Living on the edge: ecological and evolutionary dynamics along invasion fronts

Invasion fronts are the edges of non-native species’ ranges and represent dynamic, non-equilibrium boundaries where colonization, ecological interactions, and rapid evolutionary processes converge. Although biological invasions are increasingly well studied, mechanisms operating at these advancing margins remain conceptually fragmented despite their disproportionate influence on spread dynamics, exerted impact, and management. Here, we synthesize how invasion-front geometries arise from interactions among propagule pressure, landscape permeability, long-distance dispersal, and environmental heterogeneity, producing continuous, fragmented, stratified, or coalescing fronts that shift with invasion stage and scale. We integrate ecological and evolutionary evidence to show how gradients from core to front include declining density, increased trait divergence, spatial sorting, serial founder effects, expansion load, and behavioural and physiological differentiation. We synthesise parallels with climate-driven range expansions of “neonative” species while emphasizing the stronger disequilibrium and novel biotic contexts characteristic of non-native fronts. Finally, we map these dynamics onto impact trajectories, demonstrating how trait-mediated interactions, resource reallocation, and system-level reconfiguration emerge sequentially along the invasion gradient. By unifying ecological and evolutionary processes across appropriate spatial and temporal scales, we establish invasion fronts as powerful, but understudied natural laboratories and critical leverage points for predicting, monitoring, and managing biological invasions.