Effects Of Grassland Degradation And Grazing Period On Foraging Behavior And Foraging Interaction Of Cattle And Sheep

As one of the important terrestrial ecosystems in China,the grassland ecosystem's functions include ecological protection and production service,so it is of great significance to maintain the stability of its structure and function.But 90 percent of grassland is in different stages of degradation in China at present,and the extensive and unreasonable grazing use are the most obvious causes the degradation of grassland in large areas.As a managed ecosystem for grassland,the grazing management of grassland is also facing severe challenges in the context of grassland degradation in large areas,we urgently need to explore scientific and accurate grassland grazing management methods to cope with the increasingly severe grassland degradation.Cattle and sheep are the most common grazing livestock in the grassland,and they have the characteristics of large volume and high energy demand,so the foraging behavior of cattle and sheep is a key step in the nutrient cycling and energy flow of the grassland ecosystem,which plays an important role in maintaining the normal structure and function of grassland.There are significant differences in the quantity,quality and community structure of plant resources in different degraded states and during different grazing periods,which will affect the foraging behavior of cattle and sheep through the bottom-up effect,while the foraging behavior will also exert a top-down feedback on the plant community.Therefore,based on the research on the changes of important behavioral characteristics such as foraging efficiency and foraging selectivity of cattle and sheep in different degraded grasslands and during different grazing periods,we revealed the foraging behavior strategies changes and the interaction of grazing livestock(cattle and sheep)under different degraded states and grazing periods in grassland,and discussed the co-evolutionary characteristics between different livestock species and vegetation.This research not only provides an important theoretical basis for the development of more precise and scientific grazing management methods in the future,but also helps to improve our understanding of herbivore foraging theory and the mechanism of grassland ecosystem stability.The main conclusions are as follows:(1)With the seasonal growth changes of grassland vegetation,the foraging behavior of cattle and sheep changed significantly but there are differences between them.At the peak of plant growth in July,the foraging efficiency of sheep(the number of foraging bites per unit of walking steps)and the diversity of foraging(diversity of recipe composition)were significantly lower than those of early plant growth in June;In contrast,the foraging efficiency of cattle was significantly higher in July than in June,and the diversity of foraging did not change significantly.The seasonal dynamics of vegetation quantity and quality determined the different foraging response of cattle and sheep;sheep had higher requirements for food quality,the palatability of grassland plants limited the breadth of available recipes for sheep as the growing season progresses,which reduced foraging diversity and increased the cost of searching for highly palatability species,in addition,the increased complexity of plant community structure further increases the search cost of sheep in July,which reduced the foraging efficiency;on the contrary,the large-scale herbivore-cattle has a higher requirement for food quantity,so the higher plant biomass will increase the amount of food consumed and bite size for cattle,thereby increasing foraging efficiency and reducing consumption on the walking with the proceeding of growth season.(2)The degradation of grassland has significant effects on the foraging behavior of cattle and sheep.With the degradation of grassland,the foraging efficiency of sheep increased significantly in June and July,while the foraging efficiency of cattle increased significantly only at the peak of plant growth(July),and decreased significantly in early growth period(June).And the difference in plant composition and distribution characteristics of different degraded grassland determines the different foraging response of cattle and sheep;patch degradation causes the plant resources to be more spatially distributed,which helps to increase the probability of livestock searching favorite plants,thereby improving their foraging efficiency;At the same time,due to the high demand for the quantity of resources in cattle,the degraded grassland reduced the plant biomass available to cattle at early growing season due to the presence of alkali patch,which reduced the foraging efficiency of cattle in turn.But sheep have higher requirements on food quality,and the aggregative distribution of plant resources in degraded grassland cause sheep to exhibit significantly high foraging efficiency.