Fatty acid accumulation in feeding types of a natural freshwater fish population

Fatty acids are widely used to study trophic interactions in food web assemblages. Generally, it is assumed that there is a very small modification of fatty acids from one trophic step to another, making them suitable as trophic biomarkers. However, recent literature provides evidence that many fishes possess genes encoding enzymes with a role in bioconversion, thus the capability for bioconversion might be more widespread than previously assumed. Nonetheless, empirical evidence for biosynthesis occurring in natural populations remains scarce. In this study, we investigated different feeding types of perch (Perca fluviatilis) that are specialized on specific resources with different levels of highly unsaturated fatty acids (HUFAs), and analyzed the change between HUFA proportions in perch muscle tissue compared to their resources. Perch showed matching levels to their resources for EPA, but ARA and especially DHA were accumulated. Compound-specific stable isotope analyses helped us to identify the origin of HUFA carbon. Our results suggest that perch obtain a substantial amount of DHA via bioconversion when feeding on DHA-poor benthic resources. Thus, our data indicate the capability of bioconversion of HUFAs in a natural freshwater fish population

Bottom-up and top-down regulation of heterogeneous lake food webs

Food webs are networks of organisms linked by trophic interactions that regulate the responses of ecosystems to environmental change. Such regulation is a result of the effects of resources on the abundance of their consumers (i.e. bottom-up effects) and/or the influence of consumers on the abundance of their resources (i.e. top-down effects). Lake food webs comprise pelagic and benthic production pathways and are largely affected by fluxes of resources from/to adjacent terrestrial ecosystems. These pathways are often coupled by mobile generalist consumers, potentially leading to indirect interactions among prey that arise when sharing a predator. In contrast, consumers can also undergo resource specialization that restricts their ability to couple resources at a given time. In this thesis, I observed that top-down control of predators on benthic and pelagic prey at increasing productivity was highly dependent on apparent mutualism that was driven by switching behaviour of generalist fish. That, in addition to bottom-up responses of benthic pathways at increasing productivity, had important consequences for the fluxes of energy and high quality polyunsaturated fatty acids (PUFAs) to terrestrial systems via insect emergence. I also found that PUFAs were highly regulated over the ontogeny of Eurasian perch (Perca fluviatilis). Mismatches with PUFA composition in prey may in turn affect resource specialization and the timing of ontogenetic diet shifts, altering the role of perch in the food web. Finally, browning, which is a phenomenon affecting many temperate and boreal lakes, did not affect bottom-up and top-down control in open-water lake food webs. Instead, browning affected prey selectivity, probably changing the pathways of energy transfer within the open-water food web. Overall, this thesis demonstrates that predictions of food web responses in lake ecosystems and their exports to adjacent terrestrial systems depend on the coupling of different pathways and subsequent indirect interactions among prey through shared predation. This could not be explained by classic food chain theory, but rather by a framework including resource coupling and resource specialization over the ontogeny of consumers. These observations must not be overlooked when constructing a comprehensive model of food webs across time and space

