Local floral resources and edge density within the urban ecosystem promote larger and less variable body size in the great banded furrow bee, Halictus scabiosae

Abstract

An organism’s body size is a fundamental trait linked to its metabolism, life-history and dispersal. In holometabolous insects, whose size is fixed at adult eclosion, body size can be influenced by environmental factors during development (e.g. nutrition and temperature), or by ecological filtering during adulthood. In bees, larger body size has been linked to advantages in foraging efficiency, thermoregulation, and survival, while excessive variation in body size within populations may indicate developmental instability. Shifts in adult body size have been associated with temperature changes, food resource availability and habitat fragmentation, all of which can be modulated by urbanisation. However, the relationship between urban landscapes and wild bee body size remains poorly understood. In this study we investigated how local floral (food) resources, landscape structure and temperature influence the body size of the great banded furrow bee, Halictus scabiosae. Our findings highlight that food resources, semi-natural cover and edge density are the most significant environmental factors influencing body size shifts. Specifically, H. scabiosae body size increased with the species richness of flowering host plants at the local patch level. Within sampling sites, body size variation was positively associated with semi-natural cover, suggesting that habitat structure or competition may contribute to size heterogeneity, potentially disrupting size uniformity. Conversely, it was negatively associated with edge density, indicating that a higher amount of ecotones may promote greater size uniformity within populations. Our findings reinforce the idea that enhancing floral resources and improving habitat connectivity through green corridors can support wild bee populations in urban areas.