FLINT is a DFG-funded Package Proposal that consists of four projects led by twelve PIs from the  University of Hohenheim. The FLINT consortium assembles a broad range of expertise in ecology and evolutionary biology, empirical and theoretical research on plants and animals.

Two fundamental properties of life are that organisms are diverse and that organisms interact with each other. Biodiversity dynamics and biotic interactions are tightly connected since interactions promote, maintain or reduce diversity within and between species through both ecological and evolutionary processes. In particular, biodiversity dynamics depend on properties of biotic interactions, notably on their type (antagonistic, mutualistic or competitive), intensity, and degree of specialization. Consequently, the effect of biotic interactions on biodiversity has long been a focus of both ecology and evolutionary biology. However, there is still a substantial gap between theoretical and empirical research on this subject. FLINT aims to narrow the gap between theoretical and empirical research on the effect of biotic interactions on biodiversity dynamics. Specifically, we aim to (1) enhance the real-world applicability of theory, (2) quantify fitness consequences of biotic interactions in study systems for which interaction mechanisms are well understood, and (3) achieve theory-based synthesis on the effects of biotic interactions on biodiversity dynamics. To reach these goals, FLINT uses biotic interaction landscapes (i.e. a map of the fitness of each interaction partner as a function of traits of all partners) as a joint conceptual framework for all its four component projects.

Project 1: The role of biotic interaction landscapes for ecoevolutionary dynamics of biodiversity and interaction networks
(Korinna Allhoff & Frank Schurr)

Project 2: Fitness consequences of trait-mediated interactions between the invasive plant Impatiens glandulifera, native plants and their pollinators
(Christine Sheppard, Ingo Grass, Mialy Razanajatovo & Philipp Schlüter)

Project 3: Fitness consequences of phenological (a)synchrony for plants and pollinators in a sexually deceptive pollination system
(Philipp Schlüter, Simone Cappellari Rabeling, Johannes Steidle & Korinna Allhoff)

Project 4: Reciprocal fitness consequences in the defense mediated interaction between a toxic plant and a sequestering herbivore
(Georg Petschenka, Andreas Schweiger, Anke Steppuhn & Jörn Pagel)

Project 1: The role of biotic interaction landscapes for ecoevolutionary dynamics of biodiversity and interaction networks (Korinna Allhoff & Frank Schurr)

Major goals of FLINT are to (1) understand fitness consequences of biotic interactions across a range of different empirical systems and (2) promote integration of theory and empirical research on the links between biotic interactions and biodiversity. Project 1 plays a key role in this context since it develops theory on how biotic interaction landscapes affect diversification processes and emergent properties of interaction networks, such as modularity and nestedness. The project will then use this theory for synthesis across empirically-investigated interaction types. To this end, we use a new modelling framework, based on biotic interaction landscapes as an essential building block. We first investigate eco-evolutionary dynamics within archetypical biotic interaction landscapes, before applying the insights gained from this analysis to the observed landscapes measured by the empirical FLINT projects. We hypothesize that the relative proportion of antagonistic versus mutualistic regions in the biotic interaction landscape, as well as the shape of these regions, affect diversification processes in predictable ways and hence leave a fingerprint on the resulting network structures. Our research approach combines analytical calculations with numerical simulations, inspired by the mathematical framework of Adaptive Dynamics. We will furthermore establish an international working group of experts in the field who conduct empirical research on the fitness consequences of biotic interactions and/or develop theory on eco-evolutionary interaction networks. The goal of this working group is to critically evaluate and further develop the concept of biotic interaction landscapes and its application to biodiversity dynamics. The results gained from this project will thus provide deep mechanistic insights into eco-evolutionary processes within specific systems, but also theory-based synthesis across interaction types.

Project 2: Fitness consequences of trait-mediated interactions between the invasive plant Impatiens glandulifera, native plants and their pollinators (Christine Sheppard, Ingo Grass, Mialy Razanajatovo & Philipp Schlüter)

