"Elephants and Mammoths: Can Ice Ivory Save Blood Ivory?", Farah & Boyce 2015:
"We study both theoretically and empirically how the presence of a substitute alters the exploitation path of an open access resource. Elephants, poached for ivory, are the endangered species, and mammoth ivory is a non-renewable substitute. Our theory shows that the presence of the mammoth ivory substitute reduces both the elephant poaching rate and the minimum viable elephant population. Thus, there exist elephant population levels which are non-viable absent a substitute, but become viable with a substitute. Our empirical analysis finds that absent the eighty tonnes of Russian mammoth ivory exports per annum 2010-2012, the current poaching level of 34,000 elephants per year may have increased to as many as 85,000 elephants per year, out of a population of a half-million animals, and reduced elephant ivory prices by $100 per kilogram. Thus mammoth ivory trade may be saving elephants from extinction."