- مبلغ: ۸۶,۰۰۰ تومان
- مبلغ: ۹۱,۰۰۰ تومان
Wild and managed bees provide critical pollination services to both native and cultivated plants, and the invasion of exotic plants can have positive or negative effects on bee communities. In this study we investigated the influence of the exotic invasive Centaurea stoebe ssp. micranthos (spotted knapweed) on bee species diversity and abundance in old-fields (Michigan, USA). We conducted field observations in knapweed dominated fields and adjacent fields with greater forb diversity to determine whether the bee communities foraging in each field type differed in their composition, diversity, and abundance, and to determine how bees’ use of floral resources changed throughout the growing season. This was coupled with a common garden experiment that contrasted the attractiveness of C. stoebe to 12 native plant species, which occur in similar habitats. Both studies were conducted throughout the 2012–2013 growing seasons to examine the temporal effect of floral resource availability. C. stoebe was the most heavily-visited plant, in terms of total bee visitation and bee species richness in both studies. While C. stoebe-dominated old-fields had high floral resource levels during its peak bloom period, before and after this period these fields contained very few floral resources. In contrast, diverse fields had a number of flowering plant species that provided floral resources before, during, and after C. stoebe bloom. As a result, diverse fields contained significantly greater season-long floral resource availability and significantly greater season-total bee abundance, diversity and species richness. This greater species richness was driven at least in part by the ability of diverse flowering plant communities to support bee species that are active before and after the bloom period of C. stoebe. Our results suggest that efforts to manage C. stoebe should take into account the floral resources the plant is providing, and coincide with the restoration of diverse forb communities in order to enhance bee foraging habitat in old-fields.
The common garden and field level floral diversity studies both showed that C. stoebe is inherently attractive to many bee species. In the common garden, C. stoebe received a high number of total bee visits per plant in bloom, and a high number of visits per unit of floral area, indicating that each flower is individually attractive. The attractiveness of each individual flower and an abundance of flowers per plant led to a high number of visits to C. stoebe in both years in the common garden. In the field level floral diversity study, these factors combined with a high density of C.stoebe plants and resulted in more bee visits to C. stoebe than any other plant species. Because the common garden experiment was conducted in a landscape largely devoid of C. stoebe, we know that bees did not target it only because of its local abundance and familiarity. In both years and studies, C.stoebe was visited by a greater number of bee species than any other plant species, indicating its attractiveness to a wide variety of bee species. Most of the species visiting C. stoebe were generalists, but also included two bee species(Melissodessubillatus LaBerge and Megachile pugnata Say) that specialize on plants in the family Asteraceae (LaBerge 1961; Tepedino & Frohlich 1982). Furthermore,many generalist bee species were only observed visiting C. stoebe.