Variations in interspecific interactions play an essential role in community structure, and have already been widely demonstrated between pairwise species along a stress gradient. However, little is known about how the responses of multiple species affect interspecific interactions and the coexistence of multiple stressors. Here, we developed a dynamic model considering the tolerance heterogeneity of three species to investigate how interspecific interactions shift across different environmental stressors. We found the alteration of interspecific relationships for multiple species under multiple stressors depends on the tradeoffs between tolerant and competitive abilities to the limiting stress. Stress--intolerant species may be significantly improved by positive feedback effects from two or more neighbors under multiple stressors. There are complementary effects of species' heterogeneous responses under multiple stressors due to environmental feedback from different species, which may enhance interspecific interaction strength and the shift threshold from competition to facilitation.

A central and fundamental issue in ecology is to understand the relationship between complexity and stability. Increased empirical evidences demonstrated no clear relationships between complexity metrics and stability, and recent food web loop analyses suggested that maximum loop weight as well as the summation ratio between 3 and 2-link feedback loop weights could be better estimators of system stability. However, the importance of longer loops than 3-link on the stability remains unclear. Here we use 127 marine food webs and the matrix product and trace method to investigate the relationship between loops with maximum of 7 links and food web stability. We found that feedback metrics |a2n+1/a2n|α, i.e., the ratio of the sums of (2n + 1)-link and 2n-link loop weights, are strongly related with stability. These sum weight ratios can be regarded as the coupling strength between omnivory loops and their one-species-delete subloops, including the smallest three species and high-level omnivory ones. Further theoretical simulations of bioenergetic consumer-resource models with allometric constraints strengthen this finding. These results suggest that both longer loops and omnivory are important drivers of the food web stability.

Macrophyte community diversity and composition respond to ecosystem conservation and local environmental factors. In this study, we developed a multidimensional diversity framework for macrophyte communities, including the taxonomic and functional alpha and beta diversity. We used the framework to explore the relationships among water level regimes and these diversity parameters in a case study of China’s Baiyangdian Lake. Analysis of indicators of hydrologic alteration divided the water level from 1959 to 2019 into four regimes (dry, <6.42 m; low, 6.42 to 7.23 m; medium, 7.23 to 8.19 m; high, >8.19 m). Alpha and beta diversity were significantly higher in the medium regime than in the low and high regimes. Redundancy analysis indicated that the maximum water depth significantly affected taxonomic alpha diversity, and total nitrogen (TN) and chemical oxygen demand (COD) concentration significantly affected functional alpha diversity, respectively. Mantel tests showed that TN, Secchi depth, and water depth in the high water level regime significantly increased the total beta diversity and turnover components. TN was the main factor that increased total taxonomic beta diversity. Interspecific competition decreased with the decreasing range (variation) of TN values and differed opposite with the variation of COD values in response to increasing water level, and reached its maximum in the medium regime. Ecosystem stability was promoted by maintaining high species richness and evenness and high differences among communities, and by reducing competition. Based on our results, the water level should be maintained between the medium and high water level regimes to promote restoration of the macrophyte community and improve ecosystem stability.