Questioning the roles of resources nutritional quality in ecology

International audienceOur understanding of ecosystem functioning is strongly linked to the study ofpredator–prey relationships and food web structures. However, trophic ecology hasoften focused on identifying taxonomic relationships and quantifying the biomassor energy ingested by consumers, but has often failed to integrate the importanceof the nutritional quality of resources in ecological dynamics. Underlying this gap isthe multi-dimensional nature of resource quality which has hampered any consensuson the definition of resource nutritional quality. In this special issue, we aimed atgathering a subset of articles exemplifying the diversity of variables by which resourcesquality is quantified, the diversity of research topics that can be tackled in ecology– from physiological or evolutionary aspects to ecosystem processes – and proposesome perspectives on the integration of nutritional quality within broader ecologicalconcepts. Using a semi-automated literature analysis, we map the current landscapeof the ‘resources nutritional quality’ research of the last 30 years. We depict how ithas been quantified through physical, biological or chemical indicators, the use ofthese parameters being largely dependent on the type of ecosystem studied and on theinvestigated ecological process. We then position the articles published in this specialissue of Oikos within this landscape, showing they cover a small but relatively wellrepresentative subset of the domains of resources quality-related issues. Articles in thisspecial issue browse a range of individual and population-level approaches (embracingevolutionary questions) to community related questions, include methodologicalissues and ecosystem-wide approaches using trophic quality indicators as tracers ofresources origin. Based on these studies and on the literature review, we identify a nonexhaustivelist of challenges and perspectives of research that we consider of highestpriority in the large topic of trophic ecology

Investigating the origin of solutes in rock glacier springs in the Swiss Alps: A conceptual model

In the current context of climate change, rock glaciers represent potentially important water resources due to the melting of ice they contain and/or their role as high mountain water reservoirs. However, the hydrology of these high-altitude debris accumulations is poorly known. Understanding the origin and quality of rock glacier outflows is essential to evaluate their contribution and impact on headwater systems. In this study, we developed a conceptual model explaining the main hydro-chemical processes in active rock glaciers in the current context of permafrost warming. This conceptual model was derived from isotopic and physico-chemical analyses performed on six rock glacier outflows in the Swiss Alps during the warm season. Similar chemical and isotopic analyses were performed in sources not fed by rock glaciers at all study sites. The ion content (SO42-, Ca2+, Mg2+ and NO3−) of the water emerging from active rock glaciers was globally higher than that of sources not fed by rock glaciers. Besides, the electrical conductivity and the ion content (SO42-, Ca2+ and Mg2+) of the active rock glacier springs increased during the warm season, tracking the increasing perennial ground ice melting. We hypothesized that the ionic fingerprint of melting ice points mainly to the remobilization of chemical compounds stored during a colder period of the past in the cryosphere (e.g., the 1960s–1980s)

The climate change research that makes the front page: Is it fit to engage societal action?

By growing awareness for and interest in climate change, media coverage enlarges the window of opportunity by which research can engage individuals and collectives in climate actions. However, we question whether the climate change research that gets mediatized is fit for this challenge. From a survey of the 51,230 scientific articles published in 2020 on climate change, we show that the news media preferentially publicizes research outputs found in multidisciplinary journals and journals perceived as top-tier. An in-depth analysis of the content of the top-100 mediatized papers, in comparison to a random subset, reveals that news media showcases a narrow and limited facet of climate change knowledge (i.e., natural science and health). News media selectivity reduces climate change research to the role of a sentinel and whistleblower for the large-scale, observed, or end-of-century consequences of climate change for natural Earth system components. The social, economic, technological, and energy aspects of climate change are curtailed through mediatization, as well as local and short-term scales of processes and solutions. Reviewing the social psychological mechanisms that underlie behavioral change, we challenge the current criteria used to judge newsworthiness and argue that the consequent mediatization of climate change research fails to breed real society engagement in actions. A transformative agenda for the mediatization of climate change research implies aligning newsworthiness with news effectiveness, i.e., addressing the extent to which communication is effective in presenting research that is likely to produce behavioral change

Trophic history of French sub-alpine lakes over the last ~150 years: phosphorus reconstruction and assessment of taphonomic biases

