Study On Sheep Foraging Selectivity And Plant Associational Defense Based On Plant Spatial Pattern In Grasslands

In grassland ecosystem, the interaction between foraging selectivity of largeherbivore and plant defense is one of the important relationships that impactecosystem function and stability. In order to satisfy nutrition need for growing andproducing, large herbivore adopt a series of foraging strategies to obtain sufficientfood. Selective foraging is the core of herbivore foraging strategies. It not only affectsthe growth and productivity of herbivore themselves, but also influences thecomposition of plant communities and ecosystem stability. In order to escape or adaptherbivore foraging damage, plant has been evolved a series of defense policies. Plantassociational defense is one of the most important spatial defense policies of plantcommunities. It is defined as the focal plant is less damaged by herbivore because ofthe existence of neighbor plant. In other words, the focal plant resist against herbivoreforaging together with the neighbor plant. Plant associational defense always includesspatial interaction and spatial pattern among inter-or intra-plant species. Distributionof vegetation patch is a typical character of natural grasslands. Spatial interaction andspatial pattern of different plant species between-and within-patch are the vitalfactors that influence both herbivore foraging and plant associational defense policy.In this paper, we use sheep as the representative of large herbivore, to explain theirforaging mechanism as affected by plant spatial pattern as plant individual, patch andplant community scales, and to reveal the plant spatial defense polices in response ofherbivore foraging. This study will not only enrich the foraging theory andcoevolution theory between herbivore and plant, but also has the applied directivevalue in maintaining the stability of grazing grassland system, rational utilization ofgrassland resources and making effective grazing management policies.Combining the manipulated cafeteria trials, artificially grassland grazingexperiments and experiments in natural grassland, we obtained the important resultsand conclusions as follows.(1) Plant spatial micro-pattern within different quality patches can significantlyaffect sheep foraging both at plant individual scale and at between patch scale. Whenplant micro-pattern within high quality patch changed from clumped to random, sheepconsumption of both preferred species and total intake in high quality patch wasdecreased (P <0.05), and increased the consumption of preferred species and totalintake in medium and low quality patches (P <0.05). In addition, as plantmicro-pattern in medium or low quality patch changed from clumped to random,sheep foraging selectivity in high quality patch will be influenced. Therefore, plantspatial micro-pattern can greatly affect sheep foraging selectivity at both within-andbetween-patch scales. And the intensity of these effects was related to patch quality. High quality resource sites was the most influential and susceptible foraging area.(2) Plant spatial micro-pattern within different quality patch significantly canaffect sheep foraging selectivity between-and within-patch, and thus affected theconsumption of focal plant by herbivore, thereby come up with different results ofplant associational defense. Patch quality also played an important role in this effect.When plant micro-pattern changed from clumped to random in high quality patch,sheep forging selectivity was not affected (P>0.05), and there was no plantassociational defense for focal plant (Phragmites australis). However, when plantspatial micro-pattern changed in low quality patch, sheep foraging selectivitybetween-patch declined (P <0.05). Sheep foraging decision was made mainly atwithin-patch (plant individual) scale, and focal plant gained protection when it existedin high quality patch and suffered injury in low quality patch. This was consistentwith the prediction of attractant-decoy hypothesis. Besides, when plant micro-patternbecame random in medium quality patch, although there was no plant associationaldefense of focal plant in each patch, the total intake of focal plant in all patches wassignificantly lower than other plant spatial micro-patterns (P <0.05). Therefore, plantmicro-pattern in medium quality patch will affect focal plant associational defensewithin the whole plot. To sum up, regulating the plant spatial micro-pattern in lowerquality grass resource is an effective way to protect focal plant in grazingmanagement.