TY - JOUR A1 - Bauer, Barbara A1 - Vos, Matthijs A1 - Klauschies, Toni A1 - Gaedke, Ursula T1 - Diversity, functional similarity, and top-down control drive synchronization and the reliability of ecosystem function JF - The American naturalist : a bi-monthly journal devoted to the advancement and correlation of the biological sciences N2 - The concept that diversity promotes reliability of ecosystem function depends on the pattern that community-level biomass shows lower temporal variability than species-level biomasses. However, this pattern is not universal, as it relies on compensatory or independent species dynamics. When in contrast within--trophic level synchronization occurs, variability of community biomass will approach population-level variability. Current knowledge fails to integrate how species richness, functional distance between species, and the relative importance of predation and competition combine to drive synchronization at different trophic levels. Here we clarify these mechanisms. Intense competition promotes compensatory dynamics in prey, but predators may at the same time increasingly synchronize, under increasing species richness and functional similarity. In contrast, predators and prey both show perfect synchronization under strong top-down control, which is promoted by a combination of low functional distance and high net growth potential of predators. Under such conditions, community-level biomass variability peaks, with major negative consequences for reliability of ecosystem function. KW - biodiversity KW - ecosystem services KW - population dynamics KW - predator-prey system KW - species richness KW - synchrony Y1 - 2014 U6 - https://doi.org/10.1086/674906 SN - 0003-0147 SN - 1537-5323 VL - 183 IS - 3 SP - 394 EP - 409 PB - Univ. of Chicago Press CY - Chicago ER - TY - JOUR A1 - Rottstock, Tanja A1 - Joshi, Jasmin Radha A1 - Kummer, Volker A1 - Fischer, Markus T1 - Higher plant diversity promotes higher diversity of fungal pathogens, while it decreases pathogen infection per plant JF - Ecology : a publication of the Ecological Society of America N2 - Fungal plant pathogens are common in natural communities where they affect plant physiology, plant survival, and biomass production. Conversely, pathogen transmission and infection may be regulated by plant community characteristics such as plant species diversity and functional composition that favor pathogen diversity through increases in host diversity while simultaneously reducing pathogen infection via increased variability in host density and spatial heterogeneity. Therefore, a comprehensive understanding of multi-host multi-pathogen interactions is of high significance in the context of biodiversity-ecosystem functioning. We investigated the relationship between plant diversity and aboveground obligate parasitic fungal pathogen ("pathogens" hereafter) diversity and infection in grasslands of a long-term, large-scale, biodiversity experiment with varying plant species (1-60 species) and plant functional group diversity (1-4 groups). To estimate pathogen infection of the plant communities, we visually assessed pathogen-group presence (i.e., rusts, powdery mildews, downy mildews, smuts, and leaf-spot diseases) and overall infection levels (combining incidence and severity of each pathogen group) in 82 experimental plots on all aboveground organs of all plant species per plot during four surveys in 2006. Pathogen diversity, assessed as the cumulative number of pathogen groups on all plant species per plot, increased log-linearly with plant species diversity. However, pathogen incidence and severity, and hence overall infection, decreased with increasing plant species diversity. In addition, co-infection of plant individuals by two or more pathogen groups was less likely with increasing plant community diversity. We conclude that plant community diversity promotes pathogen-community diversity while at the same time reducing pathogen infection levels of plant individuals. KW - biodiversity KW - ecosystem processes KW - ecosystem services KW - grasslands KW - multi-host-multi-pathogen interactions KW - obligate parasitic fungal pathogens KW - pathogen diversity KW - pathogen proneness KW - pathogen transmission KW - plant functional types Y1 - 2014 SN - 0012-9658 SN - 1939-9170 VL - 95 IS - 7 SP - 1907 EP - 1917 PB - Wiley CY - Washington ER - TY - JOUR A1 - Gutt, Julian A1 - Zurell, Damaris A1 - Bracegridle, Thomas J. A1 - Cheung, William A1 - Clark, Melody S. A1 - Convey, Peter A1 - Danis, Bruno A1 - David, Bruno A1 - De Broyer, Claude A1 - di Prisco, Guido A1 - Griffiths, Huw A1 - Laffont, Remi