The efforts of two USGS scientists, which began over twenty-five years ago, culminated in 1998 with the publication of a 287-page book titled Yellowstone and the Biology of Time. Co-authored by Mary Meagher and Douglas Houston, the book conveys in pictures and words the changes that have occurred in Yellowstone National Park over the last century. 
The National Park Service supported the authors' work as research biologists until their reassignments in 1993 to the newly formed research agency, the National Biological Service (now USGS Biological Resources Division). The book contains a series of about 100 repeat photographs over a period of about 120 years. Paired photographs spanning roughly 100 years are followed by a second set of pictures taken about 20 years later following the Yellowstone fires of 1988. The physical and biological framework for the photographs and an interpretation of the forces that drive biological changes in the park is included.
