| The relationship among diversity,stability and productivity of ecosystems has been a central research topic in ecology and environmental science.Current researches on the relationships among diversity,stability and productivity mainly focused on their correlations,whereas researches on their causalities are scarce.However,the correlation does not necessarily mean causation,and vice versa.In addition to the mutual interactions of the three,changes of environmental conditions may lead to changes in causations among diversity,stability,and productivity of ecosystem.This research focuses on two questions:(1)What are the causal relationships among diversity,stability and productivity in the ecosystem?(2)Does environmental shifts(e.g.enrichment of N and P)have causal impacts on diversity,stability and productivity?To answer the first question,we analyzed a published high-quality 8-year observation data set(mesocosm of Baltic Sea plankton ecosystem).In addition to the α-diversity index,three food network structural diversity indices were also included.The stability indicators were long-term stability and short-term stability.Productivity was characterized by the sum of biomass.Correlation analysis was firstly performed on the diversity,stability,and productivity of the data set.We then employed Granger causality test(GC)and Convergent Cross Mapping(CCM)for causality tests.To answer the second question,we established 132 fresh water algae microcosms in our laboratory and then increased N and P concentrations as treatment.In order to explore the causal impacts of increased N and P concentrations on diversity,stability and productivity,a causal impact analysis based on Bayesian structural time-series models were utilized.According to our analysis,we found that in the mesocosm of Baltic Sea,diversity is negatively related to long-term stability and productivity,while long-term stability and productivity are positively correlated.Bidirectional causal relationships are found between diversity and longterm stability,productivity and the driving force for diversity is stronger.Besides,stability is the cause of productivity.Food web structure shows the importance for maintaining ecosystem functioning with the causality between food network structural diversity and long-term stability,productivity.Our fresh water algae microcosm experiment showed that algae communities with higher species richness in lower initial N and P concentrations are causally affected by increased N and P concentrations.The results also reflect that when the initial concentration of N and P in the water body is high,the key factors driving occurrence of algae blooms may be other environmental factors.The causality among diversity,stability,and productivity obtained in this study shows that it is desirable to regulate the stability and productivity of ecosystems through diversity.But because of the "feedback" between them,it may actually take more effort.In addition,the regulation of diversity is not just regulating the species richness,but also the structure of the food web and the evenness of the species.For the prevention and control of algae blooms,controlling the concentration of N and P is an effective method,but in the eutrophic water,it may not work well.The results of this study can provide some suggestions for ecosystem function management and risk control.More importantly,early warning and prevention of catastrophic regime shifts in ecosystems can be realized better. |
