Pilumnus sayi (Crustacea, Brachyura, Xanthidae) occupied heads, i.e., colonies, of Schizoporella pungens (Bryozoa, Cheilostomata) on seagrass beds located along a barrier shoals in the northern Gulf of Mexico. In a collection from 23 m('2), 94 adult crabs were found among 369 colonies. Sex ratio for adults was significantly skewed at 1:1.85 males to females. Schizoporella heads were significantly clumped according to nearest neighbor analyses, and were renewable within 6 1/2 months. Heads differed in size, presence or absence of cavities, and state of attachment to the substrate. Adult crabs were seen foraging on and around heads. Observed predators included the wrasse Halichoeres radiatus and the box crab Hepatus epheliticus. / Laboratory experiments tested predictions of consumer behavior deduced from characteristics of the heads and possible selective pressures for this association, i.e., predation, trophic pressures, and sexual selection. Adult P. sayi preferred heads larger than a 17 ml threshold, attached heads, and heads with cavities, contrary to predictions derived from trophic pressures and consistent with those from predation. Crab preferences for clumped heads was sex dependent, thus implicating sexual selection, used in a broad sense pertaining to mate acquisition. Movement to heads was quick and direct as expected from predatory pressures; and males moved between heads more often than did females, again implicating sexual selection. Crab size was not a factor in either movement or preferences when crabs were tested individually. However, larger crabs dominated smaller crabs in agonistic contests for individual heads, regardless of the sex or residency of participants. An ethogram of 6 modal action patterns (MAPs) and 5 non-MAP acts was compiled, and the structure of contests was analyzed. Escalation of violence was likely to be initiated by either crab, but was more readily continued by the larger one. In group experiments, the location of larger and smaller males was independent of either the location of females or the spatial pattern of heads. However, in group experiments, larger males moved between heads significantly more often than did smaller males, which moved at the same frequency as females. / Ecological patterns of head use by P. sayi were consistent with expectations derived from consumer behavior and population descriptions. The number of adult crabs equaled the number of preferred heads. Adults occupied significantly more heads with cavities than heads without cavities. They also occupied significantly larger than average heads, but not necessarily heads larger than their preferred threshold. Consequently, there was a slight but significant correlation between crab size and the size of heads occupied. Furthermore, males and females did not differ in the types of heads occupied. Adults occupied heads individually except for occasional double occupancy by a male and female. In such cases, the male tended to be larger. Further spatial pattern among crags was revealed by an analysis that incorporated head patterns; among adults, there were fewer heterosexual nearest-neighbor pairs than expected by chance alone. / The combination of behavioral experiments and ecological sampling suggested that a relative shortage of this resource existed for the population of P. sayi under study. Furthermore, behavior of crabs in experimental situations and their spatial pattern in nature was consistent with resource defense polygyny, although a capacity for male dominance polygyny was indicated. Behavioral scaling that incorporates resource structure and risk of predation is hypothesized as a determinant of this crab's mating system. / Source: Dissertation Abstracts International, Volume: 41-03, Section: B, page: 0786. / Thesis (Ph.D.)--The Florida State University, 1980.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_74158 |
| Contributors | LINDBERG, WILLIAM JAMES., The Florida State University |
| Source Sets | Florida State University |
| Detected Language | English |
| Type | Text |
| Format | 132 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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