Abstract
The intertidal isopods Gnorimosphaeroma oregonensis oregonensis (Dana) and Exosphaeroma amplicauda (Stimpson) are shown to have differing preferences for substratum particle-size categories. In field sampling, 80.9% of the total number of G. oregonensis oregonensis taken were present on substrata falling within a ϕ-4.2 to-3.8 diameter size-range, while 60.0% of E. amplicauda occupied the range ϕ-2.5 to-2.1. These relationships changed upon laboratory manipulation of density ratios, and suggest competitive interaction: when E. amplicauda is tested alone, the resultant preference assumes a greater niche breadth and overlap to that of the field. Introduction of G. oregonensis oregonensis produces a displacement of E. amplicauda, the degree being dependent upon their relative numerical strength. With an experimental ratio of 3:1 (G. oregonensis:E. amplicauda) there is a simulation of field densities, and the laboratory results approximate more closely the overlap in nature.
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Communicated by M.R. Tripp, Newark
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Rees, C.P. Competitive interactions and substratum preferences of two intertidal isopods. Mar. Biol. 30, 21–25 (1975). https://doi.org/10.1007/BF00393749
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DOI: https://doi.org/10.1007/BF00393749