DynaCom (Sp 1)
Daniela Meißner, Angelika Hansel
Vanessa Minden, Gerhard Zotz
Plants form the resource base of terrestrial food webs and understanding the dynamics of plant communities is therefore a highly relevant part for a food web study at large. Our main goal is to establish a trait-based approach to capture the spatiotemporal dynamics of plant meta-communities. We focus mostly on dispersal and competition processes in spatially interacting plant populations using a tightly integrated modelling and empirical approach. In particular, we will investigate the combined effects of plant dispersal and resource competition on the spatial structure and biodiversity patterns of plant metacommunities in a spatially heterogeneous environment.
The traits of dispersed plant species strongly affect the community assembly and sorting along heterogeneous environments where resource distributions differ among patches. Looking into dispersal processes within the salt marsh and on the experimental islands helps to identify which relevant trait combinations of salt marsh plant species determine their success under limited and unlimited dispersal. The experimental islands built on the mudflats at the distance of approximately 400 m from the natural salt marsh, thereby enable us to study the effect of dispersal on the community development
Experimental islands were built in 2014 on the mudflats near the island of Spiekeroog in the Wadden Sea. Each island has three elevations that represent the vegetation zones in the natural saltmarshes – pioneer zone, lower and upper salt marsh. Islands were lined with geotextile to hold the sediment and with plastic foil to maintain the ground water levels typical for natural salt marshes. A detailed description of the experimental set up is presented in Balke et al. 2017.
Dispersal limitation of species that are strong competitors may shift community assembly processes. Species with high dispersal abilities will dominate at first. By using theoretical and empirical approaches, we will be able to follow the development on plant communities over time and space, and analyse changes in traits along gradients of inundation, salinity, groundwater depth.
Experimental set up included a bare treatment were areas were left bare to allow for initial spontaneous colonisation. Left: an initially bare experimental island at lower salt marsh elevation after three years of vegetation development. Right: initially bare lower salt marsh plot after three years of vegetation development.
A central filter in plant metacommunity dynamics is a strong competitive effect – a species ability to reduce the performance of other species. Competitive effect and response (ability to perform in the presence of competitors) come along with differences in correlated traits that characterize the phenotype. Growth reduction is described by a competition kernel, which shows how competitive strength varies with phenotypic distance between superior and inferior species. We will use the trait perspective to study the competition mechanisms and effects of competition on the assembly of local communities.
We aim to understand the relevance of competition compared to stabilizing niche differences, i.e. species ability to use the environment in different ways that enables them to coexist. Along an environmental gradient, species sorting is assumed to depend on the fundamental niche requirements towards the extreme end of the gradient, whereas competition should determine species sorting towards the benign end of the gradient. By developing and analysing theoretical models of plant metacommunities, we will investigate the effects of these two processes on species coexistence, and on the trait distribution patterns along the resource or stress gradients.
Salt marsh gradients provide an ideal study system for understanding the distribution patterns of plant traits along different environmental gradients. We will study the role of competition and stabilizing niche differences in the pattern formation.
A recent model study of coexistence mechanisms in competitive metacommunities showed that species distributions in general are determined by the combined effect of species traits, local environmental conditions and connectivity among localities. One convenient way to reduce this complexity is to restrict the analysis from general habitat networks to spatial gradients, in which an environmental state E varies continuously along a one-dimensional spatial coordinate, E(x).
Sketch of a trait-based metacommunity model. Species are described by a quantitative trait z and live on a spatial gradient with coordinate x. Growth rates are determined by the vertical distances of trait values to the environmental cline E(x) and interspecific interactions by the pairwise vertical distances, z-z’, of species traits. Dispersal acts to displace organisms horizontally.
By using the metacommunity framework and by allowing plant dispersal in spatial environmental gradients, we will elucidate the influences of plant dispersal and competition for resources that are essential for plant growth, trait and environmental variabilities on the trait distributions of plants, and on the coexistence and diversity patterns of the metacommunity at different spatial scales. Potential theoretical models will be tested by using the empirical data, and validated models will be used to predict the spatiotemporal dynamics of the salt marsh plant communities.
Vegetation development has been monitored since the beginning of the experiment in 2014. In addition to traditional methods like frequency sampling on permanent plots (left), we will be developing non-destructive methods for trait determination. We will be creating a library of hyperspectral measurements and 3d images for most important salt marsh species, for example Salicornia europea (middle) and Limonium vulgare (right).
With another experimental setup, where lower salt marsh plant communities were transplanted to different elevations we can follow how environmental changes will affect ecosystem dynamics. The time lag between environmental change and changes in plant communities depends on the persistence of transplanted species as well as the colonisation and competitive abilities of species that could be better adapted to new conditions