@article{AllanWeisserFischeretal.2013, author = {Allan, Eric and Weisser, Wolfgang W. and Fischer, Markus and Schulze, Ernst-Detlef and Weigelt, Alexandra and Roscher, Christiane and Baade, Jussi and Barnard, Romain L. and Bessler, Holger and Buchmann, Nina and Ebeling, Anne and Eisenhauer, Nico and Engels, Christof and Fergus, Alexander J. F. and Gleixner, Gerd and Gubsch, Marlen and Halle, Stefan and Klein, Alexandra-Maria and Kertscher, Ilona and Kuu, Annely and Lange, Markus and Le Roux, Xavier and Meyer, Sebastian T. and Migunova, Varvara D. and Milcu, Alexandru and Niklaus, Pascal A. and Oelmann, Yvonne and Pasalic, Esther and Petermann, Jana S. and Poly, Franck and Rottstock, Tanja and Sabais, Alexander C. W. and Scherber, Christoph and Scherer-Lorenzen, Michael and Scheu, Stefan and Steinbeiss, Sibylle and Schwichtenberg, Guido and Temperton, Vicky and Tscharntke, Teja and Voigt, Winfried and Wilcke, Wolfgang and Wirth, Christian and Schmid, Bernhard}, title = {A comparison of the strength of biodiversity effects across multiple functions}, series = {Oecologia}, volume = {173}, journal = {Oecologia}, number = {1}, publisher = {Springer}, address = {New York}, issn = {0029-8549}, doi = {10.1007/s00442-012-2589-0}, pages = {223 -- 237}, year = {2013}, abstract = {In order to predict which ecosystem functions are most at risk from biodiversity loss, meta-analyses have generalised results from biodiversity experiments over different sites and ecosystem types. In contrast, comparing the strength of biodiversity effects across a large number of ecosystem processes measured in a single experiment permits more direct comparisons. Here, we present an analysis of 418 separate measures of 38 ecosystem processes. Overall, 45 \% of processes were significantly affected by plant species richness, suggesting that, while diversity affects a large number of processes not all respond to biodiversity. We therefore compared the strength of plant diversity effects between different categories of ecosystem processes, grouping processes according to the year of measurement, their biogeochemical cycle, trophic level and compartment (above- or belowground) and according to whether they were measures of biodiversity or other ecosystem processes, biotic or abiotic and static or dynamic. Overall, and for several individual processes, we found that biodiversity effects became stronger over time. Measures of the carbon cycle were also affected more strongly by plant species richness than were the measures associated with the nitrogen cycle. Further, we found greater plant species richness effects on measures of biodiversity than on other processes. The differential effects of plant diversity on the various types of ecosystem processes indicate that future research and political effort should shift from a general debate about whether biodiversity loss impairs ecosystem functions to focussing on the specific functions of interest and ways to preserve them individually or in combination.}, language = {en} } @article{ScherberEisenhauerWeisseretal.2010, author = {Scherber, Christoph and Eisenhauer, Nico and Weisser, Wolfgang W. and Schmid, Bernhard and Voigt, Winfried and Fischer, Markus and Schukze, Ernst-Detlef and Roscher, Christiane and Weigelt, Alexandra and Allan, Eric and Beßler, Holger and Bonkowski, Michael and Buchmann, Nina and Buscot, Fran{\c{c}}ois and Clement, Lars W. and Ebeling, Anne and Engels, Christof and Halle, Stefan and Kertscher, Ilona and Klein, Alexandra-Maria and Koller, Robert and K{\"o}nig, Stephan and Kowalski, Esther and Kummer, Volker and Kuu, Annely and Lange, Markus and Lauterbach, Dirk}, title = {Bottom-up effects of plant diversity on multitrophic interactions in a biodiversity experiment}, issn = {0028-0836}, year = {2010}, language = {en} } @article{TewsEstherMiltonetal.2006, author = {Tews, J{\"o}rg and Esther, Alexandra and Milton, Sue J. and Jeltsch, Florian}, title = {Linking a population model with an ecosystem model : assessing the impact of land use and climate change on savanna shrub cover dynamics}, doi = {10.1016/j.ecolmodel.2005.11.025}, year = {2006}, abstract = {In semiarid savannas of Southern Africa current land use practices and climate change may lead to substantial changes of vegetation structure in the near future, however uncertainty remains about the potential consequences and the magnitude of change. In this paper we study the impact of climate change, cattle