The Response Of Individuals And Populations In Plateau Pika(Ochotona Curzoniae) To Predation Risk And Changes Of Habitat Vegetation Communities

Predation is one of the important selection pressures in the process of biological evolution,and plays an important role in the anti-predator evolutionary adaptation of animals.Predators can not only control the population number of preys by direct predation,but affect the population dynamics of prey all the time.Previous studies have shown that the risk effect of predation is much greater than that of direct predation.In recent years,extensive studies have been carried out on the effects and mechanisms of predation risk effects on the behavior,reproduction and population dynamics of small mammals.However,there are relatively few studies on the response mechanism of small mammals with different population density to predation risk and the impact of this predation risk effect on their habitat plant communities.Therefore,this study took the plateau pika inhabiting the alpine meadow of the Qinghai-Tibet Plateau as the research object.From2016 to 2019,the Unmanned Aerial Vehicle?UAV?was used to simulate the predation risk.The changes of behavior,physiological hormones,genes,reproduction and habitat plant community composition of plateau pikas with different population density were studied,and the response mechanism of plateau pikas to predation risk was discussed.The differences in the response of plateau pikas with high and low population density to predation risk were clarified,and the driving mechanism of the cascade effect of predators and plants mediated by plateau pikas was revealed.This study not only have important scientific significance for improving the study of plateau pika predation risk,but have important practical significance for the protection of biodiversity and scientific prevention and control of its harm.The main results are as follows:1.The predation risk had no significant effect on the body weight of plateau pikas.Under different population densities,the body weight of male plateau pikas in the predation risk treatment group and the control group decreased,and the decline rate of the treatment group(GR_EXH=-3.05%;GR_EXL=-6.06%)was higher than that of the control group(GR_CKH=-1.86%;GR_CKL=-2.96%);the body weight of female showed an increasing trend,but the growth rate of the treatment group(GR_EXH=8.92%;GR_EXL=7.36%)was lower than that of the control group(GR_CKH=14.46%;GR_CKL=12.80%).The body weight of plateau pika was significantly different between months(F_2,81=3.356,P=0.0398)and sex(F_1,81=5.054,P=0.0273),but there was no significant difference between treatments(F_1,81=0.301,P=0.585)and population density(F_1,81=0.003,P=0.956).2.Predation risk had a significant effect on the foraging,vigilance and concealing time of low-density population,but had no significant effect on the behavior of high-density population.The foraging time of plateau pika had significant difference between density(F_1,56=16.191,P=0.00017)and treatment(F_1,56=25.112,P<0.001),but there was no significant difference between sex(F_1,56=1.593,P=0.212),and there was significant difference in the density(F_1,56=16.831,P=0.00013)and interaction between density and treatment(F_1,56=4.909,P=0.031).The interaction between density and treatment was significantly different in concealing time.The Post-hoc Tukey's test results showed that the average foraging time of female individuals in the low population density area was significantly lower than that in the control group under predation risk treatment?P=0.031?.The average time of foraging?P=0.0042?and vigilance?P=0.027?of male in the low population density area was significantly lower than that of the control group under predation risk treatment,but the concealing time under predation risk treatment was significantly higher than that of the control group?P=0.027?.3.Predation risk had the most significant effect on corticosterone,cortisol,thyroid,testosterone and leptin in low population density,but had no significant effect on high density population.There were significant differences of thyroid(F_1,171=31.626,P<0.001)and leptin(F_1,171=21.827,P<0.001)in different population density,and the corticosterone(F_1,171=14.014,P<0.001),thyroid(F_1,171=15.166,P<0.001)and leptin(F_1,171=9.112,P=0.0029)had significant differences between predation and non-predation risk group.The testosterone(F_1,86=13.722,P<0.001),cortisol(F_1,171=6.142,P=0.0142)and leptin(F_1,171=7.689,P=0.0062)had significant differences in the interaction between density and treatment.The Post-hoc Tukey's test results showed that the content of testosterone in the predation risk group was significantly lower than that in the control group?P<0.001?,while in the low population density,the contents of thyroid?P<0.001?,leptin?P=0.0017?,corticosterone?P=0.010?and cortisol?P=0.021?under perdation risk were significantly higher than those in the control group.There was no significant difference in the contents of testosterone?P=0.1658?,thyroid?P=0.357?,leptin?P=0.663?,cortisol?P=0.3628?and cortisol?P=0.286?between the predation risk treatment group and the control group in the high population density.4.Predation risk significantly inhibited the expression of AVP mRNA in male and female pikas and c-fos mRNA in female pikas,while significantly promoted the expression of c-fos mRNA in male individuals.Predation risk significantly inhibited the expression of AVP mRNA in both male(F_1,27=12.12,P<0.01)and female(F_1,27=18.564,P<0.001)individuals.Under the same treatment,there was no significant difference in the expression of AVP mRNA among individuals of different sex(predation risk:F_1,27=0.933,P>0.05;non-predaiton