The Study On The Population Dynamics Of Plateau Pika And Plateau Zokor ,the Relationships Between Population Density And Vegetation

Rodent pests is one of the most important limiting factors for the development of grassland ecosystem.It is the focus to understand the rodent population dynamics,and the relationships between their population density and vegetation characteristics for the ecological preventions and control of rodent pests.In this paper,the population dynamics of plateau pika(Ochotona curzoniae)and plateau zokor(Eospalax bailey),and the relationship between their population density with vegetation were studied in alpine meadow ecosystems in Gannan from 2005 to 2016.In the study,the seasonal and interannual population dynamics,and the temporal and spatial characteristics of this two species in their cohabitation were investigated.The feasibility of using vegetation characteristic as predictive index for rodent population dynamics was discussed.The action mechanism of vegatation regulation for control the outspread of the two species was analysed.The main results were as follows:1.There was no significant correlations between the active burrow density and the absolute density of plateau pika in the same year.The active burrow density highest in the month when the absolute density of pika was the lowest,and was relatively lower in the month with the highest absolute density;therefore,the active burrows can’t be used for comparison of pika density at different periods in a same year.The population fluctuation cycle of plateau pika included three periods of latent-rising-peak that without recession period.The latent period was 2 years,the rising period was 2 years,and the peak period was 1 year.After the peak period,the population showed a“cliff down”decline,the density approached to zero,and the fluctuation cycle was about 5 years.2.There was also no correlation between the new mound density and the absolute density of the plateau zokor in the same year.Therefore,the new mounds can’t be used for comparison of plateau zokor density at different periods in the same year.The new mound density was closely related to the searching and foraging activities of plateau zokor.There was two excavating peaks in one year,the first one was in April and May,and the second one was in October.The population fluctuation cycle of plateau zokor included four periods of latent-rising-peak-recession,the latent period was 3 years,the rising period was 1-2 years,the peak period was 1 year,the recession period was 1 year,and the fluctuation cycle was about 6-7 years.3.The species richness first increased and then decreased with the increased of the active burrow density of plateau pika.The vegetation height,coverage,aboveground biomass,the proportion of grasses biomass and the proportion of sedge biomass decreased significantly with the increased of the active burrow density of plateau pika(p<0.05),the proportion of forbs biomass increased significantly with the increased of the active burrow density of plateau pika(p<0.05).Multiple linear regression analysis showed that there had the closest relationship between the proportion of forbs biomass,aboveground biomass,vegetation cover and the active burrow density of plateau pika(R~2=0.984-0.949),which could be used as reference indicators to predict the current density and the future development trend of pika density.4.In the whole population fluctuation cycle of the plateau zokor,the species richness first increased and then decreased with the increased of new mound density of plateau zokor.The vegetation height increased significantly with increased of new mound density of plateau zokor(p<0.05).The vegetation coverage and above-ground biomass decreased significantly with the increased of new mound density of plateau zokor(p<0.05).There was no significant correlation between the new mound density and the proportion of grass biomass,the proportion of sedge biomass and the proportion of forb biomass(p>0.05).If the recession period of plateau zokor was ruled out,the proportion of grass biomass first decreased and then increased with the increased of new mound density of plateau zokor.The proportion of forb biomass and species richness first increased and then decreased with the increased of the new mound density of plateau zokor.The proportion of sedge biomass had no significant correlation with the new mound of plateau zokor(p>0.05).Multiple linear regression analysis showed that the vegetation height and coverage were highly correlated with the new mound density of plateau zokor(R~2=0.813-0.942),which could be used as reference indexes to predict the current density and future development trend of plateau zokor.5.There is a short-term cohabitation phenomenon between plateau zokor and plateau pika,and the cohabitation time was 3 years.The population density of plateau zokor decreased rapidly with the increased of plateau pika density during this cohabitation process.Therefore,it should be promptly converted to pikas if found plateau pikas invaded the habitat of plateau zokor in the control of rodent pests.6.The food composition of the plateau pika changed after enclosed and reseeded the Elymus nutans Griseb in the degraded grasslands caused by plateau pikas.The plateau pika ate 9 plant species and the foraging ratio of five species,Elymus nutans,Poa pratensis,Carex kansuensis,Kobresia capillifolia and Scirpus pumilus were>5%in Elymus nutans habitat,but ate 8 plant species and the foraging ratio of the 8 species all were>5%in open habitat.Compared with control,the moving speed of plateau pika increased from 1.25m/s to 2.08m/s,the alert distance decreased from 13.18 m to7.35 m and the proportion of vigilance increased from 23.88%to 31.41%in Elymus nutans habitat.The vegetation height and coverage were significantly positive correlated with the plateau pika’s moving speed and vigilance(p<0.05),but significantly negative correlated with the alert distance(p<0.05).Multiple linear regression showed that the vegetation height was greater than the vegetation coverage.Enclosed and reseeded the Elymus nutans can significantly increased the vegetation height and coverage,and strengthen the predation risk of plateau pika,which is an important reason for reducing pika population density.7.The population density of plateau zokor showed a decreasing trend after enclosed and reseeded the Elymus nutans Griseb in the degraded grasslands caused by plateau zokor(p<0.05).The above-ground biomass,under-ground biomass,the proportion of sedge biomass and the soil water content first increased and then decreased after enclosed and reseeded the Elymus nutans Griseb treatments.The proportion of forb biomass,the biomass of axon roots,soil hardness,and soil bulk density showed a decreasing trend after enclosed and reseeded the Elymus nutans Griseb.The proportion of grass biomass and the fibrous root biomass showed an increasing trend after enclosed and reseeded the Elymus nutans Griseb.Spearman analysis showed that the population density of plateau zokor was significantly positive correlated with soil hardness,soil bulk density and axon biomass,but was significantly negative correlated with soil water content and aboveground biomass.Multiple linear regression showed that there was a high correlation between the axon root biomass and the population density of plateau zokor(R~2=0.918).Enclosed and reseeded Elymus nutans declined the fitness of plateau zokor,which in turn inhibited its population density development.The reduction of axon root biomass is the root cause that declined the population density of plateau zokor.