TY - JOUR A1 - Bergholz, Kolja A1 - May, Felix A1 - Giladi, Itamar A1 - Ristow, Michael A1 - Ziv, Yaron A1 - Jeltsch, Florian T1 - Environmental heterogeneity drives fine-scale species assembly and functional diversity of annual plants in a semi-arid environment JF - Perspectives in plant ecology, evolution and systematics N2 - Spatial environmental heterogeneity is considered a fundamental factor for the maintenance of plant species richness. However, it still remains unclear whether heterogeneity may also facilitate coexistence at fine grain sizes or whether other processes, like mass effects and source sink dynamics due to dispersal, control species composition and diversity at these scales. In this study, we used two complimentary analyses to identify the role of heterogeneity within 15 m x 15 m plots for the coexistence of species-rich annual communities in a semi-arid environment along a steep precipitation gradient. Specifically, we: (a) analyzed the effect of environmental heterogeneity on species, functional and phylogenetic diversity within microsites (alpha diversity, 0.06 m(2) and 1 m(2)), across microsites (beta diversity), and diversity at the entire plot (gamma diversity); (b) further we used two null models to detect non-random trait and phylogenetic patterns in order to infer assembly processes, i.e. whether co-occurring species tend to share similar traits (trait convergence) or dissimilar traits (trait divergence). In general, our results showed that heterogeneity had a positive effect on community diversity. Specifically, for alpha diversity, the effect was significant for functional diversity, and not significant for either species or phylogenetic diversities. For beta diversity, all three measures of community diversity (species, functional, and phylogenetic) increased significantly, as they also did for gamma diversity, where functional measures were again stronger than for species or phylogenetic measures. In addition, the null model approach consistently detected trait convergence, indicating that species with similar traits tended to co-occur and had high abundances in a given microsite. While null model analysis across the phylogeny partly supported these trait findings, showing phylogenetic underdispersion at the 1m(2) grain size, surprisingly when species abundances in microsites were analyzed they were more evenly distributed across the phylogenetic tress than expected (phylogenetic overdispersion). In conclusion, our results provide compelling support that environmental heterogeneity at a relatively fine scale is an important factor for species co-existence as it positively affects diversity as well as influences species assembly. Our study underlines the need for trait-based approaches conducted at fine grain sizes in order to better understand species coexistence and community assembly. (C) 2017 Elsevier GmbH. All rights reserved. KW - Community assembly KW - Plant functional trait KW - Habitat heterogeneity KW - Limiting similarity KW - Environmental filtering KW - Heterogeneity species diversity relationship Y1 - 2017 U6 - https://doi.org/10.1016/j.ppees.2017.01.001 SN - 1433-8319 VL - 24 SP - 138 EP - 146 PB - Elsevier CY - Jena ER - TY - JOUR A1 - Bergholz, Kolja A1 - May, Felix A1 - Ristow, Michael A1 - Giladi, Itamar A1 - Ziv, Yaron A1 - Jeltsch, Florian T1 - Two Mediterranean annuals feature high within-population trait variability and respond differently to a precipitation gradient JF - Basic and applied ecology : Journal of the Gesellschaft für Ökologie N2 - Intraspecific trait variability plays an important role in species adaptation to climate change. However, it still remains unclear how plants in semi-arid environments respond to increasing aridity. We investigated the intraspecific trait variability of two common Mediterranean annuals (Geropogon hybridus and Crupina crupinastrum) with similar habitat preferences. They were studied along a steep precipitation gradient in Israel similar to the maximum predicted precipitation changes in the eastern Mediterranean basin (i.e. -30% until 2100). We expected a shift from competitive ability to stress tolerance with decreasing precipitation and tested this expectation by measuring key functional traits (canopy and seed release height, specific leaf area, N-and P-leaf content, seed mass). Further, we evaluated generative bet-hedging strategies by different seed traits. Both species showed different responses along the precipitation gradient. C. crupinastrum exhibited only decreased plant height toward saridity, while G. hybridus showed strong trends of generative adaptation to aridity. Different seed trait indices suggest increased bet-hedging of G. hybridus in arid environments. However, no clear trends