The Interactions Between Foraging Of Large Herbivore With Different Body Size And Songnen Grassland Vegetation Characteristics

The relationship between plants and animals is always one of the mostimportant research issues in behavioral ecology, grazing ecology and grasslandecology. In grassland ecosystems, high variation and uncertainty in foragingselective behavior of livestocks are attributed to the complex composition andstructure of plant communities, as well as the type of livestocks and the interspecificrelationships among herbivores. Our study was conducted in nature grasslandecosystem, and cattle, sheep, and goat are selected as the research animals in this situexperiment. Considered both aspects of animal and plant factors at the same time, aswell as the influence factors including animal feeding behavior, plant species, andthe vertical spatial structure of plant communities, systematical investigation fromindividual animal species to population was studied to determine the interspecificrelationship between plant characteristics and herbivore foraging. We analyzed theeffects of large herbivores on plant diversity and productivity, and clarified thedifferent influence of several types of large herbivores on vegetation characteristics.We also analyzed how plant diversity and differences structure affected the foragingbehavior of large herbivores, revealed the foraging selection mechanisms of largeherbivores with different body size, and interpreted the relationships between plantdiversity and animal diversity through the responses of animal foraging behavior toplant diversity. Intensive research on the relationship between large herbivores andvegetation features is beneficial to deeply explain the stability and sustainability ofgrassland grazing ectsystems. Moreover, our study can also provide reliable anddirect theoretical supports for maintaining and enhancing productivity, andlegitimately managing grassland ecosystems.This study adopted a series of rigorous experimental design, including animalforaging behavior experiments and the responses of plant community to animalforaging. Based on a mass of experiment data statistics and comparative analysis, weobtained the important results and conclusions as follows:(1) Animal bodysize characteristics are always been considered as the mostimportant factors affecting the resource allocation between consumers. For largebodysize herbivores, their foraging abundance of every bite plays a decisive role inenvironments with different level of plant diversity. The vertical spatial structure ofplant community and the composition of plant function groups are also changing with the increase of plant diversity. Thus, this might result in the decrease of mouthintake, and then the significant decrease of herbivores feed intake. For smallbodysize herbivores, the bite size is a key factor in influencing relationships betweenplants and animals. The frequency of high quality food resources in plant communityand the composition of function groups also change with increasing plant diversity,which maximizes the foraging selectivity of small bodysize herbivores, stimulatesthe foraging of herbivores, and significantly increases their food intake. Therefore,we conversely predict the globalization disappearance of plant species diversitymight be a severe impact on small bodysize herbivores.(2) The experimental results showed that large bodysize herbivores increasedplant diversity at low level of plant diversity. However, small bodysize herbivoresdecreased plant diversity when plant diversity was low. The influence of herbivoreson the diversity was no longer obvious with the increase of plant communitydiversity. At low plant diversity level, all herbivores obviously reduced vegetationaboveground biomass, but the maximum affecting extent was found in the grazingtreatments including large bodysize herbivores. The significant effects onaboveground biomass disappeared with the increase of plant diversity. The effect ofsmall bodysize herbivores on plant vertical structure was obviously different. Theyincreased the complexity of plant community structure at low plant diversity level,but reduced at high plant diversity level. This conclusion shows that differentbodysize herbivores have different effects on plant community characteristic, and thedegree and direction of the influences depend on the level of plant diversity.(3) Due to the overlap of the food niche between goats and cattles, theirinterspecific relationship was partial harm at low plant diversity level. With differentfood niche and similar bodysize, the interspecific relationship between goats andsheep was partial benefit. Therefore, food niche differentiation might be the onlyway to maintain the survival of small bodysize herbivores, when they consumedwith other herbivore species. The partial benefit or harm of interspecificrelationships was no longer significant at high plant diversity level. The observedchanges of these relationships between herbivores showed that more diversevegetation resources allowed different bodysize herbivore well commensalism in thesame area, even if their food niche might overlap to a certain extent. As described inthe literatures, natural selection is more inclined to make competitive species havedifferent resource requirement. Although some researchers think difference bodysizedetermines resource allocation between sympatric species, the level of plant diversity can play a more crucial role in distribution patterns of the food resources of differentbodysize large herbivores.(4) Grazing treatments had no significant impact on plant diversity at low,mediate and high plant diversity, but Herbivore assemblages including largebodysize herbivores significantly increased plant aboveground biomass at low plantdiversity level. When mixed grazing herbivores had similar foraging niche, thevegetation productivity was significantly reduced with the increase of plant diversity.When their foraging niche was different, the vegetation productivity was maintainedor improved. At high plant diversity level, diversified herbivore assemblage couldreduce the complexity of community structure. These conclusions showed thatherbivores assemblage generally decreased the productivity of plant communities atlow plant diversity, but was conducive to maintaining plant diversity. At high plantdiversity level, the complementary effect of herbivores with different food niche wasbeneficial to improve vegetation productivity; and the additive effect of herbivorewith same food niche resulted in the more homogeneity of vegetation vertical spatialstructure and a lower vegetation productivity.Based on the above obtained outcomes from our experiments, we aquired thefurther knowledge and insights into processes and mechanisms of interactionsbetween herbivore foraging and vegetation: The foraging behaviour of herbivore wasan important determinant factor affecting ecological process of grassland, which wasparamount ecological significance. We argued that the interactions betweenherbivore foraging and vegetation strongly depended on herbivore body size andplant diversity. We therefore suggested that high complexity and diversity ofgrassland plant community was one of the most important conditions to ensure largegeneralist herbivore–plant ‘mutualisms’ and stable coexistence. This study furtheremphasized the importance for protecting grassland plant diversity.