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Projektvorstellung INTEGRA: Integration von Habitatstrukturen in landwirtschaftlich genutzte Flächen zur Förderung von Bestäuberinsekten
No full textRäumliche und funktionelle Faktoren der Langzeitfekundität in serotinen Strauchgemeinschaften
No full textUnderstanding the dynamics of biological communities is a central aim of ecological research. Contemporary environmental change reinforced this interest: in order to predict how communities will react to environmental change, we have to understand the processes driving their dynamics. Ultimately, the dynamics of a community depends on the reproduction, mortality and dispersal of its component individuals, and on how these demographic processes are altered by environmental factors and biotic interactions.
A general understanding of biological communities is unlikely to arise from a species-specific approach that attempts to quantify all pairwise interactions between species. Instead, it seems promising to pursue a trait-based research program that quantifies how variation in the performance of species and individuals is shaped by the interplay of functional traits, biotic interactions and environmental factors. In this thesis, I investigated how functional plant traits determine plant-plant, plant-pollinator and plant-herbivore interactions in space and time, and how these spatiotemporal interactions affect the long-term fecundity of plants. In the South African Fynbos biome (a global biodiversity hotspot), I studied a species-rich, ecologically and economically important group of woody plants (genus Protea) and its interactions with pollinators and seed predators.
The objectives of this thesis were: (1) to combine plant traits and high-resolution maps of Protea communities in order to quantify the landscapes of nectar sugar and seed crops that plant communities provide for pollinators and seed predators, (2) to examine how sugar landscapes shape pollinator behaviour, and how pollinator behaviour and pollinator-mediated interactions between plants affect the reproduction of Protea individuals, (3) to study how the spatial structure of plant communities and seed crop landscapes determine direct and predator-mediated interactions between plants, and (4) to understand how the interplay of these biotic interactions shapes the dynamics of plant communities. I addressed these objectives by analysing spatially-explicit data and high-resolution maps from 27 sites of 4 ha each that contained 129,750 plants of 22 Protea species.
The results show that Protea plants and their pollinators interact on several spatial and temporal scales, and that these interactions are shaped by sugar landscapes. Within plants, inflorescences compete for pollination. At a neighbourhood scale, Protea reproduction benefits from nectar sugar of conspecific neighbours but not from heterospecific neighbour sugar. Seed set also increases with the amount of nectar sugar at the scale of entire study sites. This corresponds with the finding that the abundance and the visitation rates of key bird pollinators strongly depend on phenological variation of site-scale sugar amounts. Nectar sugar furthermore influences the strength of interactions between Protea species and bird pollinators: Protea species that provide nectar of high sugar concentration depend more strongly on bird pollinators to reproduce. When foraging in sugar landscapes, these bird pollinators show both temporal specialization on single plant species and a preference for common plant species.
In addition to these pollinator-mediated interactions, the long-term fecundity of Protea individuals is reduced through both competition and apparent competition mediated by seed predators. Competition is stronger between conspecifics than between heterospecifics, whereas apparent competition shows no such differentiation. The intensity of competition between plants depends on their size and the intensity of apparent competition between plants depends on their seed crops. Moreover, competition has a stronger effect on plant fecundity than apparent competition.
