UC San Diego

The “necrotic cactus niche” contains a high diversity of desert arthropods, yet few studies of this diversity have been conducted. Rove beetles (family Staphylinidae) have the highest species richness in this system, yet little is known about their distribution, ecology, specificity, or life history. For this study, over 5,000 rove beetles were collected from four species of rotting cactus. Three species—cardón (Pachycereus pringlei), senita (Lophocereus schottii), and organ pipe (Stenocereus thurberi)—were collected from Baja California Sur, Mexico and one species—California barrel cactus (Ferocactus cylindraceus)—was collected from Anza Borrego Desert State Park in southern California. Altogether, 21 morphospecies of rove beetles from six subfamilies were identified. The subfamilies Scaphidiinae and Osoriinae were found exclusively in cardón cactus. This study also assessed phylogeographic relationships and genetic diversity within the genus Belonuchus using sequence data from the barcoding locus of the mitochondrial cytochrome oxidase 1 gene. Morphological and genetic data support the presence of at least one undescribed Belonnuchus n.sp. with apparent host specificity to senita cactus. The ecological portion of this thesis consisted of a three-week study of rotting California barrel cactus in Anza Borrego Desert State Park and provided evidence that these rove beetles are specific to the rotting cactus niche and that they are primarily diurnal. This study adds to our understanding of rove beetles in the necrotic cactus niche and provide a baseline for future studies of necrotic cactus arthropods.