Henry Cowles was not alone in recognizing the significance of dynamic succession for the study of plant communities. Independently, Frederic E. Clements (1874-1945) of the University of Nebraska and the University of Minnesota developed the principles of ecology on the basis of his studies of the grasslands and sand hills of Nebraska. At the same time, Cowles's former student Victor E. Shelford (b. 1877) extended ecological theory to the study of a variety of animal communities.
Frederic Clements, a student of Charles Bessey at the University of Nebraska, began his professional ecological work shortly after Henry Cowles published his two influential papers. In The Development and Structure of Vegetation (1904), Clements argued that vegetation must be understood in its entirety as a complex organism. Further work by Clements on ecology and succession led to the publication of his most influential book, Plant Succession: An Analysis of the Development of Vegetation (1916). In 1913, the Carnegie Institution of Washington provided Clements with funding to move his research program entirely from the University of Minnesota to the Alpine Laboratory that he had established on Pikes Peak in the Colorado Rockies. There Clements and his wife Edith Schwartz Clements conducted a systematic study of succession in thousands of square miles of the surrounding mountainous area. They carefully documented all environmental influences on plant life from temperature and humidity to levels of light and evaporation and analyzed the complex interrelation of mountain plants with the insect and animal life of the region.
Just as John M. Coulter had fostered an important center for ecological studies at Chicago, Charles Bessey made Nebraska another important center for the training of a new generation of American ecologists. In addition to the two leading figures in ecology, Henry C. Cowles and Frederic Clements, those who studied at Chicago or Nebraska and developed significant careers in ecology or the biological sciences included Charles Adams, William Cooper, Henry Gleason, Herbert Hanson, Clarence Korstian, Burton Livingston, George D. Fuller, George E. Nichols, John Ernst Weaver, Edgar Transeau, Raymond Pool, Homer Shantz, and Victor Shelford.
Perhaps more than any other student of Henry Cowles, Victor Shelford was able to extend ecological concepts furthest into new areas of biological research. A zoologist who was strongly influenced by Cowles's work, Shelford applied the concepts of ecology initially to the life histories and habits of tiger beetles. His early investigations supported the publication of Animal Communities in Temperate America as Illustrated in the Chicago Region: A Study in Animal Ecology (1913). As a member of the faculty at the University of Illinois after 1914, Shelford expanded his research to include thorough studies of a wide range of animal life from fishes to moths, antelope, lemmings, owls, and termites, among others.
Sharing many common interests and theoretical perspectives, Clements and Shelford were drawn to collaborate on a major work intended to create a unified synthesis of scientific work on plant and animal ecology. Their joint book, Bio-Ecology (1939), argued for the importance of animal-plant interelationships within the area that Clements was the first to designate as the biome, "an organized unit comprising all the species of plants and animals at home in a particular habitat."
The approach adopted by Clements and Shelford marked a significant point in the transition of scientific research and theory from the examination of plant ecology and animal ecology to the study of bioecology. The concept of bioecology itself has now been superceded by a broader concern for understanding the whole structure of the ecosystem in all its scale and complexity. This encompassing focus on the ecosystem has been an important factor in recognizing, beyond the life cycles of plant and animal communities, the powerful and pervasive role of human civilization in shaping and altering the natural environment.