Effects of urbanisation and management practices on pollinators in tropical Africa

Abstract

1. Urban expansion is an increasing threat to biodiversity, especially in tropical Africa where biodiversity hot spots are being encroached upon by fast-growing cities.Threatened species include bees and other pollinators, which deliver important ecosystem services but are sensitive to land use changes.2. We investigated the impact of urbanisation and vegetation management practices on pollinator abundance, bee diversity, and bee functional traits. We sampled 126 locations in a stratified random design across an urbanisation gradient in two medium-sized cities in the West African Forests biodiversity hot spot, encompassing three management practices (farmed sites; amenity lands, i.e. green spaces managed for aesthetics; informal green spaces), and tested their effect with generalised linear models.3. Urbanisation did not affect bee abundances or diversity but had a negative impact on both wasp and beetle abundances. There was also a management-mediated impact of urbanisation on bee abundances, which decreased with urbanisation on farmed sites but not amenity land or informal green spaces. Management practices alone influenced bee abundances with farms harbouring fewer bees, and amenity lands fewer beetles. 4. Bee genera occurrence and dominance patterns were influenced by both urbanisation and management, with some otherwise common genera rare in urban areas.5. Most functional traits were influenced by management, with fewer polylectic bees, cavity-nesting bees and long-tongued bees in farmed sites. Amenity lands hosted smaller bees and fewer savanna specialists. Some traits were influenced by urbanisation, with more long-tongued bees and cavity-nesting bees found in urban areas.6. Synthesis and applications. Pollinator responses to urbanisation are complex. In our research, we demonstrate how bee, lepidopteran, and non-fruit fly abundances have been maintained across an urbanisation gradient in tropical Africa, but not wasp and beetle abundances. Moreover, bee community composition and the distribution of traits shifted markedly. How green spaces were managed was also critical. We found that farmed sites hosted the lowest bee abundances and

Functional ecology of wild bees in cities: towards a better understanding of trait-urbanization relationships

“…Some studies found social species are more frequent in urban habitats surrounded by a high amount of impervious cover compared to suburban or rural sites (Harrison et al 2018;Banaszak-Cibicka et al 2018a;Kratschmer et al 2018). Several studies found no significant urbanization effects on the abundance of eusocial species (Zanette et al 2005;Carper et al 2014;Guenat et al 2019). Urban areas may provide more diverse nesting substrate for social colony building species that can utilize features of the built environment (Cane et al 2006).…”

“…A lack of a definition of urbanization or Moretti et al 2017;Brousseau et al 2018) measurement of urbanization is a drawback because environmental effects are not comparable across different studies which hinders generality and synthesis of functional relationships. Furthermore, only a few studies covered the whole gradient from urban to rural sites with a quantification of urbanization (mostly proportion of impervious surface in a buffer around the study site) (e.g., Buchholz et al 2020, Eggenberger et al 2019, Guenat et al 2019. The majority of studies compared sites only along a narrow gradient (e.g., Carper et al 2014, Martins et al 2017, Twerd and Banaszak-Cibicka 2019, sites within one urbanization category (e.g., Pardee and Philpott 2014, Threllfall et al 2015, Quistberg et al 2016, or without properly defining urbanization (e.g., Geslin et al 2016b, Sivakoff et al 2018, Harrison et al 2019).…”

Urbanization Affects Composition but Not Richness of Flower Visitors in the Yungas of Argentina

“…However, while certain studies found a decrease in pollinator richness with increasing urbanization (Hernandez et al 2009, Bates et al 2011, Baldock et al (2015) observed that urban habitat can contain a higher bee richness than farms and protected areas. Likewise, many bees species are associated with open habitats (Klemm 1996), and due to their small body size, they could be benefitted from small habitat fragments (Tscharntke et al 2002, Guenat et al 2019. Thus, species richness, diversity, and composition exhibit contrasting responses to urbanization, and therefore, certain species traits can be good predictors of the impacts.…”

Lack of Cross-Sector and Cross-Level Policy Coherence and Consistency Limits Urban Green Infrastructure Implementation in Malawi

“…Urban greenspaces in these two cities, therefore, broadly belong to three different types: (a) amenity land, a greenspace managed for aesthetic or recreational purposes, typically lawns, trimmed hedges, cleared vegetation, or wooded areas; (b) farmed/forested sites, a greenspace managed for agricultural or wood production, including mixed-crop gardens and farms; and (c) informal greenspaces, which are vegetated areas receiving minimal to no management, such as fallows or abandoned sites (cf. Guenat et al, 2019b;Munyati and Drummond, 2020).…”