Universität zu Köln

Titocci, Jessica ORCID: 0000-0001-9157-1578 (2023). Phytoplankton-zooplankton interactions in the context of biodiversity loss: a trait-based perspective. PhD thesis, Universität zu Köln.

PDF (Doctoral Thesis) PhD_thesis_Titocci_1.pdf - Accepted Version Download (3MB)

Abstract

Freshwater biodiversity is increasingly threatened by human activities and environmental changes, which have already caused severe declines in the range and abundance of many freshwater organisms. Since ecosystem functioning is highly dependent on biodiversity, both in terms of the distribution and abundance of organisms present in the ecosystem and, even more so, in terms of their functional characteristics, it has become increasingly urgent and necessary to investigate the impact that changes in biodiversity can have on the ecological functioning of aquatic systems. Although a large number of studies have already investigated and described the role of diversity and the consequences of diversity loss using taxonomic-based biodiversity metrics, this has resulted in an insufficient explanatory power, and the implementation of realistic loss scenarios and the identification of mechanisms underlying the relationship between biodiversity and ecosystem functioning remain challenging. In this context, the field of biodiversity-ecosystem functioning (BEF) studies is increasingly adopting a trait-based perspective. Monitoring functional traits and trait variability allows to determine the nature and strength of species interactions and the community responses and organisation to changes. By looking at their underlying mechanisms, we can better understand the role of biodiversity in maintaining multiple ecosystem functions and processes. Because phytoplankton are at the base of aquatic food webs and are of immense importance for global-scale processes such as oxygen and primary production, biodiversity loss at the level of primary producers has attracted particular interest among researchers, who aim to gain a better understanding of how phytoplankton species loss and functions are likely to affect trophic structure, community trait dynamics and ecosystem processes under future loss scenarios. By feeding on phytoplankton, herbivorous zooplankton is an important link in the transfer of energy, from basal resources to consumers higher in the food web. In these predator-prey interactions, effects go both ways, with phytoplankton taxonomic and functional diversity influencing and being influenced by zooplankton grazing. Thus, species and trait losses at the producer level may lead to shifts in phytoplankton composition and nutrient availability, which are thought to have cascading effects on herbivorous zooplankton abundances, composition and population dynamics, but it is not yet possible to predict the impact and direction of these changes, nor the consequences. By combining taxonomic and trait-based approaches with experimental manipulations of phytoplankton diversity, my goal was to examine how the loss of phytoplankton species and trait diversity could affect phytoplankton-zooplankton interactions and their trait-related dynamics. Firstly, I investigated the role of phytoplankton trait diversity, examined in terms of biochemical characteristics (fatty acids) of algal food on the functional responses of the calanoid copepod Eudiaptomus sp., demonstrating how phytoplankton trait diversity is an important regulatory mechanism for the fitness, growth, reproduction, and survival of zooplankton and that key dietary contrasts, can shape adaptive evolution in consumers that seek to convert some missing dietary fatty acids through metabolic bioaccumulation and bioconversion mechanisms to maximize fitness and individual survival and growth. Secondly, I performed diversity manipulation experiments using size-fractionation and disturbance methods on natural phytoplankton assemblages to provide reliable simulations of phytoplankton-zooplankton trophic interactions and their consequences under changes or loss of phytoplankton trait-diversity. Specifically, I investigated how changes in phytoplankton morphological and biochemical trait diversity might affect different herbivorous zooplankton functional groups, cladocerans and calanoid copepods, represented by Daphnia longispina and Eudiaptomus graciloides, respectively. Alterations in phytoplankton morphological diversity revealed differences in phytoplankton morpho-functional traits and taxonomic composition in size-fractionated communities but did not significantly affect grazing of generalist unselective filter-feeders Daphnia longispina and selective feeders Eudiaptomus graciloides, in terms of grazing rates and size selectivity. On the contrary, alteration of phytoplankton functional diversity induced by the disturbance method allowed species losses and taxonomic shifts, resulting in the formation of distinct communities with different taxonomic and biochemical characteristics, which differentially affected the fitness, life history traits and lipid composition of both grazers, mainly depending on the differences in the grazers' feeding habits and their nutritional requirements. Overall, combining taxonomy and trait-based approaches have provided a more comprehensive evaluation and understanding of ecological dynamics in phytoplankton-zooplankton interactions. Furthermore, the results obtained from the manipulation of the diversity of natural phytoplankton communities highlighted the importance of conducting similar experimental studies to deeply understand the mechanistic background as well as the potential impacts of biodiversity loss between phytoplankton and zooplankton, and thus more generally, in food web dynamics in aquatic ecosystems.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Titocci, Jessica titoccij@gmail.com orcid.org/0000-0001-9157-1578 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-714846
Date:	3 August 2023
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
Uncontrolled Keywords:	Keywords Language phytoplankton-zooplankton interactions English trait-based approach English biodiversity loss English
Date of oral exam:	3 August 2023
Referee:	Name Academic Title Fink, Patrick PD. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/71484