The Rhode Island Salt Marsh Experiments on the Rush Juncus

The Rhode Island salt marsh experiments on the rush Juncus gerardii and the shrub Iva frutescens showed that Iva dominates and Juncus has a low biomass in the high intertidal zone.However, in the low intertidal, where salinity and waterlogging are greater, Iva depends on Juncus for survival.Which general statement best describes the cause of the change in this relationship?

A) Stressful environments increase competition between species.
B) Stressful environments change mutualists or commensals into competitors.
C) Environmental variation is necessary to enable certain species to survive.
D) Environmental variation may cause communities to have a higher biodiversity.
E) Environmental variations may change competitors into mutualists or commensals.