2020 Volume 16 Pages A1-A14
Seed dispersal is the movement of seeds away from parent plants, usually mediated by abiotic or biotic agents. Most Arisaema species (Araceae) bear bright orange-red fruits in autumn. We investigated the fruit removal of a poisonous herb Arisaema serratum by using cameras for three years, and identified the quantitatively effective seed dispersers in two study sites in central Japan. Furthermore, we conducted germination experiments of seeds dispersed by two bird species Hypsipetes amaurotis and Turdus pallidus, both of which were identified as quantitatively effective seed dispersers of A. serratum. The study was conducted in a cedar plantation of the Forestry Experimental Station, Ishikawa Agriculture and Forestry Research Center, and at a second forest site at the Satoyama Zone, Kanazawa University, Ishikawa Prefecture, central Japan. By conducting camera-trapping at 60 fruiting individuals of A. serratum (11 plants in 2013, 20 plants in 2014, and 29 plants in 2015), we identified the frugivore assemblage that foraged on the fruits and quantified the number of visits and the number of fruits eaten on each visit. The top three bird species with the highest frequency of visitation were 180 times (47%) by T. pallidus, 118 times (30%), by H. amaurotis, and 40 times (10%) by Luscinia akahige. The top three species with high fruit consumption were 573 fruits (31%) by H. amaurotis, 481 fruits (26%) by T. pallidus, and 98 fruits (5%) by Zoothera dauma. The germination rates of seeds were 100% (N=129) for the seeds carried by H. amaurotis, 98.8% (N=163) for T. pallidus, and 97.1% (N=834) for controls, with no significant differences. The high number of visits to fruiting plants and fruit removal rates by H. amaurotis and T. pallidus for three years at two different study sites led us to the conclusion that they show high effectiveness in terms of quantity of seeds dispersed for A. serratum. Furthermore, both bird species were likely to be qualitatively effective seed dispersers because they disperse intact seeds within tens of meters in the appropriate habitats.