Bottom-up and top-down regulation of heterogeneous lake food webs

Food webs are networks of organisms linked by trophic interactions that regulate the responses of ecosystems to environmental change. Such regulation is a result of the effects of resources on the abundance of their consumers (i.e. bottom-up effects) and/or the influence of consumers on the abundance of their resources (i.e. top-down effects). Lake food webs comprise pelagic and benthic production pathways and are largely affected by fluxes of resources from/to adjacent terrestrial ecosystems. These pathways are often coupled by mobile generalist consumers, potentially leading to indirect interactions among prey that arise when sharing a predator. In contrast, consumers can also undergo resource specialization that restricts their ability to couple resources at a given time. In this thesis, I observed that top-down control of predators on benthic and pelagic prey at increasing productivity was highly dependent on apparent mutualism that was driven by switching behaviour of generalist fish. That, in addition to bottom-up responses of benthic pathways at increasing productivity, had important consequences for the fluxes of energy and high quality polyunsaturated fatty acids (PUFAs) to terrestrial systems via insect emergence. I also found that PUFAs were highly regulated over the ontogeny of Eurasian perch (Perca fluviatilis). Mismatches with PUFA composition in prey may in turn affect resource specialization and the timing of ontogenetic diet shifts, altering the role of perch in the food web. Finally, browning, which is a phenomenon affecting many temperate and boreal lakes, did not affect bottom-up and top-down control in open-water lake food webs. Instead, browning affected prey selectivity, probably changing the pathways of energy transfer within the open-water food web. Overall, this thesis demonstrates that predictions of food web responses in lake ecosystems and their exports to adjacent terrestrial systems depend on the coupling of different pathways and subsequent indirect interactions among prey through shared predation. This could not be explained by classic food chain theory, but rather by a framework including resource coupling and resource specialization over the ontogeny of consumers. These observations must not be overlooked when constructing a comprehensive model of food webs across time and space

Regulation of fatty acid composition related to ontogenetic changes and niche differentiation of a common aquatic consumer

Fatty acids (FAs) are key nutrients for fitness which take part in multiple physiological processes over the ontogeny of organisms. Yet, we lack evidence on how FA nutrition mediates life-history trade-offs and ontogenetic niche shifts in natural populations. In a field study, we analyzed ontogenetic changes in the FAs of Eurasian perch (Perca fluviatilis L.), a widespread fish that goes through ontogenetic niche shifts and can have high individual niche specialization. Diet explained most of the variation in the FA composition of perch dorsal muscle over early ontogeny (28%), while the total length explained 23%, suggesting that perch significantly regulated FA composition over early ontogeny. Condition explained 1% of the remaining variation. 18:3n-3 (ALA) and 18:4n-3 (SDA) indicated planktivory; 18:1n-7, benthivory; and 22:6n-3 (DHA), piscivory in perch diet. Conversely, perch regulated long-chained polyunsaturated fatty acids (PUFAs), such as 20:5n-3 (EPA), 20:4n-6 (ARA) and 22:6n-3 (DHA) over ontogeny, emphasizing the role of such FAs in early growth and sexual maturation. Adult perch increasingly retained 16:1n-7 and 18:1n-9 suggesting higher energy storage in older perch. Furthermore, differences in DHA availability in diet correlated with intra-cohort differences in perch growth, potentially hindering the overall use of benthic resources and promoting earlier shifts to piscivory in littoral habitats. Overall, this study indicates that in addition to diet, internal regulation may be more important for FA composition than previously thought. Differences between FA needs and FA availability may lead to life-history trade-offs that affect the ecology of consumers, including their niche

Short-term apparent mutualism drives responses of aquatic prey at increasing productivity

According to apparent competition theory, sharing a predator should cause indirect interactions among prey that can substantially influence food-web responses to environmental drivers. However, empirical evidence of apparent competition under ongoing environmental change is still scarce. In an 8-week mesocosm experiment, we found that short-term responses of aquatic food webs to increasing productivity were strongly regulated by apparent mutualism between benthic and pelagic prey in the presence of a generalist fish. Following trends in natural systems, increasing productivity in our mesocosms favored the relative abundance of benthic prey. This elicited a shift in fish selectivity from pelagic to benthic prey driven by fish switching behavior which resulted in lower and delayed top-down control on pelagic prey. Our results highlight that apparent competition theory may explain food-web responses across environmental gradients, whereby resulting prey dynamics and stability may highly depend on the foraging behavior exhibited by generalist predators

Intraspecific differences in metabolic rates shape carbon stable isotope trophic discrimination factors of muscle tissue in the common teleost Eurasian perch (Perca fluviatilis)

