Experimental Zoogeography of Islands: Defaunation and Monitoring Techniques

In order to facilitate experiments on colonization, a technique was developed that permits the removal of the faunas of very small islands. The islands are covered by a tent and fumigated with methyl bromide at concentrations that are lethal to arthropods but not to the plants. Seven islands in Florida Bay, of varying distance and direction from immigrant sources, were censused exhaustively. The small size (diameter 11—18 m) and ecological simplicity of these islands, which consist solely of red mangrove trees (Rhizophora mangle) with no supratidal ground, allowed the location and identification of all resident species. The terrestrial fauna of these islands is composed almost exclusively of arboreal arthropods, with 20—50 species usually present at any given moment. Surveys of these taxa throughout the Florida Keys, with emphasis on the inhabitants of mangrove forests, were made during 1967 in order to estimate the size and composition of the "species pool." The seven experimental islands were defaunated in late 1966 and early 1967, and the colonists were monitored for 17—20 man—hours every 18 days. Precautions were taken to avoid artificial introductions during the monitoring periods.