Analysis Of Complexity And Stability Of Fish Community Based On Network Theory

The functional response of fish community to ecological stress is reflected in the complexity and stability of its structure.However,the biological and abiotic factors influencing the structural complexity and stability of fish community are still urgent problems to be solved.At the same time,there is always controversy about the relationship between complexity and stability.Taking the Leizhou Bay estuary and the Pearl River Estuary as an example,this study used Schoener niche overlap model to construct the fish ecological network based on the fishery resource survey and environmental data of the 8 seasonal voyages of the Leizhou Bay estuary during 2016-2018 and the 4 seasonal voyages of the Pearl River estuary during 2019-2020.To the network’s overall weighted clustering coefficient(mCw)reflect the complexity of community structure,and compared to clustering coefficient(C)for identify the types of relationships between the dominant community structure;The stability of fish community structure was calculated;The biotic variables were:Si was used to reflect the strength of the interaction between population,ki reflected the number of directly related,the tris reflected the amount of indirect association,and the species richness.The abiotic variables were:environmental variables such as water depth(Depth),dissolved oxygen(DO),water temperature(Temp),salinity(Sal),and pH;Time and space variables such as season,year,longitude(Ion)and latitude(lat).Principal component analysis(PCA)and generalized linear model(GLM)were used to study the responses of complexity and stability to biotic and abiotic variables,and the relationship between complexity and stability was investigated.The results showed that:(1)Fish communities were highly complex in both Leizhou Bay estuary and Pearl River Estuary(mCw=0.821±0.081 in Leizhou Bay estuary;mCw=0.832±0.110 in the Pearl River Estuary),which was dominated by strong interspecific associations(mCw>C).Local extinctions tended to take up more intensive niche space.However,there were a large number of direct(ki)and indirect(tris)associations among species,which reduced the possibility of large-scale "cascade extinctions".(2)The complexity of fish community structure in Leizhou Bay estuary was mainly influenced by biotic variables,i.e.interspecific relationship(ki:Estimate=-4.23,p<0.01;tris:Estimate=3.12,p<0.01;Si:Estimate=0.42,p<0.01).The complexity of fish community structure in the Pearl River Estuary is caused by the interaction of biotic,environmental,time and space factors.(3)The fish community structure in Leizhou Bay estuary showed an unstable state(mSt=-0.015±0.043),and the seasonal change of stability showed a periodicity of high in winter and spring,low in summer and low in autumn,which was mainly affected by the change of the Si(Estimate=-1.668,p<0.01)and the tris(Estimate=1.041,p<0.01);The overall structure of the fish community in the Pearl River Estuary was stable(mSt=0.074±0.047).The season(Estimate=-0.30,p<0.01)and the Sal(Estimate=-0.32,p<0.01)showed extremely significant negative effects on its stability.(4)The relationship between complexity and stability was significantly negative at bay and estuary scales(p=0.002<0.05).The increased complexity tended to undermine the stability of community dynamics.Based on the existing research results,it is inferred that the influence of environment on the community structure is indirect.Environmental changes directly affect the abundance and spatial distribution of the population,resulting in the interaction between the populations,and then indirectly affect the complexity and stability of the community structure.The strong interspecific interactions played a leading role in the formation of community organisms at a small spatial scale(bay and estuary).How this pattern,dominated by interspecific associations,affects the large scale space is an urgent issue to explore.Predicting how the functions of complex ecosystems will respond to environmental change requires understanding how the interactions between species will evolve,which is of great significance to the ecological management of watersheds and the conservation of fishery resources.The stability measure used in this study does not take into account the regulation mechanism of the ecosystem.Because the ecosystem is often deviated from the equilibrium state,this stability measure is not accurate.At the same time,the output result of the niche model is an estimate of the distribution possibility,and the restriction of species migration ability and interspecies interaction on the spatial niche should be considered in subsequent studies.Nevertheless,the results of this study are still of great reference value for further study of the relationship between stability and complexity.