1. Stable isotopes represent a unique approach to provide insights into the ecology of organisms. delta C-13 and delta N-15 have specifically been used to obtain information on the trophic ecology and food-web interactions. Trophic discrimination factors (TDF, Delta C-13 and Delta N-15) describe the isotopic fractionation occurring from diet to consumer tissue, and these factors are critical for obtaining precise estimates within any application of delta C-13 and delta N-15 values. It is widely acknowledged that metabolism influences TDF, being responsible for different TDF between tissues of variable metabolic activity (e.g., liver vs. muscle tissue) or species body size (small vs. large). However, the connection between the variation of metabolism occurring within a single species during its ontogeny and TDF has rarely been considered. 2. Here, we conducted a 9-month feeding experiment to report Delta C-13 and Delta N-15 of muscle and liver tissues for several weight classes of Eurasian perch (Perca fluviatilis), a widespread teleost often studied using stable isotopes, but without established TDF for feeding on a natural diet. In addition, we assessed the relationship between the standard metabolic rate (SMR) and TDF by measuring the oxygen consumption of the individuals. 3. Our results showed a significant negative relationship of SMR with Delta C-13, and a significant positive relationship of SMR with Delta N-15 of muscle tissue, but not with TDF of liver tissue. SMR varies inversely with size, which translated into a significantly different TDF of muscle tissue between size classes. 4. In summary, our results emphasize the role of metabolism in shaping-specific TDF (i.e., Delta C-13 and Delta N-15 of muscle tissue) and especially highlight the substantial differences between individuals of different ontogenetic stages within a species. Our findings thus have direct implications for the use of stable isotope data and the applications of stable isotopes in food-web studies

Climate warming and heat waves alter harmful cyanobacterial blooms along the benthic-\u80\u93pelagic interface

In addition to a rise in mean air and water temperatures, more frequent and intense extreme climate events (such as heat waves) have been recorded around the globe during the past decades. These environmental changes are projected to intensify further in the future, and we still know little about how they will affect ecological processes driving harmful cyanobacterial bloom formation. Therefore, we conducted a long-term experiment in 400-L shallow freshwater mesocosms, where we evaluated the effects of a constant +4°C increase in mean water temperatures and compared it with a fluctuating warming scenario ranging from 0 to +8°C (i.e., including heat waves) but with the same +4°C long-term elevation in mean water temperatures. We focused on investigating not only warming effects on cyanobacterial pelagic dynamics (phenology and biomass levels), but also on their recruitment from sedimentsâ\u80\u94which are a fundamental part of their life history for which the response to warming remains largely unexplored. Our results demonstrate that (1) a warmer environment not only induces a seasonal advancement and boosts biomass levels of specific cyanobacterial species in the pelagic environment, but also increases their recruitment rates from the sediments, and (2) these species-specific benthic and pelagic processes respond differently depending on whether climate warming is expressed only as an increase in mean water temperatures or, in addition, through an increased warming variability (including heat waves). These results are important because they show, for the first time, that climate warming can affect cyanobacterial dynamics at different life-history stages, all the way from benthic recruitment up to their establishment in the pelagic community. Furthermore, it also highlights that both cyanobacterial benthic recruitment and pelagic biomass dynamics may be different as a result of changes in the variability of warming conditions. We argue that these findings are a critical first step to further our understanding of the relative importance of increased recruitment rates for harmful cyanobacterial bloom formation under different climate change scenarios

Guías didácticas de itinerarios del Parque Natural Cañón del río Lobos : Mirador de los Gullurías, Castillo de Ucero

