FRUIT LAXATIVES AND SEED PASSAGE RATES IN FRUGIVORES - CONSEQUENCES FOR PLANT REPRODUCTIVE SUCCESS

To explore how plants may influence dispersal of their own seeds by ma nipulating the behavior and physiology of their dispersers, we studied the effect of a soluble chemical (or chemicals) in the fruits of With eringia solanacea (Solanaceae), a Costa Rican cloud forest shrub, on p assage of its seeds through the guts of one of its major dispersers, t he Black-faced Solitaire, Myadestes melanops (Muscicapidae: Turdinae). Using artificial fruits containing natural seeds, we found that the p resence of a crude pulp extract reduced the median seed retention time by nearly 50%. Estimation of seed dispersal distance as a function of retention time suggested that more rapid seed passage results in shor ter average dispersal distances, especially for seeds retained <20 min . At the same time, germination trials revealed that seeds voided rapi dly were far more likely to germinate than those remaining longer in M yadestes guts. We propose that ''laxative'' chemical(s) in Witheringia fruits balance these positive and negative consequences of ingestion by Myadestes.