1. "Ecological limit functions relating fish community response to hydrologic departures of the ecological flow regime in the Tennessee River basin, United States" is a research paper published in Ecohydrology in 2013, assessing the influence of aspects of river function/hydrology as predictors of fish communities. In the graph below, the response (vertical axis) is a measure of fish diversity (all species, or invertebrate-eaters, or fish that broadcast their eggs onto the stream bottom) and the predictor is a hydrological variable. The lines are marking 90^th(or 95^thor 85^th) percentile measurements of the responses (the fish diversity). In this paper, the authors do not calculate a correlation coefficient between the hydrological variable and the fish diversity measure. Why?