| In the past 20 years,the study of the temporal stability of ecosystems had been widely concerned by ecologists who had put forward six kinds of mechanisms of maintenance temporal stability.These mechanisms can be broadly divide into two categories including the complementary effects and the selection effects.The former,based on the change of species diversity,results from ecological niche differentiation and compensatory response of species to increasing species diversity as community is disturbed,and can effectively maintain the temporal stability of community.The latter,also named as dominance effect,is stabilized effects results from the stability of dominant species that can determine the functioning and the temporal stability of community and ecosystem,and is finally unrelated to species diversity or species richness.These two kinds of mechanisms can exist independently or coexist in a community to maintain the temporal stability.But what are the preconditions or divers resulting in these two situations?Which stabilization effect had greater influence on the temporal stability for a given community?These questions are still unsettled.Different disturbance factors have affected differently on community.Both species diversity and dominance are important index showing community characters,and often have different pattern in the face of a specific disturbance factor.So we can predict that the mechanism of community temporal stability would be different as the disturbance factor.When disturbance factor is beneficial to improve the species diversity,complementary effect should has stronger effect on the community temporal stability,by contrast,when the disturbance is beneficial to increase the dominance,selection effects would be greater,that is,selection effects would maintain the temporal stability of community.In this paper,alpine meadow in the Qinghai-Tibet Plateau was used as the object of study to confirm the above speculations by studying the changes of species diversity,dominance and temporal stability within and among communities under clipping and fertilization which are quite common disturbance factor in alpine meadow ecosystem.Investigated contents that were included in the study as follows:(1)The effects of clipping and fertilization on species diversity,stability of dominant species and community temporal stability.(2)Potential relationships between the species diversity and the temporal stability of community;the relationships between the stability of the dominance species and the temporal stability of community.(3)The effects of clipping and fertilization on the relationship of species diversity(and/or dominant species stability)and temporal stability of community.(4)Relative contributes of complementary effects and selection effects to the temporal stability of community within a given treatment community.(5)Relative contributes of complementary effects and selection effects to the temporal stability across treatment communities.The results were shown as follows:(1)Species diversity and community dominance changed oppositely with years and they are all self-correlated in the inter-annual(p<0.001).Species diversity decreased year by year,but the dominance of community increased.Clipping enhanced species diversity(p<0.05),decreased the dominance of community(p<0.05);but fertilization reduced diversity effect(p<0.05),enhanced dominance of community(p<0.05).We did not detected the interaction of clipping with fertilization on species diversity and community dominance(p>0.05).Because clipping and fertilization reversely altered species diversity and community dominance,their interaction had no significant effect on the stability of community(p>0,05).(2)There are positive,negative or no correlation between species diversity and temporal stability when using different index of species diversity.For example,species richness(SR)was negatively correlated with ICVCOM(p<0.05);species evenness(E)and ICVcom had positive and/or negative correlation as in different communities(p<0.05);Shannon-Wiener diversity index(H')was negatively correlated with ICVCOM(p<0.05).The main reason resulting in these differences was associated with changes of disturbance factor in different communities.However,there was a consistent positive correlation between dominant species and community stability in different communities(p<0.05).(3)Clipping changed the intercept(p<0.01),rather than the slope(p>0.05)of the relationship between species diversity and temporal stability under no fertilized community.By contrast,clipping improved the slope(p<0.01)and did not changed the intercept in fertilized community(p>0.05);Fertilization changed the intercept of the relationship in moderate and severe clipped community.These results showed a more strength effect of clipping on this relationship after nutrient addition.Despite clipping and fertilization increased the intercept(p<0.01)of the relationship between the population stability of the most dominant species(ICVR1)and the temporal stability(ICVCOM),but have on significant effect on the slope of that(p>0.05).Because of positive correlation between dominant species and community stability,and clipping and fertilization increased the intercept and slope(p<0.01)of the relationship between the population stability of the sub-dominant species(ICVR2+R3)and ICVCOM,so we concluded that the promoted effect of population stability of the sub-dominant species on ICVcom was greater than that of the most dominant species.(4)Compared with unclipped community,main stability mechanism was complementary effect in moderate clipped community,and was selection effect in severe clipped community.Furthermore,complementary effect existed in all no fertilization communities,whereas selection effect existed in fertilization communities.Thus clipping has a filtering effect on the mechanism of temporal stability,and fertilization promoted the selection effect,which approved that the community stability mechanism was disturbance-dependent.(5)Our analysis shown that though both complementary effect and selection effect all existed across whole communities,selection effect was more effective mechanism than complementary effect in maintaining the temporal stability of alpine meadow community.In our study,the mechanisms maintaining temporal stability of total species abundance of alpine meadow in the area were dependent on the changes of disturbance factors;the complementary effect based on species diversity and the selection effect based on population stability of dominant species transformed along disturbance gradient.Selection effect played a major role to maintaining temporal stability compared with complementary effect because the stabilization effect of sub-dominant species was enhanced greatly by clipping and fertilizing.Findings from this study highlight the important role of stabilization effects results from species diversity and dominant species ought to be considering in management practices in the region,emphasizing the importance of connection between grazing(or clipping)utilization and fertilizing restoring grasslands to long-term stability of alpine meadow. |
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