A comparison of yeast communities found in necrotic tissue of cladodes and fruits ofOpuntia stricta on Islands in the Caribbean Sea and where introduced into Australia.

Yeast communities growing in the decaying tissues (cladodes and fruits) ofOpuntia stricta (prickly pear cactus) and associated yeast vectors (Drosophila species) were compared in two geographic regions (Caribbean and eastern Australia). The Australian yeast community provides an interesting comparison to the Caribbean community, because the host plantO. stricta was introduced to Australia over 100 years ago. Many of the yeasts found in the Australian system also were introduced during a period of biological control (1926-1935) when they accompanied rotting prickly pear cladodes and insects shipped to Australia from the Americas. The yeast community composition (proportion of each species) is compared at several levels of organization: (1) within and between regions, (2) across seasons and years, and (3) within and between tissue types. The yeast species composition of the cladode communities are similar from locality to locality, season to season, and year to year, with the region-to-region similarity slightly less. The composition of the fruit-yeast communities are distinct from region to region and only show some overlap with the cladodes within regions when collected simultaneously in the same locality. It is suggested that the cladode-microorganism-Drosophila system is relatively closed (little extrinsic influence) whereas the fruit-microorganism-Drosophila system is open (large extrinsic influence).