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Effects Of Plant Diversity On Foraging Behavior Of Large Herbivore With Different Body Size On Songnen Grasslands

Posted on:2015-10-10Degree:DoctorType:Dissertation
Country:ChinaCandidate:C FengFull Text:PDF
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Herbivores and plant which can affect the whole grazed ecosystem is the key elements in grassland ecosystem. The complicated mass exchange and energy transfer occurred at plant-animal-interface is the key to maintain the ecosystem function.Herbivore can be known as a decision maker that can affect plant community compositions and ecosystem function, and herbivore foraging behavior is the core characteristics of grazed grassland ecosystem. The grazing behavior of large herbivore can not only affect the grassland vegetation structure and decide the resources conversion efficiency, but also achieve the co-evolution of herbivore and grassland.The condition of food resources that is confronted by herbivores may be quite complicated. This complexity can be reflected in many aspects such as nutrient content and richness and plant diversity is the main measurement of such characteristics. Our study was conducted in nature grassland ecosystem, and then we selected cattle and sheep as the research animals in this situ experiment. Considered both aspects of benefits and costs of herbivore foraging, as well as the animal and plant factors that can affect the foraging behavior of large herbivores, we carried out the related research systematically about the effects of vegetation characteristic on large herbivore foraging behavior. Through analyzing the response of different body-sized large herbivores on plant diversity, this study illuminated that there was unique mechanism of diet selectivity among different individual difference herbivores.Based on the cognition of complicated foraging behavior, we deeply revealed the regulatory mechanism of interspecific relationships among different herbivore species by analyzing the interspecific interactions. Meanwhile, to describe the foraging strategy in details, this research revealed the relation of plant diversity and foraging efficiency to discuss the adaptive mechanism for the effects of livestock on complicated food resources. Experimental and theoretical work on herbivore foraging behavior is of great importance for the development of foraging theory, as well as maintaining biodiversity, and protecting the functioning of grassland ecosystems,sustaining the stability of grassland systems, effectively managing the grassland and developing stocking raising in grassland.This study adopted a series of rigorous experimental design. Based on a mass of experiment data statistics and comparative analysis, we obtained the important results and conclusions as follows:(1) The characteristics of large herbivores body size are closely related with food resources richness for large herbivores. For sheep grazing, the foraging behavior is sensitive to the changes of plant diversity levels. The elevation of plant diversity levels can promote the characteristics of sheep foraging behavior. At high plant diversity levels, the occurrence frequency of high quality food resources and overall nutrition levels can be both raised in plant community, which may maximize the ability of diet selectivity, and stimulate the foraging behavior. These factors are the primary cause of increasing total consumption, foraging time and bite number. When large body-sized cattle faced with different plant diversity, the characteristics of foraging behavior changed non-significantly. Cattle can tolerate low quality food resources because of the digestive ability determined by their physiological feature,therefore, the promotion of forage palatability and food quality may not impact on cattle grazing. The study on preference indicated that the diet selectivity of different herbivores was the main reason of differences in foraging behavior. We can make the prediction that the world-wide decline of plant diversity levels could have a more serious impact on small body-sized herbivores.(2) The experimental results showed that the response of cattle and sheep’s foraging behavior on grazing treatments was quite different. Between different grazing treatments, the total consumption, foraging time and bite number of sheep changed both non-significantly. However, the diet composition in mixed grazing treatment was different from sheep-grazing treatments. The proportion of forbs in total intake was significantly increased when grazed with cattle, which indicated the raising of food quality level. We deemed that the existence of cattle might promote the efficiency of sheep in obtaining preferred food resources. The difference in diet selectivity of cattle and sheep caused the positive effects in grazing process. The remove of grasses by cattle can promote the success of sheep in searching forbs which considered as preferred food resources for sheep. Different from sheep grazing, the total intake, foraging time and bite number was both increased significantly in mixed grazing treatments. In fact, the selectivity of sheep in forbs can vastly raise the proportion of grasses in grazing area. As bulk grazers, cattle preferred the dense and unitary grass patch to satisfy their food demand. We considered that mixed grazing could promote the efficiency of utilization for grassland resources.