These findings have interesting implications for understanding the dynamics of Protea communities and the maintenance of plant diversity in the Fynbos biome. The positive interspecific density-dependence resulting from pollinator-mediated interactions causes community-level Allee effects that may lead to extinction cascades. My analyses also imply that competition stabilizes the coexistence of Protea species (because intraspecific competition is stronger than interspecific competition), whereas apparent competition via seed predators does not have such a stabilizing effect. In summary, this study highlights the benefits of ‘community demography’, the demographic study of multiple interacting species. Community demographic studies have the potential to identify general determinants of biotic interactions that act across species and communities. In this thesis, I identified nectar sugar and seed crops as interaction currencies that determine how multiple plant species interact through shared pollinators and seed predators. In megadiverse systems such as Fynbos, such generalizations are urgently needed to understand and forecast community dynamics. The analysis of community dynamics with respect to such interaction currencies provides an alternative to the classical species-specific approach in community ecology.Räumliche und Zeitliche Interaktionen zwischen Pflanzen, Pflanzen und ihren Bestäubern und Räubern spielen eine Schlüsselrolle in der Dynamik von terrestrischen Gemeinschaften. Doch in der Ökologie fehlt weitgehend ein quantitatives Verständnis der Merkmale und Prozesse, die sowohl räumliche und zeitliche Interaktionen einschließen. Deshalb untersuchte ich in dieser Doktorarbeit, wie funktionale Pflanzenmerkmale Pflanzen-Pflanzen-Interaktionen und Pflanzen-Tier-Interaktionen in Raum und Zeit bestimmen, und wie diese räumlich-zeitliche Interaktionen die Pflanzenreproduktion beeinflussen. Ich studierte eine artenreiche, ökologisch und ökonomisch wichtige Gruppe von südafrikanischen Büschen (Gattung Protea) mit ihren wichtigsten Bestäubern (Cape Sugarbird, Promerops cafer and sunbird, Anthobaphes violacea) in der Cape Floristic Region (CFR). Durch die Kombination von Experimenten und Beobachtungen in verschiedenen Protea Gesellschaften die mit hoher Auflösung kartiert wurden, untersuchte ich wie die räumliche und zeitliche Verteilung von Protea-Ressourcen („Ressourcen-Landschaften") die Verhaltensweisen von Bestäubern prägt und wie sich Nachbarpflanzen auf die Verhaltensweisen von Bestäubern auswirken und im Umkehrschluss wie sich die Bestäuber auf die Reproduktion von Protea Individuen auswirkt. Darüber hinaus studierte ich, wie Ressourcen-Landschaften die Konkurrenz und die Prädationsrate beeinflusst und wie sich die Kombination von beiden auf die Dynamik der Protea-Gesellschaften auswirkt. Um dies zu tun, habe ich Pflanzenmerkmale durch raumzeitliche Interaktionen aus der Perspektive der beiden Pflanzen und Tiere quantifiziert und analysierte Interaktionen zwischen Protea Individuen (insgesamt 129750 Protea Positionen mit 22 Arten in 27 verschiedene Pflanzengesellschaften). Die Ergebnisse dieser Studie tragen zum Verständnis von demographischen Prozessen und Gesellschaftsdynamiken bei und zeigen die Auswirkungen auf die Erhaltung der biologischen Vielfalt in diesem „Biodiversitäts-Hotspot“
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Spatial and functional determinants of long-term fecundity in serotinous shrub communities
Get PDFUnderstanding the dynamics of biological communities is a central aim of ecological research. Contemporary environmental change reinforced this interest: in order to predict how communities will react to environmental change, we have to understand the processes driving their dynamics. Ultimately, the dynamics of a community depends on the reproduction, mortality and dispersal of its component individuals, and on how these demographic processes are altered by environmental factors and biotic interactions.
A general understanding of biological communities is unlikely to arise from a species-specific approach that attempts to quantify all pairwise interactions between species. Instead, it seems promising to pursue a trait-based research program that quantifies how variation in the performance of species and individuals is shaped by the interplay of functional traits, biotic interactions and environmental factors. In this thesis, I investigated how functional plant traits determine plant-plant, plant-pollinator and plant-herbivore interactions in space and time, and how these spatiotemporal interactions affect the long-term fecundity of plants. In the South African Fynbos biome (a global biodiversity hotspot), I studied a species-rich, ecologically and economically important group of woody plants (genus Protea) and its interactions with pollinators and seed predators.
The objectives of this thesis were: (1) to combine plant traits and high-resolution maps of Protea communities in order to quantify the landscapes of nectar sugar and seed crops that plant communities provide for pollinators and seed predators, (2) to examine how sugar landscapes shape pollinator behaviour, and how pollinator behaviour and pollinator-mediated interactions between plants affect the reproduction of Protea individuals, (3) to study how the spatial structure of plant communities and seed crop landscapes determine direct and predator-mediated interactions between plants, and (4) to understand how the interplay of these biotic interactions shapes the dynamics of plant communities. I addressed these objectives by analysing spatially-explicit data and high-resolution maps from 27 sites of 4 ha each that contained 129,750 plants of 22 Protea species.
