Spatial and functional determinants of long-term fecundity in serotinous shrub communities

Understanding 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

An operational definition of the biome for global change research

CITATION: Conradi, T. et al. 2020. An operational definition of the biome for global change research. New Phytologist, 227:1294–1306, doi:10.1111/nph.16580.The original publication is available at https://nph.onlinelibrary.wiley.comBiomes are constructs for organising knowledge on the structure and functioning of the world’s ecosystems, and serve as useful units for monitoring how the biosphere responds to anthropogenic drivers, including climate change. The current practice of delimiting biomes relies on expert knowledge. Recent studies have questioned the value of such biome maps for comparative ecology and global-change research, partly due to their subjective origin. Here we propose a flexible method for developing biome maps objectively. The method uses range modelling of several thousands of plant species to reveal spatial attractors for different growth-form assemblages that define biomes. The workflow is illustrated using distribution data from 23 500 African plant species. In an example application, we create a biome map for Africa and use the fitted species models to project biome shifts. In a second example, we map gradients of growth-form suitability that can be used to identify sites for comparative ecology. This method provides a flexible framework that (1) allows a range of biome types to be defined according to user needs and (2) enables projections of biome changes that emerge purely from the individualistic responses of plant species to environmental changes.Publisher's versio

An operational definition of the biome for global change research

CITATION: Conradi, T. et al. 2020. An operational definition of the biome for global change research. New Phytologist, 227:1294–1306, doi:10.1111/nph.16580.The original publication is available at https://nph.onlinelibrary.wiley.comBiomes are constructs for organising knowledge on the structure and functioning of the world’s ecosystems, and serve as useful units for monitoring how the biosphere responds to anthropogenic drivers, including climate change. The current practice of delimiting biomes relies on expert knowledge. Recent studies have questioned the value of such biome maps for comparative ecology and global-change research, partly due to their subjective origin. Here we propose a flexible method for developing biome maps objectively. The method uses range modelling of several thousands of plant species to reveal spatial attractors for different growth-form assemblages that define biomes. The workflow is illustrated using distribution data from 23 500 African plant species. In an example application, we create a biome map for Africa and use the fitted species models to project biome shifts. In a second example, we map gradients of growth-form suitability that can be used to identify sites for comparative ecology. This method provides a flexible framework that (1) allows a range of biome types to be defined according to user needs and (2) enables projections of biome changes that emerge purely from the individualistic responses of plant species to environmental changes.Publisher's versio

Systematics and evolution of predatory flower flies (Diptera Syrphidae) based on exon-capture sequencing

Flower flies (Diptera: Syrphidae) are one of the most species-rich dipteran families and provide important ecosystem services such as pollination, biological control of pests, recycling of organic matter and redistributions of essential nutrients. Flower fly adults generally feed on pollen and nectar, but their larval feeding habits are strikingly diverse. In the present study, high-throughput sequencing was used to capture and enrich phylogenetically and evolutionary informative exonic regions. With the help of the baitfisher software, we developed a new bait kit (SYRPHIDAE1.0) to target 1945 CDS regions belonging to 1312 orthologous genes. This new bait kit was successfully used to exon capture the targeted loci in 121 flower fly species across the different subfamilies of Syrphidae. We analysed different amino acid and nucleotide data sets (1302 loci and 154 loci) with maximum likelihood and multispecies coalescent models. Our analyses yielded highly supported similar topologies, although the degree of the SRH (global stationarity, reversibility and homogeneity) conditions varied greatly between amino acid and nucleotide data sets. The sisterhood of subfamilies Pipizinae and Syrphinae is supported in all our analyses, confirming a common origin of taxa feeding on soft-bodied arthropods. Based on our results, we define Syrphini stat.rev. to include the genera Toxomerus and Paragus. Our divergence estimate analyses with beast inferred the origin of the Syrphidae in the Lower Cretaceous (125.5-98.5 Ma) and the diversification of predatory flower flies around the K-Pg boundary (70.61-54.4 Ma), coinciding with the rise and diversification of their prey.Peer reviewe

