Much of the ecological work of the present time is concerned with the direct observation of natural variations in environment and biota, followed by an examination of the relationships between variables and speculation as to their meaning….
Riley, Gordon A.. 1939. "Correlations in aquatic ecology with an example of their application to problems of plankton productivity." Journal of Marine Research 2, (1). https://elischolar.library.yale.edu/journal_of_marine_research/545