grazing, and wood cutting on shrub cover dynamics in savannas of the southern Kalahari. We use an established savanna ecosystem model to simulate landscape dynamics in terms of rainfall, fire and distribution of the dominant tree Acacia erioloba. We then incorporate these data into a spatial population model of the common, fleshy-fruited shrub Grewia flava and investigate shrub cover dynamics for a period of 100 years. Depending on the intensity of commercial wood cutting practices tree removal of A. erioloba led to a strong decline of the G. flava population, as shrub recruitment is concentrated in tree sub-canopies due to bird-mediated seed dispersal. Under climate change shrub cover slightly decreased with decreasing precipitation and was unchanged with increase in precipitation variability. Contrarily, grazing by cattle strongly increased shrub cover and facilitated shrub encroachment because of cattle-induced distribution of G. flava seeds into the matrix vegetation. Knowledge of the latter process is particularly important because shrub invasion is a major concern for conservation and savanna rangeland management as a result of its adverse effects on livestock carrying capacity and biodiversity}, language = {en} } @misc{Esther2002, type = {Master Thesis}, author = {Esther, Alexandra}, title = {Modellgest{\"u}tzte Untersuchungen zum {\"U}berleben einer Steinkauzpopulation (Athene noctua) in Th{\"u}ringen}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-44519}, school = {Universit{\"a}t Potsdam}, year = {2002}, abstract = {Der R{\"u}ckgang des Steinkauzes (Athene noctua) hat in Th{\"u}ringen und Sachsen seit den 60er Jahren dramatische Ausmaße angenommen. In den 50er Jahren noch fl{\"a}chendeckend beobachtet, wurden f{\"u}r das Jahr 2000 nur noch 18 Individuen durch Bestandserfassungen registriert. Die vielfach diskutierten R{\"u}ckgangsursachen beziehen sich vor Allem auf die großfl{\"a}chige {\"A}nderung der Landschaftsstrukturen, die zum Verlust der Lebensgrundlagen des Steinkauzes f{\"u}hrten. So haben u.a. der Verlust an Brut- und Vorratsh{\"o}hlen und an ganzj{\"a}hrig kurzgehaltenen Gr{\"u}nlandfl{\"a}chen, sowie der zunehmende Einfluss von Pr{\"a}datoren erheblich zum R{\"u}ckgang beigetragen. Eingeleitete Schutzmaßnahmen, ehrenamtlich oder auf dem allgemeinen Naturschutzprogramm des Freistaates Th{\"u}ringen beruhend, wie das Anbringen von Nisthilfen mit Marderschutz oder Pflegevertr{\"a}ge f{\"u}r Streuobstwiesen, zeigen bisher keine sichtbare Wirkung. Als weitergehende Maßnahmen stehen die Reduzierung von F{\"u}chsen (Vulpes vulpes) und Steinmardern (Martes foina), Ausbreitungskorridore f{\"u}r Steink{\"a}uze und ein Auswilderungsprogramm zur Diskussion. Angesichts des Populationsr{\"u}ckgangs des Steinkauz war es Aufgabe dieser Arbeit durch ein Simulationsmodell Untersuchungen zum {\"U}berleben einer Steinkauzpopulation (Athene noctua) in Th{\"u}ringen durchzuf{\"u}hren. Die zusammengetragenen Bestandszahlen ergaben geringe Individuenzahlen in den th{\"u}ringischen Landkreisen Altenburger Land, Greiz und der Stadt Gera sowie in den s{\"a}chsischen Landkreisen Chemnitzer Land und Mittweida. Die Bestandszahlen der Jahre 1989-2001, sowie weitere der Literatur entnommene Daten zum populations{\"o}kologischen Hintergrund, wie auch Analysen des Gebietes in Th{\"u}ringen und Sachsen und dessen besetzter Reviere der Jahre 1989- 2001, wurden in ein stochastisches, r{\"a}umlich-explizites, auf Individuen basierendes Simulationsmodell eingebracht. Es wurde eine Sensitivit{\"a}tsanalyse durchgef{\"u}hrt, die beruhend auf den erfassten Populationsentwicklungen in Th{\"u}ringen und Sachsen und auf Literaturangaben, ausgew{\"a}hlte Parameterkonstellationen f{\"u}r die Untersuchungenergab. Die Untersuchungen zum {\"U}berleben vor dem Hintergrund m{\"o}glicher Gef{\"a}hrdungsfaktoren und zur Ermittelung des Nutzens von Managementoptionen, wurden mit Schwerpunkten auf „Pr{\"a}dation", „Habitatverbesserung" und „Auswilderung" durchgef{\"u}hrt. Als Ergebnis der Simulationen kam heraus, dass die Pr{\"a}dation keinen großen Einfluss auf das {\"U}berleben der Population hat, und Schutzmaßnahmen die Chancen f{\"u}r das {\"U}berleben der Population nicht erh{\"o}hen w{\"u}rden. Habitatverbesserungen, die die Juvenilen animieren sich im Umkreis von bis zu 5 km vom elterlichen Revier anzusiedeln, w{\"u}rden aber deutlich zum {\"U}berleben der Population, auch in l{\"a}ngerfristiger Perspektive, beitragen. Habitatverbesserungen, die zu weiter entfernteren Ansiedlungen animieren, k{\"o}nnten sich dagegen ung{\"u}nstig auf das {\"U}berleben der Population auswirken. F{\"u}r eine m{\"o}gliche Auswilderung als Schutzmaßnahme ergab sich im Modell, dass eine Auswilderung von 5 Individuen pro Jahr {\"u}ber einen Zeitraum von 5 Jahren, die {\"U}berlebenswahrscheinlichkeit kurzfristig deutlich verbessern w{\"u}rde. Es ergab sich allerdings kein Unterschied, ob 5, 10 oder 15 Individuen ausgewildert werden. Eine l{\"a}nger durchgef{\"u}hrte Auswilderung w{\"u}rde vermutlich die {\"U}berlebenswahrscheinlichkeit entsprechend langfristiger verbessern.