Klaus Hackländer studied Zoology at Philipps University Marburg/Lahn and the University of Vienna. He is currently a Full Professor of Wildlife Biology and Wildlife Management at the University of Natural Resources and Life Sciences, Vienna, where he also coordinates the master's degree program on Wildlife Ecology and Wildlife Management. Hackländer is a member of numerous mammalogical societies and served as president of the German Society for Mammalian Biology from 2009 to 2016. He was Editor-in Chief of the journal Mammal Review from 2009 to 2015 and has coedited two books on the Lagomorpha, his favorite mammalian taxon. Hackländer's research covers all aspects of mammalian biology, including ecology, behavior, physiology, diseases, and management. Frank E. Zachos is head of the Mammal Collection at the Natural History Museum Vienna, Austria, affiliated lecturer at the University of Vienna and affiliated professor at the Department of Genetics at the University of the Free State in Bloemfontein, South Africa. He studied biology, history of science and philosophy in Kiel and Jena, Germany, and received his PhD in zoology in 2005. In 2009, he completed his habilitation for zoology and evolutionary biology. His main research topics comprise the intraspecific biodiversity, phylogeography, population genetics and conservation of mammals and birds, with a particular focus on red deer and other ungulates. He also has a long-standing interest in species concepts and the species problem as well as other theoretical and philosophical issues in evolutionary biology and systematics. He was the editor-in-chief of the journal Mammalian Biology from 2007 to 2021, and he is currently the editor of the Mammalia series within the Handbook of Zoology.