Vegetation complexity and nesting resource availability predict bee diversity and functional traits in community gardens

Abstract

Urban gardens can support diverse bee communities through resource provision in resource poor environments. Yet the effects of local habitat and landscape factors on wild bee communities in cities is still insufficiently understood, nor is how this information could be applied to urban wildlife conservation. Here we investigate how taxonomic and functional diversity of wild bees and their traits in urban community gardens are related to garden factors and surrounding landscape factors (e.g., plant diversity, amount of bare ground, amount of nesting resources, amount of landscape imperviousness). Using active and passive methods in 18 community gardens in Berlin, Germany, we documented 26 genera and 102 species of bees. We found that higher plant species richness and plant diversity as well as higher amounts of deadwood in gardens leads to higher numbers of wild bee species and bee (functional) diversity. Furthermore, higher landscape imperviousness surrounding gardens correlates with more cavity nesting bees, whereas a higher amount of bare ground correlates with more ground‐nesting bees. Pollen specialization was positively associated with plant diversity, but no factors strongly predicted the proportion of endangered bees. Our results suggest that, aside from foraging resources, nesting resources should be implemented in management for more pollinator‐friendly gardens. If designed and managed using such evidence‐based strategies, urban gardens can create valuable foraging and nesting habitats for taxonomically and functionally diverse bee communities in cities.

SolBeePop: A model of solitary bee populations in agricultural landscapes

“…Studies on solitary bees indicate that intra‐ or interspecific competition for food or nesting resources can affect reproductive outputs of nesting females, resulting in density‐dependent population regulation (Cane, 2008; Felderhoff et al., 2022; Pitts‐Singer & Bosch, 2010; Steffan‐Dewenter & Schiele, 2008). However, the strength and mechanism of density dependence may vary considerably dependent on species, landscape, species community composition and environmental factors such as weather.…”

Effects of forest management on native bee biodiversity under the tallest trees in the world

“…We also found a higher species richness of bees that are known to nest in the ground in other habitats (Michener, 2007) in OG forests, like Lasioglossum and Halictus tripartitus (Table A1: ). It is well established that the abundance and diversity of ground‐nesting bee species increases with the cover of bare ground (Decker & Harmon‐Threatt, 2019; Felderhoff et al, 2023; Quistberg et al, 2016). Bare ground was very rare in the mature redwood forests that we studied, as the forest floor was frequently covered with a layer of fallen redwood needles, and denser secondary coniferous forests have a thicker layer of leaf litter (Willett, 2001).…”

In defence of urban community gardens

“…We have also detected rarer species in gardens, such as Anthophora furcata, which is the only oligolectic digging bee that prefers Stachys species, planted in gardens for their diverse medicinal properties. This species is also one of the few that can excavate its brood cells in rotting wood (Felderhoff et al, 2023).…”

“…An urban ecosystem in which we see this dialogue play out is urban gardens, generally described as horticultural systems in which food and flower production dominates alongside other social and recreation activities (Kingsley et al., 2021; McClintock, 2014). Urban gardens are considered important refuges for declining native plant species (Segar et al., 2022) and are recognized for contributions to animal habitat through the provision of food and nesting resources (Felderhoff et al., 2023; Goddard et al., 2010; Majewska & Altizer, 2018). In addition, urban gardens contribute to the health and well‐being of city residents through stress reduction (Marsh et al., 2021), community cohesion (Clarke et al., 2023) and fresh fruit and vegetable production (Alaimo et al., 2008) that improves physical health (Kunpeuk et al., 2020).…”