}, language = {de} } @phdthesis{Esther2010, author = {Esther, Alexandra}, title = {Investigating mechanisms maintaining plant species diversity in fire prone Mediterranean-type vegetation using spatially-explicit simulation models}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-44632}, school = {Universit{\"a}t Potsdam}, year = {2010}, abstract = {Fire prone Mediterranean-type vegetation systems like those in the Mediterranean Basin and South-Western Australia are global hot spots for plant species diversity. To ensure management programs act to maintain these highly diverse plant communities, it is necessary to get a profound understanding of the crucial mechanisms of coexistence. In the current literature several mechanisms are discussed. The objective of my thesis is to systematically explore the importance of potential mechanisms for maintaining multi-species, fire prone vegetation by modelling. The model I developed is spatially-explicit, stochastic, rule- and individual-based. It is parameterised on data of population dynamics collected over 18 years in the Mediterranean-type shrublands of Eneabba, Western Australia. From 156 woody species of the area seven plant traits have been identified to be relevant for this study: regeneration mode, annual maximum seed production, seed size, maximum crown diameter, drought tolerance, dispersal mode and seed bank type. Trait sets are used for the definition of plant functional types (PFTs). The PFT dynamics are simulated annual by iterating life history processes. In the first part of my thesis I investigate the importance of trade-offs for the maintenance of high diversity in multi-species systems with 288 virtual PFTs. Simulation results show that the trade-off concept can be helpful to identify non-viable combinations of plant traits. However, the Shannon Diversity Index of modelled communities can be high despite of the presence of 'supertypes'. I conclude, that trade-offs between two traits are less important to explain multi-species coexistence and high diversity than it is predicted by more conceptual models. Several studies show, that seed immigration from the regional seed pool is essential for maintaining local species diversity. However, systematical studies on the seed rain composition to multi-species communities are missing. The results of the simulation experiments, as presented in part two of this thesis, show clearly, that without seed immigration the local species community found in Eneabba drifts towards a state with few coexisting PFTs. With increasing immigration rates the number of simulated coexisting PFTs and Shannon diversity quickly approaches values as also observed in the field. Including the regional seed input in the model is suited to explain more aggregated measures of the local plant community structure such as species richness and diversity. Hence, the seed rain composition should be implemented in future studies. In the third part of my thesis I test the sensitivity of Eneabba PFTs to four different climate change scenarios, considering their impact on both local and regional processes. The results show that climate change clearly has the potential to alter the number of dispersed seeds for most of the Eneabba PFTs and therefore the source of the 'immigrants' at the community level. A classification tree analysis shows that, in general, the response to climate change was PFT-specific. In the Eneabba sand plains sensitivity of a PFT to climate change depends on its specific trait combination and on the scenario of environmental change i.e. development of the amount of rainfall and the fire frequency. This result emphasizes that PFT-specific responses and regional process seed immigration should not be ignored in studies dealing with the impact of climate