PARENT SESSION
Poster Session # 20: Predator - Prey / Mutualism - Parasitism Ecology.
Thursday, August 7 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Seed dispersal of California bay-laurel (Umbellularia californica) by western gray squirrels (Sciurus griseus).
Faden, Mike 1, Parker, V.T.*,1, 1 San Francisco State University, San Francisco, CA
ABSTRACT- Western gray squirrels (Sciurus griseus) act as seed dispersers in mixed-evergreen forest in coastal California by scatterhoarding seeds of dominant tree species including California bay-laurel (Umbellularia californica) and oaks. Factors influencing dispersal distance and survival of cached Umbellularia seeds were investigated in fall 2001 and 2002, by following the fate of thread-marked seeds placed under Umbellularia canopies. Factors measured or estimated in one or both years included seed mass, fruit mass, cache pilferage, and local abundance of fruits eaten by squirrels including Umbellularia fruits and acorns. In fall 2001, numbers of seeds cached, cache survival, and dispersal distance were correlated with the local ambient abundance of fallen Umbellularia fruits. Mean dispersal distance was greater (11.2-15m) at sites where fruits were scarce or absent, compared with a mean distance of 1.7-3.7m at sites where fallen fruits were abundant. Overall, 26% of caches survived intact for more than six months; of these, 84% were at sites where fallen fruit was abundant in fall 2001. Field experiments suggested that burial at depths typical of rodent caches is essential for Umbellularia germination and seedling establishment. In fall 2002, trends in caching rates and dispersal distance were less clear. It is suggested that caching behavior may have been influenced by the fact that in contrast to 2001, oaks (Quercus chrysolepis, Lithocarpus densiflorus) at study sites produced a large acorn crop that coincided with Umbellularia fruitfall. The squirrels cached thread-marked acorns as well as Umbellularia fruits.
Key words: scatterhoarding, seed dispersal, mutualism