Proyecto realizado por cuatro profesores de diferentes Institutos de Educación Secundaria de las provincias de Soria y Salamanca. Tiene como objetivos: -Elaborar materiales didácticos que faciliten la observación y el estudio de dos itinerarios del Parque Natural del 'Cañón del río Lobos'. -Fomentar el conocimiento, estima y cuidado de un espacio castellano-leonés, profundizando en el estudio del entorno natural y del patrimonio cultural. El desarrollo del trabajo sigue cada itinerario diferenciando tramos y paradas en función de los aspectos a observar y estudiar en cada una de las actividades que desarrollan contenidos interdisciplinares (geología, flora, fauna, vestigios históricos, cultura popular, etc). El sistema de trabajo seguido: reuniones, salidas y estudio individual. El contenido del estudio se distribuye en dos cuadernillos: 1) Guía didáctica 'El Mirador de las Gullurías'. 2) Guía didáctica 'El Castillo de Ucero'. Cada una de estas guías contiene: -Textos descriptivos de cada tramo de los itinerarios, indicando las actividades a realizar en cada momento. -Fichas de actividades. -Orientaciones didácticas y pautas a seguir en las recorridos. -Materiales complementarios: planos, claves, ilustraciones, tablas y diapositivas. El trabajo no ha sido publicado.Comunidad Autónoma de Castilla y León, Consejería de Educación y Cultura, Dirección General de EducaciónCastilla y LeónES

Life-history traits buffer against heat wave effects on predator-prey dynamics in zooplankton

In addition to an increase in mean temperature, extreme climatic events, such as heat waves, are predicted to increase in frequency and intensity with climate change, which are likely to affect organism interactions, seasonal succession, and resting stage recruitment patterns in terrestrial as well as in aquatic ecosystems. For example, freshwater zooplankton with different life-history strategies, such as sexual or parthenogenetic reproduction, may respond differently to increased mean temperatures and rapid temperature fluctuations. Therefore, we conducted a long-term (18 months) mesocosm experiment where we evaluated the effects of increased mean temperature (4°C) and an identical energy input but delivered through temperature fluctuations, i.e., as heat waves. We show that different rotifer prey species have specific temperature requirements and use limited and species-specific temperature windows for recruiting from the sediment. On the contrary, co-occurring predatory cyclopoid copepods recruit from adult or subadult resting stages and are therefore able to respond to short-term temperature fluctuations. Hence, these different life-history strategies affect the interactions between cyclopoid copepods and rotifers by reducing the risk of a temporal mismatch in predator-prey dynamics in a climate change scenario. Thus, we conclude that predatory cyclopoid copepods with long generation time are likely to benefit from heat waves since they rapidly "wake up" even at short temperature elevations and thereby suppress fast reproducing prey populations, such as rotifers. In a broader perspective, our findings suggest that differences in life-history traits will affect predator-prey interactions, and thereby alter community dynamics, in a future climate change scenario

Colored organic matter increases CO2 in meso-eutrophic lake water through altered light climate and acidity

Many surface waters across the boreal region are browning due to increased concentrations of colored allochthonous dissolved organic carbon (DOC). Browning may stimulate heterotrophic metabolism, may have a shading effect constraining primary production, and may acidify the water leading to decreased pH with a subsequent shift in the carbonate system. All these effects are expected to result in increased lake water carbon dioxide (CO2) concentrations. We tested here these expectations by assessing the effects of both altered allochthonous DOC input and light conditions through shading on lake water CO2 concentrations. We used two mesocosm experiments with water from the meso‐eutrophic Lake Erken, Sweden, to determine the relative importance of bacterial activities, primary production, and shifts in the carbonate system on CO2 concentrations. We found that DOC addition and shading resulted in a significant increase in partial pressure of CO2 (pCO2) in all mesocosms. Surprisingly, there was no relationship between bacterial activities and pCO2. Instead the experimental reduction of light by DOC and/or shading decreased the photosynthesis to respiration ratio leading to increased pCO2. Another driving force behind the observed pCO2 increase was a significant decrease in pH, caused by a decline in photosynthesis and the input of acidic DOC. Considering that colored allochthonous DOC may increase in a warmer and wetter climate, our results could also apply for whole lake ecosystems and pCO2 may increase in many lakes through a reduction in the rate of photosynthesis and decreased pH