Comparative seed predation of woolly cupgrass (Eriochloa villosa) and yellow foxtail (Setaria pumila) along a field border in Canada.

The seed predation of woolly cupgrass (Eriochloa villosa), an invasive weed of East-Asian origin, was compared to that of yellow foxtail (Setaria pumila), an established and widespread weed, along a field border in Canada. The seeds of both species were glued to sandpaper cards and their removal in field conditions was recorded from July to September during the 3 years of 2009, 2010 and 2011. Predator exclusion cages allowed the evaluation of seed loss to be attributed to invertebrates, vertebrates and total seed loss due to predation for both species. Pitfall traps were installed and collected once in 2010 and during all the seed sampling dates in 2011 in order to evaluate predatory pressure from ground beetles and crickets. The average amount of seed loss that could be attributed to invertebrates was higher for S.pumila than for E.villosa, while the amount of seed loss that could be attributed to vertebrates was higher for E.villosa than for S.pumila in 2009 and 2010. The level of S.pumila seed loss to invertebrates was correlated with the sum of crickets (Gryllus pennsylvanicus) and beetles (Harpalus spp. and Ophonus rufibarbis) trapped during the 2011 season. During the same period, correlations between E.villosa seed loss to invertebrates and trapped insects were not observed. Reduced postdispersal seed predation by invertebrates could increase the local fall survival of the unburied seeds of invasive E.villosa populations, compared to other naturalized, smaller-seeded weedy grasses.