A Primary Study On Foraging Spatial Heterogeneity Of Large Herbivore

Grazing is not only important utilization mode of grassland and also management tool in grassland systems. Foraging of grazing livestock directly impacts both grassland ecosystem function and herbivore productivity of grassland. Typical characteristic of grassland is strong spatial heterogeneity, which includes not only the diversity of species composition, but also the varied spatial pattern. Foraging selectivity of large herbivore not only is reflected on plant individual, species, but also spatial location. Experimental and theoretical work on the interaction between foraging selectivity of large herbivore and plant heterogeneity is very important for maintaining the stability of grazing grassland systems, managing and developing stocking raising in grassland. This study revealed the foraging spatial heterogeneity of different grazing herbivore species (cattle and sheep) and effects of different herbivore assemblage (single grazing and mixed grazing) on spatial heterogeneity of grassland grazing intensity in the context of different grassland plant diversity. We analyzed the relationship between plant heterogeneity and foraging spatial heterogeneity of large herbivore, and the regulating effects of plant diversity on foraging spatial heterogeneity of large herbivore. Finally we attempted to elucidate the mechanisms of foraging spatial heterogeneity of different large herbivore. This study is vital in rational utilization of grassland and making effective grazing management policies.We obtained the important results and conclusions as follows.1) Plant diversity significantly affected foraging spatial heterogeneity of large herbivores in grassland. At low plant diversity, grazing livestock showed the spatial characteristics of the patchy foraging, and spatial distribution of food intake showed exponential models. At high plant diversity, spatial distribution of food intake by grazing livestock was linear or exponential model and spatial characteristics of herbivore foraging is random or patchy foraging.2) Different herbivore species exhibited obviously different characteristics of foraging spatial heterogeneity. At low plant diversity, sheep showed smaller patchy foraging, while cattle showed larger patchy foraging at low plant diversity. However, at high plant diversity, semi-variance was linearly related for consumption of sheep and cattle. The relative structure variation of sheep consumption was stronger than cattle at both two plant diversity levels.3) In mixed grazing treatment, spatial heterogeneity of consumption was significantly different from cattle or sheep single grazing treatment, which depending on plant diversity backgrounds. At low plant diversity, mixed grazing exhibited patchy foraging characteristics, which was similar to the cattle or sheep single grazing treatment. And the patch size and the degree of spatial heterogeneity were between cattle and sheep single grazing treatments. At high plant diversity, mixed grazing exhibited random foraging characteristics with a strong variation of spatial heterogeneity compared with single sheep or cattle single grazing.4) Both grassland plant diversity and herbivore type significantly affect the spatial heterogeneity of utilization intensity. At low plant diversity, sheep exhibited patchy utilization intensity, while cattle exhibited non-patchy utilization intensity. On the contrary, at high plant diversity, cattle exhibited patchy utilization intensity, while sheep exhibited non-patchy utilization intensity. At both two plant diversities, mixed grazing exhibited a strong variation of patchy utilization intensity.In summary, herbivores exhibited non-homogeneous foraging characteristics, which may depend on the spatial patterns and degree of spatial heterogeneity of plant species composition, biomass and so on. Both foraging spatial heterogeneity and plant spatial heterogeneity leaded to the spatial heterogeneity of utilization intensity of large herbivore. That is, the spatial heterogeneity of grazing pressure. This change of the degree of spatial heterogeneity was bound to affect the effects of grazing on grassland ecological function. Therefore, it was a new alert for the current grazing management, namely, moderate grazing pressure defined.