Effects of Open and Forest Habitats on Distribution and Diversity of Bumblebees (Bombus) in the Małopolska Upland (Southern Poland): Case Study

SIMPLE SUMMARY: Southern Poland represents one of the most diverse habitats for bumblebees (Bombus sp.); however, little is known about the abundance and distribution of many insect species in this region. Bumblebees are important for crop and wildflower pollination in different temperate latitudes because many plant species are only pollinated by them. Studies were conducted in natural and semi-natural habitats in southern Poland during the years 2003–2006 and compared with material collected from 2017–2020. During this eight-year-long study, more than 6214 bumblebee specimens of 25 species were found in the Małopolska Upland. The most frequently observed bumblebee species were: Bombus pascuorum, B. lapidarius, B. pratorum, and B. lucorum. The low-numbered bumblebees were: Bombus humilis, B. pomorum, B. veteranus, B. muscorum, and B. semenoviellus. There were also four rarely found species: Bombus confuses, B. ruderatus, B. soroeensis, and B. jonellus. ABSTRACT: Bumblebees are an important insect group occurring in different land ecosystems, but the number of these species has declined dramatically across Poland as well as in Europe in recent years. The fragmentation of bumblebee habitats influences the abundance and richness in community composition and trophic and competitive interactions. During the years 2003–2006 and 2017–2020, we studied the diversity and distribution of bumblebee species in two natural (boron-mixed Vaccinio-Piceetea and riparian forest Querco-Fagetea) and two semi-natural (segetal-ruderal Stellarietea mediae ruderal Artemisietea vulgaris) habitats in southern Poland. For that, we evaluated how habitats as well as local flowering communities influenced bumblebees’ abundance, richness, and community composition in 16 sites (which are located in four parks). Bumblebee communities responded to environmental factors in different ways according to the type of habitat. Vegetation factors were the most important drivers of bumblebee community structures. Forests showed the lowest bumblebee abundance, richness, and diversity, and the highest dominance levels of these parameters were found in the open ruderal-segetal habitats. The meadows from the Molinio arrhenatheretea class were characterized by bumblebee communities with a more complex structure. Species diversity was positively correlated with open ruderal-segetal habitats, and negatively with mixed forest cover, while abundance was positively correlated with forest cover. Studies like this are necessary to anticipate the impact of habitat fragmentation on bumblebee decline.