A1 - Peck, Lloyd S. A1 - Pierrat, Benjamin A1 - Riddle, Martin J. A1 - Saucede, Thomas A1 - Turner, John A1 - Verde, Cinzia A1 - Wang, Zhaomin A1 - Grimm, Volker T1 - Correlative and dynamic species distribution modelling for ecological predictions in the Antarctic a cross-disciplinary concept JF - Polar research : a Norwegian journal of Polar research N2 - Developments of future scenarios of Antarctic ecosystems are still in their infancy, whilst predictions of the physical environment are recognized as being of global relevance and corresponding models are under continuous development. However, in the context of environmental change simulations of the future of the Antarctic biosphere are increasingly demanded by decision makers and the public, and are of fundamental scientific interest. This paper briefly reviews existing predictive models applied to Antarctic ecosystems before providing a conceptual framework for the further development of spatially and temporally explicit ecosystem models. The concept suggests how to improve approaches to relating species' habitat description to the physical environment, for which a case study on sea urchins is presented. In addition, the concept integrates existing and new ideas to consider dynamic components, particularly information on the natural history of key species, from physiological experiments and biomolecular analyses. Thereby, we identify and critically discuss gaps in knowledge and methodological limitations. These refer to process understanding of biological complexity, the need for high spatial resolution oceanographic data from the entire water column, and the use of data from biomolecular analyses in support of such ecological approaches. Our goal is to motivate the research community to contribute data and knowledge to a holistic, Antarctic-specific, macroecological framework. Such a framework will facilitate the integration of theoretical and empirical work in Antarctica, improving our mechanistic understanding of this globally influential ecoregion, and supporting actions to secure this biodiversity hotspot and its ecosystem services. KW - Environmental change KW - integrative modelling framework KW - spatially and temporally explicit modelling macroecology KW - biodiversity KW - habitat suitability models Y1 - 2012 U6 - https://doi.org/10.3402/polar.v31i0.11091 SN - 0800-0395 VL - 31 IS - 6 PB - Co-Action Publ. CY - Jarfalla ER - TY - JOUR A1 - Socher, Stephanie A. A1 - Prati, Daniel A1 - Boch, Steffen A1 - Müller, Jörg A1 - Klaus, Valentin H. A1 - Hölzel, Norbert A1 - Fischer, Markus T1 - Direct and productivity-mediated indirect effects of fertilization, mowing and grazing on grassland species richness JF - The journal of ecology N2 - Recent declines in biodiversity have given new urgency to questions about the relationship between land-use change, biodiversity and ecosystem processes. Despite the existence of a large body of research on the effects of land use on species richness, it is unclear whether the effects of land use on species richness are principally direct or indirect, mediated by concomitant changes in ecosystem processes. Therefore, we compared the direct effects of land use (fertilization, mowing and grazing) on species richness with indirect ones (mediated via grassland productivity) for grasslands in central Europe. We measured the richness and above-ground biomass in 150 grassland plots in 3 regions of Germany (the so-called Biodiversity Exploratories). We used univariate and structural equation models to examine direct and indirect land-use effects. The direct effects of mowing (-0.37, effect size) and grazing (0.04) intensity on species richness were stronger compared with the indirect effects of mowing (-0.04) and grazing (-0.01). However, the strong negative effect of fertilization (-0.23) on species richness was mainly indirect, mediated by increased productivity compared with the weak direct negative effect (-0.07). Differences between regions in land-use effects showed five times weaker negative effects of mowing (-0.13) in the region with organic soils (Schorfheide-Chorin), strong overall negative effects of grazing (-0.29) for the region with organic soils opposed to a similar strong positive effect (0.30) in the Hainich-Dun region, whereas the Schwabische Alb region displayed a five times weaker positive effect (0.06) only. Further, fertilization effects on species richness were positive (0.03) for the region with organic soils compared to up to 25 times stronger negative effects in the other two regions. Synthesis. Our results clearly show the importance of studying both direct