Changes in wild bee fauna of a grassland in Brazil reveal negative effects associated with growing urbanization during the last 40 years

Abstract

ABSTRACT. Bee fauna and associated flora from a grassland site in Brazil, surveyed 40 and 20 years ago, were newly surveyed with comparable methodology to evaluate changes in the bee fauna of this site, considering that human population and urbanization has exponentially increased in the last 40 years. In general, bee species richness has declined in 22%, as well as their abundance. Some of the previously abundant species are now absent, including Bombus bellicosus Smith, 1879, Gaesischia fulgurans (Holmberg, 1903) and Thectochlora basiatra (Strand, 1910). No particular trend of differential decrease among either taxonomic or functional groups was observed, except for a minor increase in the proportion of oligolectic species and a 50% reduction in the number of large species. The first two surveys were more similar to each other in species richness per bee genus, while the two most recent grouped together based on measures of anthropogenic impact. Furthermore, the number of plant species visited by bees increased, with a pronounced increase in ruderal and exotic species. Crop cultivation, competition with honeybees and climate changes may all be related to bee decline. Nevertheless, the effects of urbanization, in particular intense land occupation and few preserved natural areas can be pointed as the main causes of species decline. Due to continuing increase in human population, increased erosion in diversity is expected. Habitat protection is an additional challenge to bee conservation in the region, with no local conservation units set aside for grasslands. State and municipal agencies should urgently consider the establishment of reserves for the few remaining patches of natural grasslands.

Climatic Risk and Distribution Atlas of European Bumblebees

“…Several hypotheses have been proposed to explain this global decline such as (i) habitat fragmentation (Williams, 1982;Williams & Osborne, 2009;Darvill et al, 2010;Mayer et al, 2012;Hatten et al, 2013), (ii) shortage of flower resources (Peters, 1972;Williams, 1989;Rasmont & Mersch, 1988;Rasmont et al, 1993Goulson et al, 2005Goulson et al, , 2008a, (iii) killing by car traffic (Donath, 1986), (iv) overgrazing of bumblebee habitat by cattle (Özbek, 1995;Xie et al, 2008), (vi) parasites and pathogens resulting from spillover from domesticated species Arbetman et al, 2013), (vii) urbanization (Ahrné et al, 2009;Martins et al, 2013), or (viii) vegetation displacement due to nitrogen deposition (Rasmont, 2008). Pesticides have most likely also played a role because of their extreme toxicity for some bumblebee species (e.g.…”

Plant diversity and composition compensate for negative effects of urbanization on foraging bumble bees

“…In many European countries, up to 80 % of the population lives in cities with urbanization further increasing (Antrop 2004). Increasing urbanization is generally associated with an increase in concrete and a decrease in animal and plant diversity (Geslin et al 2013;Martins et al 2013;Williams and Winfree 2013).…”

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“…Although there are some differences in sampling effort between the two studies (see Materials and Methods), the 2008/2009 survey showed a significant increase in species richness and nest abundance. Martins et al (2013) assessed the effects of urbanization in the past 40 years in an area of natural vegetation surrounded by urban or agricultural areas and found decreased bee diversity, including the loss of some species. The primarily occurred because intense urbanization deteriorated the bee foraging matrix.…”