01514nas a2200133   4500008004100000245005400041210005200095300001300147490000800160520109700168100001801265700001701283856008001300       2006                        eng d00aRedefining the community:a species-based approach0 aRedefining the communitya speciesbased approach  a464 -4720 v1123 aWe propose that effective community size can be defined on the basis of the web of indirect interactions experienced on average by each individual species. Indirect interaction chains are composed of links provided by direct interactions. We analyzed previously published data on 20 assemblages of species. Chain strengths were estimated by the weakest link and by the product of link strength. The average strength of the interaction chain decreased with increasing numbers of links with both models. Positive indirect interactions in chains with an even number of links offset negative direct interactions. We set the community size by the chain length where 95% of the indirect interactions are weaker than 10% of the mean of the absolute value of direct interaction strength. Using the multiplicative model, seven assemblages had a community size (web of interaction length) of three links, one of four links, and the remainder of communities were too small to set community size. The analysis suggests that effective communities of size are rarely investigated in ecological experiments.1 aDodds, W., K.1 aNelson, J.A.  uhttp://knz.lternet.edu/content/redefining-communitya-species-based-approach02490nas a2200265   4500008004100000245008100041210006900122300001300191490000600204520166200210653001401872653001701886653002501903653002701928653001801955653002001973653002101993100001902014700001602033700001702049700002002066700002002086700001602106856010202122       2005                        eng d00aRegional patterns in carbon cycling across the Great Plains of North America0 aRegional patterns in carbon cycling across the Great Plains of N  a106 -1210 v83 aThe large organic carbon (C) pools found in noncultivated grassland soils suggest that historically these ecosystems have had high rates of C sequestration. Changes in the soil C pool over time are a function of alterations in C input and output rates. Across the Great Plains and at individual sites through time, inputs of C (via aboveground production) are correlated with precipitation; however, regional trends in C outputs and the sensitivity of these C fluxes to annual variability in precipitation are less well known. To address the role of precipitation in controlling grassland C fluxes, and thereby soil C sequestration rates, we measured aboveground and belowground net primary production (ANPP-C and BNPP-C), soil respiration (SR-C), and litter decomposition rates for 2 years, a relatively dry year followed by a year of average precipitation, at five sites spanning a precipitation gradient in the Great Plains. ANPP-C, SR-C, and litter decomposition increased from shortgrass steppe (36, 454, and 24 g C m−2 y−1) to tallgrass prairie (180, 1221, and 208 g C m−2 y−1 for ANPP-C, SR-C, and litter decomposition, respectively). No significant regional trend in BNPP-C was found. Increasing precipitation between years increased rates of ANPP-C, BNPP-C, SR-C, and litter decomposition at most sites. However, regional patterns of the sensitivity of ANPP-C, BNPP-C, SR-C, and litter decomposition to between-year differences in precipitation varied. BNPP-C was more sensitive to between-year differences in precipitation than were the other C fluxes, and shortgrass steppe was more responsive than were mixed grass and tallgrass prairie.10agrassland10aGreat Plains10alitter decomposition10aNet primary production10aPrecipitation10aRegional trends10asoil respiration1 aMcCulley, R.L.1 aBurke, I.C.1 aNelson, J.A.1 aLauenroth, W.K.1 aKnapp, Alan, K.1 aKelly, E.F.  uhttp://knz.lternet.edu/content/regional-patterns-carbon-cycling-across-great-plains-north-america