Effets de la fragmentation forestière sur l'activité des coléoptères coprophages: Dispersion secondaire des graines en Guyane Française

The effect of seed burial by dung beetles on seed survival and seedling establishment in Tetragastris altissima (Burseraceae) was measured on 3 sites of continuous forest and 7 islands in the man-inundated rain forest of Saint-Eugène, French Guiana. Experiments using a total of 250 seeds were performed using wire enclosures open to dung beetles but excluding terrestrial seed predators. Fragmentation had no effect on the rate of dung disappearance at 12, 24 and 48 h because there was a high variability between sites. On average, 24 % of seeds were buried by dung beetles after 72 h. Overall, there was no effect of fragmentation due to variation between sites. Dung burial rates were positively correlated with rarefaction of the dung beetle samples collected on the different sites. They were also positively correlated with weighted abundances of large diurnal tunneliers after 12 h and to total tunneliers after 24 h. Seed burial was positively correlated to weighted abundance of large noctumal tunneliers and of total tunneliers. The species diversity and abundance were positively related to area that did not involve a correlation between seed burial rates and area. After 72 h, survival rate of protected seeds at ground surface was significantly larger (78 %) than for non protected seeds (22 %), which were attacked by rodents. There was no difference between continuous forest and islands. Eight percent of buried seeds emerged, i.e. 2 % of all seeds deposited. Burial depth significantly affected the rate of emergence of buried seeds. Ninety percent of seeds at surface gerrninated versus 0 % at 10 and 15 cm. The effects of seed burial by dung beetles on early recruitment of T. altissima was low and highly variable between sites in relation with the structure of the community of Scarabaeidae and intensity of seed predation