Endemism in native floras of California’s Channel Islands correlated with seasonal patterns of aeolian processes

Abstract

This study revisits the hypothesis that dispersal to California’s Channel Islands follows a stepping-stone pattern from mainland California, based on earlier work indicating that the floras conform to classic island-biogeographic expectations. A re-examination of data incorporating the directions of prevailing and seasonal Santa Ana winds greatly strengthens the power of the model to explain levels of endemism in the Channel Island floras, and suggests the importance of aoelian processes for island colonization. Regression analysis of percent endemism in the native flora against distances measured along the axis of winds improves the r2 from 0.099 to 0.482. The endemic species that flower in the dry season as a percent of the native flora of the islands is also strongly related to these revised source distances (r2 = 0.665). Furthermore, the native floras of the southern islands are nested subsets of the floras of the northern islands, and angiosperm flowering peaks during the dry season, providing seed for seasonally based dispersal. These results suggest that the northern islands may have served as a source of colonists for the southern islands, and that the pattern of aeolian inputs into an island system should be considered in other plant biogeographic studies.