Browsing by Author "Essl, Franz"
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- Environmental drivers and spatial scaling of species abundance distributions in Palaearctic grassland vegetationPublication . Ulrich, Werner; Matthews, Thomas J.; Biurrun, Idoia; Campos, Juan Antonio; Czortek, Patryk; Dembicz, Iwona; Essl, Franz; Filibeck, Goffredo; del Galdo, Gian‐Pietro Giusso; Güler, Behlül; Naqinezhad, Alireza; Török, Péter; Dengler, JürgenSpecies abundance distributions (SADs) link species richness with species abundances and are an important tool in the quantitative analysis of ecological communities. Niche-based and sample-based SAD models predict different spatial scaling properties of SAD parameters. However, empirical research on SAD scaling properties is largely missing. Here we extracted percentage cover values of all occurring vascular plants as proxies of their abundance in 1725 10-m2 plots from the GrassPlot database, covering 47 regional data sets of 19 different grasslands and other open vegetation types of the Palaearctic biogeographic realm. For each plot, we fitted the Weibull distribution, a model that is able to effectively mimic other distributions like the log-series and lognormal, to the species–log abundance rank order distribution. We calculated the skewness and kurtosis of the empirical distributions and linked these moments, along with the shape and scale parameters of the Weibull distribution, to plot climatic and soil characteristics. The Weibull distribution provided excellent fits to grassland plant communities and identified four basic types of communities characterized by different degrees of dominance. Shape and scale parameter values of local communities on poorer soils were largely in accordance with log-series distributions. Proportions of subdominant species tended to be lower than predicted by the standard lognormal SAD. Successive accumulation of plots of the same vegetation type yielded nonlinear spatial scaling of SAD moments and Weibull parameters. This scaling was largely independent of environmental correlates and geographic plot position. Our findings caution against simple generalizations about the mechanisms that generate SADs. We argue that in grasslands, lognormal-type SADs tend to prevail within a wider range of environmental conditions, including more extreme habitats such as arid environments. In contrast, log-series distributions are mainly restricted to comparatively species-rich communities on humid and fertile soils.
- Fine‐grain beta diversity of Palaearctic grassland vegetationPublication . Dembicz, Iwona; Dengler, Jürgen; Steinbauer, Manuel J.; Matthews, Thomas J.; Bartha, Sándor; Burrascano, Sabina; Chiarucci, Alessandro; Filibeck, Goffredo; Gillet, François; Janišová, Monika; Palpurina, Salza; Storch, David; Ulrich, Werner; Aćić, Svetlana; Boch, Steffen; Campos, Juan Antonio; Cancellieri, Laura; Carboni, Marta; Ciaschetti, Giampiero; Conradi, Timo; De Frenne, Pieter; Dolezal, Jiri; Dolnik, Christian; Essl, Franz; Fantinato, Edy; García‐Mijangos, Itziar; Giusso del Galdo, Gian Pietro; Grytnes, John‐Arvid; Guarino, Riccardo; Güler, Behlül; Kapfer, Jutta; Klichowska, Ewelina; Kozub, Łukasz; Kuzemko, Anna; Löbel, Swantje; Manthey, Michael; Marcenò, Corrado; Mimet, Anne; Naqinezhad, Alireza; Noroozi, Jalil; Nowak, Arkadiusz; Pauli, Harald; Peet, Robert K.; Pellissier, Vincent; Pielech, Remigiusz; Terzi, Massimo; Uğurlu, Emin; Valkó, Orsolya; Vasheniak, Iuliia; Vassilev, Kiril; Vynokurov, Denys; White, Hannah J.; Willner, Wolfgang; Winkler, Manuela; Wolfrum, Sebastian; Zhang, Jinghui; Biurrun, IdoiaQUESTIONS: Which environmental factors influence fine-grain beta diversity of vegetation and do they vary among taxonomic groups? LOCATION: Palaearctic biogeographic realm. METHODS: We extracted 4,654 nested-plot series with at least four different grain sizes between 0.0001 m² and 1,024 m² from the GrassPlot database, covering a wide range of different grassland and other open habitat types. We derived extensive environmental and structural information for these series. For each series and four taxonomic groups (vascular plants, bryophytes, lichens, all), we calculated the slope parameter (z-value) of the power law species–area relationship (SAR), as a beta diversity measure. We tested whether z-values differed among taxonomic groups and with respect to biogeographic gradients (latitude, elevation, macroclimate), ecological (site) characteristics (several stress–productivity, disturbance and heterogeneity measures, including land use) and alpha diversity (c-value of the power law SAR). RESULTS: Mean z-values were highest for lichens, intermediate for vascular plants and lowest for bryophytes. Bivariate regressions of z-values against environmental variables had rather low predictive power (mean R² = 0.07 for vascular plants, less for other taxa). For vascular plants, the strongest predictors of z-values were herb layer cover (negative), elevation (positive), rock and stone cover (positive) and the c-value (U-shaped). All tested metrics related to land use (fertilization, livestock grazing, mowing, burning, decrease in naturalness) led to a decrease in z-values. Other predictors had little or no impact on z-values. The patterns for bryophytes, lichens and all taxa combined were similar but weaker than those for vascular plants. CONCLUSIONS: We conclude that productivity has negative and heterogeneity positive effects on z-values, while the effect of disturbance varies depending on type and intensity. These patterns and the differences among taxonomic groups can be explained via the effects of these drivers on the mean occupancy of species, which is mathematically linked to beta diversity.
