From pastures to forests: Changes in Mediterranean wild bee communities after rural land abandonment

Abstract

1. In farmland landscapes worldwide, there are pervasive trends for either intensification or abandonment. Intensification is a widely recognised driver of wild bee declines, but little is known about the consequences of land abandonment, though it involves major habitat shifts from fallows, pastures and meadows, to shrublands and forests.2. Focusing on a Mediterranean landscape, we investigated long-term changes in wild bee communities during secondary vegetation succession after land abandonment.We used a space-for-time substitution approach, sampling plants and wild bees on five successional stages, from grasslands, through shrublands, to oak woodlands.3. We recorded 2721 bees, representing over 150 species. Grasslands had the highest wild bee abundance and high diversity of oligolectic species. Moving through successional stages, there was a rapid decline in bee abundance combined with a progressive accumulation of rare species, resulting in maximum diversity of the overall community, ground nesters, polyleges, and oligoleges in oak woodlands. Bee diversity was positively related to plant taxonomic and phylogenetic diversity. There was high turnover in community composition along the succession, with species occurring in grasslands being largely absent from later successional stages, and vice versa. From 21 indicator species, 17 were associated with grasslands, including the only threatened species. 4. Our results suggest that a mosaic of habitats at different successional stages, particularly grasslands and oak woodlands, are necessary to maximise the diversity and abundance of wild bees at the landscape scale. Sustained management is thus needed under land abandonment to retain early-successional herbaceous habitats and to ensure woodland regeneration and protection.

Different types of semi‐natural habitat are required to sustain diverse wild bee communities across agricultural landscapes

“…This is shown by the high turnover in species composition among habitats and high modularity of the network in our study, which implies that each habitat harboured a relatively unique set of species. Therefore, our findings support evidence from other ecosystems (Penado et al, 2022) that sustaining different habitat types within an agricultural landscape is essential for conserving diverse wild bee meta‐communities. For example, the oligolectic longhorn bee Eucera nigrescens was strongly associated with the module consisting of intensively managed meadows and hedgerows (high within‐module degree z and low among‐module connectivity c ).…”

“…This is shown by the high turnover in species composition among habitats and high modularity of the network in our study, which implies that each habitat harboured a relatively unique set of species. Therefore, our findings support evidence from other ecosystems (Penado et al, 2022) that sustaining different habitat types within an agricultural landscape is essential for conserving diverse wild bee meta-communities.…”

The bee fauna (Hymenoptera: Apoidea: Anthophila) of allotments in downtown Lisbon

“…Similarly, studies focusing on bee LHTs instead of taxonomic diversity have a better potential for making comparisons and drawing better hypotheses/conclusions (Sheffi eld et al, 2013). On the other hand, compared with studies in the Mediterranean countryside (Pisanty et al, 2015;Hevia et al, 2016;Rodrigo Gómez et al, 2021;Penado et al, 2022), the number of species in urban settings should be lower, as was recorded here.…”

Canopy arthropod declines along a gradient of olive farming intensification

“…We estimated arthropod community diversity for each intensification level and season, using the Hill diversity framework 75 and the package iNEXT 76 , following Penado et al 77 . To account for the effects of rarity on diversity estimates, we computed taxa richness (Hill number q = 0), and Hill-Shannon (q = 1) and Hill-Simpson (q = 2) diversities, because increasing the Hill number reduces the leverage of rare taxa 75 .…”

“…Estimates were made considering identifications to the highest possible taxonomic resolution, that is, family level except for orders Ephemeroptera, Psocoptera, Thysanoptera and sub-order Nematocera. Because diversity metrics are sensitive to sampling effort and relative abundance, we standardised diversity estimates to equal-coverage 75 , 77 , with coverage estimating the proportion of individuals in the (whole) community that belong to the taxa present in the sample 75 . To standardise diversity estimates, we first assessed variation in sample coverage with increasing number of individuals identified, and then set a fixed coverage value, corresponding to the minimum coverage obtained when each sample (traditional, intensive, superintensive) is extrapolated to double the number of individuals identified 75 , 77 .…”