Fungal immigration dynamics and community development on apple leaves.

Fungal immigration dynamics and community development were followed over time on sets of surface-disinfested apple leaves in the field. Immigration was defined as the arrival of viable propagules on the leaf surface. In three separate experiments (May, June, July), total numbers of fungal immigrants, numbers of filamentous fungal immigrants, and numbers of yeast immigrants per leaf were estimated for successive 12-hour immigration periods. Communities developing over 2-14 immigration periods (1-7 days) were compared with the corresponding estimates of cumulative immigration. There were significant differences among both experiments and immigration periods within each experiment in mean numbers of immigrants per leaf. Leaf area was often significantly correlated with numbers of immigrants. Developing communities supported progressively fewer individuals than the corresponding sums of immigrants, suggesting that losses due to emigration and/or death play a critical role in shaping these communities.