Functional trait interactions drive seed buoyancy and dispersal strategies in Echinocystis lobata

Echinocystis lobata is an invasive vine species that successfully colonized riverine habitats in Central and Eastern Europe. Although barochory and blastochory have been considered the main mechanisms of its dispersal, increasing evidence indicates an important role of hydrochory, especially nautohydrochory. The study aimed to determine how morphological features of seeds – mass, thickness, surface area, and entrapment status – affect their ability to float. Results obtained from a generalized mixed-effect model assessing the probability of E. lobata seeds sinking showed that seed mass affected their buoyancy depending on thickness and entrapment status: thinner seeds with higher mass were more likely to float. In contrast, heavier, entrapment seeds sank faster. Seed thickness significantly reduced the probability of sink, regardless of other features, while the effect of surface area on buoyancy depends on mass; in the case of lighter seeds, a larger surface area increased the risk of sinking. Trapped seeds differ in the way they are released and the course of dispersion – their structure, despite a more frequent loss of buoyancy with a larger mass, may delay the moment of fruit abandonment and promote colonization during periods of water surges. The observed variability of diaspore features supports a plastic strategy, enabling both hydrochory and barochory, depending on habitat conditions. The ability of seeds to float on water for a long time highlights the important role of morphological and ecological adaptations in the invasive success of E. lobata .