HC Resource1 - Shell Selection and Invasion Rates of Some...

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Shell Selection and Invasion Rates of Some Pacific Hermit Crabs GORDON H. ORIANS and CHARLES E. KING 1 ABSTRACT : Three species of littoral hermit crabs from Horseshoe Cove, Bodega Head, Sonoma County, California, and three sublittoral pagurids from Chinimi Island, Eniwetok Atoll, Marshall Islands, have been examined with respect to their shell selection and invasion rates. Periodic removal of crabs from marked areas resulted in immigrations of surprising magnitude. By comparison of actual collection patterns with those predictable from the alternates of density dependence and density independence, there is an indication that the observed immigration rates result from density- dependent dispersal. While our data are not conclusive, the method presented is of interest and of possible utility for examining problems of this nature. Shell selection is discussed from the bases of both laboratory and field observa- tions. Each of the species is shown to utilize the shells of different gastropods with different frequencies. Finally, behavioral aspects are examined as they relate to the distribution of the California hermit crabs. SHELLS of various species of gastropod molluscs constitute a necessarycomponent in the environ- ment of pagurid crabs. In addition to housing the crab the shell may act as an important determinant of behavior; for instance, several species will not feed unless in a shell (Allee and Douglis, 1945; Brightwell, 1952). Different species of pagurids regularly utilize different species of shells and it has been suggested that shell availability may be a limiting factor for some species (Provenzano, 1960). This paper reports on observations of shell utilization by six species of Pacific hermit crabs and on some simple laboratory experiments on shell selection. In addition, a number of removal and repopulation experiments were performed. Orians worked mainly at Horseshoe Cove, Bo- dega Head, Sonoma County, California, during the summer of 1957, and King at Chinimi Island of Eniwetok Atoll during the summer of 1961. The study area at Horseshoe Cove consisted of a section of rocky, shelving shore partially 1 Dept. of Zoology, Univ . of Washington, Seattle. Manuscript received January 31, 1963 . Orians' research was carried out under the auspices of the Dept. of Zoology, Univ. of California, Berkeley. King's research was supported by the U. S. Atomic Energy Commis- sion at their Eniwetok Marine Biological Laboratory. protected from heavy ocean swell, with an abun- dance of small tidal pools at high and medium intertidal ranges. Twenty-seven pools in the tidal range 2.5-4.5 ft above. datum (which is mean low water) and subjected to long periods of exposure at low tides, were selected because they were easily reached at most tides. They ranged in length from 0.43 to 9.5 m and in depth from 15 cm to approximately 1 m.·Plant cover varied from virtually nothing to dense algal growth covering the bottoms and sides of the pools. During the period of study, tempera- tures never rose above 17 C in the lower and
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This note was uploaded on 02/27/2010 for the course PHYSICS 215 taught by Professor Lawn during the Spring '10 term at Academy of Art University.

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HC Resource1 - Shell Selection and Invasion Rates of Some...

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