Colombia's best-known drug trafficker, Pablo Escobar, may have been killed in 1993 but his influence continues to be felt in the country, sometimes in unexpected ways. Hippopotamuses brought to Colombia as part of Escobar's private zoo at his ranch, Hacienda Napoles, have bred so successfully that there is serious concern over their environmental impact and human safety, according to a new study by researchers at Mexican and Colombian universities. The hippos have spread out from their original home, some 100 miles east of the city of Medellin, in the Antioquia department, dispersing around the Magdalena river basin as their population continues to grow steadily.