JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Wiley-Blackwell andNordic Society Oikos are collaborating with JSTOR to digitize, preserve and extend access to Oikos. MMinireviews provides an opportunity to summarize existing knowledge of selected ecological areas, with special emphasis on current topics where rapid and significant advances are occurring. Reviews should be concise and not too wide-ranging. All key REVIENV s *references should be cited. A summary is required. Community composition and nested-subset analyses: basic descriptors for community ecology Wade B. Worthen Worthen, W. B. 1996. Community composition and nested-subset analyses: basic descriptors for community ecology. -Oikos 76: 417-426.Three primary descriptors of community structure are the number, identities (composition), and abundances of species therein. Over the past 35 years, most attention has focused on relationships involving number (species-area and species-energy relationships) or abundance distributions (broken-stick, geometric, log-normal, core-satellite, etc.). Composition patterns have been underemphasized, even though several tools for addressing particular non-random patterns in species composition are available. One non-random pattern in community composition is nested subset structure. A community has a nested subset structure if the species found in depauperate replicates are also found in progressively more species-rich assemblages. In this review, the problems of failing to consider composition patterns like nestedness are described, using species-area relationships and the SLOSS debate (single large or several small reserves) as an example. In addition, nestedness analyses are promoted as: 1) important descriptive tools for determining whether a community has this common non-random pattern of species composition, and 2) as important investigative tools for suggesting mechanisms potentially structuring a community.W. B. Worthen, Biology Dept, Furman Univ., SC 29613, USA (worthengfurman.edu).

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Nested subset structure has been studied in archipelagoes and fragmented habitats, and has been attributed to differential colonization and extinction rates among species and nested environmental tolerances. In this experiment, we tested for nestedness in assemblages of mycophagous fly larvae. Twenty mushrooms in each of three size classes (4.8-6.0 g, 10-15 g, 21-32 g) were placed on moist potting soil in experimental cups. The cups were placed in oak and pine forests in Greenville, S.C., USA for 5 days, where they were available to ovipositing flies. Upon collection, the mushrooms were incubated in the laboratory for 3 weeks and all emerging flies were sorted by species, counted, and weighed. A random placement analysis was conducted to determine whether the species richness pattern was a sampling artifact of the species abundance distributions. The actual species richness pattern did not conform to the random placement model; most mushrooms contained significantly fewer species than predicted by random sampling. The communities were strongly nested as measured by two different indices, and the nestedness pattern was related to mushroom size. Small mushrooms usually produced no flies or a single species, Dohrniphora sp. (Phoridae). Medium and large mushrooms typically produced more species-rich communities that usually contained the phorid and Drosophila putrida, D. tripunctata, and Leucophenga varia. This core guild was nested within a more diverse assemblage that included D. falleni, Mycodrosophila dimidiata, a muscid, and two Leptocera sp. (sphaeroceridae). These patterns are tentatively explained in the context of nested desiccation tolerances, mediated by differences in mushroom size.

Ten common libellulid species perch along the shoreline of lakes and ponds in South Carolina, USA. We collected individuals at five ponds throughout summer 2005, weighed them in the field, and calculated wing loading (N·m-2 ) and wing aspect ratios from digital photographs. We measured the perch-height preferences of these species in 'low perch' (10, 20, 30, and 40 em) and 'high perch' (20, 40, 60 and 80 em) experiments. Flywheel anemometers recorded wind speeds at each perch height. Species differed significantly in mean body mass, spanning nearly an order of magnitude from Perithemis tenera (67 mg) to Libellula vibrans (633 mg).There were also significant differences in wing morphology that correlated with mean mass; larger species had greater wing loadings and greater wing aspect ratios that smaller species. Species also differed significantly in their perch-height preferences in both experiments, in a manner correlating with body mass and hindwing aspect ratios. Erythemis simplicicollis and P. tenera preferred short perches, Celithemis fasciata, Pachydiplax longipennis and Plathemis lydia used perches of intermediate height, and Libellula auripennis, L. cyanea, L. incesta, L. luctuosa, and L. vibrans preferred the tallest perches. Because mean wind speed and maximum wind speed also increased with perch height, larger species may prefer taller perches to experience greater wind speed and generate more compensatory lift to offset their larger wing loadings. However, it is also possible that correlations between body mass and perch height are the result of large species competitively restricting smaller species to lower perches.

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