along the precipitation gradient were observed in leaf traits (specific leaf area and leaf N-/P-content) in both species. Moreover, variance decomposition revealed that most of the observed trait variation (>> 50%) is found within populations. The findings of our study suggest that responses to increased aridity are highly species-specific and local environmental factors may have a stronger effect on intraspecific trait variation than shifts in annual precipitation. We therefore argue that trait-based analyses should focus on precipitation gradients that are comparable to predicted precipitation changes and compare precipitation effects to effects of local environmental factors. (C) 2017 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved. KW - Climate change KW - Functional ecology KW - Plant height KW - Drought stress KW - Rainfall gradient KW - Trait-environment relationship KW - Local adaptation KW - Phenotypic plasticity Y1 - 2017 U6 - https://doi.org/10.1016/j.baae.2017.11.001 SN - 1439-1791 SN - 1618-0089 VL - 25 SP - 48 EP - 58 PB - Elsevier CY - Jena ER - TY - JOUR A1 - Crawford, Michael A1 - Jeltsch, Florian A1 - May, Felix A1 - Grimm, Volker A1 - Schlägel, Ulrike E. T1 - Intraspecific trait variation increases species diversity in a trait-based grassland model JF - Oikos N2 - Intraspecific trait variation (ITV) is thought to play a significant role in community assembly, but the magnitude and direction of its influence are not well understood. Although it may be critical to better explain population persistence, species interactions, and therefore biodiversity patterns, manipulating ITV in experiments is challenging. We therefore incorporated ITV into a trait‐ and individual‐based model of grassland community assembly by adding variation to the plants’ functional traits, which then drive life‐history tradeoffs. Varying the amount of ITV in the simulation, we examine its influence on pairwise‐coexistence and then on the species diversity in communities of different initial sizes. We find that ITV increases the ability of the weakest species to invade most, but that this effect does not scale to the community level, where the primary effect of ITV is to increase the persistence and abundance of the competitively‐average species. Diversity of the initial community is also of critical importance in determining ITV's efficacy; above a threshold of interspecific diversity, ITV does not increase diversity further. For communities below this threshold, ITV mainly helps to increase diversity in those communities that would otherwise be low‐diversity. These findings suggest that ITV actively maintains diversity by helping the species on the margins of persistence, but mostly in habitats of relatively low alpha and beta diversity. KW - community assembly KW - individual-based model KW - intraspecific trait variation Y1 - 2018 U6 - https://doi.org/10.1111/oik.05567 SN - 0030-1299 SN - 1600-0706 VL - 128 IS - 3 SP - 441 EP - 455 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Giladi, Itamar A1 - May, Felix A1 - Ristow, Michael A1 - Jeltsch, Florian A1 - Ziv, Yaron T1 - Scale-dependent species-area and species-isolation relationships: a review and a test study from a fragmented semi-arid agro-ecosystem JF - Journal of biogeography N2 - Aim Patterns that relate species richness with fragment area (the species-area relationship, SAR) and with isolation (the species-isolation relationship, SIR) are well documented. However, those that relate species density - the number of species within a standardized area - with fragment area (D-SAR) or isolation (D-SIR) have not been sufficiently explored, despite the potential for such an analysis to disentangle the underlying mechanisms of SARs and SIRs. Previous spatial theory predicts that a significant D-SAR or D-SIR is unlikely to emerge in taxa with high dispersal limitation, such as plants. Furthermore, a recent model predicts that the detection and the significance of D-SARs or D-SIRs may decrease with grain size. We combined a literature review with grain size-dependent sampling in a fragmented landscape to evaluate the prevalence and grain size-dependent nature of D-SARs and D-SIRs in plants. Location Worldwide (review) and a semi-arid agro-ecosystem in Israel (case study). Methods We combined an extensive literature review of 31 D-SAR studies of plants in fragmented landscapes with an empirical study in which we analysed grain size-dependent D-SARs and D-SIRs using a grain size-dependent hierarchical sampling of species density and species richness in a fragmented, semi-arid agro-ecosystem. Results We found that significantly increasing D-SARs are rare in plant studies. Furthermore, we found that the detection of a significant D-SAR is often