change on future species distribution. The results of the three chapters are finally analysed in a general discussion. The model is discussed and improvements and suggestions are made for future research. My work leads to the following conclusions: i) It is necessary to support modelling with empirical work to explain coexistence in species-rich plant communities. ii) The chosen modelling approach allows considering the complexity of coexistence and improves the understanding of coexistence mechanisms. iii) Field research based assumptions in terms of environmental conditions and plant life histories can relativise the importance of more hypothetic coexistence theories in species-rich systems. In consequence, trade-offs can play a lower role than predicted by conceptual models. iv) Seed immigration is a key process for local coexistence. Its alteration because of climate change should be considered for prognosis of coexistence. Field studies should be carried out to get data on seed rain composition.}, language = {en} } @misc{LettowWendlandEbeletal.2008, author = {Lettow, Julia and Wendland, Mirko and Ebel, Karina and Haack, Johannes and Esther, Alexandra and Klauss, Frank and Angelow, J{\"u}rgen}, title = {Portal = Exzellente Geistesleistungen: Die Kognitionswissenschaften}, number = {04-06/2008}, organization = {Universit{\"a}t Potsdam, Referat f{\"u}r Presse- und {\"O}ffentlichkeitsarbeit}, issn = {1618-6893}, doi = {10.25932/publishup-44014}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-440149}, pages = {55}, year = {2008}, abstract = {Aus dem Inhalt: - Exzellente Geistesleistungen: Die Kognitionswissenschaften - Studierende werben Sch{\"u}ler - Uni f{\"o}rdert Spitzensportler}, language = {de} } @article{EstherGroeneveldEnrightetal.2010, author = {Esther, Alexandra and Groeneveld, Juergen and Enright, Neal J. and Miller, Ben P. and Lamont, Byron B. and Perry, George L. W. and Blank, F. Benjamin and Jeltsch, Florian}, title = {Sensitivity of plant functional types to climate change : classification tree analysis of a simulation model}, issn = {1100-9233}, doi = {10.1111/j.1654-1103.2009.01155.x}, year = {2010}, abstract = {Question: The majority of studies investigating the impact of climate change on local plant communities ignores changes in regional processes, such as immigration from the regional seed pool. Here we explore: (i) the potential impact of climate change on composition of the regional seed pool, (ii) the influence of changes in climate and in the regional seed pool on local community structure, and (iii) the combinations of life history traits, i.e. plant functional types (PFTs), that are most affected by environmental changes. Location: Fire-prone, Mediterranean-type shrublands in southwestern Australia. Methods: Spatially explicit simulation experiments were conducted at the population level under different rainfall and fire regime scenarios to determine the effect of environmental change on the regional seed pool for 38 PFTs. The effects of environmental and seed immigration changes on local community dynamics were then derived from community-level experiments. Classification tree analyses were used to investigate PFT- specific vulnerabilities to climate change. Results: The classification tree analyses revealed that responses of PFTs to climate change are determined by specific trait characteristics. PFT-specific seed production and community patterns responded in a complex manner to climate change. For example, an increase in annual rainfall caused an increase in numbers of dispersed seeds for some PFTs, but decreased PFT diversity in the community. Conversely, a simulated decrease in rainfall reduced the number of dispersed seeds and diversity of PFTs. Conclusions: PFT interactions and regional processes must be considered when assessing how local community structure will be affected by environmental change.