and indirect effects of land-use intensity. They demonstrate the indirect nature, via productivity, of the negative effect of fertilization intensity on plant species richness in the real-world context of management-induced gradients of intensity of fertilization, mowing and grazing. Finally, they highlight that careful consideration of regional environments is necessary before attempting to generalize land-use effects on species diversity. KW - biodiversity KW - determinants of plant community diversity and structure KW - ecosystem functioning KW - functional plant group KW - land use KW - productivity KW - species richness KW - structural equation modelling Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-2745.2012.02020.x SN - 0022-0477 VL - 100 IS - 6 SP - 1391 EP - 1399 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Schwarzer, Christian A1 - Heinken, Thilo A1 - Luthardt, Vera A1 - Joshi, Jasmin Radha T1 - Latitudinal shifts in species interactions interfere with resistance of southern but not of northern bog-plant communities to experimental climate change JF - The journal of ecology N2 - The persistence of species under changed climatic conditions depends on adaptations and plastic responses to these conditions and on interactions with their local plant community resulting in direct and indirect effects of changed climatic conditions. Populations at species' range margins may be especially crucial in containing a gene pool comprising adaptations to extreme climatic conditions. Many species of northern European bog ecosystems reach their southern lowland range limit in central Europe. In a common-garden experiment, we experimentally assessed the impact of projected climatic changes on five bog-plant species (including peat moss Sphagnum magellanicum) sampled along a latitudinal gradient of 1400km from Scandinavia to the marginal lowland populations in Germany. Populations were cultivated in monocultures and in experimental communities composed of all five species from their local community, and exposed to five combinations of three climate treatments (warming, fluctuating water-tables, fertilization) in a southern common garden. Whereas most monocultures showed a decreasing biomass production from southern to northern origins under southern environmental conditions, in the experimental mixed-species communities, an increasing biomass production towards northern communities was observed together with a shift in interspecific interactions along the latitudinal gradient. While negative dominance effects prevailed in southern communities, higher net biodiversity effects were observed in northern subarctic communities. The combined effects of climate treatments increased biomass production in monocultures of most origins. In communities, however, overall the treatments did not result in significantly changed biomass production. Among individual treatments, water-table fluctuations caused a significant decrease in biomass production, but only in southern communities, indicating higher vulnerability to changed climatic conditions. Here, negative effects of climate treatments on graminoids were not compensated by the slightly increased growth of peat moss that benefited from interspecific interactions only in northern communities.Synthesis. We conclude that shifting interactions within multispecies communities caused pronounced responses to changed climatic conditions in wetland communities of temperate southern marginal, but not of northern subarctic origin. Therefore, future models investigating the impacts of climate change on plant communities should consider geographical variation in species interactions an important factor influencing community responses to changed climatic conditions. KW - additive partitioning of biodiversity effects KW - biodiversity KW - ecosystem services KW - ecosystem stability KW - intraspecific divergence KW - multifactorial environmental change KW - nitrogen deposition KW - northern peatlands KW - Sphagnum magellanicum KW - wetland ecosystems Y1 - 2013 U6 - https://doi.org/10.1111/1365-2745.12158 SN - 0022-0477 SN - 1365-2745 VL - 101 IS - 6 SP - 1484 EP - 1497 PB - Wiley-Blackwell CY - Hoboken ER - TY - THES A1 - Wasiolka, Bernd T1 - The impact of overgrazing on reptile diversity and population dynamics of Pedioplanis l. lineoocellata in the southern Kalahari T1 - Der Einfluss von Überweidung auf Reptiliendiversität und die Poplationsdynamik von Pedioplanis l. lineoocellata in der südlichen Kalahari N2 - Die Vegetationskomposition und –struktur, beispielsweise die unterschiedliche Architektur von Bäumen, Sträuchern, Gräsern und