9Dumont B, Carrere P, D' hour P. Foraging in patchy grassland:Diet selection by sheep and cattle is affect- ed by the abundance and spatial distribution of pre ferred species[J]. Animal Research, 2002, 51:367- 381.
10Adler P B,Raff D A, Lauenroth W K. The effect of grazing on the spatial heterogeneity of vegetation[J]. Oecologia,2001,128:465- 479.
