A5: Drivers of long-term population dynamics of plant species along the shore of Lake Constance

Mark van Kleunen

State of the art

The hydrology and nutrient availability in lake-shore habitats are strongly influenced by the water level and nutrient content of the lake. These lake-shore habitats in turn regulate the run-off of water, organic matter and nutrients into the lake, and thus are an important component of lake ecosystems (N. G. Hairston and Fussmann 2014). Annual water-level fluctuations, flooding regimes, nutrient deposition and land-use regimes in the Lake Constance ecosystem have strongly changed in the last century. These extrinsic environmental changes – in interaction with intrinsic species traits – may have modified important interactions among species, demography and genetics, and consequently are likely to be responsible for changes in regional distribution and local abundance of species. Indeed, not only the aquatic but also the terrestrial vegetation of the Lake Constance ecosystem has changed considerably during the last century (Peintinger 2012; Strang et al. 2012). While some species have responded by population declines, others have shown resilience and remained stable or have even increased. Furthermore, some species that have declined or increased in the past have returned to historical levels, and thereby showed reversibility. Although there is a strong interest in determinants of decline and increase of both native and alien species (van Kleunen and Richardson 2007), still little is known about the exact drivers of these different dynamics. Such information, however, is crucial to predict responses of plants to ongoing environmental change, and to develop management strategies.

Preparatory work

The PI did his PhD research on Ranunculus reptans, a species that in Central Europe has its major distribution along the shore of Lake Constance. He studied population genetics, evolutionary change and ecological responses of this endangered species to competition and flooding. The PI is thus well experienced with the lake shore habitat. The PI’s current work focusses largely on what drives the success and failure of exotic plant species (e.g. van Kleunen et al. 2015). Here, he uses a multi-species comparative approach (van Kleunen et al. 2014), which will also be fundamental to the proposed project focussing on drivers of long-term dynamics in the distribution and population sizes of plants in lake-shore habitats. The project will take advantage of two unique data sets; one for the entire Untersee region and one for the Wollmatinger Ried nature reserve. More than 100 years ago, Baumann (1911) published detailed plant inventories of the Untersee region, which provide a unique baseline data set to which we can compare the current occurrence of plant species in the Untersee region. As part of a project celebrating the 100th year anniversary of Baumann’s work, some of the plant inventories have been recently repeated (Peintinger 2012; Strang et al. 2012). The second data set that will be used is from a long-term (40 years) plant monitoring program in the Wollmatinger Ried, the largest nature reserve along Lake Constance. This dataset provides unique data on population dynamics of c. 60 rare plant species. Both the Baumann data set and the Wollmatinger Ried data set can be used in the proposed project through established collaborations with Dr Markus Peintinger and the NABU Naturschutzzentrum Wollmatinger Ried, respectively.

Proposed project and role within the RTG

The aim of this project is to test which extrinsic environmental factors and which intrinsic species characteristics drive the long-term population dynamics of plant species along Lake Constance. The two datasets described above are the basis for the project. For the Baumann data set, we will do further plant inventories to improve the data on the current distribution of plant species in the Untersee region. For species in both data sets, we will compile data on important traits from BiolFlor (http://www.biolflor.de/) and other databases. For the Baumann dataset, we will use GIS data on environmental variables to assess extrinsic environmental variables that might have caused changes in the distribution of species. For the Wollmatinger Ried data set, we will use long-term data on water levels (flooding events), climatic data and data on management to assess the extrinsic variables that might have driven the population dynamics. In addition, we will select declining, stable (resilient) and increasing species for garden experiments in which we assess their competitive abilities, water-use efficiencies and nutrient-uptake efficiencies. Furthermore, we will do molecular marker (AFLP or micro satellites) studies on these species to assess the importance of genetic drift and inbreeding for changes in population size.

By focusing on terrestrial plants and shore habitats – an important part of lake ecosystems – the project will contribute to a comprehensive assessment of lake ecosystems under changing conditions. The proposed project on lake-shore plants will directly link to project A4 on spatiotemporal changes in phytoplankton and macrophyte distributions, as we will use some of the same data sources. For studies on water-use efficiency and nutrient uptake dynamics of the species, which will require the analysis of stable isotopes, we will collaborate with C3. For the molecular marker study, we will collaborate with A1 and A2.