Habitat-dependent seed dispersal of an introduced tree species by native rodents

Abstract

Invasions of many plant species strongly depend on propagule pressure. Thus, habitat-related differences in seed dispersal could affect susceptibility of distinct habitat types to plant invasions. We examined the fate of northern red oak (Quercus rubra, invasive in Europe) and pedunculate oak (Quercus robur, native in Europe) acorns dispersed by yellow-necked mice (Apodemus flavicollis) in (i) hardwood stands invaded by northern red oak, (ii) uninvaded hardwood stands dominated by native oaks, and (iii) uninvaded coniferous stands dominated by Scots pine (Pinus sylvestris). Regardless of forest type, mice preferred to harvest and consume pedunculate rather than red oak acorns. Similarly, acorn harvest rates were unaffected by forest type. However, the fate of acorns, and thus effectiveness of seed dispersal, varied considerably among forest types. Acorns had the highest probability of being cached in uninvaded hardwood stands, while coniferous stands were characterized by the longest seed dispersal distances and a high proportion of missing seeds (probably indicating larderhoarding). Relative to the other forest types, stands with northern red oak were characterized by a combination of low acorn caching rates and short dispersal distances. These findings suggest that differences in rodent-mediated seed dispersal might increase recruitment rates of northern red oak at the edges of invaded range.