}, language = {en} } @article{EstherGroeneveldEnrightetal.2008, author = {Esther, Alexandra and Groeneveld, J{\"u}rgen and Enright, Neal J. and Miller, Ben P. and Lamont, Byron B. and Perry, George L. W. and Schurr, Frank Martin and Jeltsch, Florian}, title = {Assessing the importance of seed immigration on coexistence of plant functional types in a species-rich ecosystem}, issn = {0304-3800}, doi = {10.1016/j.ecolmodel.2008.01.014}, year = {2008}, abstract = {Modelling and empirical studies have shown that input from the regional seed pool is essential to maintain local species diversity. However, most of these studies have concentrated on simplified, if not neutral, model systems, and focus on a limited subset of species or on aggregated measures of diversity only (e.g., species richness or Shannon diversity). Thus they ignore more complex species interactions and important differences between species. To gain a better understanding of how seed immigration affects community structure at the local scale in real communities we conducted computer simulation experiments based on plant functional types (PFTs) for a species-rich, fire-prone Mediterranean-type shrubland in Western Australia. We developed a spatially explicit simulation model to explore the community dynamics of 38 PFTs, defined by seven traits - regeneration mode, seed production, seed size, maximum crown diameter, drought tolerance, dispersal mode and seed bank type - representing 78 woody species. Model parameterisation is based on published and unpublished data on the population dynamics of shrub species collected over 18 years. Simulation experiments are based on two contrasting seed immigration scenarios: (1) the 'equal seed input number' scenario, where the number of immigrant seeds is the same for all PFTs, and (2) the 'equal seed input mass' scenario, where the cumulative mass of migrating seeds is the same for all PFTs. Both scenarios were systematically tested and compared for different overall seed input values. Without immigration the local community drifts towards a state with only 13 coexisting PFTs. With increasing immigration rates in terms of overall mass of seeds the simulated number of coexisting PFTs and Shannon diversity quickly approaches values observed in the field. The equal seed mass scenario resulted in a more diverse community than did the seed number scenario. The model successfully approximates the frequency distributions (relative densities) of all individual plant traits except seed size for scenarios associated with equal seed input mass and high immigration rate. However, no scenario satisfactorily approximated the frequency distribution for all traits in combination. Our results show that regional seed input can explain the more aggregated measures of local community structure, and some, but not all, aspects of community composition. This points to the possible importance of other (untested) processes and traits (e.g., dispersal vectors) operating at the local scale. Our modelling framework can readily allow new factors to be systematically investigated, which is a major advantage compared to previous simulation studies, as it allows us to find structurally realistic models, which can address questions pertinent to ecological theory and to conservation management.}, language = {en} } @article{EstherGroeneveldEnrightetal.2011, author = {Esther, Alexandra and Groeneveld, J{\"u}rgen and Enright, Neal J. and Miller, Ben P. and Lamont, Byron B. and Perry, George L. W. and Tietjen, Britta and Jeltsch, Florian}, title = {Low-dimensional trade-offs fail to explain richness and structure in species-rich plant communities}, series = {Theoretical ecology}, volume = {4}, journal = {Theoretical ecology}, number = {4}, publisher = {Springer}, address = {Heidelberg}, issn = {1874-1738}, doi = {10.1007/s12080-010-0092-y}, pages = {495 -- 511}, year = {2011}, abstract = {Mathematical models and ecological theory suggest that low-dimensional life history trade-offs (i.e. negative correlation between two life history traits such as competition vs. colonisation) may potentially explain the maintenance of species diversity and community structure. In the absence of trade-offs, we would expect communities to be dominated by 'super-types' characterised by mainly positive trait expressions. However, it has proven difficult to find strong empirical evidence for such trade-offs in species-rich communities. We developed a spatially explicit, rule-based and individual-based stochastic model to explore the importance of low-dimensional trade-offs. This model simulates the community dynamics of 288 virtual plant functional types (PFTs), each of which is described by seven life history traits. We consider trait combinations that fit into the trade-off concept, as well as super-types with little or no energy constraints or resource limitations, and weak PFTs, which do not exploit resources efficiently. The model is parameterised using data from a fire-prone, species-rich