Islands in the desert for cavity‐nesting bees and wasps: Ecology, patterns of diversity, and conservation at oases of Baja California Peninsula

Abstract

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 tested the effect of habitat and anthropogenic disturbance on communities of cavity-nesting taxa, with specific emphasis on bees, wasps, and their natural enemies.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 correlates of nest abundance and patterns of diversity, as well as ecological analyses to determine the effect of habitat and human disturbance on species diversity and community structure.Results: Solar irradiation, distance to a perennial waterbody and relative humidity influenced the presence of nests, number of brood cells, and parasitism. In general, abundance, species richness, and parasitism were higher in oases, especially in those with less human disturbance. Bees did not discriminate between oases and deserts to nest, whereas mud-daubing wasps were more dependent of oases. The degree of anthropogenic disturbance did not affect the occurrence of parasitism, but it had an adverse effect on the parasitism intensity (number of attacked cells). The community structure was more complex and even in oases and low-disturbed sites. The similarity between sites did not exceed 30%, and the proportion of shared species between oases and deserts varied from 2.7% to 26.6%. Main conclusions:The oases of Baja California are functioning as mesic islands in the desert, each oasis hosting a unique community of cavity-nesting taxa. About 65% of the nests and 50% of species occurred exclusively in the oasis. Thus, cavity-nesting species that depend on mesic conditions could be threatened if the oases of BCP disappear in the future. Local conditions in the oases and deserts of the BCP are shaping the community structure. However, large-scale factors such as climate can influence the seasonality and occurrence of species within the community of cavity-nesting dwellers. Since habitat loss and fragmentation can degrade the oases' functionality,

Metabarcoding reveals seasonal and spatial patterns of arthropod community assemblages in two contrasting habitats: Desert and oasis of the Baja California Peninsula, Mexico

“…This considerable differentiation among sites suggests that habitat degradation would lead to the local extirpation of specific lineages and the posterior extinction of entire communities. For example, the site with the lowest phylogenetic diversity, like Santiago (SO), was also one of the biggest oases with the highest human disturbance (Falcón‐Brindis et al, 2019). Independent of site, we also had difficulty locating palms with untouched dried foliage; usually, all foliage was cut or burned.…”

“…On the other hand, the highest diversity was found at one of the smallest oases (SP), where no permanent human settlements or agricultural practices exist. Thus, arthropod diversity in oases is affected more by the habitat deterioration level than the habitat's dimensions or location (Bogan et al, 2014; Falcón‐Brindis et al, 2019; Murphy et al, 2013).…”

“…The sampled oases differed in size and level of human disturbance. The extent of the anthropogenic disturbance was determined according to methods from Falcón‐Brindis et al (2019), considering the following variables: the presence/absence of permanent human settlement, agriculture practice, land use change and ranching, among others. Please see Table S1 for more details.…”

“…We used latitude, oasis size (area), season, humidity and level of human disturbance as explanatory variables. The human disturbance was estimated as the intensity score of human activities based on population size, land use change, agriculture, distance to the paved road, livestock presence and slash‐and‐burn practices, as described in Pérez Navarro et al (2019) and Falcón‐Brindis et al (2019). Humidity was obtained through HoBo data loggers, placing two data loggers inside each oasis and two outside in the desert at 1 km from the oasis edge.…”

“…These studies found high species richness and many undescribed species with adaptations to the specific physiographic and geographic areas (Jiménez et al, 2015; Jiménez‐Jiménez & Palacios‐Cardiel, 2010). More recent work highlighted the sensitivity of some arthropod groups, like Hymenoptera, to human‐induced disturbance (Falcón‐Brindis et al, 2019). Although these fundamental works have described the diversity dynamics of the particular arthropod groups, they generally were focused on a limited geographic area or a particular taxon and, therefore, cannot be considered representative of the whole species communities.…”