Objectives: identify the dispersers of two species of Melocactus; verify their patterns of fruit offering and correlate this with removal by frugivores and with temperature variations of the cephalium; and analyze the relationship between the spatial distribution of the Melocactus species and the behavior of their dispersers. Focal observations were made of fruit emergence, extrusion and removal, cephalium temperature, ant-diaspore interactions, and plant spatial distribution. Germination tests were also made. Two lizard and three ant species were dispersers of the two species of Melocactus. Seed dormancy was not broken in the digestive tracts of the lizards. The greatest rates of fruit removal by the lizards occurred during the mid hours of the day, coinciding with or following the extrusion peak. Fruit emergence and extrusion rates were highest in the morning, increasing their chances of being taken on the same day, thus avoiding desiccation and predation. No correlation was observed between fruit liberation and thermal variations of the cephalium. Fruit development generates tension within the fiber mass of the cephalium that provokes fruit emergence/expulsion. The expulsion of the fruits may also be aided by the dilation of the cephalium fibers as they warm, tension generated at the cephalium base where the fibers unite, and by the expulsion of other fruits. The spatial distribution of these cacti is influenced by disperser behavior.
Dispersion; germination; spatial distribution; cephalium temperature