(3) We studied the effects of patch quality on sheep foraging selectivity and plantassociational defense. The results showed that Sheep foraging selectivity occurredmainly in plant individual scale, and the focal plant will escape foraging by sheepwhen it had good neighbor in high quality patch. When the difference of patch qualitybetween patches become great, sheep foraging selectivity at patch scale will increasedand selectivity at within patch (plant individual scale) will decreased. Sheep decreasedthe visits to low quality patch. Hence, focal plant with bad neighbor in lower qualitypatch will gain protection. Thus, as the difference between patches increased, mainlyscale of sheep foraging decision was changed from within-patch to between-patch.The protection site for focal plant changed from high quality patch to low qualitypatch. This study investigated the foraging responses of sheep to different qualitypatches and demonstrated sheep made foraging decisions at multiple spatial scalesand this induced different plant associational defense. Regulation patch quality was aneffective way to change herbivore foraging selectivity and predict the results of plantassociational defense. It was important to protect special plant species throughcontrolling local patch quality in grassland grazing management.(4) We investigated the effects of five plant spatial distribution pattern of focalplan（tKalimeris integrifolia）, high preference plant Lathyrus quinquenervius and lowpreference plant Leymus chinensis on sheep foraging behavior and plant associationaldefense (focal plant distributed clumped and the other two species distributed randomly; half of focal plant distributed clumped, half of it distributed randomly withthe other two species; focal plant distributed in three patches with high preferencespecies as neighbors, low preference species as background plants; focal plantdistributed in three patches with low preference species as neighbors, high preferencespecies as background plants; three species distributed randomly). The results are asfollows: sheep obtained the most intake of focal pant when focal plant distributedtotally clumped, or when focal plant distributed totally randomly (66.43g，P <0.05).As plant spatial pattern became complicated, sheep intake of focal plant was leastwhen half of the focal plant distributed clumped and half of it distributed randomly(9.21g，P <0.05). The defense of focal plant is most effective under this spatialpattern. Because there was no neighbor in this pattern, focal plant defend herbivoreforaging mainly by its own distribution pattern, we assume this defense intra-speciesassociational defense. When focal plant had spatial relationship with other species(neighbor plants), the consumption by sheep was also low (25.89g，16.73g). It wasdefined as plant inter-species associational defense. Thus, we highlighted focal plantexisted both intra-and inter-species associational defense. The complex ofdistribution pattern was the best spatial defense policy. This conclusion not onlydevelops the plant associational theory, but also interprets the mechanisms of speciescoexists. Our study also has the great value in sustaining the stability ofplant-herbivore relationship in grassland ecosystem.(5) Based on foraging experiment in natural grassland environment, we test theeffects of plant spatial distribution pattern at multiple scales on sheep foragingbehavior (clumped distribution focal plant; random distribution of focal plant;clumped distribution when focal plant together with neighbors; random distributionwhen focal plant together with neighbors). Results were as follows: focal plant wasconsumed by sheep more in random distribution pattern than in clumped distributionpattern (P <0.05). When neighbor plant existed, focal plant was consumed less inrandom pattern than in clumped pattern (P <0.05). This indicated that the existence ofneighbor plant disturbed sheep’s judgments on patch scale. Distribution pattern atplant community scale influenced sheep foraging at plant population scale.Meanwhile, the plant spatial distribution pattern at population scale also affectedsheep foraging selectivity at plant community scale. Distribution pattern of focal plantpatches influenced the sheep foraging selection of neighbor plants. In conclusion,foraging decision of large herbivore at coarser scales can constrain the diet selectionat finer scales, and grazing decision at finer scale can also affect the foragingjudgments at coarser scales. Studies on foraging behavior of herbivore at multiplescales can not only enrich the foraging hierarchy theory, but also have appliedimportance in regulating foraging distribution and protecting specific plant species inestablishing grazing management policies.Our study has investigated sheep foraging selectivity and plant associational defense in response to complicated plant spatial pattern, and we acquired the furtherknowledge and insights into the relationship between plant and animal. Foragingprocess of herbivore is the results integration of foraging decisions making at differentspatial scales. Foraging decisions at different scales will affect and constrain eachother. Plant associational defense is the final results of the interaction of decisions ateach scale. This relationship between herbivore foraging and plant defense is a vitalfactor influencing grassland ecosystem functions and stability. The complexity andheterogeneity of plant spatial pattern is important and significant to ensure largegeneralist herbivore–plant ‘mutualisms’ and stable coexistence. This study furtheremphasized the importance for grazing management, protecting grassland plantdiversity and rational use of grassland recourses.