Understanding how animals interact with their environment is critical for evaluating, mitigating and coping with anthropogenic alteration of Earth's biosphere. Researchers have attempted to understand some aspects of these interactions by examining patterns in animal body mass distributions. Energetic, phylogenetic, biogeographical, textural discontinuity and community interaction hypotheses have been advanced to explain observed patterns. Energetic and textural discontinuity hypotheses focus upon the allometry of resource use. The community interaction hypothesis contends that biotic interactions within assemblages of species are of primary importance. Biogeographical and phylogenetic hypotheses focus on the role of constraints on the organization of communities. This paper examines and organizes these various propositions about species body mass distributions and discusses the multiple competing hypotheses, how their predictions vary, and possible methods by which the hypotheses can be distinguished and tested. Each of the hypotheses is partial, and explains some elements of pattern in body mass distributions. The scale of appropriate application, relevance and interpretation varies among the hypotheses, and the mechanisms underlying observed patterns are likely to be multicausal and vary with scale.

Aquatic ecologists have many models for size distributions of pelagic communities. However, few studies have looked for discontinuities (clumps of similarly sized species or gaps of sizes that contain no or relatively few species) in pelagic community size structure. We investigated size distribution characteristics in aquatic communities by calculating kernel density functions for plankton and fish in 11 lakes in Wisconsin. Size distributions in aquatic communities of these lakes were not smooth. Rather, multiple lump and gap regions were found within each functional group of phytoplankton, zooplankton, and fish. Simulations showed the gaps could not be explained by incomplete censuses of species or by systematic underestimation of intraspecific size variation. In an experimentally enriched lake, before and after comparisons showed lumps were not affected by large additions of P and N, even though biomass and production changed substantially. Lump regions in the two lakes with both food web manipulations and nutrient enrichment were substantially less similar pre-versus postenrichment than the reference lake and the lake with only nutrients added, but lump number remained relatively unchanged. Lakes that differed widely in nutrient status, trophic structure, species diversity, and area had similar size distributions. Comparisons of functional groups showed that phytoplankton had more lumps than zooplankton. In these north temperate lakes, size distribution characteristics seem to be conservative properties shaped by common regional ecosystem processes and organism patterns and not by lake-specific factors.

ABSTRACT. We investigated vegetation responses in terms of canopy, ground-layer diversity, and ecological species groups using two restoration treatments at two degraded oak barren and savanna sites in central Wisconsin, USA. The two restoration models tested were (1) process-only, which reintroduced fire in the form of prescribed burning, and (2) structural manipulation, which used prescribed burning following selective timber removal. Both methods have been widely promoted, debated, and investigated in the fire-prone ecosystems of western North America, but they have not been studied in midwestern ecosystems. Vegetation was monitored in permanent quadrats prior to and following treatment applications. All treatment responses were compared against trends at control sites. We used diversity, canopy, and cover estimates within ecological groups between pre-and post-treatment periods as our response. Effect size was calculated, and the statistical significance of effects was determined using one-factor analysis of variance. Following treatments, canopy levels were restored to prior savanna levels with structural manipulation, but failed to respond to process-only approaches. Likewise, multiple positive responses were detected in the ground layer with structural manipulation, but few with process-only treatments. Despite initial responses, ground-layer restoration appears to be constrained by the dominance of Pennsylvania sedge (Carex pensylvanica). Many savanna forbs, legumes, and C 4 graminoids were missing. We presume that 70 yr of fire suppression and associated succession to oak woodlands were largely responsible for sedge conversion and the loss of savanna species. Despite observed limitations, structural manipulation treatments appeared to be more effective than process-only approaches. Sites with holdover savanna species that have not been dominated by sedge should be targeted for immediate restoration before further losses occur. Further investigation of sedge mat thresholds and long-term restoration dynamics is required.

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