1. The stress gradient hypothesis suggests a shift from predominant competition tofacilitation along gradients of increasing environmental severity. This shift is proposedto cause parallel changes from prevailing spatial segregation to aggregation among thespecies within a community. 2. We used 904 1-m2 plots, each subdivided into 100 10x10 cm, or 25 20x20 cm cells,respectively, from 67 European mountain summits grouped into 18 regional altitudinaltransects, to test this hypothesized correlation between fine-scale spatial patterns andenvironmental severity. 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 the10x10 cm and 20x20 cm grain sizes. 4. The hypothesized trends were generally weak and could only be detected by using the mean temperature of the coldest month or the percentage cover of vascular plants as the indicator of environmental severity. The spatial arrangement of the full species set proved more responsive to changes in severity than that of herbs or graminoids. The expected trends were more pronounced at a grain size of 10x10 cm than at 20x20 cm. 5. Synthesis. In European alpine plant communities the relationships between smallscale co-occurrence patterns of vascular plants and environmental severity are weak and variable. This variation indicates that shifts in net interactions with environmental severity may differ among indicators of severity, growth forms and scales. Recognition of such variation may help to resolve some of the current debate surrounding the stress gradient hypothesis.

Weak and variable relationships between environmental severity and small-scale co-occurrence in alpine plant communities / Dullinger, S; Kleinbauer, I; Pauli, H; Gottfried, M; Brooker, R; Nagy, L; THEURILLAT J., P; HOLTEN J., I; Abdaladze, O; BENITO J., L; BOREL J., L; Coldea, G; Ghosn, D; Kanka, R; Merzouki, A; Klettner, C; Moiseev, P; Molau, U; Reiter, K; Rossi, G; Stanisci, A; Tomaselli, Marcello; Unterlugauer, P; Vittoz, P. GRABHERR G.. - In: JOURNAL OF ECOLOGY. - ISSN 0022-0477. - 95:(2007), pp. 1284-1295. [10.1111/j.1365-2475.2007.01288.x]

Weak and variable relationships between environmental severity and small-scale co-occurrence in alpine plant communities.

TOMASELLI, Marcello;
2007

Abstract

1. The stress gradient hypothesis suggests a shift from predominant competition tofacilitation along gradients of increasing environmental severity. This shift is proposedto cause parallel changes from prevailing spatial segregation to aggregation among thespecies within a community. 2. We used 904 1-m2 plots, each subdivided into 100 10x10 cm, or 25 20x20 cm cells,respectively, from 67 European mountain summits grouped into 18 regional altitudinaltransects, to test this hypothesized correlation between fine-scale spatial patterns andenvironmental severity. 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 the10x10 cm and 20x20 cm grain sizes. 4. The hypothesized trends were generally weak and could only be detected by using the mean temperature of the coldest month or the percentage cover of vascular plants as the indicator of environmental severity. The spatial arrangement of the full species set proved more responsive to changes in severity than that of herbs or graminoids. The expected trends were more pronounced at a grain size of 10x10 cm than at 20x20 cm. 5. Synthesis. In European alpine plant communities the relationships between smallscale co-occurrence patterns of vascular plants and environmental severity are weak and variable. This variation indicates that shifts in net interactions with environmental severity may differ among indicators of severity, growth forms and scales. Recognition of such variation may help to resolve some of the current debate surrounding the stress gradient hypothesis.
Weak and variable relationships between environmental severity and small-scale co-occurrence in alpine plant communities / Dullinger, S; Kleinbauer, I; Pauli, H; Gottfried, M; Brooker, R; Nagy, L; THEURILLAT J., P; HOLTEN J., I; Abdaladze, O; BENITO J., L; BOREL J., L; Coldea, G; Ghosn, D; Kanka, R; Merzouki, A; Klettner, C; Moiseev, P; Molau, U; Reiter, K; Rossi, G; Stanisci, A; Tomaselli, Marcello; Unterlugauer, P; Vittoz, P. GRABHERR G.. - In: JOURNAL OF ECOLOGY. - ISSN 0022-0477. - 95:(2007), pp. 1284-1295. [10.1111/j.1365-2475.2007.01288.x]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11381/1679228
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