Effects of dispersal pattern and mammalian herbivores on seedling recruitment for Virola michelii (Myristicaceae) in French Guiana

The effects of dispersal pattern (seeds in small clumps vs. seeds scattered in pain) and distance to the nearest Carapa procera (Meliaceae; a tree tha t produces seeds preferred by terrestrial vertebrates) on survival of seeds and seedlings were examined for the anima-dispersed tree species Virola mi chelii (Myristicaceae) in a mature forest at Paracou, French Guiana, in 199 2 and 1993. We assessed the putative role of ground-dwelling mammalian herb ivores, rodents, and ungulates that filter the seed shadow, acting either a s dispersers or predators and thus modifying the original pattern of seed d ispersal made by frugivores. We measured the effects of simulated seed buri al by rodents using marked seeds and quantified the effect of protecting se eds and seedlings from ground-dwelling vertebrates on seedling germination and survival with fence exclosures in 1992. Dispersal pattern had short-ter m but no long-term effect on the proportion of V, michelii seeds that survi ved one year later as seedlings. In the short term, within six weeks, clump ed seeds survived better than scattered seeds in both years. Marked seeds t hat were removed from their site of dispersal were eaten; rodents only rare ly buried seeds of V. michelii, and seed burial reduced seed and seedling s urvivorship. The combined effect of the factors year and Carapa proximity s ignificantly affected seed survival within six weeks. Although six-week see d survival was greater in 1993 than in 1992, seedling establishment was low er in 1993 than in 1992 following a lower rainfall regime during the key pe riod of seed germination (February). One-year seed and seedling survivorshi p was similar between treatments and years. Seed survival and seedling esta blishment in V. michelii was dependent on vertebrates in the short term and on climate in the long term. Overall, seed and seedling survivorship depen ded on a combination of these factors.