Community assembly processes of intertidal salt marsh microarthropods
by Md Ekramul Haque
Date of Examination:2025-11-17
Date of issue:2025-12-01
Advisor:Prof. Dr. Stefan Scheu
Referee:Prof. Dr. Stefan Scheu
Referee:Prof. Dr. Christoph Bleidorn
Persistent Address:
http://dx.doi.org/10.53846/goediss-11660
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Description:Doctoral dissertation
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Abstract
English
Salt marshes are highly dynamic ecosystems at the land–sea interface, shaped by steep environmental gradients and frequent disturbances. They provide critical ecosystem services, including coastal protection, nutrient cycling and biodiversity maintenance, while also serving as natural laboratories for studying how dispersal, environmental filtering and competitive interactions structure ecological communities. Among the diverse organisms inhabiting these systems, microarthropods such as Collembola, Oribatida and Mesostigmata are both abundant and ecologically important, contributing to decomposition, nutrient cycling and food-web regulation. Despite their ubiquity and functional importance, the mechanisms underlying their colonization, persistence and assembly in intertidal salt marshes remain poorly understood. Ecological theory emphasizes two broad categories of processes in community assembly: deterministic and stochastic. Deterministic forces, including environmental filtering and competitive interactions, predictably structure communities along abiotic gradients such as tidal inundation or salinity. By contrast, stochastic forces such as dispersal limitation, ecological drift and historical contingency introduce randomness into community formation. The relative importance of these processes often depends on spatial scale, disturbance frequency and habitat connectivity. In salt marshes, where tidal regimes and geographic isolation constrain colonization opportunities, both deterministic and stochastic influences are strong. This thesis investigates how dispersal, environmental gradients and functional adaptations structure salt marsh microarthropod communities in the Wadden Sea, Germany. Using experiments on natural shorelines and isolated artificial offshore islands, it explores colonization dynamics, trait-mediated persistence and the relative influence of deterministic versus stochastic assembly processes across taxa and spatial contexts. The first chapter examines colonization across tidal zones and offshore artificial islands, testing how dispersal distance, inundation frequency and body size influence community assembly. Results show that dispersal limitation and filtering due to inundation frequency differently affect Collembola, Oribatida and Mesostigmata, with Oribatida emerging as particularly poor and Mesostigmata as particularly effective colonizers. The second chapter adopts a trait-based perspective, harmonizing morphological and functional traits across taxa to evaluate whether analogous traits buffer species against extinction. Traits related to anchoring, buoyancy and hydrophobicity were shown to mitigate displacement and extinction under frequent inundation, revealing convergent strategies that stabilize communities despite phylogenetic differences. The third chapter focuses on predatory Mesostigmata, integrating phylogenetic and trait-based analyses to disentangle deterministic and stochastic influences across tidal inundation gradients and geographic isolation. The findings demonstrate that deterministic filters dominate in connected systems, while stochasticity prevails in isolated ones, underscoring the dual roles of dispersal and environmental stress in shaping intertidal predator communities. Collectively, these studies advance understanding of how dispersal, environmental filtering and functional traits interact to structure ecological communities in disturbance-prone environments. By combining colonization experiments, trait harmonization and phylogenetic analysis, this thesis contributes to theoretical ecology and trait-based community assembly research, while offering new insights into the resilience and vulnerability of salt marsh microarthropod communities under global change.
Keywords: Intertidal salt marsh; Community assembly processes; Microarthropods; Collembola; Oribatida; Mesostigmata; Community phylogeny; Functional traits
