The California Channel Islands support an impressive array of biological diversity, including numerous endemic species. Although the flora and vertebrate fauna of this archipelago are relatively well studied, information about terrestrial arthropods remains fragmentary, and most islands are inadequately surveyed for arthropods. Here, we report the results of the first archipelago-wide survey of ants from the California Channel Islands. We visited each island between 2011 and 2016 and employed standardized ant survey methods on all 8 islands. We also conducted targeted collecting of carpenter ants (Camponotus) from at least 5 distinct locations on each island for phylogeographic analyses. Represented by 11 different species on the islands, carpenter ants exhibit apparent differentiation within islands (C. clarithorax), among islands (C. semitestaceus), and between the islands and the mainland (C. hyatti /C. bakeri). We used DNA barcoding and median-joining haplotype network analyses to test hypotheses relating to dispersal and subsequent differentiation of island populations. These ongoing studies represent the first examination of historical diversification for ants on California Channel Islands.
Fifty-one native species and four introduced species of ants occur on the California Channel Islands. Our surveys contribute new island records for 7 of the 8 islands, totaling 41 new island records for the archipelago. As would be expected, native ant richness increases with island area and decreases with distance from the mainland. Several islands appear to be outliers in this species-area relationship, possibly as a result of the combined effects of disturbance history and proximity to other islands. Species-level endemism is in general low, with 1-3 species endemic to the level of the island, and 1-3 species endemic to multiple islands. Endemism is mostly restricted to the southern islands, which share biogeographical affinities to the ants from Isla Guadalupe. Preliminary haplotype networks based on mtCO1 sequences reveal genetic differentiation between carpenter ants among each island population and between each island and mainland population. These networks also reveal high genetic differentiation between Camponotus populations on San Clemente Island and those on other California Channel Islands and the mainland. Our ongoing studies of carpenter ant phylogeography reveal interesting patterns of carpenter ant diversification and provide the basis for further investigation into the taxonomic status of several carpenter ant populations.