02081nas a2200241 4500008004100000245008200041210006900123300001500192490000700207520135700214100001801571700001401589700001801603700002401621700001801645700001701663700001901680700001601699700001601715700001701731700001701748856007401765 2014 eng d00aBiotic mechanisms of community stability shift along a precipitation gradient0 aBiotic mechanisms of community stability shift along a precipita a1693 -17000 v953 a

Understanding how biotic mechanisms confer stability in variable environments is a fundamental quest in ecology, and one that is becoming increasingly urgent with global change. Several mechanisms, notably a portfolio effect associated with species richness, compensatory dynamics generated by negative species covariance and selection for stable dominant species populations can increase the stability of the overall community. While the importance of these mechanisms is debated, few studies have contrasted their importance in an environmental context. We analyzed nine long-term data sets of grassland species composition to investigate how two key environmental factors, precipitation amount and variability, may directly influence community stability and how they may indirectly influence stability via biotic mechanisms. We found that the importance of stability mechanisms varied along the environmental gradient: strong negative species covariance occurred in sites characterized by high precipitation variability, whereas portfolio effects increased in sites with high mean annual precipitation. Instead of questioning whether compensatory dynamics are important in nature, our findings suggest that debate should widen to include several stability mechanisms and how these mechanisms vary in importance across environmental gradients.

1 aHallett, L.M.1 aHsu, J.S.1 aCleland, E.E.1 aCollins, Scott., L.1 aDickson, T.L.1 aFarrer, E.C.1 aGherardi, L.A.1 aGross, K.L.1 aHobbs, R.J.1 aTurnbull, L.1 aSuding, K.N. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/13-0895.103196nas a2200241 4500008004100000245010800041210006900149300001500218490000700233520244600240100001802686700002402704700001802728700001702746700001602763700001902779700001802798700001602816700001402832700001702846700001702863856007402880 2013 eng d00aSensitivity of grassland plant community composition to spatial vs. temporal variation in precipitation0 aSensitivity of grassland plant community composition to spatial  a1687 -16960 v943 a

Climate gradients shape spatial variation in the richness and composition of plant communities. Given future predicted changes in climate means and variability, and likely regional variation in the magnitudes of these changes, it is important to determine how temporal variation in climate influences temporal variation in plant community structure. Here, we evaluated how species richness, turnover, and composition of grassland plant communities responded to interannual variation in precipitation by synthesizing long-term data from grasslands across the United States. We found that mean annual precipitation (MAP) was a positive predictor of species richness across sites, but a positive temporal relationship between annual precipitation and richness was only evident within two sites with low MAP. We also found higher average rates of species turnover in dry sites that in turn had a high proportion of annual species, although interannual rates of species turnover were surprisingly high across all locations. Annual species were less abundant than perennial species at nearly all sites, and our analysis showed that the probability of a species being lost or gained from one year to the next increased with decreasing species abundance. Bray-Curtis dissimilarity from one year to the next, a measure of species composition change that is influenced mainly by abundant species, was insensitive to precipitation at all sites. These results suggest that the richness and turnover patterns we observed were driven primarily by rare species, which comprise the majority of the local species pools at these grassland sites. These findings are consistent with the idea that short-lived and less abundant species are more sensitive to interannual climate variability than longer-lived and more abundant species. We conclude that, among grassland ecosystems, xeric grasslands are likely to exhibit the greatest responsiveness of community composition (richness and turnover) to predicted future increases in interannual precipitation variability. Over the long term, species composition may shift to reflect spatial patterns of mean precipitation; however, perennial-dominated systems will be buffered against rising interannual variation, while systems that have a large number of rare, annual species will show the greatest temporal variability in species composition in response to rising interannual variability in precipitation.

1 aCleland, E.E.1 aCollins, Scott., L.1 aDickson, T.L.1 aFarrer, E.C.1 aGross, K.L.1 aGherardi, L.A.1 aHallett, L.M.1 aHobbs, R.J.1 aHsu, J.S.1 aSuding, K.N.1 aTurnbull, L. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/12-1006.101097nas a2200193 4500008004100000245005100041210005100092260003400143300001300177520051400190100001800704700001500722700001800737700001600755700001700771700001600788700001700804856008200821 1990 eng d00aSatellite remote sensing and field experiments0 aSatellite remote sensing and field experiments aNew York, NYbSpringer-Verlag a169 -2013 a

The past few years have seen an increasing pressure brought to bear on biologists to apply their research efforts to larger spatial scales. The motivation for this pressure has scientific as well as sociopolitical roots. First, from the science viewpoint, it has become apparent that satellite-based and atmospheric observing techniques can allow researchers a different view of biospheric functioning by spatially integrating the effects of biospheric states and fluxes, respectively, at moderate cost

1 aSellers, P.J.1 aHall, F.G.1 aStrebel, D.E.1 aAsrar, G.A.1 aMurphy, R.E.1 aHobbs, R.J.1 aMooney, H.A. uhttp://knz.lternet.edu/content/satellite-remote-sensing-and-field-experiments