Effects of dung beetles (Scarabaeidae) on seeds dispersed by howler monkeys (Alouatta seniculus) in the French Guianan rain forest

The dispersal of seeds by howler monkeys (Alouatta seniculus) and the role of dung beetles in determining the fate of the dispersed seeds were studied at Nouragues Station, French Guiana, during three 2-mo periods (April-May, 1995-97). Howler monkeys were observed to disperse seeds of 47 plant speci es. Monkey dung attracted 57 species of dung beetles (Scarabaeidae), includ ing tunnellers (maximum size 37 mm) and ball rollers (12.6 mm). The rate of seed burial was negatively correlated with seed size (10 plant species) an d positively correlated with dung beetle size (six species of tunnellers). More than 80% of small seeds (< 5 mm) and 30% of large seeds (22 mm), were buried by the largest tunnellers. Dung beetles buried 13 to 23% of seeds ra nging 8-13 mm in width. The maximum average depth of burial was 28 cm and v aried according to the species of dung beetle. The rate of disappearance of large dung clumps varied during the day and was completed by nocturnal dun g beetles. Seeds of Chrysophyllum lucentifolium (Sapotaceae) buried at 5 an d 10 cm depths did not suffer predation, but showed low germination success compared to seeds left at the soil surface. Dung beetles affected the surv ival and distribution of a portion of the seeds dispersed by monkeys, and t heir relative importance in shaping seed fate depended on seed and beetle s ize.