Kräutern, bietet ein großes Spektrum an Habitaten und Nischen, die wiederum eine hohe Tierdiversität in den Savannensystemen des südlichen Afrikas ermöglichen. Dieses Ökosystem wurde jedoch über Jahrzehnte weltweit durch intensive anthropogene Landnutzung (z.B. Viehwirtschaft) nachhaltig verändert. Dabei wurden die Zusammensetzung, Diversität und Struktur der Vegetation stark verändert. Überweidung in Savannensystemen führt zu einer Degradation des Habitates einhergehend mit dem Verlust von perennierenden Gräsern und krautiger Vegetation. Dies führt zu einem Anstieg an vegetationsfreien Bodenflächen. Beides, sowohl der Verlust an perennierenden Gräsern und krautiger Vegetation sowie der Anstieg an vegetationsfreien Flächen führt zu verbesserten Etablierungsbedingungen für Sträucher (z.B. Rhigozum trichotomum, Acacia mellifera) und auf lange Sicht zu stark verbuschten Flächen. Die Tierdiversität in Savannen ist hiervon entscheidend beeinflusst. Mit sinkender struktureller Diversität verringert sich auch die Tierdiversität. Während der Einfluss von Überweidung auf die Vegetation relativ gut untersucht ist sind Informationen über den Einfluss von Überweidung auf die Tierdiversität, speziell für Reptilien, eher spärlich vorhanden. Zusätzlich ist sehr wenig bekannt zum Einfluss auf die Populationsdynamik (z.B. Verhaltensanpassungen, Raumnutzung, Überlebensrate, Sterberate) einzelner Reptilienarten. Ziel meiner Doktorarbeit ist es den Einfluss von Überweidung durch kommerzielle Farmnutzung auf die Reptiliengemeinschaft und auf verschiedene Aspekte der Populationsdynamik der Echse Pedioplanis lineoocellata lineoocellata zu untersuchen. Hinsichtlich bestimmter Naturschutzmaßnahmen ist es einerseits wichtig zu verstehen welchen Auswirkungen Überweidung auf die gesamte Reptiliengemeinschaft hat. Und zum anderen wie entscheidende Faktoren der Populationsdynamik beeinflusst werden. Beides führt zu einem besseren Verständnis der Reaktion von Reptilien auf Habitatdegradation zu erlangen. Die Ergebnisse meiner Doktorarbeit zeigen eindeutig einen negativen Einfluss der Überweidung und der daraus resultierende Habitatdegradation auf (1) die gesamte Reptiliengemeinschaft und (2) auf einzelne Aspekte der Populationsdynamik von P. lineoocellata. Im Teil 1 wird die signifikante Reduzierung der Reptiliendiversität und Abundanz in degradierten Habitaten beschrieben. Im zweiten Teil wird gezeigt, dass P. lineoocellata das Verhalten an die verschlechterten Lebensbedingungen anpassen kann. Die Art bewegt sich sowohl häufiger als auch über einen längeren Zeitraum und legt dabei größere Distanzen zurück. Zusätzlich vergrößerte die Art ihr Revier (home range) (Teil 3). Im abschließenden Teil wird der negative Einfluss von Überweidung auf die Populationsdynamik von P. lineoocellata beschrieben: In degradierten Habitaten nimmt die Populationsgröße von adulten und juvenilen Echsen ab, die Überlebens- und Geburtenrate sinken, währen zusätzlich das Prädationsrisiko ansteigt. Verantwortlich hierfür ist zum einen die ebenfalls reduzierte Nahrungsverfügbarkeit (Arthropoden) auf degradierten Flächen. Dies hat zur Folge, dass die Populationsgröße abnimmt und die Fitness der Individuen verringert wird, welches sich durch eine Reduzierung der Überlebens- und Geburtenrate bemerkbar macht. Und zum anderen ist es die Reduzierung der Vegetationsbedeckung und der Rückgang an perennierenden Gräsern welche sich negativ auswirken. Als Konsequenz hiervon gehen Nischen und Mikrohabitate verloren und die Möglichkeiten der Reptilien zur Thermoregulation sind verringert. Des Weiteren hat dieser Verlust an perennierender Grasbedeckung auch ein erhöhtes Prädationsrisikos zur Folge. Zusammenfassend lässt sich sagen, dass nicht nur Bäume und Sträucher, wie in anderen Studien gezeigt, eine bedeutende Rolle für die Diversität spielen, sondern auch das perennierende Gras eine wichtige Rolle für die Faunendiversität spielt. Weiterhin zeigte sich, dass Habitatdegradation nicht nur die Population als gesamtes beeinflusst, sondern auch das Verhalten und Populationsparameter einzelner Arten. Des Weiteren ist es Reptilien möglich durch Verhaltensflexibilität auf verschlechterte Umweltbedingen zu reagieren. N2 - In semi-arid savannah ecosystems, the vegetation structure and composition, i.e. the architecture of trees, shrubs, grass tussocks and herbaceous plants, offer a great variety of habitats and niches to sustain animal diversity. In the last decades intensive human land use practises like livestock farming have altered the vegetation in savannah ecosystems worldwide. Extensive grazing leads to a reduction of the perennial and herbaceous