Global change and local--regional dynamics in size-structured communities

Global change alters both temperature regimes and spatial connectivity, reshaping the mechanisms that link local and regional biodiversity. We developed a temperature-dependent community model, parameterized with stream macroinvertebrate data, to assess how warming and dispersal influence population dynamics, community size, size structure, and temporal β-diversity in local communities. The model integrates temperature effects through metabolic body-size scaling and local recruitment inputs from a regional species pool to explore how energetic constraints cascade across scales. Warming reduced population and community sizes, increasing demographic stochasticity and leading to higher temporal β‐diversity. Enhanced connectivity produced the opposite pattern: larger, more stable communities with lower compositional turnover. Community size thus emerged as the critical mediator of biodiversity responses, integrating metabolic and spatial processes within a unified framework. Although warmer conditions lowered overall biomass and altered size‐spectra intercepts, slopes were more variable than predicted, reflecting stochastic fluctuations among small‐bodied species rather than systematic loss of large taxa. Together, these findings show that temperature‐driven metabolic acceleration and dispersal‐mediated rescue jointly determine biodiversity stability under global change. Our results highlight the role of community size in buffering or amplifying the effects of warming and provide a mechanistic bridge between metabolic theory and local-regional dynamics.