Crab wars: Testing the ideal free distribution with invasive Carcinus maenas and native Hemigrapsus nudus

Abstract

Invasive species can cause changes in community composition, native species’ habitat acquisition and reduce abundance of native species. The Ideal Free Distribution (IFD) provides a conceptual framework for describing intraspecific distributions of individuals and can be modified for interspecific interactions to correct for differing competitive ability. We examined whether the IFD of Hemigrapsus nudus (H. nudus), native to the west coast of North America, varies with the introduction of invasive Carcinus maenas (C. maenas) with respect to food availability. We tested this experimentally by constructing artificial habitats with patches of high and low food availability and monitoring the distributions and feeding rates of H. nudus and C. maenas among these food patches. C. maenas was six times more competitive in acquiring food than H. nudus. Based on this foraging discrepancy, spatial distributions between food patches did not follow those predicted mathematically by the IFD. H. nudus did not distribute ideally in terms of food, while C. maenas did. Thus, the ability of C. maenas’ to ideally distribute combined with its high food acquisition rate, has the potential to affect H. nudus survival with the spread of C. maenas in the Pacific Northwest.