- Snapshot isolation and isolation history challenge the analogy between mountains and islands used to understand endemismPublication . Flantua, Suzette G. A.; Payne, Davnah; Borregaard, Michael K.; Beierkuhnlein, Carl; Steinbauer, Manuel J.; Dullinger, Stefan; Essl, Franz; Irl, Severin D. H.; Kienle, David; Kreft, Holger; Lenzner, Bernd; Norder, Sietze; Rijsdijk, Kenneth F.; Rumpf, Sabine B.; Weigelt, Patrick; Field, RichardAIM: Mountains and islands are both well known for their high endemism. To explain this similarity, parallels have been drawn between the insularity of "true islands" (land surrounded by water) and the isolation of habitats within mountains (so-called "mountain islands"). However, parallels rarely go much beyond the observation that mountaintops are isolated from one another, as are true islands. Here, we challenge the analogy between mountains and true islands by re-evaluating the literature, focusing on isolation (the prime mechanism underlying species endemism by restricting gene flow) from a dynamic perspective over space and time. FRAMEWORK: We base our conceptualization of "isolation" on the arguments that no biological system is completely isolated; instead, isolation has multiple spatial and temporal dimensions relating to biological and environmental processes. We distinguish four key dimensions of isolation: (a) environmental difference from surroundings; (b) geographical distance to equivalent environment [points (a) and (b) are combined as "snapshot isolation"]; (c) continuity of isolation in space and time; and (d) total time over which isolation has been present [points (c) and (d) are combined as "isolation history"]. We evaluate the importance of each dimension in different types of mountains and true islands, demonstrating that substantial differences exist in the nature of isolation between and within each type. In particular, different types differ in their initial isolation and in the dynamic trajectories they follow, with distinct phases of varying isolation that interact with species traits over time to form present-day patterns of endemism. CONCLUSIONS: Our spatio-temporal definition of isolation suggests that the analogy between true islands and mountain islands masks important variation of isolation over long time-scales. Our understanding of endemism in isolated systems can be greatly enriched if the dynamic spatio-temporal dimensions of isolation enter models as explanatory variables and if these models account for the trajectories of the history of a system.
- Species–area relationships in continuous vegetation : Evidence from Palaearctic grasslandsPublication . Dengler, Jürgen; Matthews, Thomas J.; Steinbauer, Manuel J.; Wolfrum, Sebastian; Boch, Steffen; Chiarucci, Alessandro; Conradi, Timo; Dembicz, Iwona; Marcenò, Corrado; García‐Mijangos, Itziar; Nowak, Arkadiusz; Storch, David; Ulrich, Werner; Campos, Juan Antonio; Cancellieri, Laura; Carboni, Marta; Ciaschetti, Giampiero; De Frenne, Pieter; Dolezal, Jiri; Dolnik, Christian; Essl, Franz; Fantinato, Edy; Filibeck, Goffredo; Grytnes, John‐Arvid; Guarino, Riccardo; Güler, Behlül; Janišová, Monika; Klichowska, Ewelina; Kozub, Łukasz; Kuzemko, Anna; Manthey, Michael; Mimet, Anne; Naqinezhad, Alireza; Pedersen, Christian; Peet, Robert K.; Pellissier, Vincent; Pielech, Remigiusz; Potenza, Giovanna; Rosati, Leonardo; Terzi, Massimo; Valkó, Orsolya; Vynokurov, Denys; White, Hannah; Winkler, Manuela; Biurrun, IdoiaAIM: Species-area relationships (SARs) are fundamental scaling laws in ecology although their shape is still disputed. At larger areas, power laws best represent SARs. Yet, it remains unclear whether SARs follow other shapes at finer spatial grains in continuous vegetation. We asked which function describes SARs best at small grains and explored how sampling methodology or the environment influence SAR shape. Location Palaearctic grasslands and other non-forested habitats. TAXA: Vascular plants, bryophytes and lichens. METHODS: We used the GrassPlot database, containing standardized vegetation-plot data from vascular plants, bryophytes and lichens spanning a wide range of grassland types throughout the Palaearctic and including 2,057 nested-plot series with at least seven grain sizes ranging from 1 cm(2) to 1,024 m(2). Using nonlinear regression, we assessed the appropriateness of different SAR functions (power, power quadratic, power breakpoint, logarithmic, Michaelis-Menten). Based on AICc, we tested whether the ranking of functions differed among taxonomic groups, methodological settings, biomes or vegetation types. RESULTS: The power function was the most suitable function across the studied taxonomic groups. The superiority of this function increased from lichens to bryophytes to vascular plants to all three taxonomic groups together. The sampling method was highly influential as rooted presence sampling decreased the performance of the power function. By contrast, biome and vegetation type had practically no influence on the superiority of the power law. MAIN CONCLUSIONS: We conclude that SARs of sessile organisms at smaller spatial grains are best approximated by a power function. This coincides with several other comprehensive studies of SARs at different grain sizes and for different taxa, thus supporting the general appropriateness of the power function for modelling species diversity over a wide range of grain sizes. The poor performance of the Michaelis-Menten function demonstrates that richness within plant communities generally does not approach any saturation, thus calling into question the concept of minimal area.