Habitat fragmentation can affect species richness directly through habitat loss and isolation, and indirectly by facilitating the spread of introduced species. We investigated the roles of habitat fragmentation and invasion on the structure of ground-foraging ant communities in 40 scrub habitat fragments in coastal southern California. These same areas were sampled 20 years ago allowing us to ask how fragment age, size, and the relative abundance of an exotic species, the Argentine ant (Linepithema humile), influence the ability of habitat fragments to retain diversity over two decades.
Results/Conclusions
As in our previous survey, Argentine ants were most abundant near developed edges and in small fragments. The number of native ground foraging ant species at any point declined from an average of 7 to less than 2 species when Argentine ants were present. Among fragments, the abundance of Argentine ants, the size of the fragment, and the number of years since it was isolated from larger continuous areas of scrub habitat best predict the number of remaining native ant species. The Argentine ant was found in 39 out of 40 fragments surveyed suggesting that their prevalence has not declined over the last 20 years. Moreover, some native species that were identified as highly vulnerable 20 years ago were not detected in this survey (e.g. army ants). We also detected a widespread introduced ant that was absent from our surveys 20 years (Brachymyrmex patagonicus). These data highlight the value of long-term monitoring to determine the response of communities to different types of disturbance and global change.