Universität zu Köln

Martínez Rendón, Ana Cristina (2025). Exploring Microbial Dynamics: Cercozoan Algivory in Polar Biocrusts. PhD thesis, Universität zu Köln.

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Abstract

Biological soil crusts (hereafter biocrusts) dominate polar landscapes, where cyanobacteria and microalgae drive primary production in the absence of higher plants. However, the structure and functioning of biocrust food webs remain poorly understood, particularly regarding microbial predators that regulate algal populations and influence nutrient cycling. This study investigated the role of cercozoans as algivorous predators in polar biocrusts, combining network analyses, trait-based approaches, and experimental validation to assess their trophic interactions. Using FlashWeave and HMSC, we inferred microbial interaction networks, revealing consistent predator-prey associations between cercozoans and microalgae across distinct polar regions. While FlashWeave enabled high-throughput detection of putative interactions, HMSC incorporated environmental covariates and hierarchical dependencies, refining our understanding of species co-occurrence and co-abundance patterns. FlashWeave and the trait-based approach revealed that only 4.7 to 9.3% of these correlations linked cercozoans to suitable algal prey. HMSC yielded similar numbers, with 7.5% found with co-occurrence and 4.8% with co-abundance networks. These network-based predictions were experimentally tested through co-culture feeding assays, which confirmed predation in 82% of tested interactions. Collectively, these results highlight the value of network analyses for inferring predator-prey interactions while underscoring the need for cautious interpretation of microbial association patterns. They also reinforce the importance of integrating trait-based approaches to enhance the accuracy and reliability of predicted biological interactions. Beyond direct predation, cercozoans likely contribute to nutrient cycling, facilitating carbon and nitrogen fluxes through microbial food webs. However, their predatory roles might be shaped by prey defences, resource availability, and competitive interactions with other microbial grazers, underscoring the complexity of biocrust trophic networks. While our findings establish cercozoans as key microalgal consumers, further research is needed to quantify their in situ ecological impact and interactions with other biotic and abiotic factors. This study provides critical insights into microbial predator-prey dynamics in polar soils, laying the foundation for future research on microbial food webs in extreme environments. By integrating network ecology, trait-based functional classification, and experimental approaches, we contribute to a broader understanding of microbial community structuring and the ecological significance of protistan predation in terrestrial ecosystems.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Martínez Rendón, Ana Cristina UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-782437
Date:	2025
Place of Publication:	Cologne
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Biology > Zoologisches Institut
Subjects:	Natural sciences and mathematics Life sciences
Uncontrolled Keywords:	Keywords Language Cross-kingdom network analyses UNSPECIFIED Trait-based ecology UNSPECIFIED Predator-prey interactions UNSPECIFIED Biocrusts UNSPECIFIED Microbial ecology UNSPECIFIED Microbial communities UNSPECIFIED Experimental validation UNSPECIFIED
Date of oral exam:	25 April 2025
Referee:	Name Academic Title Dumack, Kenneth Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/78243