Ripple, W. J.; Beschta, R. L. (January 2012). "Trophic cascades in Yellowstone: The first 15 years after wolf reintroduction". Biological Conservation. 145 (1). Elsevier Ltd: 205–213. Bibcode:2012BCons.145..205R. doi:10.1016/j.biocon.2011.11.005.
Ripple, W. J.; Beschta, R. L. (January 2012). "Trophic cascades in Yellowstone: The first 15 years after wolf reintroduction". Biological Conservation. 145 (1). Elsevier Ltd: 205–213. Bibcode:2012BCons.145..205R. doi:10.1016/j.biocon.2011.11.005.