possible only after the data have been stratified by species, habitat or landscape characteristics. The results from our case study indicated that the significance and the slopes of both D-SARs and D-SIRs increase as grain size decreases. Main conclusions These results call for a careful consideration of scale while analysing and interpreting the responses of species richness and species density to fragmentation. Our results suggest that grain size-dependent analyses of D-SARs and D-SIRs may help to disentangle the mechanisms that generate SARs and SIRs and may enable early detection of the effects of fragmentation on plant biodiversity. KW - species density KW - isolation KW - scale-dependence KW - habitat fragmentation KW - extinction debt KW - Conservation biogeography KW - species-area relationship KW - island ecology KW - habitat islands KW - island biogeography theory Y1 - 2014 U6 - https://doi.org/10.1111/jbi.12299 SN - 0305-0270 SN - 1365-2699 VL - 41 IS - 6 SP - 1055 EP - 1069 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Giladi, Itamar A1 - Ziv, Yaron A1 - May, Felix A1 - Jeltsch, Florian T1 - Scale-dependent determinants of plant species richness in a semi-arid fragmented agro-ecosystem JF - Journal of vegetation science N2 - Aims: (1) Understanding how the relationship between species richness and its determinants depends on the interaction between scales at which the response and explanatory variables are measured. (2) Quantifying the relative contributions of local, intermediate and large-scale determinants of species richness in a fragmented agro-ecosystem. (3) Testing the hypothesis that the relative contribution of these determinants varies with the grain size at which species richness is measured. Location: A fragmented agro-ecosystem in the Southern Judea Lowland, Israel, within a desert-Mediterranean transition zone. Methods: Plant species richness was estimated using hierarchical nested sampling in 81 plots, positioned in 38 natural vegetation patches within an agricultural matrix (mainly wheat fields) among three land units along a sharp precipitation gradient. Explanatory variables included position along that gradient, patch area, patch isolation, habitat heterogeneity and overall plant density. We used general linear models and hierarchical partitioning of variance to test and quantify the effect of each explanatory variable on species richness at four grain sizes (0.0625, 1, 25 and 225m(2)). Results: Species richness was mainly affected by position along a precipitation gradient and overall plant density, and to a lesser extent by habitat heterogeneity. It was also significantly affected by patch area and patch isolation, but only for small grain sizes. The contribution of each explanatory variable to explained variance in species richness varied with grain size, i.e. scale-dependent. The influence of geographic position and habitat heterogeneity on species richness increased with grain size, while the influence of plant density decreased with grain size. Main conclusions: Species richness is determined by the combined effect of several scale-dependent determinants. Ability to detect an effect and effect size of each determinant varies with the scale (grain size) at which it is measured. The combination of a multi-factorial approach and multi-scale sampling reveals that conclusions drawn from studies that ignore these dimensions are restricted and potentially misleading. KW - Habitat fragmentation KW - Hierarchical partitioning of variance KW - Multi-grain sampling KW - Scale-dependence KW - Species density KW - Uniform sampling Y1 - 2011 U6 - https://doi.org/10.1111/j.1654-1103.2011.01309.x SN - 1100-9233 VL - 22 IS - 6 SP - 983 EP - 996 PB - Wiley-Blackwell CY - Malden ER - TY - THES A1 - May, Felix T1 - Spatial models of plant diversity and plant functional traits : towards a better understanding of plant community dynamics in fragmented landscapes T1 - Räumliche Modelle der Diversität und der funktionellen Eigenschaften von Pflanzen : für ein besseres Verständnis der Dynamik von Pflanzengemeinschaften in fragmentierten Landschaften N2 - The fragmentation of natural habitat caused by anthropogenic land use changes is one of the main drivers of the current rapid loss of biodiversity. In face of this threat, ecological research needs to provide predictions of communities' responses to fragmentation as a prerequisite for the effective mitigation of further biodiversity loss. However, predictions of communities' responses to fragmentation require a thorough understanding of ecological processes, such as species dispersal and persistence. Therefore, this thesis seeks an improved understanding of community dynamics in fragmented landscapes. In order to approach