Inter-Research
Marine Ecology Progress Series

ABSTRACT: Three sympatric species of semi-terrestrial hermit crabs (Coenobita cavipes, C. rugosus and C. pseudorugosus) occur on SW Madagascar shores on the edge of a semi-desert. They have similar resource requirements, some of which are restricted, yet their populations are very abundant. All 3 species seek refuges, the type and extent of which were assessed in 5 size classes for each of the species at 6 sites. Refuge-use, principally burrowing, was governed by a series of factors: tidal range, individual size (mass), species identity, site, shade. Shell architecture did not, however, directly influence refuge-use. An existing ordination technique (detrended correspondence analysis, DCA) was modified by inserting refuge identities as 'species terms' to interpret the structure underlying multi-dimensional niche space. The results show that variability in the refuge suite sought by hermit crabs serves to partition niche space both overall at the species level, and on a site-by-site basis for each species. On high spring tides, the extent of burrowing (a strategy common to all 3 species) was reduced, and a DCA of this data set showed niche compression at this tidal phase. Whilst biologically mediated niche shifts are a well-established concept, the changing of niche overlap described here clearly differs, as it is temporally dynamic and physically (tidally) driven. Inclusion of intertidal and subtidal hermit crabs at the study site into a data matrix showed that most species were separated ecologically by 4 niche dimensions: shore zone, habitat type, shell type and refugial behaviour. Niche complimentarity was clear, as species which were similar in 1 or more dimensions (such as C. rugosus and C. pseudorugosus) differed in other dimensions. Refuge-use of Coenobita spp. hermit crabs (and equivalent clustering behaviour of intertidal species) seems, therefore, to be multifunctional. The behaviour appears crucial to environment extremity avoidance, but may be equally important in resource management through water conservation and shell-, habitat- and shore-zone-partitioning. The results indicate that the SW Madagascar hermit crab assemblage is a speciose guild with (5D) niche complimentarity and temporally dynamic niche overlap.

KEY WORDS: Niche dynamism · Detrended correspondence analysis · DCA · Littoral burrowing · Coenobita · Africa

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Published in MEPS Vol. 238 (2002) on August 8
Print ISSN: 0171-8630; Online ISSN: 1616-1599. Copyright © Inter-Research, Oldendorf/Luhe, 2002