Weak and variable relationships between environmental severity
and small-scale co-occurrence in alpine plant communities
I. Kleinbauer, H. Pauli, M. Gottfried, R. Brooker, L. Nagy, J.-P.
Theurillat, J. I. Holten, O. Abdaladze, J.-L. Benito Alonso, J.-L.
Borel, G. Coldea, D. Ghosn, R. Kanka, A. Merzouki, C. Klettner, P.
Moiseev, U. Molau, K. Reiter, G. Rossi, A. Stanisci, M. Tomaselli, P.
Unterlugauer, P. Vittoz, G. Grabherr
Instituto Pirenaico de Ecología,
CSIC. Apdo. 64. E-22700 Jaca (Huesca) - www.jolube.net
Journal of Ecology 95 (6): 1284–1295 (noviembre
Ocupa el puesto 12/114 (Ecología) en el ISI Journal Citation Reports®
de 2006. Factor de impacto: 4.239
1. The stress gradient hypothesis suggests a shift from predominant
competition to facilitation along gradients of increasing
environmental severity. This shift is proposed to cause parallel
changes from prevailing spatial segregation to aggregation among the
species within a community.
2. We used 904 1-m2 plots, each subdivided into 100 10×10 cm, or 25
20×20 cm cells, respectively, from 67 European mountain summits
grouped into 18 regional altitudinal transects, to test this
hypothesized correlation between fine-scale spatial patterns and
3. The data were analysed by first calculating standardized
differences between observed and simulated random co-occurrence
patterns for each plot. These standardized effect sizes were
correlated to indicators of environmental severity by means of
linear mixed models. In a factorial design, separate analyses were
made for four different indicators of environmental severity (the
mean temperature of the coldest month, the temperature sum of the
growing season, the altitude above tree line, and the percentage
cover of vascular plants in the whole plot), four different species
groups (all species, graminoids, herbs, and all growth forms
considered as pseudospecies) and at the 10×10 cm and 20×20 cm grain
KEY WORDS: alpine plant
community, competition, co-occurrence, environmental severity,
facilitation, growth forms, null model, spatial arrangement, scale,
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