this overall aim, I identified key questions on the response of plant diversity and plant functional traits to variations in species' dispersal capability, habitat fragmentation and local environmental conditions. All questions were addressed using spatially explicit simulations or statistical models. In chapter 2, I addressed scale-dependent relationships between dispersal capability and species diversity using a grid-based neutral model. I found that the ratio of survey area to landscape size is an important determinant of scale-dependent dispersal-diversity relationships. With small ratios, the model predicted increasing dispersal-diversity relationships, while decreasing dispersal-diversity relationships emerged, when the ratio approached one, i.e. when the survey area approached the landscape size. For intermediate ratios, I found a U-shaped pattern that has not been reported before. With this study, I unified and extended previous work on dispersal-diversity relationships. In chapter 3, I assessed the type of regional plant community dynamics for the study area in the Southern Judean Lowlands (SJL). For this purpose, I parameterised a multi-species incidence-function model (IFM) with vegetation data using approximate Bayesian computation (ABC). I found that the type of regional plant community dynamics in the SJL is best characterized as a set of isolated “island communities” with very low connectivity between local communities. Model predictions indicated a significant extinction debt with 33% - 60% of all species going extinct within 1000 years. In general, this study introduces a novel approach for combining a spatially explicit simulation model with field data from species-rich communities. In chapter 4, I first analysed, if plant functional traits in the SJL indicate trait convergence by habitat filtering and trait divergence by interspecific competition, as predicted by community assembly theory. Second, I assessed the interactive effects of fragmentation and the south-north precipitation gradient in the SJL on community-mean plant traits. I found clear evidence for trait convergence, but the evidence for trait divergence fundamentally depended on the chosen null-model. All community-mean traits were significantly associated with the precipitation gradient in the SJL. The trait associations with fragmentation indices (patch size and connectivity) were generally weaker, but statistically significant for all traits. Specific leaf area (SLA) and plant height were consistently associated with fragmentation indices along the precipitation gradient. In contrast, seed mass and seed number were interactively influenced by fragmentation and precipitation. In general, this study provides the first analysis of the interactive effects of climate and fragmentation on plant functional traits. Overall, I conclude that the spatially explicit perspective adopted in this thesis is crucial for a thorough understanding of plant community dynamics in fragmented landscapes. The finding of contrasting responses of local diversity to variations in dispersal capability stresses the importance of considering the diversity and composition of the metacommunity, prior to implementing conservation measures that aim at increased habitat connectivity. The model predictions derived with the IFM highlight the importance of additional natural habitat for the mitigation of future species extinctions. In general, the approach of combining a spatially explicit IFM with extensive species occupancy data provides a novel and promising tool to assess the consequences of different management scenarios. The analysis of plant functional traits in the SJL points to important knowledge gaps in community assembly theory with respect to the simultaneous consequences of habitat filtering and competition. In particular, it demonstrates the importance of investigating the synergistic consequences of fragmentation, climate change and land use change on plant communities. I suggest that the integration of plant functional traits and of species interactions into spatially explicit, dynamic simulation models offers a promising approach, which will further improve our understanding of plant communities and our ability to predict their dynamics in fragmented and changing landscapes. N2 - Die Fragmentierung von Landschaften umfasst die Zerschneidung und den Verlust von Flächen mit natürlicher Vegetationsentwicklung und ist eine der Hauptursachen für den gegenwärtigen drastischen Verlust an Biodiversität. Diese Dissertation soll zu einem besseren Verständnis der Vegetationsdynamik in fragmentierten Landschaften beitragen. Damit verbunden ist das Ziel, Vorhersagen über die Reaktion von Pflanzengemeinschaften auf Fragmentierung zu