Abstract
Plant
populations in fragmented ecosystems rely largely on internal dispersal by animals. To unravel the mechanisms
underlying this mode of dispersal, an increasing number of experimental feeding studies is carried out. However, while
physical activity is known to affect vertebrate digestive processes, almost all current knowledge on mechanisms of internal
seed dispersal has been obtained from experiments with resting animals. We investigated how physical activity of the mallard
Anas platyrhynchos, probably the quantitatively most important biotic dispersal agent in aquatic habitats in the entire
Northern Hemisphere, affects gut passage survival and retention time of ingested plant seeds. We fed seeds of nine common
wetland plants to mallards trained to subsequently swim for six hours in a flume tank at different swimming speeds (activity
levels). We compared gut passage survival and retention times of seeds against a control treatment with mallards resting in
a conventional dry cage. Intact gut passage of seeds increased significantly with mallard activity (up to 80% in the fastest
swimming treatment compared to the control), identifying reduced digestive efficiency due to increased metabolic rates as a
mechanism enhancing the dispersal potential of ingested seeds. Gut passage speed was modestly accelerated (13% on average)
by increased mallard activity, an effect partly obscured by the interaction between seed retention time and probability
of digestion. Gut passage acceleration will be more pronounced in digestion-resilient seed species, thereby modulating their
dispersal distances. Our findings imply that seed dispersal potential by mallards calculated from previous experiments with
resting birds is highly underestimated, while dispersal distances may be overestimated for some plant species. Similar effects
of physical activity on digestive efficiency of mammals suggests that endozoochorous dispersal of plant seeds by vertebrates
is more effective and plays a quantitatively more important ecological role in both terrestrial and aquatic ecosystems than
previously thought.
populations in fragmented ecosystems rely largely on internal dispersal by animals. To unravel the mechanisms
underlying this mode of dispersal, an increasing number of experimental feeding studies is carried out. However, while
physical activity is known to affect vertebrate digestive processes, almost all current knowledge on mechanisms of internal
seed dispersal has been obtained from experiments with resting animals. We investigated how physical activity of the mallard
Anas platyrhynchos, probably the quantitatively most important biotic dispersal agent in aquatic habitats in the entire
Northern Hemisphere, affects gut passage survival and retention time of ingested plant seeds. We fed seeds of nine common
wetland plants to mallards trained to subsequently swim for six hours in a flume tank at different swimming speeds (activity
levels). We compared gut passage survival and retention times of seeds against a control treatment with mallards resting in
a conventional dry cage. Intact gut passage of seeds increased significantly with mallard activity (up to 80% in the fastest
swimming treatment compared to the control), identifying reduced digestive efficiency due to increased metabolic rates as a
mechanism enhancing the dispersal potential of ingested seeds. Gut passage speed was modestly accelerated (13% on average)
by increased mallard activity, an effect partly obscured by the interaction between seed retention time and probability
of digestion. Gut passage acceleration will be more pronounced in digestion-resilient seed species, thereby modulating their
dispersal distances. Our findings imply that seed dispersal potential by mallards calculated from previous experiments with
resting birds is highly underestimated, while dispersal distances may be overestimated for some plant species. Similar effects
of physical activity on digestive efficiency of mammals suggests that endozoochorous dispersal of plant seeds by vertebrates
is more effective and plays a quantitatively more important ecological role in both terrestrial and aquatic ecosystems than
previously thought.
| Original language | English |
|---|---|
| Number of pages | 9 |
| Journal | Oikos |
| DOIs | |
| Publication status | Published - 2014 |