The rapid spread of exotic plants is a global concern, but the mechanisms behind their dispersal are still not fully understood. A research team, with participation from the Doñana Biological Station (CSIC), focused on endozoochory: the dispersal of seeds through ingestion, transport, and expulsion by waterbirds. Given their observed rapid expansions, the team hypothesized that these exotic species would have inherent advantages in endozoochory compared to native plants. Specifically, they proposed that exotic seeds, after passing through the digestive tract, would show a higher passage rate, longer retention times, greater germination capacity, and a shorter time to sprout.

To test this hypothesis, the researchers compared the survival of seeds from six exotic plant species and six genetically related native wetland species in a feeding experiment using Mallards (Anas platyrhynchos). Seed shape and volume were corrected for in the analysis, as these traits are known to significantly affect seed outcomes.

When all species were combined, the results showed that 32% of exotic seeds passed intact through the digestive tract, compared to 29% of native seeds, indicating a slightly higher probability of survival for the exotic plant seeds. Among the control seeds, the exotic seeds germinated in greater numbers and faster than the native ones. Furthermore, seed traits such as size and shape explained the differences in germinability and time to germination in the control seeds

Exotic plant seeds possess traits that correlate directly with successful endozoochory. This gives exotic species a significant competitive advantage over native plants by ensuring higher endozoochory rates in new environments, which potentially fuels their rapid expansion. This new study highlights the crucial role of seed traits in determining the endozoochory potential of both exotic and native species, particularly through their influence on retention time and germination success.