verbessern. Diese Vorhersagen sind notwendig, um gezielte Naturschutzmaßnahmen zur Verminderung eines weiteren Verlustes an Biodiversität umsetzen zu können. In Kapitel 2 der Dissertation wird mit einem Simulationsmodell untersucht, wie sich die Ausbreitungsdistanz von Samen auf die lokale Artenzahl von Pflanzengemeinschaften auswirkt. Dabei zeigte sich, dass längere Ausbreitungsdistanzen die lokale Artenvielfalt sowohl erhöhen, als auch verringern können. Der wichtigste Einflussfaktor war dabei die Artenvielfalt der über-geordneten Pflanzengemeinschaft, in der die betrachtete lokale Gemeinschaft eingebettet war. Im dritten Kapitel wird die Konnektivität zwischen Pflanzengemeinschaften in Habitat-fragmenten, d.h. der Austausch von Arten und Individuen durch Samenausbreitung, im Unter-suchungsgebiet in Israel analysiert. Dafür wurde ein zweites räumliches Simulationsmodell mit statistischen Verfahren an Felddaten angepasst. Der Vergleich des Modells mit den Daten wies auf eine sehr geringe Konnektivität zwischen den Habitatfragmenten hin. Das Modell sagte vorher, dass innerhalb von 1000 Jahren 33% - 60% der Arten aussterben könnten. In Kapitel 4 wird zuerst analysiert, welche Prozesse die Verteilung von funktionellen Eigenschaften in Pflanzengemeinschaften bestimmen. In einem zweiten Schritt wird dann unter-sucht, wie sich funktionelle Eigenschaften von Pflanzengemeinschaften mit dem Niederschlag und der Fragmentierung im Untersuchungsgebiet in Israel verändern. Der Zusammenhang zwischen den Eigenschaften Pflanzenhöhe, sowie spezifischer Blattfläche und der Fragmentierung änderte sich nicht entlang des Niederschlagsgradienten. Im Gegensatz dazu, änderte sich der Zusammenhang zwischen der Samenmasse bzw. der Samenzahl und der Fragmentierung mit dem Niederschlag. Aus den Ergebnissen der ersten Teilstudie wird deutlich, dass Naturschutzmaßnahmen, die natürliche Habitate stärker vernetzen sollen, die Diversität, sowie die Zusammensetzung der übergeordneten Artengemeinschaft berücksichtigen müssen, um Verluste an Biodiversität zu vermeiden. Die Verknüpfung eines räumlichen Simulationsmodells mit Felddaten in der zweiten Teilstudie stellt einen neuen und vielversprechenden Ansatz für die Untersuchung der Auswirkungen verschiedener Management-Szenarien dar. Die dritte Teilstudie ist die erste Analyse der gemeinsamen Auswirkungen von Klima und Fragmentierung auf funktionelle Pflanzen-eigenschaften und zeigt die hohe Bedeutung der Untersuchung von Synergie-Effekten verschiedener Umweltfaktoren. Für zukünftige Forschung legt diese Dissertation nahe, funktionelle Eigenschaften und Konkurrenz zwischen Arten in räumlichen Simulationsmodellen zu berücksichtigen, um das Verständnis von Artengemeinschaften in fragmentierten Landschaften noch weiter zu verbessern. KW - Diversität KW - Ausbreitung KW - Pflanzengemeinschaften KW - Fragmentierung KW - ökologische Modellierung KW - diversity KW - dispersal KW - plant communities KW - fragmentation KW - ecological modelling Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-68444 ER - TY - JOUR A1 - May, Felix A1 - Giladi, Itamar A1 - Ristow, Michael A1 - Ziv, Yaron A1 - Jeltsch, Florian T1 - Metacommunity, mainland-island system or island communities? : assessing the regional dynamics of plant communities in a fragmented landscape JF - Ecography : pattern and diversity in ecology ; research papers forum N2 - Understanding the regional dynamics of plant communities is crucial for predicting the response of plant diversity to habitat fragmentation. However, for fragmented landscapes the importance of regional processes, such as seed dispersal among isolated habitat patches, has been controversially debated. Due to the stochasticity and rarity of among-patch dispersal and colonization events, we still lack a quantitative understanding of the consequences of these processes at the landscape-scale. In this study, we used extensive field data from a fragmented, semi-arid landscape in Israel to parameterize a multi-species incidence-function model. This model simulates species occupancy pattern based on patch areas and habitat configuration and explicitly considers the locations and the shapes of habitat patches for the derivation of patch connectivity. We implemented an approximate Bayesian computation approach for parameter inference and uncertainty assessment. We tested which of the three types of regional dynamics - the metacommunity, the mainland-island, or the island communities type - best represents the community dynamics in the study area and applied the simulation model to estimate the extinction debt in the investigated landscape. We found that the regional dynamics in the patch-matrix study landscape is best represented as a system of highly isolated island' communities