37859
In the 1960 s he collaborated with mathematician and ecologist Robert MacArthur in developing the theory of species equilibrium .
 person: Robert MacArthur
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
 Entities: Robert MacArthur 
Answer:
 person: Robert MacArthur