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 Bromus tectorum (cheatgrass) seeds occur in rodent caches in the Great Basin. Rodent caching behavior may influence establishment and persistence of these two desert grasses. Seed caches of rodents clearly introduce exaggerated seedling competition in these species. Greenhouse experiments were used to determine if establishment and persistence of these species were affected differently by densities of seeds in caches. Germination and establishment of Indian ricegrass, a native perennial grass, were less affected by high seed densities than germination and establishment of cheatgrass, an introduced annual weed. The different natural histories of these species, as well as data presented here, suggest that the high seed densities introduced by caching behavior of desert rodents may be beneficial to Indian ricegrass and harmful to cheatgrass.
INTRODUCTION Birds, harvester ants, and rodents (primarily of the family Heteromyidae) are major granivores of North American deserts. Like some other rodents, species of the family Heteromyidae cache seeds in [...]