Habitat suitability of an at-risk, monolectic, ground-nesting bee Hesperapis oraria and its floral host Balduina angustifolia at two spatial scales along the Northern Gulf of Mexico

Hesperapis oraria, Snelling and Stage (Hymenoptera: Melittidae) is endemic to northern coastal habitats of the Gulf of Mexico and is a pollen specialist of floral host Balduina angustifolia Pursh. (Asteraceae). Specialization and restricted geographic distribution along the coast of the Gulf of Mexico warrants further investigation into habitat requirements of the bee. This study quantifies the habitat use of H. oraria in association with B. angustifolia distribution at regional and landscape spatial scales using a classification tree species distribution modeling approach. Hesperapis oraria density was lower on barrier island sites compared with coastal mainland sites; no H. oraria were found on non-coastal mainland sites. The regional distribution of H. oraria was driven by the number of B. angustifolia patches, while at the landscape scale H. oraria presence was predicted most strongly by B. angustifolia patch area, plant density, as well as distance from ephemeral wetlands. The regional distribution of B. angustifolia was influenced by the proximity to the bay and within a landscape B. angustifolia distribution was strongly influenced by the stability of the landscape feature in which it was found.