Animal dispersal costs are not universal

Dispersal is a keystone process shaping ecological and evolutionary dynamics, often assumed to be inherently costly. We synthesized 696 effect sizes from 206 studies across 148 animal species, spanning all continents and ecosystems, to test this assumption. Contrary to long-standing dogma, we found no overall effect of dispersal on fitness (mean effect size: -0.03, 95% CIs: -0.09 to 0.03). No tested biological or methodological moderators explained this variation. Instead, heterogeneity was highest within studies, suggesting that dispersal is highly context-dependent within studies and species. These findings align with game-theoretic expectations that dispersal and philopatry are alternative strategies maintained by balancing or frequency-dependent selection. Our findings are consistent with the view that dispersal involves a balancing act between strategies that yield equivalent long-term payoffs across variable conditions.