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Abstract
Insects associated with cycad cones within the Cycas rumphii and the Zamia pumila species complexes were examined relative to colonization predictions based on island biogeography theory. Both of these cycad groups disperse via ocean currents and are distributed across Indo-Pacific and Caribbean islands, respectively; thus they are suitable subjects for testing these predictions. Distance from the mainland source, age of island, and age of pollinator lineage are suggested as main predictors of whether island cycads are colonized by mainland pollinators. The beetle pollinator, Pharaxonotha (Erotylidae), believed to have an ancient association with cycads, is widely distributed on mainland Zamia species and on the most distant Caribbean islands inhabited by this cycad. In contrast, the genus Rhopalotria (Belidae), a younger lineage of Zamia beetle pollinator present in Mexico and Central America, is found only on islands closer to Mexico. The primary cone insects of mainland Asian Cycas species are Tychiodes (Curculionidae) and Erotylidae beetles closely related to Pharaxonotha. Tychiodes beetles are found on C. zeylanica, a species within C. rumphi complex inhabiting the Andaman and Nicobar Islands ca. 600 km from continental cycads in Asia. These beetles are absent from C. micronesica cones of Guam and Rota, located ca. 1500 km from Indonesian cycads. Instead, cones of this species are visited by many generalists, including nitidulid and staphylinid beetles, and the moth, Anatrachyntis sp. (Cosmopterygidae), is a specialist pollen-cone inhabitant that visits ovulate cones. This moth has not been reported from mainland Cycas species. Both time and distance appear to have limited the dispersal of the mainland beetles. Based on the limited available information, the results fit basic colonization predictions of island biogeography theory.