with low rates of propagule exchange among habitat patches and consequently low colonization rates in local communities. Accordingly, the extinction rates in the local communities are the main drivers of community dynamics. Our findings indicate that the landscape carries a significant extinction debt and in model projections 33-60% of all species went extinct within 1000 yr. Our study demonstrates that the combination of dynamic simulation models with field data provides a promising approach for understanding regional community dynamics and for projecting community responses to habitat fragmentation. The approach bears the potential for efficient tests of conservation activities aimed at mitigating future losses of biodiversity. Y1 - 2013 U6 - https://doi.org/10.1111/j.1600-0587.2012.07793.x SN - 0906-7590 VL - 36 IS - 7 SP - 842 EP - 853 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - May, Felix A1 - Giladi, Itamar A1 - Ristow, Michael A1 - Ziv, Yaron A1 - Jeltsch, Florian T1 - Plant functional traits and community assembly along interacting gradients of productivity and fragmentation JF - Perspectives in plant ecology, evolution and systematics N2 - Quantifying the association of plant functional traits to environmental gradients is a promising approach for understanding and projecting community responses to land use and climatic changes. Although habitat fragmentation and climate are expected to affect plant communities interactively, there is a lack of empirical studies addressing trait associations to fragmentation in different climatic regimes. In this study, we analyse data on the key functional traits: specific leaf area (SLA), plant height, seed mass and seed number. First, we assess the evidence for the community assembly mechanisms habitat filtering and competition at different spatial scales, using several null-models and a comprehensive set of community-level trait convergence and divergence indices. Second, we analyse the association of community-mean traits with patch area and connectivity along a south-north productivity gradient. We found clear evidence for trait convergence due to habitat filtering. In contrast, the evidence for trait divergence due to competition fundamentally depended on the null-model used. When the null-model controlled for habitat filtering, there was only evidence for trait divergence at the smallest sampling scale (0.25 m x 0.25 m). All traits varied significantly along the S-N productivity gradient. While plant height and SLA were consistently associated with fragmentation, the association of seed mass and seed number with fragmentation changed along the S-N gradient. Our findings indicate trait convergence due to drought stress in the arid sites and due to higher productivity in the mesic sites. The association of plant traits to fragmentation is likely driven by increased colonization ability in small and/or isolated patches (plant height, seed number) or increased persistence ability in isolated patches (seed mass). Our study provides the first empirical test of trait associations with fragmentation along a productivity gradient. We conclude that it is crucial to study the interactive effects of different ecological drivers on plant functional traits. KW - Connectivity KW - Drought-stress KW - Habitat filtering KW - Limiting similarity KW - Null models KW - Plant height KW - Seed mass KW - Seed number KW - Specific leaf area (SLA) Y1 - 2013 U6 - https://doi.org/10.1016/j.ppees.2013.08.002 SN - 1433-8319 VL - 15 IS - 6 SP - 304 EP - 318 PB - Elsevier CY - Jena ER - TY - JOUR A1 - May, Felix A1 - Giladi, Itamar A1 - Ziv, Yaron A1 - Jeltsch, Florian T1 - Dispersal and diversity - unifying scale-dependent relationships within the neutral theory JF - Oikos N2 - The response of species diversity to dispersal capability is inherently scale-dependent: increasing dispersal capability is expected to increase diversity at the local scale, while decreasing diversity at the metacommunity scale. However, these expectations are based on model formulations that neglect dispersal limitation and species segregation at the local scale. We developed a unifying framework of dispersaldiversity relationships and tested the generality of these expectations. For this purpose we used a spatially-explicit neutral model with various combinations of survey area (local scale) and landscape size (metacommunity scale). Simulations were conducted using landscapes of finite and of conceptually infinite size. We analyzed the scale-dependence of dispersal-diversity relationships for exponentially-bounded versus fat-tailed dispersal kernels, several levels of speciation rate and contrasting assumptions on recruitment at short dispersal distances. We found that the ratio