Limiting Similarity Robert Helmer MacArthur (April 7, 1930 – November 1, 1972) was a Canadian-born American ecologist who made a major impact on many areas of community and population ecology.

[3] A student of G. Evelyn Hutchinson, MacArthur earned his Ph.D. from Yale University in 1957; his thesis was on the division of ecological niches among five warbler species in the conifer forests of Maine and Vermont.

[8] Robert MacArthur, in collaboration with Edward O. Wilson, developed the influential theory of island biogeography, which revolutionized how ecologists understand species diversity and distribution.

[13] This model likens the division of resources in an ecosystem to breaking a stick into randomly sized pieces, predicting the relative abundance of species in a community.

MacArthur was a pioneer in developing mathematical models for consumer-resource dynamics, aiming to explain how interactions between species shape ecological communities.

He showed that these systems tend to minimize a quantity related to resource overlap, providing a theoretical foundation for understanding competitive exclusion and coexistence.

Their model is notable for predicting population cycles in predator-prey interactions, which occur due to the lag between prey growth and predator consumption.