The ecology of the yeast flora in necroticOpuntia cacti and of associatedDrosophila in Australia.

A survey was made of the yeast communities isolated from necrotic tissue of 4 species of prickly-pear cacti (Opuntia stricta, O. tomentosa, O. monacantha, andO. streptacantha) which have colonized in Australia. Yeast communities were sampled from a number of localities and at different times. Cactus specific yeasts accounted for 80% of the total isolates, and the 3 most common species contributed 63% of the total. Comparisons of the species compositions of the yeast communities indicated that the differences among communities were greater betweenOpuntia species than between different localities within a single cactus species, and also that differences between years were greater than average differences between localities within years. Multivariate statistical tests of association between yeast community and physical features of rots indicated that temperature, pH, and age of rot all exerted some influence on the structure of the yeast community. Similar analyses involvingDrosophila species inhabiting these cactus rots suggested the existence of complex associations betweenDrosophila community, yeast community, and physical and chemical attributes of the cactus necroses.