From wings to tails: the aspect ratio of propulsive surfaces as a general proxy for vertebrate dispersal potential
Dispersal shapes many fundamental processes, however, comprehensive measures of dispersal are unavailable for most taxa, limiting our ability to evaluate ecological theory at broad scales. Existing tracking data are often taxonomically and geographically biased, highlighting the need for alternative trait-based approaches to infer dispersal potential. Here, we test whether the aspect ratio of propulsive surfaces provides a general morphological basis for inferring dispersal potential. We show that caudal fin shape is a morphological indicator of dispersal potential in sharks, as it predicts swimming speed and geographic range size. Across 452 (82%) shark species, we find no latitudinal gradient in dispersal potential, contrasting with patterns observed in birds. Instead, dispersal potential is structured by ecological specialization, with no direct effect of environmental temperature on caudal fin shape. We find high dispersal potential is associated with pelagic habitats and metabolically relevant traits, including body size and oxygen uptake capacity. Because morphology can be measured from museum specimens and illustrations, this approach offers opportunities to compare dispersal potential across air and water dwelling vertebrates.