Effects Of Livestock Assemblages On The Plateau Pika And Arthropods In An Alpine Meadow Of Sanjiangyuan Area

The influence of livestock on grassland flora and fauna in grazing ecosystems is complex and far-reaching.Livestock can affect multiple trophic levels through direct and indirect effects,which in turn affect biodiversity and ecosystem processes and functions.Previously,studies on the effects of livestock grazing have been widely recognized,but grazing livestock often has differences in identities,and the current understanding of the mechanism of livestock assemblage on grassland is still lacking.In this study,grazing livestock enclosure experiments were carried out in a typical alpine meadow of Sanjiangyuan Area,revealing the effects and mechanisms of livestock grazing assemblage on the local common small animal plateau pika(Ochotona curzoniae)and arthropods.In view of the fact that the plateau pika population can be affected by grazing livestock,it also has a significant impact on arthropods.Therefore,the study first carried out large-scale(2 hm~2 plot)controlled grazing experiments to reveal the effects of different grazing livestock(yak,Tibetan sheep)and their assemblage on grassland soil characteristics,plant communities and plateau pika population;on this basis,in order to explore the effects of interaction between grazing livestock and pika on grassland,a mesoscale(400 m~2 subplot)pairing pika removal experiment was carried out nested within the grazing control experiment,and further research was conducted on this scale for the responses of arthropods.The study obtained the following main results:(1)Grazing experiments that lasted for 4 years(2013-2016)found that grazing is beneficial to the growth of pikas and can increase their population abundance.Grazing livestock reduced the above-ground biomass,vegetation height,and heterogeneity of the vertical space of the vegetation,thereby reducing the risk of predation of livestock.It can change the species composition of plant communities and increase the access of pikas to legume resources.This allows the pika population to benefit from multiple pathways of livestock grazing on plant communities.After two years of monitoring in 2015-2016,it was found that in the grazing plots,the abundance index of the pika during the peak breeding period increased by 33%-143%compared with the no-grazing plots.In addition,different body sizes of livestock have different effects on the pika population due to differences in their feeding habits.There are certain recipe overlaps between Tibetan sheep and pikas.When plant resources are poor,there is a certain degree of food competition between them.Therefore,Tibetan sheep have less influence on the population of pikas.When yak and Tibetan sheep are in mixed grazing,the mutually beneficial relationship between the two kinds of livestock feeding can improve the utilization efficiency of their respective plant resources,thereby producing the effect of resource partitioning,and is more conducive to the acquisition of food resources by the pika,which stimulates the growth of the pika population.(2)Through the pika removal experiment for 2 years(2015-2016),it was found that the plateau pika population activity had a significant effect on vegetation and soil landscape characteristics(including vegetation structure,burrow density pattern,etc.),which was beneficial to the total abundance of arthropod community.In alpine meadow areas,pika burrow is an important resource for many arthropods,such as habitat or shelter.Especially in the early stage of the plant growing season,the vegetation habitat has not yet taken shape,and the burrowing activity of the pika can maintain and increase the density of the effective hole and enhance hence improving the heterogeneity level of the habitat.It provides indispensable habitat conditions for the growth and development of larvae of arthropods such as Lepidoptera.Pika could also significantly reduce the vegetation height and plant aboveground biomass on a small scale(0.25 m~2).However,due to the secondary succession of vegetation around the pika abandoned burrows,the restored vegetation characteristics such as aboveground biomass and diversity can also produce compensation effect on a larger scale,which is beneficial to the total abundance of arthropod community.In addition,most arthropods have a high ability of active migration and depend on habitat during their development to adults.Due to the different degree of dependence of arthropods on habitat,the response of arthropods to pika was also different.(3)Through experiments of grazing and pika control for 2 years(2015-2016),it was found that grazing livestock and pika could interact with each other on different spatial scales,and then had effects on plant communities and arthropods.Grazing alone can reduce the total abundance of arthropods,but under the condition of mixed grazing by yak and sheep,the total abundance of arthropods is similar to that of non-grazing areas.The positive effect of livestock and pika on the total abundance of arthropods is opposite,but when the pika and livestock exist together,the pika can compensate the negative effect of livestock grazing on the total abundance of arthropods,so as to maintain the total abundance level of arthropods.Due to the above-ground burrow density pattern caused by pika activities and the secondary succession of surrounding vegetation,there is an interaction on different spatial scales between grazing livestock and pika on the diversity and structural characteristics of plant communities.Compared with single livestock grazing,herbivorous mammal assemblages have significant effects on vegetation coverage,vegetation height variation,and plant diversity index.In addition,there were some differences in the responses of arthropods from different feeding groups to livestock assemblage and pika.Among them,both yak and sheep had negative effects on herbivores and predators of arthropods,but had positive effects on detritivores,while pikas had positive effects on all three species groups.Grazing livestock mainly affects the abundance of herbivorous arthropods by changing the composition ratio of the plant community(such as broad-leaf plant density)and predacious arthropods by changing the spatial structure of vegetation;the excreta of livestock affects detritivores by increasing their food resources;while pika mainly affects arthropods by increasing the density of above-ground burrow entrances.Based on the composition and structure of the plant community,as well as soil landscape and physical characteristics,this study analyzed the multi-nutrient relationship and cascade effect of livestock grazing on grassland.The effects and pathways of livestock assemblage on the main animal communities in the alpine meadow of Sanjiangyuan Area were further understood.This study provides some experience for the further exploration of the arthropod community in Qinghai-Tibet Plateau and can provide a theoretical basis for biodiversity conservation and grassland grazing management in an alpine meadow.The results showed that grazing alone could reduce the abundance and diversity of arthropod community in an alpine meadow,but increase the population abundance of plateau pika.Pika has a positive effect on arthropod community,so it has some effects on the maintenance of arthropod fauna.The results show that there are great differences in the effects of livestock species identities on grassland.Under the background of grassland degradation,it is particularly important to pay attention to the livestock species identities and assemblage,in addition to the traditional management of grazing intensity.In grassland management,it is also necessary to monitor the population density of small mammals and arthropod community according to the vegetation conditions such as grassland productivity,plant diversity and so on,in order to avoid the imbalance of the interspecific relationship network of grassland biota and to prevent the population outbreak of some species from leading to the accelerated degradation of grassland.