(3) Plant diversity can regulate the interspecies relationships between different body-sized herbivores. Although sheep obtain more benefits when grazed with cattle,the cost of searching food resources is much higher than that in sheep-grazing treatments at low plant diversity level. The interactions between cattle and sheep may be undefined. However, herbivores can greatly decrease the cost and increase the benefit when grazed together at high plant diversity. We considered that high plant diversity can lead to positive interactions between two different body-sized herbivores.(4) The study of herbivore foraging efficiency indicated that plant diversity had great impact on herbivore searching area and path length. Sheep adopted the foraging strategy of higher searching speed and larger searching area at low plant diversity than that at high plant diversity to obtain preferred food resources. However, better food resources quality can significantly decrease the searching speed, and increase the forging speed, which may lead to higher foraging efficiency. The step number, path length, step speed and movement speed were both non-significantly changed to plant diversity, the reason of which may be caused by the tolerance of cattle to foraging environment. Compared with sheep grazing, the diet selectivity of cattle was much weaker. To satisfy the food demand, cattle was more preferred the quantity than the quality of food, which was a result of evolution. With regard to the searching area of herbivores, cattle and sheep both searched larger area at high plant diversity level than that at low plant diversity level, which generated higher grazing intensity in better food resource condition. This conclusion corresponded with the area-restricted search theory.(5) Grazing treatments can affect foraging efficiency of large herbivores.Although the foraging cost of cattle was not changed to grazing treatments, foraging benefit was promoted when grazed with sheep, which means that cattle may adopt higher foraging efficiency in mixed grazing treatments. Considered searching area of cattle, the increasing of foraging efficiency may be caused by both the existence of sheep and the larger searching area. The grazing treatment had great impact on foraging efficiency of sheep, which also can be adjusted by plant diversity levels. In conditions of poor supplement in food resources, the step numbers, path length and searching area of sheep in mixed grazing treatment were both higher than that in sheep grazing treatment. The reason can be explained by recipe overlap of sheep and cattle, which may potentially induce competitive relationship.(6) This study indicated that there were great differences in foraging behavior oflarge herbivores among different grazing season. In early grazing stage, the total intake, foraging time and bite number were both much lower, which may relate with the poor palatability and high fiber content in June. Meanwhile, vegetation composition has great variances among different grazing seasons in this study area. In June, the vegetation was mainly constituted with grasses which was un-preferred by sheep. Affected by temperature and moisture conditions in different month, the diet composition of herbivores showed regular changes. The proportion of grasses was decreased, and the proportion of forbs and legumes was increased with the season changed. This was corresponding with the seasonal changes of plant diversity, which considered that plant diversity level was higher in early autumn. The higher plant diversity level was considered as better food resources for herbivore grazing. The diet composition in cattle grazing varied less, which related with the low diet selectivity and high tolerance to different food resources.Based on the study about the responses of two different body-sized herbivores on changed high plant diversity levels, and foraging efficiency, interspecies relationships,seasonal dynamics of animals, we obtain the new understanding and cognition of large herbivore foraging behavior. Herbivorous animals have complex selective feeding behavior, which was considered as a result of adaptive evolution to foraging environment. The diet selectivity of herbivore is the core element of grassland ecological processes, however, the feedback effects of herbivores to vegetation characteristics depend on plant diversity level. Therefore, there are obvious diversity and complexity in the reciprocal relationships between animal and plant, which can be considered as the base of positive interactions in the interplay of animal and plant.With a new perspective, the study on foraging behavior may develop the theory of herbivore grazing, manage livestock efficiently, and promote the animal husbandry in grassland. Meanwhile, this study further emphasized the importance for protecting grassland plant diversity.
Keywords/Search Tags:plant diversity, large herbivore, body size, foraging behavior, food resource, diet selectivity, interspecies relationship, benefit, cost, foraging efficiency
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