Mean predation of A. ludoviciana, R. obtusifolius and H. spontaneum seeds during six weeks of experiment in two barley fields. Error bars represent the standard error of the means (SE). Within fields, the means with the same letter are not significantly different according to LSD test . In graphs (a), (b) and (c), the white columns are without seed covering tissue and the black ones are with seed covering tissues treatment. In graph (d): field number 1: First column (c) represents: H. spontaneum, second column (a) represents: A. ludoviciana, third column (b) represents: R. obtusifolius, forth column (A) represents: Mean predation, field number 2: First column (b) represents: H. spontaneum, second column (a) represents: A. ludoviciana, third column (a) represents: R. obtusifolius and forth column (B) represents: Mean predation.