Over the past 150 years, numerous populations of native shrubs worldwide have increased in density and cover, effectively invading neighboring grassland communities. Depending on the ecosystem evaluated, both positive and negative effects have been observed as a consequence. In the American Southwest, desert grasslands have been extensively replaced by Larrea tridentata, causing decreased plant cover and diversity. The consequent reduction in floral rewards is likely to affect insect pollinators, which are crucial to ecosystem function, with a great majority of flowering plants depending on them for reproduction. However, the floral resources provided by the encroacher species itself might be considerable. The consequences of shrub encroachment in this habitat are therefore likely to be complex, and will depend on the extent that the invading species can be utilized by the bee community as well as on whether the decreased abundance of forb species can successfully attract and sustain those bees which cannot rely on the shrub. This study evaluates the effect of L. tridentataencroachment on the diversity and abundance of bee communities. Thirty minute bee surveys were conducted at side-by-side plots (grassland vs. shrubland) once a week from July to September 2016 to evaluate differences in overall bee community composition.
Results/Conclusions
A total of 418 bees belonging to 19 different genera were collected visiting a total of 17 plant species. Preliminary results show that overall bee abundance was higher in the grassland sites, compared to the neighboring shrubland. Species diversity was similar in both environments; however, most species were restricted to a particular habitat, with a relative low number of bee species present in both grassland and shrubland sites. In the shrubland sites, most bee species were found visiting L. tridentata, whereas the diversity of plants visited was higher in the grassland sites. These results reveal that the bee community was altered as a consequence of shrub encroachment, most likely as an indirect consequence of the altered plant diversity.