchoe pinnata, Pennisetum clandestinum, P. purpureum, Cedrela odorata, Eugenia jambos [Syzygium jambos], Passiflora edulis [passion fruits] and Cestrum auriculatum. The origins of the species and the correlation of species numbers with the human population over time are considered. Problems posed by introduced species and the need to limit further introductions are discussed.