vegetation cover, which results in an increased availability of bare soil. Both, the missing competition with perennial grasses and the increase of bare soils favour shrub on open ground and lead to area-wide shrub encroachment. As a consequence of the altered vegetation structure and composition, the structural diversity declines. It has been shown that with decreasing structural diversity animal diversity decline across a variety of taxa. Knowledge on the effects of overgrazing on reptiles, which are an important part of the ecosystem, are missing. Furthermore, the impact of habitat degradation on factors of a species population dynamic and life history, e.g., birth rate, survival rate, predation risk, space requirements or behavioural adaptations are poorly known. Therefore, I investigated the impact of overgrazing on the reptile community in the southern Kalahari. Secondly I analysed population dynamics and the behaviour of the Spotted Sand Lizard, Pedioplanis l. lineoocellata. All four chapters clearly demonstrate that habitat degradation caused by overgrazing had a severe negative impact upon (i) the reptile community as a whole and (ii) on population parameters of Pedioplanis l. lineoocellata. Chapter one showed a significant decline of regional reptile diversity and abundance in degraded habitats. In chapter two I demonstrated that P. lineoocellata moves more frequently, spends more time moving and covers larger distances in degraded than in non-degraded habitats. In addition, home range size of the lizard species increases in degraded habitats as shown by chapter three. Finally, chapter four showed the negative impacts of overgrazing on several population parameters of P. lineoocellata. Absolute population size of adult and juvenile lizards, survival rate and birth rate are significantly lower in degraded habitats. Furthermore, the predation risk was greatly increased in degraded habitats. A combination of a variety of aspects can explain the negative impact of habitat degradation on reptiles. First, reduced prey availability negatively affects survival rate, the birth rate and overall abundance. Second, the loss of perennial plant cover leads to a loss of niches and to a reduction of opportunities to thermoregulate. Furthermore, a loss of cover and is associated with increased predation risk. A major finding of my thesis is that the lizard P. lineoocellata can alter its foraging strategy. Species that are able to adapt and change behaviour, such as P. lineoocellata can effectively buffer against changes in their environment. Furthermore, perennial grass cover can be seen as a crucial ecological component of the vegetation in the semi-arid savannah system of the southern Kalahari. If perennial grass cover is reduced to a certain degree reptile diversity will decline and most other aspects of reptile life history will be negatively influenced. Savannah systems are characterised by a mixture of trees, shrubs and perennial grasses. These three vegetation components determine the composition and structure of the vegetation and accordingly influence the faunal diversity. Trees are viewed as keystone structures and focal points of animal activity for a variety of species. Trees supply animals with shelter, shade and food and act as safe sites, nesting sites, observation posts and foraging sites. Recent research demonstrates a positive influence of shrub patches on animal diversity. Moreover, it would seem that intermediate shrub cover can also sustain viable populations in savannah landscapes as has been demonstrated for small carnivores and rodent species. The influence of perennial grasses on faunal diversity did not receive the same attention as the influence of trees and shrubs. In my thesis I didn’t explicitly measure the direct effects of perennial grasses but my results strongly imply that it has an important role. If the perennial grass cover is significantly depleted my results suggest it will negatively influence reptile diversity and abundance and on several populations parameters of P. lineoocellata. Perennial grass cover is associated with the highest prey abundance, reptile diversity and reptile abundance. It provides reptiles both a refuge from predators and opportunities to optimise thermoregulation. The relevance of each of the three vegetation structural elements is different for each taxa and species. In conclusion, I can all three major vegetation structures in the savannah system are important for faunal diversity. KW - Shrub encroachment KW - overgrazing KW - biodiversity KW - reptiles Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-16611 ER -