Fructificación, frugivoría y disperción en el cactus globular Melocactus Schatzlii en el enclave semiárido de Lagunillas, Mérida, Venezuela

Abstract

The objectives of this study were: i) monitoring the fruiting process from anthesis to fruit emergency in the globular cactus Melocactus schatzlii in the Lagunillas semiarid enclave, Merida-Venezuela, and ii) to identify their main fruit consumers and detect their potential seed dispersers. The number of fruits produced was registered in 102 sexually mature cacti, five days/month, during an entire year. Composition and structure of frugivorous guilds associated to M. schatzlii fruit production were also studied, in a 398 hour film record. Fruit production occurs throughout the year, with two periods of maximum production, the first between May and June, the second between October and December. The average range between pollination and fruit formation was 60±12 (DE) days. Fruit production patterns seem to be highly correlated with precipitation regimes (r=0.86), as we inferred from forwarding one month of fruit production data. Vertebrates are the main fruit consumer of this species; represented in first place by lizards, which account for the 90% of the consumption events, represented mainly Ameiva provitae and Cnemidophorus lemniscatus, while the remaining 10% is represented by two species of birds, Tiaris bicolor and Mimus gilvus. Despite the fact that vertebrates were responsible for more than 90% of seed mobilization, we recorded 12 species of invertebrate fruit consumers. In this guild, Ectatomma ruidum ants employ the longest time of consumption, according to the film records (>50 hours; 23 diurnal and nocturnal 27) followed by Blattidae nymphs (>25 hours, primarily nocturnal). Seedling germination experiments revealed that: 50% (T 50 ) of the washed seeds germinated within 8 days; T 50 of the seeds bearing pulp withim 11 days; and T 50 of the seeds defecated by C. lemniscatus and A. provitae within 11 and 13 days, respectively. Regarding the controls of the washed seeds and of the seeds with remains of pulp, germination percentages were 96% and 92%, respectively; whereas, in the case of the controls of the seeds ingested by C. lemniscatus and A. provitae, germination rates were of 93% and 83%, respectively, confirming their role as seed dispersors of M. schatzlii. Statiscally significant differences were observed in all of the germination treatments when compared as pairs, save the pair seeds trated by C. lemniscatus and unwashed seeds. Potential germination inhibitors only appear to retard imbibhition onset. The lizards A. provitae and C. lemniscatus were the main fruit consumers and the responsible of seed movement of M. schatzlii, which support saurocory as the dispersion syndrome for the Melocactus genus.