Project 2 focuses on the fitness consequences of interactions between plants and their pollinators. Plant-pollinator interactions can be strongly altered by the arrival of a new dominant species such as an invasive plant. So far, little is known about the impact of invasive plants on pollinator fitness. Moreover, there are conflicting results on how pollinators mediate interactions between invasive and native plants. These pollinator-mediated interactions can either be negative if invaders compete for pollinators or positive if native plants benefit from the spill-over of pollinators attracted to invaders. In Project 2 we aim to reconcile these seemingly conflicting findings by analyzing how traits determine fitness consequences for invasive plants, native plants and pollinators. To this end, we investigate how intra- and interspecific variation in plant and pollinator traits determine interactions between the invasive plant Impatiens glandulifera, native plant species and the pollinator community. We hypothesize that fitness effects of I. glandulifera on native plants and pollinators range from negative to positive depending on the traits of native plants and pollinators. Our research approach includes experimental measurements of biotic interaction landscapes hypothesized to be shaped by plant-pollinator trait matching and alien-native plant trait similarity. These are complemented by field studies of plant-pollinator communities under natural conditions, investigating interaction networks in landscapes with high vs. low pollinator diversity. The project mainly focuses on fitness consequences of interspecific trait variation but will complement this by testing for adaptive intraspecific trait differentiation in I. glandulifera. The results from our empirical project will allow us to understand the mechanisms and predict the fitness consequences of the impact of an invasive plant on native plants and pollinators, contributing to synthesis on biotic interaction landscapes for the different interaction types studied in FLINT.

Project 3: Fitness consequences of phenological (a)synchrony for plants and pollinators in a sexually deceptive pollination system (Philipp Schlüter, Simone Cappellari Rabeling, Johannes Steidle & Korinna Allhoff)

Project 3 investigates a text-book example of a highly specialised biotic interaction in great detail, namely sexually deceptive pollination in Ophrys orchids. This system contains three players: plants, solitary male bees as pollinators and their non-pollinating female conspecifics. Specifically, it aims to evaluate the previously untested assumption that interaction with Ophrys orchids bears no fitness consequences for their pollinators. By combining experiments, field observations, genetic analyses and modelling, we will investigate whether and how this interaction affects the fitness of Ophrys orchids, their male pollinators and the conspecific females. In particular, we will study how the fitness of each interaction partner depends on its phenological overlap with the other partners.

To investigate the potential fitness effects generated via this biotic interaction, we first propose to gather plant and solitary bee phenology data for males and females so as to test if individual variation in flowering time influences plant fitness. Next, we shall test if the presence of sexually deceptive plants imposes a measurable fitness effect on individual male and female bees and the populations they form by experimentally manipulating their relative frequencies in insect enclosures. This will be complemented by studying their behavioural reaction towards deceptive plants and bees of the opposite sex, as well as by investigating the effects on bee genetic diversity, patterns of paternity and sex ratio of offspring in the presence or absence of orchids. Finally, we plan to employ process-based modelling to disentangle the parameters that affect fitness and shape the observed plant and insect phenologies. In summary, this project will close important gaps in of a model system of macroevolutionary diversification. Moreover, it will quantify biotic interaction landscapes of biotic interactions among plants, male and female bees that will feed into synthesis across FLINT projects.

Project 4: Reciprocal fitness consequences in the defense mediated interaction between a toxic plant and a sequestering herbivore (Georg Petschenka, Andreas Schweiger, Anke Steppuhn & Jörn Pagel)

Project 4 studies the reciprocal fitness consequences of the interaction between a toxic plant and its specialized seed predator that sequesters plant toxins for defense. Secondary metabolites are key mediators of biotic interactions at multiple scales: Chemical properties of secondary metabolites influence global distribution of plant mutualisitc interactions and local differences in herbivore composition are known to select for geographic variation in plant chemical defense. However, our understanding of the reciprocal fitness consequences in antagonistic plant-herbivore interactions mediated by defense chemistry is very limited. In particular, how the interplay of biotic and abiotic factors at different spatial scales affects fitness on both sides has never been investigated. Here, we propose a set of hierarchical objectives to investigate the abiotic and biotic drivers of antagonistic plant-herbivore interactions and their fitness consequences at scales ranging from the molecular level of defense chemistry to geographic distribution patterns. We hypothesize that the reproductive fitness and chemical defenses of plants vary across their distributions due to interactions with their abiotic and biotic environments. This variation will affect toxin-sequestering seed predators, which have a direct fitness impact by feeding on plant reproductive organs and benefit from plant toxins for their own defense. As a model system, we use the Eurasian milkweed bug Spilostethus saxatilis (Heteroptera: Lygaeinae), which is obligately associated with autumn crocus (Colchicum autumnale) and sequesters high levels of colchicine alkaloids for defense. We study C. autumnale populations across Germany and Europe, colonized or not by S. saxatilis, along gradients of temperature, precipitation and soil nutrient availability. In Project 4, we integrate (1) chemical analyses of alkaloids and other plant metabolites in insects and plants across geographic and biotic gradients, (2) characterization of the abiotic and biotic environment along with fitness assessments of plants and specialist herbivores, (3) reciprocal feeding, sequestration, and seed predation assays to test for local adaptation, and (4) demographic and biogeographic modeling to unravel how fitness feedbacks from biotic interactions drive plant-insect co-occurrence across their distributional ranges.