Abstract
It was proposed previously that passive
dispersal by migratory aquatic birds explain the widespread distribution of
many wetland organisms. Several experimental studies have shown that many
widespread wetland plant species can be readily dispersed within the guts of
Anatidae. However, it is unclear whether plants with a more restricted
distribution are able to disperse via waterbirds. This paper addresses the
dispersal ability and germination ecology of the little-known Hungarian
milkvetch Astragalus contortuplicatus, which occurs on banks of
continental rivers and has a limited and unpredictable distribution. To test
whether limited capacity for endozoochory by waterfowl could explain the
sporadic appearance of this species, we force-fed ten captive mallards (Anas
platyrhynchos) with 100 milkvetch seeds each. Droppings were collected for
up to 45 h after feeding. Intact and viable seeds were found in the droppings
of each mallard, and altogether 24.7% of seeds fed were recovered intact. The
proportion of retrieved seeds that germinated (27.0%) was significantly higher
than that of untreated control seeds (0.5%), but significantly lower than that
of mechanically scarified seeds (96.0%). Retrieved seeds that germinated
developed into healthy mature plants. Given the average flight velocity of
mallards, seeds of A. contortuplicatus may travel up to 1600 km inside the
digestive tract of migrating individuals. Our results suggest that avian
vectors may be more important for the dispersal of rare higher plants
(especially those with a hard seed-coat) than hitherto considered. Moreover,
they suggest that rarity does not necessarily indicate limited dispersal ability,
and may instead be explained by specific habitat requirements.
Keywords
Anas
platyrhynchos, germination experiment, mallard, ornitochory, seed dispersal,
seed ecology, seed viability
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