Biology subjects

Wollrab, S.

Publications and source records attributed to Wollrab, S..

3 recordsLinked to original sources

bioRxiv2025

Resource competition between buoyancy-regulating and sinking phytoplankton species along a stratified water column

In temperate lakes plankton dynamics are closely linked to seasonal shifts in water stratification, following air temperature. The onset of summer stratification typically coincides with spring bloom for-mation of algae in the well mixed surface layer (epilimnion). However, extended stratification periods lead to nutrient depletion and increases the risk of algae to sink out of the sunlit epilimnion. Planktonic primary producers have evolved different traits to counteract sinking, such as specific morphological shapes, but also adaptive mechanisms like active buoyancy regulation. The latter is very common for cyanobacteria and gives them a competitive advantage over sinking taxa specifically during extended stratified periods. Existing conceptual models on plankton phenology neglect the vertical dimension of plankton bloom formation, focusing mainly on epilimnion blooms. This limits projections of how changes in stratification through global warming will affect plankton composition, productivity, and water quality. Here we develop a theoretical framework to investigate resource competition between a passively sinking (S) and a buoyancy-regulating (BR) phytoplankton species along a one-dimensional water column. The BR species adaptively moves towards optimal light and nutrient availability along the water column. Our results indicate that coexistence between BR and S algae is critically dependent on differences in resource-use efficiencies, which can lead to situations of competitive exclusion but also coexistence in overlapping or vertically separated depths. Our results highlight the importance of vertical movement strategies in structuring phytoplankton communities and its consideration for projections on plankton phenology, com-position and lake primary production under changing stratification regimes.

ecology↗

bioRxiv2023

Synergistic effects of predation and parasitism on competition between edible and inedible phytoplankton

Fungi can affect aquatic ecosystems through syntrophic and parasitic interactions with other organisms and organic matter. In pelagic systems, fungal parasites on phytoplankton can control trophic interactions and food-web dynamics, e.g., zooplankton grazing on fungal parasite zoospores creates an alternative energy pathway (termed "mycoloop") from otherwise inedible phytoplankton species. We aim to investigate how the mycoloop influences community dynamics in aquatic food-webs combining experimental and modelling approaches. We assembled an experimental system consisting of an inedible (host) phytoplankton species and its parasitic chytrid, an edible (non-host) phytoplankton species, and a zooplankton grazer. Chytrids parasitizing increased edible phytoplankton abundance, while zooplankton grazing decreased edible phytoplankton abundance. In the presence of zooplankton and chytrids, competition effects between edible and inedible phytoplankton species depended on nutrient levels. At high nutrient levels, competition was balanced by an indirect positive chytrid effect and negative zooplankton grazing effects on edible phytoplankton. In contrast, at low nutrient levels, we found chytrid had a negative impact on edible phytoplankton synergistically with zooplankton. Mathematical investigations suggest that the synergistic effect can be caused by the mycoloop. This indicates that the mycoloop substantially affects predator-prey interactions and phytoplankton competition with yet unknown ecological consequences.

ecology↗

bioRxiv2022

From microbes to mammals: pond biodiversity homogenization across different land-use types in an agricultural landscape

Local biodiversity patterns are expected to strongly reflect variation in topography, land use, dispersal boundaries, nutrient supplies, contaminant spread, management practices and other anthropogenic influences. In contrast, studies focusing on specific taxa revealed a biodiversity homogenization effect in areas subjected to long-term intensive industrial agriculture. We investigated whether land use affects biodiversity and metacommunity structure in 67 kettle holes (KH) representing small aquatic islands embedded in the patchwork matrix of a largely agricultural landscape comprising grassland, forest, and arable fields. These KH, similar to millions of standing water bodies of glacial origin, spread across northern Europe, Asia, and North America, are physico-chemically diverse, differ in the degree of coupling with their surroundings. We assessed biodiversity patterns of eukaryotes, Bacteria and Archaea in relation to environmental features of the KH, using deep-amplicon-sequencing of eDNA. First, we asked whether deep sequencing of eDNA provides a representative picture of KH biodiversity across the three domains of life. Second, we investigated if and to what extent KH biodiversity is influenced by the surrounding land-use. Our data shows that deep eDNA amplicon sequencing is useful for in-depth assessments of cross-domain biodiversity comprising both micro- and macro-organisms, but, has limitations with respect to single-taxa conservation studies. Using this broad method, we show that sediment eDNA, integrating several years to decades, depicts the history of agricultural land-use intensification. The latter, coupled with landscape wide nutrient enrichment (including by atmospheric deposition), groundwater connectivity between KH and organismal movement in the tight network of ponds, resulted in a biodiversity homogenization in the KH water, levelling off todays detectable differences in KH biodiversity between land-use types.

ecology↗