Animal communities in temperate America as illustrated in the Chicago region. A study in animal ecology.

This book represents the beginning of organized theoretical principles for animal ecology, including Shelford's "law of toleration"  or "law of tolerance." "Analogous to the physiologists' law of the minimum [developed by Liebig], this principle explained limits to the occurrence of a species with whatever physical factor exceeded its tolerance" (DSB Vol. 18, 812). Digital facsimile from the Internet Archive at this link.