Local, regional and global patterns of resource use in ecology: hermit crabs and gastropod shells as an example

To see the 'big pictures', it seems increasingly clear that experimental design, data collection and analyses of ecological investigation need to be at multiple scales. This causes problems with data complexity, sampling (level) and independence. Many ecological programmes are currently conducting multi-scale investigation of organismal trends (e.g. diversity). In this study, by contrast, the assemblages analysed were the resources used by animals (rather than animals per se). Variability in shell use was studied in 5 members of a taxon (hermit crabs) from global to site spatial levels. The novel adaptation of an existing technique used 1-factor, 3-level ANOVA of Bray-Curtis similarity values based on 'centroids' for each scale. Similarity in the number of shells used, the proportional usage of shell types, shell diversity and other variables were examined at site (> 10 m apart), locality (> 1 km apart) and region levels (> 1000 km apart). There was significant variability amongst scales and between regions in shell use of all species. For some species, observed variability differed with location, while in others the trend was similar in all 3 regions. Between 18 and 3 shell types were used by different study species with diversity (Shannon H') values ranging from 2.54 to 0.1 and evenness values from 0.99 to 0.1. Shell use by hermit crabs was less similar (to each other) between regions than between the study hermit crab species. No significant spatial effects at any level were found on the proportion of damaged shells used by different species. The numbers of shell types used by hermit crabs had both a taxon-specific component and a global pattern. Data from the literature in combination with that from the present study showed Dardanus, Diogenes and Pagurus species used fewer shell types than Coenobita, Clibanarius and Calcinus species. No inter-oceanic patterns were evident in any genus. Shell numbers used by Clibanarius and Calcinus species both, however, exhibited distinct latitudinal clines. Adaptation of a novel technique has, thus, demonstrated global (and differential between scale) trends in resource use by a guild of animals, although interpretation of the mechanism or meaning underlying this is not straightforward.

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