In 1978, a removal experiment based on observations was conducted by Mark A. Chappell which took four different species of chipmunk into account. This experiment was to detail the process of removal by the different species. In the experiment, it was noted that the four different species were allopatric, meaning they formed non-overlapping borders in their Sierra Nevada habitat. Each species ("N. alpinus", "N. speciosus", "N. amoenus", and "N. minimus") was noted to live at different zones in the Sierra Nevada. The Lodgepole chipmunk ("N. speciosus)" was observed living from 2400–3000 meters in the lodgepole pine zone, between the alpine zone (3000+ meters) and the Piñon pine/mountain mahogany zone (1900–2400 meters). This ecological competition for different zones of a single area is determined by physiological and environmental limits, where each species is limited specifically to a zone that best fit each species' habitat preferences.