Predation and dispersal of acorns by European Jay (Garrulus glandarius) differs between a native (Pedunculate Oak Quercus robur) and an introduced oak species (Northern Red Oak Quercus rubra) in Europe

Abstract

Invasive species have a substantial influence on the environment, especially through competition with local, native species. In Europe, oak trees provide a good example of competition between species native to the region and species introduced from elsewhere in the Northern Hemisphere. When introduced species start to have a negative impact they are considered invasive. Here we focus on the seed dispersal of a native (Pedunculate Oak Quercus robur) compared to an introduced oak (Northern Red Oak Quercus rubra) where the main animal disperser of acorns is the European Jay Garrulus glandarius. The study was conducted in two forests in western Poland by placing acorns of both species in trays and monitoring their removal, and by recording establishing oaks on transects. We showed that jays were about twice as likely to harvest the acorns of the native oak compared to those of the introduced oak. Nevertheless, the extent of dispersal by jays of the acorns of the introduced oak species will facilitate colonization of new areas. Establishment of young trees of the introduced species was much greater than that of the native species despite the former having lower dispersal and being considerably underrepresented in the canopy. Thus, consequences for patterns of oak survival and forest development seem very likely.