ANT NESTS AS PRIMARY HABITATS OF SILYBUM-MARIANUM (COMPOSITAE)

The common Mediterranean ruderal thistle Silybum marianum is associated with nutrient-rich sites. Its wind-dispersed achenes possess an oily food body, that is attractive to harvester-ants. Following removal of the oily body, the achenes are deposited in the refuse zone together with rich organic material and soil removed from the nest; while in the nest the achenes are partly protected from fires. The thistle grows successfully in the nutrient-enriched refuse zone and thus dominates patches in the grassland. Preadaptations to live in association with harvester-ants enable S. marianum to occur also on marking stations of male gazelle, on cattle dung deposits, and in synanthropic ruderal habitats. © 1990 Springer-Verlag.