EFFECTS OF SEED DENSITY ON GERMINATION AND ESTABLISHMENT OF A NATIVE AND AN INTRODUCED GRASS SPECIES DISPERSED BY GRANIVOROUS RODENTS

Dense aggregations of Oryzopsis hymenoides (Indian ricegrass) and Brom us tectorum (cheatgrass) seeds occur in rodent caches in the Great Bas in. Rodent caching behavior may influence establishment and persistenc e of these two desert grasses. Seed caches of rodents clearly introduc e exaggerated seedling competition in these species. Greenhouse experi ments were used to determine if establishment and persistence of these species were affected differently by densities of seeds in caches. Ge rmination and establishment of Indian ricegrass, a native perennial gr ass, were less affected by high seed densities than germination and es tablishment of cheatgrass, an introduced annual weed. The different na tural histories of these species, as well as data presented here, sugg est that the high seed densities introduced by caching behavior of des ert rodents may be beneficial to Indian ricegrass and harmful to cheat grass.