Genomic Analyses of Transport Proteins in Ralstonia metallidurans

Ralstonia (Wautersia, Cupriavidus) metallidurans (Rme) is better able to withstand high concentrations of heavy metals than any other well-studied organism. This fact renders it a potential agent of bioremediation as well as an ideal model organism for understanding metal resistance phenotypes. We have analysed the genome of Rme for genes encoding homologues of established and putative transport proteins; 13% of all genes in Rme encode such homologues. Nearly one-third of the transporters identified (32%) appear to function in inorganic ion transport with three-quarters of these acting on cations. Transporters specific for amino acids outnumber sugar transporters nearly 3 : 1, and this fact plus the large number of uptake systems for organic acids indicates the heterotrophic preferences of these bacteria. Putative drug efflux pumps comprise 10% of the encoded transporters, but numerous efflux pumps for heavy metals, metabolites and macromolecules were also identified. The results presented should facilitate genetic manipulation and mechanistic studies of transport in this remarkable bacterium

TRY plant trait database - enhanced coverage and open access

Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

MscS-like mechanosensitive channels in plants and microbes

The challenge of osmotic stress is something all living organisms must face as a result of environmental dynamics. Over the past three decades, innovative research and cooperation across disciplines have irrefutably established that cells utilize mechanically gated ion channels to release osmolytes and prevent cell lysis during hypoosmotic stress. Early electrophysiological analysis of the inner membrane of Escherichia coli identified the presence of three distinct mechanosensitive activities. The subsequent discoveries of the genes responsible for two of these activities, the mechanosensitive channels of large (MscL) and small (MscS) conductance, led to the identification of two diverse families of mechanosensitive channels. The latter of these two families, the MscS family, consists of members from bacteria, archaea, fungi, and plants. Genetic and electrophysiological analysis of these family members has provided insight into how organisms use mechanosensitive channels for osmotic regulation in response to changing environmental and developmental circumstances. Furthermore, determining the crystal structure of E. coli MscS and several homologues in several conformational states has contributed to our understanding of the gating mechanisms of these channels. Here we summarize our current knowledge of MscS homologues from all three domains of life and address their structure, proposed physiological functions, electrophysiological behaviors, and topological diversity

Responses of nectar-feeding birds to floral resources at multiple spatial scales

The responses of animal pollinators to the spatially heterogeneous distribution of floral resources are important for plant reproduction, especially in species-rich plant communities. We explore how responses of pollinators to floral resources varied across multiple spatial scales and studied the responses of two nectarivorous bird species (Cape sugarbird Promerops cafer, orange-breasted sunbird Anthobaphes violacea) to resource distributions provided by communities of co-flowering Protea species (Proteaceae) in South African fynbos. We used highly resolved maps of about 125 000 Protea plants at 27 sites and estimated the seasonal dynamics of standing crop of nectar sugar for each plant to describe the spatiotemporal distribution of floral resources. We recorded avian population sizes and the rates of bird visits to ˃1300 focal plants to assess the responses of nectarivorous birds to floral resources at different spatial scales. The population sizes of the two bird species responded positively to the amount of sugar resources at the site scale. Within sites, the effects of floral resources on pollinator visits to plants varied across scales and depended on the resources provided by individual plants. At large scales (radii ˃25 m around focal plants), high sugar density decreased per-plant visitation rates, i.e. plants competed for animal pollinators. At small scales (radii ˂5 m around focal plants), we observed either competition or facilitation for pollinators between plants, depending on the sugar amount offered by individual focal plants. In plants with copious sugar, per-plant visitation rates increased with increasing local sugar density, but visitation rates decreased in plants with little sugar. Our study underlines the importance of scale-dependent responses of pollinators to floral resources and reveals that pollinators’ responses depend on the interplay between individual floral resources and local resource neighbourhood

TRY plant trait database – enhanced coverage and open access

Plant traits—the morphological, anatomical, physiological, biochemical and phenological characteristics of plants—determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits—almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives