Juvenile-adult asymmetry in species interactions and risk-taking behavior: mechanisms governing population stability

Within-species size variation is known to create asymmetries in resource competition and, increasingly, is recognized to correlate with systematic shifts in behavioral responses (e.g., boldness) between juveniles and adults. The combined effects of these asymmetries on population stability, especially under anthropogenic pressures, however, remain poorly understood. We use a size-structured consumer-resource model, analyzed via a delayed system framework, to investigate the stability and resilience implications of juvenile-adult asymmetry in competitive ability and average boldness levels. Our analysis reveals that when juveniles are bolder than adults, population stability and resilience to disturbance increase significantly, particularly in systems where adults are stronger competitors. However, this stabilizing effect is context-dependent. Although the effect is weakened by higher juvenile mortality, it remains strong enough to offset the destabilizing impact of large adult-offspring size ratios. These findings underscore the critical need to incorporate ontogenetic shifts in key traits, especially in competitive and behavioral traits, when assessing population stability and resilience in changing environments.