Mediterranean-type shrubland in southwestern Australia. We performed an exclusion experiment, where we sequentially removed the strongest PFT in the simulation and studied the remaining communities. We analysed the impact of traits on performance of PFTs in the exclusion experiment with standard and boosted regression trees. Regression tree analysis of the simulation results showed that the trade-off concept is necessary for PFT viability in the case of weak trait expression combinations such as low seed production or small seeds. However, species richness and diversity can be high despite the presence of super-types. Furthermore, the exclusion of super-types does not necessarily lead to a large increase in PFT richness and diversity. We conclude that low-dimensional trade-offs do not provide explanations for multi-species co-existence contrary to the prediction of many conceptual models.}, language = {en} } @article{GossnerLewinsohnKahletal.2016, author = {Gossner, Martin M. and Lewinsohn, Thomas M. and Kahl, Tiemo and Grassein, Fabrice and Boch, Steffen and Prati, Daniel and Birkhofer, Klaus and Renner, Swen C. and Sikorski, Johannes and Wubet, Tesfaye and Arndt, Hartmut and Baumgartner, Vanessa and Blaser, Stefan and Bl{\"u}thgen, Nico and B{\"o}rschig, Carmen and Buscot, Francois and Diek{\"o}tter, Tim and Jorge, Leonardo Re and Jung, Kirsten and Keyel, Alexander C. and Klein, Alexandra-Maria and Klemmer, Sandra and Krauss, Jochen and Lange, Markus and M{\"u}ller, J{\"o}rg and Overmann, J{\"o}rg and Pasalic, Esther and Penone, Caterina and Perovic, David J. and Purschke, Oliver and Schall, Peter and Socher, Stephanie A. and Sonnemann, Ilja and Tschapka, Marco and Tscharntke, Teja and T{\"u}rke, Manfred and Venter, Paul Christiaan and Weiner, Christiane N. and Werner, Michael and Wolters, Volkmar and Wurst, Susanne and Westphal, Catrin and Fischer, Markus and Weisser, Wolfgang W. and Allan, Eric}, title = {Land-use intensification causes multitrophic homogenization of grassland communities}, series = {Nature : the international weekly journal of science}, volume = {540}, journal = {Nature : the international weekly journal of science}, publisher = {Nature Publ. Group}, address = {London}, issn = {0028-0836}, doi = {10.1038/nature20575}, pages = {266 -- +}, year = {2016}, abstract = {Land-use intensification is a major driver of biodiversity loss(1,2). Alongside reductions in local species diversity, biotic homogenization at larger spatial scales is of great concern for conservation. Biotic homogenization means a decrease in beta-diversity (the compositional dissimilarity between sites). Most studies have investigated losses in local (alpha)-diversity(1,3) and neglected biodiversity loss at larger spatial scales. Studies addressing beta-diversity have focused on single or a few organism groups (for example, ref. 4), and it is thus unknown whether land-use intensification homogenizes communities at different trophic levels, above-and belowground. Here we show that even moderate increases in local land-use intensity (LUI) cause biotic homogenization across microbial, plant and animal groups, both above- and belowground, and that this is largely independent of changes in alpha-diversity. We analysed a unique grassland biodiversity dataset, with abundances of more than 4,000 species belonging to 12 trophic groups. LUI, and, in particular, high mowing intensity, had consistent effects on beta-diversity across groups, causing a homogenization of soil microbial, fungal pathogen, plant and arthropod communities. These effects were nonlinear and the strongest declines in beta-diversity occurred in the transition from extensively managed to intermediate intensity grassland. LUI tended to reduce local alpha-diversity in aboveground groups, whereas the alpha-diversity increased in belowground groups. Correlations between the alpha-diversity of different groups, particularly between plants and their consumers, became weaker at high LUI. This suggests a loss of specialist species and is further evidence for biotic homogenization. The consistently negative effects of LUI on landscape-scale biodiversity underscore the high value of extensively managed grasslands for conserving multitrophic biodiversity and ecosystem service provision. Indeed, biotic homogenization rather than local diversity loss could prove to be the most substantial consequence of land-use intensification.}, language = {en} }