The results show that Protea plants and their pollinators interact on several spatial and temporal scales, and that these interactions are shaped by sugar landscapes. Within plants, inflorescences compete for pollination. At a neighbourhood scale, Protea reproduction benefits from nectar sugar of conspecific neighbours but not from heterospecific neighbour sugar. Seed set also increases with the amount of nectar sugar at the scale of entire study sites. This corresponds with the finding that the abundance and the visitation rates of key bird pollinators strongly depend on phenological variation of site-scale sugar amounts. Nectar sugar furthermore influences the strength of interactions between Protea species and bird pollinators: Protea species that provide nectar of high sugar concentration depend more strongly on bird pollinators to reproduce. When foraging in sugar landscapes, these bird pollinators show both temporal specialization on single plant species and a preference for common plant species.
In addition to these pollinator-mediated interactions, the long-term fecundity of Protea individuals is reduced through both competition and apparent competition mediated by seed predators. Competition is stronger between conspecifics than between heterospecifics, whereas apparent competition shows no such differentiation. The intensity of competition between plants depends on their size and the intensity of apparent competition between plants depends on their seed crops. Moreover, competition has a stronger effect on plant fecundity than apparent competition.
These findings have interesting implications for understanding the dynamics of Protea communities and the maintenance of plant diversity in the Fynbos biome. The positive interspecific density-dependence resulting from pollinator-mediated interactions causes community-level Allee effects that may lead to extinction cascades. My analyses also imply that competition stabilizes the coexistence of Protea species (because intraspecific competition is stronger than interspecific competition), whereas apparent competition via seed predators does not have such a stabilizing effect. In summary, this study highlights the benefits of community demography, the demographic study of multiple interacting species. Community demographic studies have the potential to identify general determinants of biotic interactions that act across species and communities. In this thesis, I identified nectar sugar and seed crops as interaction currencies that determine how multiple plant species interact through shared pollinators and seed predators. In megadiverse systems such as Fynbos, such generalizations are urgently needed to understand and forecast community dynamics. The analysis of community dynamics with respect to such interaction currencies provides an alternative to the classical species-specific approach in community ecology.Räumliche und Zeitliche Interaktionen zwischen Pflanzen, Pflanzen und ihren Bestäubern und Räubern spielen eine Schlüsselrolle in der Dynamik von terrestrischen Gemeinschaften. Doch in der Ökologie fehlt weitgehend ein quantitatives Verständnis der Merkmale und Prozesse, die sowohl räumliche und zeitliche Interaktionen einschließen. Deshalb untersuchte ich in dieser Doktorarbeit, wie funktionale Pflanzenmerkmale Pflanzen-Pflanzen-Interaktionen und Pflanzen-Tier-Interaktionen in Raum und Zeit bestimmen, und wie diese räumlich-zeitliche Interaktionen die Pflanzenreproduktion beeinflussen. Ich studierte eine artenreiche, ökologisch und ökonomisch wichtige Gruppe von südafrikanischen Büschen (Gattung Protea) mit ihren wichtigsten Bestäubern (Cape Sugarbird, Promerops cafer and sunbird, Anthobaphes violacea) in der Cape Floristic Region (CFR). Durch die Kombination von Experimenten und Beobachtungen in verschiedenen Protea Gesellschaften die mit hoher Auflösung kartiert wurden, untersuchte ich wie die räumliche und zeitliche Verteilung von Protea-Ressourcen (Ressourcen-Landschaften") die Verhaltensweisen von Bestäubern prägt und wie sich Nachbarpflanzen auf die Verhaltensweisen von Bestäubern auswirken und im Umkehrschluss wie sich die Bestäuber auf die Reproduktion von Protea Individuen auswirkt. Darüber hinaus studierte ich, wie Ressourcen-Landschaften die Konkurrenz und die Prädationsrate beeinflusst und wie sich die Kombination von beiden auf die Dynamik der Protea-Gesellschaften auswirkt. Um dies zu tun, habe ich Pflanzenmerkmale durch raumzeitliche Interaktionen aus der Perspektive der beiden Pflanzen und Tiere quantifiziert und analysierte Interaktionen zwischen Protea Individuen (insgesamt 129750 Protea Positionen mit 22 Arten in 27 verschiedene Pflanzengesellschaften). Die Ergebnisse dieser Studie tragen zum Verständnis von demographischen Prozessen und Gesellschaftsdynamiken bei und zeigen die Auswirkungen auf die Erhaltung der biologischen Vielfalt in diesem Biodiversitäts-Hotspot
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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