Impacts of Aggregation Methods and Trophospecies Number on the Structure and Function of Marine Food Webs

Aggregation of species with similar ecological properties is one of the effective methods to simplify food web researches.However,species aggregation will affect not only the complexity of modeling process but also the accuracy of models’outputs.Selection of aggregation methods and the number of trophospecies are the keys to study the simplification of food web.In this study,three aggregation methods,including taxonomic aggregation(TA),structural equivalence aggregation(SEA),and self-organizing maps(SOM),were analyzed and compared with the linear inverse model–Markov Chain Monte Carlo(LIM-MCMC)model.Impacts of aggregation methods and trophospecies number on food webs were evaluated based on the robustness and unitless of ecological net-work indices.Results showed that aggregation method of SEA performed better than the other two methods in estimating food web structure and function indices.The effects of aggregation methods were driven by the differences in species aggregation principles,which will alter food web structure and function through the redistribution of energy flow.According to the results of mean absolute percentage error(MAPE)which can be applied to evaluate the accuracy of the model,we found that MAPE in food web indices will increase with the reducing trophospecies number,and MAPE in food web function indices were smaller and more stable than those in food web structure indices.Therefore,trade-off between simplifying food webs and reflecting the status of ecosystem should be con-sidered in food web studies.These findings highlight the importance of aggregation methods and trophospecies number in the analy-sis of food web simplification.This study provided a framework to explore the extent to which food web models are affected by dif-ferent species aggregation,and will provide scientific basis for the construction of food webs.

Reactive oxidative species enhance amyloid toxicity in APP/PS1 mouse neurons

Objective To investigate whether intracellular amyloid β （iAβ） induces toxicity in wild type （WT） and APP/PS1 mice, a mouse model of Alzheimer＇s disease. Methods Different forms of Aβ aggregates were microinjected into cultured WT or APP/PS1 mouse hippocampal neurons. TUNEL staining was performed to examine neuronal cell death. Reactive oxidative species （ROS） were measured by MitoSOXTM Red mitochondrial superoxide indicator. Results Crude, monomer and protofibrilAβ induced more toxicity inAPP/PS1 neurons than in WT neurons. ROS are involved in mediating the vulnerability of APP/PS1 neurons to iAβ toxicity. Conclusion Oxidative stress may mediate cell death induced by iAβ in neurons.

Directional changes of species spatial dispersion and realized environmental niches drive plant community assembly during early plant succession

Aims Probabilistic models of species co-occurrences predict aggre-gated intraspecific spatial distributions that might decrease the degree of joint species occurrences and increase community rich-ness.Yet,little is known about the influence of intraspecific aggre-gation on the co-occurrence of species in natural,species-rich communities.Here,we focus on early plant succession and ask how changes in intraspecific aggregation of colonizing plant spe-cies influence the pattern of species co-existence,richness and turnover.Methods We studied the early vegetation succession in a six ha constructed catchment within the abandoned part of a lignite mine in NE Germany.At two spatial scales(1-and 25-m2 plots),we compared for each pair of species the intraspecific degree of aggregation and the pattern of co-occurrence and compared observed rela-tionships with temporal changes in important species functional traits.Important Findings The majority of species occurred in an aggregated manner,particu-larly in the first 2 years of succession.In pairwise comparisons,we found an excess of segregated species occurrences leading to a posi-tive link between intraspecific aggregation and pairwise species seg-regation as predicted by the aggregation hypothesis,particularly at the lower spatial resolution.The degree of intraspecific aggregation was negatively correlated with the community-wide level of species spatial turnover and with plot species richness.Our results are the first direct confirmation that increasing intraspecific aggregation and interspecific competitive interactions counteract in shaping plant community structure during succession.The respective effects of aggregation were strongest at intermediate states of early succession.