risk:F_1,27=0.866,P>0.05);predation risk significantly inhibited the expression of c-fos mRNA in female individuals(F_1,27=5.674,P<0.05),but significantly promoted the expression of c-fos mRNA in male individuals(F_1,27=8.154,P<0.01).In the non-predation risk group,the expression of c-fos mRNA in females was significantly higher than that in males(F_1,27=26.187,P<0.001),while in the predation risk treatment group,there was no significant difference in c-fos mRNA expression between males and females(F_1,27=1.567,P>0.05).5.Predation risk significantly affected the reproduction of low-density plateau pika population.Under different population densities,the testicular weight of male plateau pikas in the predation risk treatment group and the control group increased at first and then decreased,and the change rate of the treatment group(GR_EXH=-23.73%;GR_EXL=79.87%)was higher than that of the control group(GR_CKH=-6.92%;GR_CKL=79.65%),and the litter size of female also increased at first and then decreased,but the change rate of the treatment group(GR_EXH=-42.86%;GR_EXL=31.43%)was lower than that of the control group(GR_CKH=-41.03%;GR_CKL=9.52%).There were significant differences in testicular weight between months(F_2,33=287.635,P<0.001),treatments(F_1,33=9.333,P=0.0044)and population densities(F_1,33=6.531,P=0.0154)of plateau pikas.There were significant differences in months(F_2,48=55.98,P<0.001)and the interaction between month and density(F_2,48=4.584,P=0.0151)of litter size.The Post-hoc Tukey's test showed that the testicular weight of plateau pika in the low population density area was significantly lower than that in the control group?P=0.0053?,but there was no significant difference in the high population density area?P=0.76?.The testicular weight of plateau pikas was significantly different among different population densities in April?P=0.037?.Under the predation risk,the litter size of plateau pikas was only significantly different among different population densities in May?P=0.012?.6.Under the predation risk,the relative population density of plateau pika varies with different population density.The growth rate of relative population density of plateau pika was significantly different among population densities(F_1,17=50.57,P<0.001),treatments(F_1,17=116.67,P<0.001)and the interaction between density and treatments(F_1,17=45.92,P<0.001).The Post-hoc Tukey's test showed that in the low density populaiton,the growth rate of relative population density in the predation risk treatment group was significantly lower than that in the non-predation risk group?P=0.0008?.The growth rate of relative population density of plateau pika in high population density had no significant difference between predation risk treatment and control?P=0.2266?.7.Under the predation risk,there were differences in plant functional group dominance,diversity and aboveground biomass in plateau pika habitats with different population density.There were significant differences in dominance and aboveground biomass growth rate of Gramineae,Cyperaceae and Forbs in different population densities(dominance growth rate(Gramineae:F_1,17=124.3,P<0.001;Cyperaceae:F_1,17=123.8,P<0.001;Forbs:F_1,17=54.63,P<0.001);aboveground biomass growth rate(Gramineae:F_1,17=70.209,P<0.001;Cyperaceae:F_1,17=11.778,P=0.0015;Forbs:F_1,17=36.736,P<0.001))and the interaction between density and treatments(dominance growth rate(Gramineae:F_1,17=100.4,P<0.001;Cyperaceae:F_1,17=47.9,P<0.001;Forbs:F_1,17=113.2,P<0.001);aboveground biomass growth rate(Gramineae:F_1,17=15.512,P<0.001;Cyperaceae:F_1,17=9.618,P=0.0032;Forbs:F_1,17=16.404,P<0.001)).There were significant differences in the growth rate of dominance of Gramineae(F_1,17=263.3,P<0.001),Cyperaceae(F_1,17=130.8,P<0.001)and Forbs(F_1,17=25.3,P<0.001)and aboveground biomass of Forbs(F_1,17=6.399,P=0.0264)between predation and non-predation risk group.The Post-hoc Tukey's test showed that in the low density population,the growth rate of Gramineae dominance?P=0.0042?and Cyperaceae aboveground biomass?P=0.0022?in the predation risk treatment group were significantly lower than those in the control group.The growth rate of Gramineae aboveground biomass?P=0.0017?,Cyperaceae dominance?P=0.0089?and Forbs aboveground biomass?P=0.016?in the predation risk group were significantly higher than those in the non-predation group.In the high density population,the dominance growth rate of Forbs in the predation risk group was significantly higher than that in the non-predation group?P<0.001?,while in the low density area,the aboveground biomass growth rate of Forbs under predation risk was significantly higher than that in the non-predation group?P=0.016?.however,there was no significant difference in dominance growth rate and aboveground biomass growth rate of Gramineae and Cyperaceae between predation and non-predation risk group.In conclusion,this study found that the plateau pikas with different population density had different response to predation risk.Under the predation risk,the expression of AVP and c-fos mRNA in the hypothalamus of the plateau pika with low population density increased significantly resulting in reducing the foraging time and increasing the vigilance and concealing time to avoid the predation risk.Moreover,the testosterone content of the male individuals of the plateau pika with low population density was also significantly decreased,while the contents of thyroid,leptin,corticosterone and cortisol were significantly increased,as a result,the population size was declined because of lower reproduction capacity.The aboveground biomass of Gramineae and Forbs and the dominance of Cyperaceae in the low population density area were significantly increased.