Multilevel ecological interactions: Impact of weather, forest extreme events and seed production on squirrel population dynamics.

In resource-limited producer-consumer systems, environmental variables such as weather, habitat structure, and resource availability interact to shape consumer dynamics. We conducted a comparative analysis on territorial Fremont's squirrel (Tamiasciurus fremonti) in Arizona mountain ranges (three sites) and non-territorial Eurasian red squirrel (Sciurus vulgaris) in the Italian Alps (five sites) to investigate the effects of forest composition, pulsed seed resources, weather, and climate change-induced forest disturbances on population density. We also explored potential synchrony in spatial and temporal dynamics between squirrel populations, driven by endogenous and exogenous processes. Our long-term, multi-site datasets revealed shared density-dependent patterns: annual oscillations in Fremont's squirrel populations and biennial oscillations in Eurasian red squirrels. Both species exhibited strong bottom-up responses, with higher densities following tree-seed production and warmer spring temperatures. Despite the absence of synchronized trends in population density across time or regions, we found consistent responses to resource availability and abiotic conditions, demonstrating shared mechanisms across ecologically distinct systems. By integrating field data, remotely sensed forest disturbances, and multi-factorial modeling, this study highlights the role of climate, forest dynamics, and climate change-induced forest disturbance in shaping population processes in pulsed resource systems. Our findings underscore the importance of understanding producer-consumer interactions under climate change, providing globally relevant insights into the interplay of abiotic drivers, species-specific behaviours, and ecological resilience. These results contribute to advancing strategies for wildlife conservation and forest management in the face of ongoing environmental change.