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A TEST OF THE GENERALITY OF THE EFFECTS OF SHELTER BOTTLENECKS IN FOUR STONE CRAB POPULATIONS
Author(s) -
Beck Michael W.
Publication year - 1997
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/0012-9658(1997)078[2487:atotgo]2.0.co;2
Subject(s) - ecology , biology , habitat , population density , population , interspecific competition , predation , fecundity , population size , competition (biology) , fishery , demography , sociology
The structural complexity of a habitat dictates the availability of shelter, and shelter may affect population and community structure in many systems. I tested predictions from the shelter bottleneck hypothesis, which proposes that shelter (or refuge) limitation can control population size structure and density by acting strongly on only one size class. I manipulated shelter for stone crabs in four haphazardly chosen bays in the northeast Gulf of Mexico to examine the shelter bottleneck hypothesis in a mixed‐model design. I also examined four biotic factors (habitat structure, food, predation, and interspecific competition) that may contribute to population‐level differences among bays. I found differences among bays in stone crab size structure and density and in crab responses to size‐specific shelter supplementation. These differences in stone crabs among bays included: (1) natural median crab size differed by 5.5‐fold, (2) size at maturity changed by 33%, (3) adult density varied 10‐fold, (4) the density response of molting individuals and gravid females to supplemental shelter differed by more than 7‐fold, and (5) the shelter preferred by crabs changed from 25 to 100 mm diameter pipes. The shelter bottleneck hypothesis and differences in habitat structure best account for these differences in stone crabs among bays. There appeared to be bottlenecks in three of the four bays, and the location of the bottleneck was predictable from measures of habitat structure. There were demographic consequences of shelter limitation on stone crab growth and fecundity at the individual level, and these effects appeared to explain population‐level differences among bays. However, the bottleneck effects may be mediated by differences in food quantity and competition among bays. The experiments suggest that shelter bottlenecks have important effects on stone crabs across a wide region in the northeast Gulf of Mexico, and illustrate the benefits of using random factors in experimental designs to examine the generality of ecological effects.