Abundance, diversity and body size: patterns from a grassland arthropod community

1. The empirical relationships among body size, species richness and number of individuals may give insight into the factors controlling species diversity and the relative abundances of species. To determine these relationships, we sampled the arthropods of grasslands and savannahs at Cedar Creek, MN using sweep nets (90 525 individuals of 1225 species) and pitfall traps (12 721 individuals of 92 species). Specimens were identified, enumerated and measured to determine body size.
2. Both overall and within abundant taxonomic orders, species richness and numbers of individuals peaked at body sizes intermediate for each group. Evolution could create unimodal diversity patterns by random diversification around an ancestral body size or from size-dependent fitness differences. Local processes such as competition or predation could also create unimodal diversity distributions.
3. The average body size of a species depended significantly on its taxonomic order, but on contemporary trophic role only within the context of taxonomic order.
4. Species richness ( S _i) within size classes was related to the number of individuals ( I _i) as S _i =  I i^0·5. This relationship held across a 100 000-fold range of body sizes. Within size classes, abundance distributions of size classes were all similar power functions. A general rule of resource division, together with similar minimum population sizes, is sufficient to generate the relationship between species richness and number of individuals.
5. Smaller bodied species had slightly shallower abundance distributions and may, in general, persist at lower densities than larger species.
6. Our results suggest there may be fewer undescribed small arthropod species than previously thought and that most undescribed species will be smaller than arthropods.     

Dynamic and static views of succession: Testing the descriptive power of the chronosequence approach

Chronosequence and permanent plot studies are the two most common methods for evaluating successional dynamics in plant communities. We combined these two approaches by re-sampling an old-field chronosequence at Cedar Creek Natural History Area (Minnesota, USA) to: (1) measure rates of secondary succession; and (2) to test the ability of the chronosequence approach to predict actual successional dynamics over a 14-year survey interval. For each of 19 chronosequence fields we calculated four complimentary indices of succession rate for community changes that actually occurred within each of these fields between 1983 and 1997. We found that measures of compositional dissimilarity, species turnover, and the change rates of perennial and native species cover over this 14-year period were all negatively correlated with field age, indicating that the rate of successional change in these old-fields generally declines over time. We also found that data collected from the initial static chronosequence survey (1983) accurately predicted many of the observed changes in species abundance that occurred between 1983 and 1997, but was a poor predictor of changes in species richness. In general, chronosequence re-sampling confirmed the validity of using the chronosequence approach to infer basic patterns of successional change.     

Proteins bearing oxidation-induced carbonyl groups are not preferentially ubiquitinated

A substantial part of soluble, oxidized proteins are degraded by the proteasome. However, it is still under debate whether these oxidized proteins are degraded by the 26S proteasome in an ubiquitin-dependent way or in an ubiquitin-independent way by the 20S proteasome. Therefore, we treated cells with H₂O₂ and UV-A irradiation and detected protein carbonyls and ubiquitination by immunoblotting. Separation of ubiquitinated proteins from non-ubiquitinated reveals that most oxidized proteins are not ubiquitinated.     

Food webs obscure the strength of plant diversity effects on primary productivity

Plant diversity experiments generally find that increased diversity causes increased productivity; however, primary productivity is typically measured in the presence of a diverse food web, including pathogens, mutualists and herbivores. If food web impacts on productivity vary with plant diversity, as predicted by both theoretical and empirical studies, estimates of the effect of plant diversity on productivity may be biased. We experimentally removed arthropods, foliar fungi and soil fungi from the longest‐running plant diversity experiment. We found that fungi and arthropods removed a constant, large proportion of biomass leading to a greater reduction of total biomass in high diversity plots. As a result, the effect of diversity on measured plant productivity was much higher in the absence of fungi and arthropods. Thus, diversity increases productivity more than reported in previous studies that did not control for the effects of heterotrophic consumption.