Institute of Evolution and Ecology (EvE)

Upcoming theses (MSc and BSc) opportunities starting in 2021

Here you will find a description and further details for each of the proposed theses themes.


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-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.

E) 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).

F) Evolution of invasive plants over time (responsible: Dr. Jinlong Wang)

Greenhouse work: May – September

Background: The success of invasive plants has been attributed to their escape from natural enemies (herbivores and pathogens) and subsequent evolutionary changes. The evolution of increased competitive ability hypothesis (EICA) predicts that the reduced herbivory is hypothesized to allow invasive plants to shift their allocation of resources from defence towards growth or reproduction, resulting in the evolution of increased competitive ability. However, native enemies can accumulate on invasive plants over time, because they can gradually adapt to these new introduced species. Hence, the evolutionary responses predicted by the EICA hypothesis should be reversed over time.

Methods: Here, in order to examine this hypothesis, we plan to use the invasive plant Senecio inaequidens (South African ragwort, Asteraceae) as our model plant and conduct common garden experiments from the end of May to the end of August 2021. We will compare multiple defence-related traits (e.g. trichome density and leaf toughness) and growth and reproduction ability from Senecio inaequidens populations across its invasion chronosequence (about 120 years) in Europe. The results shall contribute to revealing the evolutionary potential of resource allocation in invasive plants from a new perspective.


Contact Maja Majekova

­A) Plants traits as determinants of species vulnerability to global change in the South African Cape Floristic Region

Master project; start any time in 2021

Background: The South African Cape Floristic Region is one of six global biodiversity hotspots in Africa. Sugarbushes (Proteaceae) play a key role for ecosystem functioning (e.g. water provisioning, pollinator diversity) in this region and represent national flagship species for nature conservation. They are expected to be particularly vulnerable to climate change, increased frequencies of wildfire, land use change and biological invasions.

Aim and Methods: The project aims at understanding threats to functional plant diversity by trait-based aggregation of species-specific predictions of vulnerability to environmental change. The combined analyses of functional trait data and simulated population viability will identify sub-regions where sugarbushes are particularly threatened and provide a trait-based understanding of species’ vulnerability to multiple drivers of environmental change. These results will also contribute to ongoing broader stakeholder initiatives on biodiversity risk assessments and conservation prioritization.

What you should know: We are searching for a highly motivated candidate with a good knowledge of statistical analyses in R or a high motivation to learn and a strong scientific interest in both theoretical and community exology and applied global change biology.

Please contact maria.majekovaspam prevention@uni-tuebingen.de or joern.pagelspam prevention@uni-hohenheim.de if you are interested or have any further questions.

 

B) Asynchrony and stability of winter annual communities along a steep environmental gradient in the Eastern Mediterranean Basin

Master project; start any time, no field work involved, good command of R required

Background: What determines stability of populations and communities remains one of the most debated questions in both theoretical and applied ecology. An important factor affecting the stability of communities over time is the degree of synchrony in fluctuations of individual species populations that coexist within a community.

Aim and Methods: Here we will investigate the crucial question whether deviations from perfect synchrony (asynchrony) lead to more stable communities. For this, we will use a long-term dataset on winter annuals assembled along a steep gradient of aridity and intensity of environmental fluctuations in the Eastern Mediterranean Basin in Israel. The dataset encompasses four sites (arid, semi-arid, Mediterranean and mesic-Mediterranean) and climate change manipulations (increased drought and increased precipitation) within two of them.

What you should know: You should have a good command of R to handle the big dataset (packages tidyr, dplyr, ggplot2). You can start any time, and duration will depend on your speed in handling the data. There is no field work involved, but as a member of our Plant Ecology group, you are welcome to sniff into empirical projects, too.


Contact Sara Heshmati

A) Land degradation assessment using residual trend analysis in Namibia

Dryland ecosystems cover a large share of the world’s terrestrial surface. Deficiency and spatio-temporal variability of precipitation as well as low vegetation growth rates make dry rangelands prone to degradation, especially under changing climate and intensified land use. Drivers of aboveground net primary productivity (ANPP) in drylands are manifold but it is generally believed that precipitation is the main factor. The best correlation between ANPP and precipitation ascends to ANPP and lagging precipitation. Precipitation is not directly available to plants but is partitioned into run off, evapotranspiration, soil moisture and ground water recharge. Therefore, soil moisture might be a better indicator of the increased ANPP. Within this study we want to find which factor is more correlated with ANPP, precipitation or soil moisture? RESTREND method give us an opportunity to reveals the proportion of ANPP change is not due to climate variability by analysing the residuals from ANPP-precipitation or ANPP-soil moisture regression model over time. To do this study you need to have a good command of R and ArcGIS or QGIS.

(Starting day is flexible, MSC thesis in English.)

If you are interested in a topic and you don’t have a knowledge of ArcGIS or QGIS, I could teach you ArcGIS to the point to be able to do this project.