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      Grassland structural heterogeneity in a savanna is driven more by productivity differences than by consumption differences between lawn and bunch grasses

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          Abstract

          Savanna grasslands are characterized by high spatial heterogeneity in vegetation structure, aboveground biomass and nutritional quality, with high quality short-grass grazing lawns forming mosaics with patches of tall bunch grasses of lower quality. This heterogeneity can arise because of local differences in consumption, because of differences in productivity, or because both processes enforce each other (more production and consumption). However, the relative importance of both processes in maintaining mosaics of lawn and bunch grassland types has not been measured. Also their interplay been not been assessed across landscape gradients. In a South African savanna, we, therefore, measured the seasonal changes in primary production, nutritional quality and herbivore consumption (amount and percentage) of grazing lawns and adjacent bunch grass patches across a rainfall gradient. We found both higher amounts of primary production and, to a smaller extent, consumption for bunch grass patches. In addition, for bunch grasses primary production increased towards higher rainfall while foliar nitrogen concentrations decreased. Foliar nitrogen concentrations of lawn grasses decreased much less with increasing rainfall. Consequently, large herbivores targeted the biomass produced on grazing lawns with on average 75 % of the produced biomass consumed. We conclude that heterogeneity in vegetation structure in this savanna ecosystem is better explained by small-scale differences in productivity between lawn and bunch grass vegetation types than by local differences in consumption rates. Nevertheless, the high nutritional quality of grazing lawns is highly attractive and, therefore, important for the maintenance of the heterogeneity in species composition (i.e. grazing lawn maintenance).

          Electronic supplementary material

          The online version of this article (doi:10.1007/s00442-016-3698-y) contains supplementary material, which is available to authorized users.

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          Most cited references 63

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          Ecology of a Grazing Ecosystem: The Serengeti

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            Grazing Lawns: Animals in Herds, Plant Form, and Coevolution

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              Extension of Nakagawa & Schielzeth's R2GLMM to random slopes models

              Nakagawa & Schielzeth extended the widely used goodness-of-fit statistic R 2 to apply to generalized linear mixed models (GLMMs). However, their R 2 GLMM method is restricted to models with the simplest random effects structure, known as random intercepts models. It is not applicable to another common random effects structure, random slopes models. I show that R 2 GLMM can be extended to random slopes models using a simple formula that is straightforward to implement in statistical software. This extension substantially widens the potential application of R 2 GLMM.
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                Author and article information

                Affiliations
                [1 ]Groningen Institute for Evolutionary Life Sciences, University of Groningen, P.O. Box 11103, 9700 CC Groningen, The Netherlands
                [2 ]Department of Ecological Science, VU University Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands
                Author notes

                Communicated by Katherine L. Gross.

                Contributors
                +31614404939 , m.p.veldhuis@rug.nl
                Journal
                Oecologia
                Oecologia
                Oecologia
                Springer Berlin Heidelberg (Berlin/Heidelberg )
                0029-8549
                1432-1939
                13 August 2016
                13 August 2016
                2016
                : 182
                : 3
                : 841-853
                3698
                10.1007/s00442-016-3698-y
                5042998
                27522607
                © The Author(s) 2016

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

                Funding
                Funded by: Ubbo Emmius Grant, University of Groningen
                Categories
                Community Ecology–Original Research
                Custom metadata
                © Springer-Verlag Berlin Heidelberg 2016

                Ecology

                hluhluwe-imfolozi park, grazing, primary production, grassland mosaic, nutritional quality

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