Contact Katja Tielbörger

A) Evolution of heterocarpic plants

Many composites produce two or more types of seeds which differ in dispersal and germination characteristics. This heterocarpy is considered a type of bet-hedging strategy whereby different seed morphs are produced in environments which are spatially and/or temporally variable.

A1) Along a gradient of environmental unpredictability (i.e. an aridity gradient in Israel), the ratio of far vs. short dispersing seeds should change: more seeds with high dormancy should be produced towards the arid. There should be a trade-off with dispersal, i.e. dispersal distance and seed dormancy should be inversely related. This hypothesis will be tested using a collection seeds from of annual heterocarpic species. They will be grown in Winter 2021/22. Start: Sept-Nov 2021 (preparation), peak work March-May 2022 (i.e. between Nov and March there is time for taking courses).

A2) Plasticity should be more pronounced for plants coming from more variable (i.e. arid environments). Thus we assume that plants will plastically change the ratio between the two seed morphs more when coming from arid sites. This hypothesis will be tested with growing several species of annual plants from an aridity gradient under drought and well-watered conditions. Start: Sept-Nov 2021 (preparation), peak work March-May 2022 (i.e. between Nov and March there is time for taking courses)

B) Competition intensity and relatedness

In an equilibrium world, coexistence requires that plants differ from each other. Therefore, competition should be stronger between plants that are very similar. Thus, competition intensity should increase along a gradient of relatedness, ranging from between regions, between family within a region, between species within a family, between individuals within a species from different climates, between individuals from same climate and species, between sibling plants. Relatedness should also affect symmetry of interactions and should be more symmetric on an intraspecific level.
This topic is more relevant for an MSc level and will be tested with the collection of Israeli annuals, i.e. this is a winter topic (Nov-May).

C) Plant-soil feedbacks

Plants can modify the microbial community in the soil they are growing in and very often, there are negative plant-soil feedbacks. These result in intensified intraspecific negative interactions and have thus been proposed as a mechanism promoting coexistence among species. Plant-soil feedbacks have also been studied in the context of invasion biology, i.e. studies have tested whether conditioned soil may inhibit invasion.

In this topic, we can make use of a huge common garden experiment with 2800 pots that were conditioned with altogether 30 common grassland species. We would like to start a pilot study in Spring 2020, probably with Arabidopsis thaliana as this species grows fast and has no mycorrhiza, i.e. we can rule out positive plant-soil feedback effects. We could then also make a larger experiment where we test the use of native species for suppressing common invasives such as Solidago canadensis or Impatiens glandulifera.

D) Plant-microbe interactions under climate change

Climate change in our region is predicted to generate a higher frequency of extreme drought events. This may affect organisms directly, by decreasing resource availability, or indirectly, by modifying organismic interactions. This project, which is embedded in a long-term experiment entitled ‘Drier’, aims at studying the change in the microbial community associated with common grassland plants, when these are exposed to extreme drought events in the field.

Methods: The microbial community of several common grassland plant species has been sampled in Summer 2020, after a 1- to 3-year drought in a long-term field experiment. The first step in this project is to characterize this community in terms of differences among plant species and drought treatments. This will be done by high-end molecular methods, and will be mostly conducted in the lab of Eric Kemen (ZMBP).

E) Drought and overgrazing as drivers of a desertification tipping point in semi-arid rangelands (Bachelor thesis)

Background: Changing environmental conditions, such as frequent and intense drought events, coupled with unsustainable management practices like overgrazing, continue to degrade drylands. One main concern is the irreversible transition of productive rangelands into degraded states, a phenomenon known as tipping points. Because tipping points remain difficult to anticipate in real-world systems, they often come as an unpleasant surprise. Research under the NamTip project (https://rb.gy/owbk6d) aims to gain a better understanding of these shifts, by focusing specifically on desertification, which is the most common tipping point in dryland ecosystems.

Methods: Drone multispectral data were collected between 2021 and 2024 at an experimental site called ‘TipEx’. The experiment attempts to push a semi-arid rangeland in Namibia to cross a tipping point by simulating drought (using rainout shelters) and grazing (through clipping) at various intensities. The assumption is that once the system crosses the tipping point, the effects will cascade through various ecosystem components, usually with a fast response observed for primary production. The first step in this project is to analyze drone imagery to produce vegetation index maps from which primary production can be estimated. The results will contribute to understanding the effects of drought and overgrazing on forage provision and the potential to identify a desertification tipping point.

Contact Max Schmid

A) Competition for resources, plastic consumer traits, and the rise of diversity

Background: Species are confronted with resource variation within and between habitat patches, for instance when plants experience variation in nutrient composition on small and large spatial scales. Such resource heterogeneity could drive the evolution of diversity in consumers, such that multiple, specialized consumers coexist within the population. Resource specialization depends on so-called consumer traits that control the access to resources. For instance, the root length in plants controls at which soil depths nutrients and water could be exploited. Many consumer traits, however, are plastic and their morphology is not only determined genetically, but also changes with the environment. Plant roots, for instance, grow differently in dry or humid soils. Such phenotypic plasticity is well known to change the course of evolution, but it is less well understood how resource variation drives diversity in consumers when consumer traits are plastic.

Aims and Methods: This Master project aims to better understand how locally and spatially varying resources drive diversity in consumers when consumer traits are plastic. To explore this question, you will build computational models (i.e. individual-based simulations) or mathematical models. Eventually, you will compare your findings to real-world data from the plant ecology group. This should help understand fundamental processes causing biodiversity, while merging ecological and evolutionary processes.

What you should know: For this project, it would be beneficial if you are familiar with basic elements of programming (e.g., in R or Julia) or with mathematical modelling in ecology and evolution. Ideally, you are fascinated by fundamental ecological and evolutionary processes that control the rise and fall of biodiversity.

There is no specific time constraint and you could start at any occasion. Importantly, you are welcome to contribute your own ideas and follow your own line of thoughts. It is also possible that you start a project from scratch, or in collaboration with another research group.

B) Annual plants with a seed bank: On the evolution of diversity in light of genetic architecture

Background: Biological diversity is one of the most fundamental topics in ecology and evolution. How biological diversity evolves and is maintained, however, is still subject of ongoing research. While we made substantial progress in our understanding of which processes favor biological diversity, we know much less on how the buildup of diversity depends on genetic mechanisms. For instance, we are currently investigating how environmental variation drives diversity when both seed germination and plant survival vary with the environment. Whether and how much this process depends on genetic properties, like genetic linkage, is not clear at this point.

Aims and Methods: In this Master project, you will explore the evolution and maintenance of diversity when seed germination and plant survival is controlled by separate, but linked genetic traits. You will study this question by the use of individual-based simulations.

There is no specific time constraint and you could start at any occasion. Importantly, you are welcome to contribute your own ideas and follow your own line of thoughts. It is also possible that you start a project from scratch, or in collaboration with another research group. Importantly, you are explicitly welcome to contribute your own ideas and follow your interests and preferred topics.

Contact Sara Tomiolo