Urbanization altered the functional traits of acorns, weevil larva and their interactions: Implications for urban forest conservation

Urban forests serve as a critical green landscape for supporting species diversity and regulating microclimate in urban areas. However, urbanization-driven phenotypic plasticity in plants and insects may reshape their interactions and trigger cascading effects on forest regeneration, deriving challenges in ecological-based conservation and management. In this study, we focused on common oaks in Wuhan, a megacity in central China, to investigate the species of insect acorn predators. We then quantified the functional traits of acorns and insect predators of a dominant oak (Quercus variabilis) to examine whether these traits change along the urbanization gradient and how such changes influence insect infestation rate. Finally, we assessed the consequences of these interactions on acorn dispersal and germination rates. We identified three weevil larvae species and three moth larvae species in the infested acorns. Larval abundance, rather than species richness, increased along the urbanization gradient. In Q. variabilis, acorns decreased in palatability (e.g., reduced nutrients and increased pericarp thickness and condensed tannin), and acorn predators decreased in body size along the urbanization gradient, leading to a reduction in insect infestation in the urban areas. However, the low infestation failed to mitigate its low acorn dispersal or regeneration in the urbanized areas. These results suggest that rapid urbanization has caused plasticity in plants, insects, and their interactions, resulting in low dispersal and germination of plants. To preempt potential pest outbreaks and ensure the sustainability of urban forests, we should consider the phenotypic plasticity of plants and insects when carrying out conservation plans.