Stability and dynamics of size-structured freshwater communities along environmental gradients

Dijoux, Samuel

dc.contributor.advisor	Boukal, David
dc.contributor.author	Dijoux, Samuel
dc.date.accessioned	2026-01-06T11:55:46Z
dc.date.available	2026-01-06T11:55:46Z
dc.date.issued	2023
dc.date.submitted	2023-05-23
dc.identifier.uri	https://dspace.jcu.cz/handle/20.500.14390/48693
dc.description.abstract	This thesis focuses on the dynamics and stability of size-structured communities in freshwater in response to environmental stressors. It reviews the influences of anthropogenic stressors on the stability, structure and diversity of freshwater communities, with a particular focus on the multiscale influences of rising temperature and nutrient enrichment. The three main chapters use recent advances in food web theory to explore the dynamics, stability and structure of communities under multiple threats (species invasions, nutrient enrichment and warming). The theoretical outcomes provide robust predictions for ecologists to link individual-level responses to global patterns observed at community scale. This thesis demonstrates the importance of considering species traits (body size, trophic position, performance of vital rates) and life histories to improve predictions on future responses to environmental stressors and to develop appropriate conservation measures.	cze
dc.format	190
dc.format	190
dc.language.iso	eng
dc.publisher	Jihočeská univerzita	cze
dc.rights	Bez omezení
dc.subject	warming; eutrophication; species invasions; food webs; freshwater communities; community dynamics; metabolic ecology; emergent Allee effect; body size; life history trait	cze
dc.subject	warming; eutrophication; species invasions; food webs; freshwater communities; community dynamics; metabolic ecology; emergent Allee effect; body size; life history trait	eng
dc.title	Stability and dynamics of size-structured freshwater communities along environmental gradients	cze
dc.title.alternative	Stability and dynamics of size-structured freshwater communities along environmental gradients	eng
dc.type	disertační práce	cze
dc.identifier.stag	48941
dc.description.abstract-translated	This thesis focuses on the dynamics and stability of size-structured communities in freshwater in response to environmental stressors. It reviews the influences of anthropogenic stressors on the stability, structure and diversity of freshwater communities, with a particular focus on the multiscale influences of rising temperature and nutrient enrichment. The three main chapters use recent advances in food web theory to explore the dynamics, stability and structure of communities under multiple threats (species invasions, nutrient enrichment and warming). The theoretical outcomes provide robust predictions for ecologists to link individual-level responses to global patterns observed at community scale. This thesis demonstrates the importance of considering species traits (body size, trophic position, performance of vital rates) and life histories to improve predictions on future responses to environmental stressors and to develop appropriate conservation measures.	eng
dc.date.accepted	2023-06-16
dc.description.department	Přírodovědecká fakulta	cze
dc.thesis.degree-discipline	Ecosystem Biology	cze
dc.thesis.degree-grantor	Jihočeská univerzita. Přírodovědecká fakulta	cze
dc.thesis.degree-name	Ph.D.
dc.thesis.degree-program	Biology	cze
dc.description.grade	Dokončená práce s úspěšnou obhajobou	cze
dc.contributor.referee	Diehl, Sebastian
dc.contributor.referee	Gaedke, Ursula
dc.description.defence	<p>Představení uchazeče školitelem doc. Boukalem.</p> <p>Představení disertace uchazečem ve 30 min.</p> <p><strong>Oponentské posudky a diskuze:</strong></p> <p>Opponent’s evaluation by Prof. Ursula Gaedke – a brief summary of the candidate’s thesis. Questions: Under which conditions is the value of the feeding efficiency at 0.85 legitimate? If this value is higher that it should be, what would be the consequences? What does “cost” imply? Is it in your equation? Is “lost” proportional to biomass in your equation? In your diagram, “lost” is proportional to ingestion and digestion. For what type of animal is that appropriate? How could this apply to ectotherm and endotherm animals? What does an inverted pyramid imply for your results? With lower efficiency and higher respiration rate, would you still have a high biomass at the top of the pyramid? Is the model robust?</p> <p> </p> <p>Opponent’s evaluation by Prof. Sebastian Diehl – a brief summary of the candidate’s thesis. Questions: What are the strengths of your approach? What are the benefits of taking such a theoretical approach? What can we, ecologists, learn from this theoretical approach, without empirical data? I have doubts concerning the fact that you did not consider the carrying capacity as temperature independent; you might want to address that in the revision of your paper. I would suggest removing the temperature dependence from the equation to see what happens. The fact that a lot of information is in appendix can make the paper difficult to read as a lot of information are missing in the main text. The way you set the parameters in your model always gives the advantage to the smaller individuals. You could do change the rules in your model and see what the outcome is. You are suggesting that fish would equally feed on prey from two habitats, but I think that fish may leave the unproductive habitat. Concerning your final paper, you made the assumption of temperature dependency for the consumers, which you did not in other chapters. Why did you not apply it for the top predator? Why does adding the temperature dependency to the predator trait lead to an asymmetrical effect to the left of the optimal temperature?</p> <p> </p> <p><strong>Otázky členů komise: </strong></p> <p>Prof. Ursula Gaedke: Do you think your work could be extrapolated to marine or terrestrial systems? Which assumptions would not hold in the case of terrestrial system? Is an inverted pyramid confirmed by empirical data?</p> <p>Dr. Ludek Berec: The committee member commented on the introduction that he found oversimplified. He also expressed his doubts on the fact that a competition hypothesis cannot explain everything. Question: Why did you use Type 2 functional response in your models? How can your models be generalized to complex food webs?</p> <p>Dr. Petr Blabolil: Your nutrient levels are based on work developed in the past. New ones have been developed by now, and you might want to look into it.</p> <p>Dr. Julien Mocq: Can a decrease in food quality be considered in your models? And how global warming may affect this?</p> <p>Dr. Jana Jersáková: Do the outcomes of your models align with empirical data?</p> <p>Prof. Sebastian Diehl: Can you explain how does the emergent Allee effect work? How can the predator still be maintained if the prey density is lower?</p> <p> </p> <p><strong>Hodnocení:</strong> Student prokázal schopnost vědecké práce a uspokojivě zvládl odpovědět na otázky.</p> <p><strong>Hlasování:</strong> Počet hlasů 6, prospěl 6x, neprospěl 0x</p>	cze