An ecologist is investigating the relationship between the concentration of copper ions in soil samples (measured in μg g−1\mu\text{g}\,\text{g}^{-1}μgg−1) and the percentage cover of a copper-tolerant grass species (Agrostis capillaris) across 12 different locations on an abandoned mine site.
Which statistical test should the ecologist use to determine whether there is a significant association between these two variables?
Chi-squared (χ2\chi^2χ2) test
Student's ttt-test
Spearman's rank correlation coefficient
Standard error of the mean