(3)There are certain differences and similarities on the foraging behavior of cattle and sheep.The difference is mainly reflected in the foraging efficiency,the study found that the foraging efficiency of cattle is significantly higher than that of sheep no matter what kind of vegetation conditions,which is determined by the huge difference in the body size between cattle and sheep,and also is the most direct manifestation of the niche differentiation of cattle and sheep;The similarity is mainly reflected in the foraging selectivity,cattle and sheep mainly eat grasses such as Leymus chinensis and Phragmitis australis which grow early in June,and the foraging is mainly concentrated on Setaria viridis in degraded and undegraded grassland in July,which is related to the majority of gramineous plants in degraded and undegraded grassland and the high palatability and patcy distribution patterns of Setaria viridis in July.At the same time,we also found that it's different when cattle and sheep are in a community structure with high plant diversity,uniform distribution and complex vertical structure at the peak of growing season,cattle are difficult to make fine selectivity for food resources and more inclined to eat the most abundant gramineous plants,including Leymus chinensis and Setaria viridis due to their lower selectivity,so cattle's dietary diversity is lower,but their resource utilization efficiency is higher and their tolerance to food resources is stronger;while sheep eat certain Setaria viridis,but more is biased towards the foraging of the legumes and forbs,the foraging diversity of sheep is higher,and its resource utilization efficiency is low.So there exists obvious niche differentiation in the diet selection between cattle and sheep.(4)The interaction between cattle and sheep is related to the abundance of plant resources and plant community structure.Through comparative analysis of single-grazing mixed-grazing data,it was found that cattle foraging was not affected by sheep in a short period of time,but sheep were inhibited by cattle in June,and did not show significant differences in July,which was related to plant resources in the early grazing period.The high foraging rate of cattle in June are related to the fast foraging rate,which has formed a foraging inhibition on the use of space resources.Therefore,we suggest that the utilization of cattle and sheep mixed grazing should be selected in the season of plant-rich grazing season.In addition,our study also found that the interaction between cattle and sheep is closely related to the structure of plant communities.When grazing in a plot with high diversity,uniformity and vertical structure,the sheep eat longer in the plots where the cattle have been eaten.It indicates that there may be positive interaction between cattle and sheep due to niche differentiation of foraging.In summary,this study obtained a deeper understanding on the foraging behavior of livestock from the perspective of grazing livestock species,grassland degradation states and different grazing periods.Foraging behavior of cattle and sheep should change with the growth season of the vegetation to meet the physiological needs for the foraging behavior.Therefore,the results of this study suggest that the grazing period is also an important consideration when formulating scientific and rational grazing management policies.The intake of cattle and sheep has changed significantly during different grazing periods,which can provide an important basis for us to judge the utilization of grassland resources in different periods and to regulate the utilization of grassland resources according to animal foraging options.Secondly,this study also reflects the special attention to grazing degraded grassland grazing use,patch degraded grassland is more suitable for sheep grazing utilization,and for cattle grazing use should pay attention to grazing season or period,It is more appropriate in the context of more abundant plant resources.If cattle is grazed in the early grazing season,on the one hand,the lower foraging efficiency of cattle is not conducive to the improvement of its production performance.On the other hand,the lower foraging efficiency may have too much trampling effects on grassland.However,the intensity and time of grazing should be strictly controlled regardless of the use of cattle and sheep grazing,because our research results also indicate that the patch distribution on the larger scale of grassland resources is not conducive to resisting livestock selective foraging,unreasonable grazing and utilization may cause further heterogeneity and lower diversity of grassland,so maintaining the integrity of grassland plant community structure will help maintain the stability of the entire grazing ecosystem.Finally,this study demonstrates that the differences in foraging behavior between cattle and sheep are closely related to vegetation conditions.The foraging efficiency and food tolerance of cattle is higher,Therefore,we suggest considering different mixed grazing pattern between patched and homogeneous grassland,it can be used that sheep grazing firstly and cattle grazing subsequently in patched grassland,and cattle grazing firstly and sheep subsequently or simultaneously in a more homogeneous,higher plant diversity of grassland,so that grassland resources can be used more effectively,and reduced the adverse effects that animals with excessive selective feeding on the grass.