of survey area to landscape size is a major determinant of dispersaldiversity relationships. With increasing survey-to-landscape area ratio the dispersaldiversity relationship switches from monotonically increasing through a U-shaped pattern (with a local minimum) to a monotonically decreasing pattern. Therefore, we provide a continuous set of dispersaldiversity relationships, which contains the response shapes reported previously as extreme cases. We suggest the mean dispersal distance with the minimum of species diversity (minimizing dispersal distance) for a certain scenario as a key characteristic of dispersaldiversity relationships. We show that not only increasing mean dispersal distances, but also increasing variances of dispersal can enhance diversity at the local scale, given a diverse species pool at the metacommunity scale. In conclusion, the response of diversity to variations of dispersal capability at spatial scales of interest, e.g. conservation areas, can differ more widely than expected previously. Therefore, land use and conservation activities, which manipulate dispersal capability, need to consider the landscape context and potential species pools carefully. Y1 - 2012 U6 - https://doi.org/10.1111/j.1600-0706.2011.20078.x SN - 0030-1299 VL - 121 IS - 6 SP - 942 EP - 951 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - May, Felix A1 - Grimm, Volker A1 - Jeltsch, Florian T1 - Reversed effects of grazing on plant diversity : the role of below-ground competition and size symmetry N2 - Grazing is known as one of the key factors for diversity and community composition in grassland ecosystems, but the response of plant communities towards grazing varies remarkably between sites with different environmental conditions. It is generally accepted that grazing increases plant diversity in productive environments, while it tends to reduce diversity in unproductive habitats (grazing reversal hypothesis). Despite empirical evidence for this pattern the mechanistic link between modes of plant-plant competition and grazing response at the community level still remains poorly understood. Root-competition in particular has rarely been included in theoretical studies, although it has been hypothesized that variations in productivity and grazing regime can alter the relative importance of shoot- and root-competition. We therefore developed an individual-based model based on plant functional traits to investigate the response of a grassland community towards grazing. Models of different complexity, either incorporating only shoot competition or with distinct shoot- and root-competition, were used to study the interactive effects of grazing, resource availability, and the mode of competition (size-symmetric or asymmetric). The pattern predicted by the grazing reversal hypothesis (GRH) can only be explained by our model if shoot- and root-competition are explicitly considered and if size asymmetry of above- and symmetry of below-ground competition is assumed. For this scenario, the model additionally reproduced empirically observed plant trait responses: erect and large plant functional types (PFTs) dominated without grazing, while frequent grazing favoured small PFTs with a rosette growth form. We conclude that interactions between shoot- and root-competition and size symmetry/asymmetry of plant-plant interactions are crucial in order to understand grazing response under different habitat productivities. Our results suggest that future empirical trait surveys in grassland communities should include root traits, which have been largely ignored in previous studies, in order to improve predictions of plants" responses to grazing. Y1 - 2009 UR - http://www3.interscience.wiley.com/journal/118531693/home U6 - https://doi.org/10.1111/j.1600-0706.2009.17724.x SN - 0030-1299 ER - TY - JOUR A1 - Weiss, Lina A1 - Pfestorf, Hans A1 - May, Felix A1 - Körner, Katrin A1 - Boch, Steffen A1 - Fischer, Markus A1 - Müller, Jörg A1 - Prati, Daniel A1 - Socher, Stephanie A. A1 - Jeltsch, Florian T1 - Grazing response patterns indicate isolation of semi-natural European grasslands JF - Oikos N2 - Identifying drivers of species diversity is a major challenge in understanding and predicting the dynamics of species-rich semi-natural grasslands. In particular in temperate grasslands changes in land use and its consequences, i.e. increasing fragmentation, the on-going loss of habitat and the declining importance of regional processes such as seed dispersal by livestock, are considered key drivers of the diversity loss witnessed within the last decades. Y1 - 2014 U6 - https://doi.org/10.1111/j.1600-0706.2013.00957.x SN - 0030-1299 SN - 1600-0706 VL - 123 IS - 5 SP - 599 EP - 612 PB - Wiley-Blackwell CY - Hoboken ER -