@article{HoulahanCurrieCottenieetal.2007, author = {Houlahan, Jeff E. and Currie, David J. and Cottenie, Karl and Cumming, Graeme S. and Ernest, S. K. Morgan and Findlay, C. Scott and Fuhlendorf, Samuel D. and Gaedke, Ursula and Legendre, Pierre and Magnuson, John J. and McArdle, Brian H. and Muldavin, Esteban H. and Noble, David and Russell, Robert and Stevens, Richard D. and Willis, Trevor J. and Woiwod, Ian P. and Wondzell, Steve M.}, title = {Compensatory dynamics are rare in natural ecological communities}, issn = {0027-8424}, doi = {10.1073/pnas.0603798104}, year = {2007}, abstract = {In population ecology, there has been a fundamental controversy about the relative importance of competition- driven (density-dependent) population regulation vs. abiotic influences such as temperature and precipitation. The same issue arises at the community level; are population sizes driven primarily by changes in the abundances of cooccurring competitors (i.e., compensatory dynamics), or do most species have a common response to environmental factors? Competitive interactions have had a central place in ecological theory, dating back to Gleason, Volterra, Hutchison and MacArthur, and, more recently, Hubbell's influential unified neutral theory of biodiversity and biogeography. If competitive interactions are important in driving year-to-year fluctuations in abundance, then changes in the abundance of one species should generally be accompanied by compensatory changes in the abundances of others. Thus, one necessary consequence of strong compensatory forces is that, on average, species within communities will covary negatively. Here we use measures of community covariance to assess the prevalence of negative covariance in 41 natural communities comprising different taxa at a range of spatial scales. We found that species in natural communities tended to covary positively rather than negatively, the opposite of what would be expected if compensatory dynamics were important. These findings suggest that abiotic factors such as temperature and precipitation are more important than competitive interactions in driving year-to-year fluctuations in species abundance within communities.}, language = {en} } @article{KnapmeyerEndrunKruegerLegendreetal.2013, author = {Knapmeyer-Endrun, Brigitte and Kr{\"u}ger, Frank and Legendre, C. P. and Geissler, Wolfram H.}, title = {Tracing the influence of the trans-european suture zone into the mantle transition zone}, series = {Earth \& planetary science letters}, volume = {363}, journal = {Earth \& planetary science letters}, publisher = {Elsevier}, address = {Amsterdam}, organization = {PASSEQ Working Grp}, issn = {0012-821X}, doi = {10.1016/j.epsl.2012.12.028}, pages = {73 -- 87}, year = {2013}, abstract = {Cratons with their thick lithospheric roots can influence the thermal structure, and thus the convective flow, in the surrounding mantle. As mantle temperatures are hard to measure directly, depth variations in the mantle transition zone (MTZ) discontinuities are often employed as a proxy. Here, we use a large new data set of P-receiver functions to map the 410 km and 660 km discontinuities beneath the western edge of the East European Craton and adjacent Phanerozoic Europe across the most fundamental lithospheric boundary in Europe, the Trans-European Suture Zone (TESZ). We observe significantly shorter travel times for conversions from both MTZ discontinuities within the craton, caused by the high velocities of the cratonic root. By contrast, the differential travel time across the MTZ is normal to only slightly raised. This implies that any insulating effect of the cratonic keel does not reach the MTZ. In contrast to earlier observations in Siberia, we do not find any trace of a discontinuity at 520 km depth, which indicates a rather dry MTZ beneath the western edge of the craton. Within most of covered Phanerozoic Europe, the MTZ differential travel time is remarkably uniform and in agreement with standard Earth models. No widespread thermal effects of the various episodes of Caledonian and Variscan subduction that took place during the amalgamation of the continent remain. Only more recent tectonic events, related to Alpine subduction and Quarternary volcanism in the Eifel area, can be traced. While the East European craton shows no distinct imprint into the MTZ, we discover the signature of the TESZ in the MTZ in the form of a linear region of about 350 km width with a 1.5 s increase in differential travel time, which could either be caused by high water content or decreased temperature. Taking into account results of recent S-wave tomographies, raised water content in the MTZ cannot be the main cause for this observation. Accordingly, we explain the increase, equivalent to a 15 km thicker MTZ, by a temperature decrease of about 80 K. We discuss two alternative models for this temperature reduction, either a remnant of subduction or an indication of downwelling due to small-scale, edge-driven convection caused by the contrast in lithospheric thickness across the TESZ. Any subducted lithosphere found in the MTZ at this location is unlikely to be related to Variscan subduction along the TESZ, though, as Eurasia has moved significantly northward since the Variscan orogeny.}, language = {en} }