Enhanced effects of biotic interactions on predicting multispecies spatial distribution of submerged macrophytes after eutrophication

Abstract

Water eutrophication creates unfavorable environmental conditions for submerged macrophytes. In these situations, biotic interactions may be particularly important for explaining and predicting the submerged macrophytes occurrence. Here, we evaluate the roles of biotic interactions in predicting spatial occurrence of submerged macrophytes in 1959 and 2009 for Dianshan Lake in eastern China, which became eutrophic since the 1980s. For the four common species occurred in 1959 and 2009, null species distribution models based on abiotic variables and full models based on both abiotic and biotic variables were developed using generalized linear model (GLM) and boosted regression trees (BRT) to determine whether the biotic variables improved the model performance. Hierarchical Bayesian‐based joint species distribution models capable of detecting paired biotic interactions were established for each species in both periods to evaluate the changes in the biotic interactions. In most of the GLM and BRT models, the full models showed better performance than the null models in predicting the species presence/absence, and the relative importance of the biotic variables in the full models increased from less than 50% in 1959 to more than 50% in 2009 for each species. Moreover, co‐occurrence correlation of each paired species interaction was higher in 2009 than that in 1959. The findings suggest biotic interactions that tend to be positive play more important roles in the spatial distribution of multispecies assemblages of macrophytes and should be included in prediction models to improve prediction accuracy when forecasting macrophytes’ distribution under eutrophication stress.

Historical contingency via priority effects counteracts environmental change on metacommunity dynamics across decades

“…was probably mediated by the release of allelochemicals and its relatively larger allocation of biomass to rhizomes (Lacoul and Freedman 2006). Perhaps more importantly, these findings are likely to be consistent with the suggestion that functional divergence in lake plants (e.g., life forms) can switch the inhibition–facilitation balance at the metacommunity level (Song et al 2017) and contrast with previous studies that divided lake plant associations on the basis of the trophic state of the habitats (Toivonen and Huttinen 1995). However, the existence of the species‐to‐species associations highlighted here should be examined in more detail using manipulative in‐lake experiments (Dormann et al 2018), not least because biotic interactions inferred from HMSC can only be considered as working hypotheses (Tikhonov et al 2017).…”

“…was probably mediated by the release of allelochemicals and its relatively larger allocation of biomass to rhizomes (Lacoul and Freedman 2006). Perhaps more importantly, these findings are likely to be consistent with the suggestion that functional divergence in lake plants (e.g., life forms) can switch the inhibition-facilitation balance at the metacommunity level (Song et al 2017) and contrast with previous studies that divided lake plant associations on the basis of the trophic state of the habitats (Toivonen and Huttinen 1995). However, as non-manipulative data on species observations do not allow one to establish conclusively whether co-occurrences are due to biotic interactions or to other confounding issues, the species-to-species associations unraveled here should be treated merely as hypotheses of true interactions (Dormann et al 2018), the validity of which should be further verified in controlled experiments.…”

“…mechanisms (Ot'ahel'ová et al 2011). We finally expected (H5) that we would find multiple species-to-species associations after controlling the fixed and community-level random effects, either as a result of facilitation or eventual competitive exclusion in lake plants (Lacoul and Freedman 2006;Song et al 2017).…”

“…However, we also predicted (H4) that these mechanisms would appear highly variable across different species, and across species classified as helophytes or hydrophytes, not least because plant functional groups usually show different assembly mechanisms (Ot'ahel'ová et al 2011). We finally expected (H5) that we would find multiple species‐to‐species associations after controlling the fixed and community‐level random effects, either as a result of facilitation or eventual competitive exclusion in lake plants (Lacoul and Freedman 2006; Song et al 2017).…”