Aims: The oases of Baja California peninsula (BCP) have been proposed as important hotspots of biodiversity that hold an exceptional richness in the middle of desert conditions. We provide the effect of habitat, climatic, biogeographic and anthropogenic disturbance on communities of cavity nesting taxa, emphasizing on bees, wasps and their natural enemies. Location: Baja California Peninsula, Northwest Mexico.

Methods: In oases of BCP and desert neighbor environments, trap-nesting taxa were evaluated in response to factors affecting the nest abundance, richness, and community structure. We used statistical models to find the variables controlling the nest abundance and ecological analyses to determine the habitat effect on diversity under different scenarios of disturbance and latitude.

Results: The nest abundance varied between bees and wasps, but solar irradiation and relative humidity influenced the abundance of both groups. In general, abundance and richness were higher in oases. Bees did not discriminate between oasis and desert habitats to nest and mud-daubing wasps were highly dependent of oases. However, there were exceptions in both groups. The degree of anthropogenic disturbance affected the species composition, richness, and natural enemies.

Main conclusions: The oases of Baja California seem to be functioning as mesic islands into the desert, each oasis hosting a great and unique richness of cavity-nesting taxa. About 65% of nest abundance and 50% of species occurred exclusively in the oasis. Thus, at least 21 species could be threatened if the oases of BCP disappear in the future. Local conditions are shaping the community structure of species, but also large-scale factors, e.g. climate and biogeographic patterns seem to be influencing the community structure. Since habitat loss and fragmentation can be a major problem in most oases, strategies to maintain the ecosystem services of pollinators and predators should be included in the conservation programs of these fragile habitats.

SF= San Fernando
SB = San Borja
ES = El Sauzal
LP = La Purisima
EP = El Pilar
SA = Santiago

Disturbance level= low, medium, high
Habitat = oasis, desert