Browsing by Autor "Alain Danet"

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Effects of indirect facilitation on functional diversity, dominance and niche differentiation in tropical alpine communities
(Wiley, 2018) Alain Danet; Fabien Anthelme; Nicolas Gross; Sonia Kéfi
Abstract Question Positive interactions between plants have well‐known effects on community species richness and biomass via micro‐environment improvements. However, the effects of indirect facilitation performed by a nurse on an associated plant community, occurring e.g., through protection against grazing, have not attracted much attention in the literature so far, in particular regarding the functional traits of the associated plant communities. Because characteristics of trait distributions can reveal selective pressures at play, they offer valuable information for the study of grazing pressure. Here, we tested the extent to which indirect facilitation affects the amount of distinct trait combinations (H1), trait dominance (H2) and niche differentiation between species (H3) of associated plant communities living under nurse plants. Location Tropical alpine peatlands, Cordillera Real, Bolivia. Methods We set up a grazing exclusion experiment over two dominant nurse cushion species: one providing indirect facilitation under grazing pressure and the other not. We measured three functional traits in the associated communities, which are known to vary depending on the grazing level: LDMC , leaf thickness and maximum height. We assessed the amount of distinct trait combinations by computing the volume of the phenotypic space (H1). The variation in trait dominance was quantified with kurtosis and skewness of the trait distributions (H2). The variation in niche differentiation was evaluated using mean intra‐population trait variance relative to intra‐community trait variance (H3). Results We did not find a significant effect of grazing and indirect facilitation on the volume of the phenotypic space (H1). However, our study revealed a significant effect of indirect facilitation on dominance in the associated communities by maintaining the evenness of the trait distributions (maximum height and leaf thickness) in grazed compared to ungrazed plots (H2), and on niche differentiation by maintaining trait overlaps ( LDMC and maximum height) between species in grazed compared to ungrazed contexts (H3). Conclusion Our results suggest that indirect facilitation promotes the co‐existence of contrasting functional strategies (H2) and species niches (H3) in associated plant communities subject to grazing. These results reflect the buffering effect of indirect facilitation on the grazing selective pressures exerted on associated plant communities living under the protection of nurses.
Nurse species and indirect facilitation through grazing drive plant community functional traits in tropical alpine peatlands
(Wiley, 2017) Alain Danet; Sonia Kéfi; Rosa Isela Meneses; Fabien Anthelme
Facilitation among plants mediated by grazers occurs when an unpalatable plant extends its protection against grazing to another plant. This type of indirect facilitation impacts species coexistence and ecosystem functioning in a large array of ecosystems worldwide. It has nonetheless generally been understudied so far in comparison with the role played by direct facilitation among plants. We aimed at providing original data on indirect facilitation at the community scale to determine the extent to which indirect facilitation mediated by grazers can shape plant communities. Such experimental data are expected to contribute to refining the conceptual framework on plant-plant-herbivore interactions in stressful environments. We set up a 2-year grazing exclusion experiment in tropical alpine peatlands in Bolivia. Those ecosystems depend entirely on a few, structuring cushion-forming plants (hereafter referred to as "nurse" species), in which associated plant communities develop. Fences have been set over two nurse species with different strategies to cope with grazing (direct vs. indirect defenses), which are expected to lead to different intensities of indirect facilitation for the associated communities. We collected functional traits which are known to vary according to grazing pressure (LDMC, leaf thickness, and maximum height), on both the nurse and their associated plant communities in grazed (and therefore indirect facilitation as well) and ungrazed conditions. We found that the effect of indirectly facilitated on the associated plant communities depended on the functional trait considered. Indirect facilitation decreased the effects of grazing on species relative abundance, mean LDMC, and the convergence of the maximum height distribution of the associated communities, but did not affect mean height or cover. The identity of the nurse species and grazing jointly affected the structure of the associated plant community through indirect facilitation. Our results together with the existing literature suggest that the "grazer-nurse-beneficiary" interaction module can be more complex than expected when evaluated in the field.