Correlation and spatial concordance between cleptoparasitic and non-parasitic bee assemblages across urban nature reserves within Rome (Italy)

1. Wild bees play a crucial role in pollination, yet their populations are declining world- wide. Monitoring bee diversity is important for their conservation, but traditional species identification is challenging and time-consuming, particularly in regions with high species richness and limited taxonomic expertise. 2. A potential approach to facilitate the monitoring of bee populations is to focus on a representative subset of bee taxa that reflects overall bee diversity. Here, we tested whether cleptoparasitic bees—characterised by distinct morphology, dependence on host species and sensitivity to environmental disturbances—exhibit spatial con- cordance and correlated diversity with non-parasitic bee assemblages across eight urban nature reserves of a large Mediterranean metropolis (Rome, Italy). 3. Sampling was carried out along fifteen standardised transects between April and September 2022. Shannon diversity index was used to quantify landscape hetero- geneity within the area surrounding each transect. 4. Observed and estimated diversity indices of non-parasitic bees showed a significant positive relationship with cleptoparasitic bee species richness, whereas community- level concordance between the two groups was weak, showing no association in species turnover and only marginal alignment in their spatial configurations. Both cleptoparasitic and non-parasitic bee species richness increased with landscape het- erogeneity, with a stronger response observed for cleptoparasitic bees. 5. This work suggested that cleptoparasitic bee species richness reflects the overall bee diversity even in urban environments, where they are typically less abundant and potentially more susceptible to landscape homogeneity, though not reliably indicating community composition.