Like many lakes worldwide, French sub-alpine lakes (lakes Annecy, Bourget and Geneva) have suffered from eutrophication in the mid-20th century. Although restoration measures have been undertaken and resulted in significant reductions in nutrient inputs and concentrations over the last 30 years in all three lakes, the limnological monitoring does not extend back far enough to establish the reference conditions, as defined by the European Water Framework Directive. The over-arching aim of this work was to reconstruct, using a paleolimnological approach, the pre-eutrophication levels and subsequent temporal changes in the lakes trophic status over the last century. The objectives were three-fold: i) to test whether fossil diatoms archived in deep sediment cores adequately reflect past changes in the planktonic diatom communities for these deep sub-alpine lakes based on data from lake Geneva; ii) to investigate changes in the diatom communities over the last 150 years in the three lakes; and iii) to infer the past total phosphorus (TP) concentrations of the lakes from a diatom based transfer function. Annual paleolimnological and limnological diatom countings for lake Geneva were strongly correlated over the last 30 years. Most notable differences essentially resulted from both taphonomic and depositional biases, as evidenced by the underestimation of thin skeleton species such as Asterionella formosa and Diatoma tenuis in the paleolimnological dataset and the presence of many benthic taxa. The fossil diatom records revealed shifts in the communities in the three lakes over time, most of which were changes typically associated with nutrient enrichment. Indeed, in all three lakes, the proportion of Cyclotella spp. was very high before the 1950s, but these species were then replaced by more eutrophic taxa, such as Stephanodiscus spp, by the mid-20th century. From the 1980s, some but not all diatom species typical of re-oligotrophicated conditions (i.e. Cyclotella sp.) re-appeared in all three lakes. Yet, not all changes that occurred in the diatom communities since then may be attributed to decreasing TP. TP concentrations inferred from weighted averaging with classical deshrinking in lake Annecy and lake Geneva and weighted averaging with inverse deshrinking in Lake Bourget were very close to the monitored values. Comparisons of diatom-inferred TP concentrations to other paleo-proxies for trophic status revealed though that the transfer functions were rather insensitive to changes occurring below 10 ?g L-1, which limits the study ability to set accurate TP reference conditions below this threshold. However, current diatom community compositions arestill rather different from the pre-eutrophication ones, suggesting that reference conditions are still not achieved

Long-Term Spatiotemporal Variability of Whitings in Lake Geneva from Multispectral Remote Sensing and Machine Learning

Whiting events are massive calcite precipitation events turning hardwater lake waters to a milky turquoise color. Herein, we use a multispectral remote sensing approach to describe the spatial and temporal occurrences of whitings in Lake Geneva from 2013 to 2021. Landsat-8, Sentinel-2, and Sentinel-3 sensors are combined to derive the AreaBGR index and identify whitings using appropriate filters. 95% of the detected whitings are located in the northeastern part of the lake and occur in a highly reproducible environmental setting. An extended time series of whitings in the last 60 years is reconstructed from a random forest algorithm and analyzed through a Bayesian decomposition for annual and seasonal trends. The annual number of whiting days between 1958 and 2021 does not follow any particular monotonic trend. The inter-annual changes of whiting occurrences significantly correlate to the Western Mediterranean Oscillation Index. Spring whitings have increased since 2000 and significantly follow the Atlantic Multidecadal Oscillation index. Future climate change in the Mediterranean Sea and the Atlantic Ocean could induce more variable and earlier whiting events in Lake Geneva

Lake surface cooling drives littoral-pelagic exchange of dissolved gases

The extent of littoral influence on lake gas dynamics remains debated in the aquatic science community due to the lack of direct quantification of lateral gas transport. The prevalent assumption of diffusive horizontal transport in gas budgets fails to explain anomalies observed in pelagic gas concentrations. Here, we demonstrate through high-frequency measurements in a eutrophic lake that daily convective horizontal circulation generates littoral-pelagic advective gas fluxes one order of magnitude larger than typical horizontal fluxes used in gas budgets. These lateral fluxes are sufficient to redistribute gases at the basin-scale and generate concentration anomalies reported in other lakes. Our observations also contrast the hypothesis of pure, nocturnal littoral-to-pelagic exchange by showing that convective circulation transports gases such as oxygen and methane toward both the pelagic and littoral zones during the daytime. This study challenges the traditional pelagic-centered models of aquatic systems by showing that convective circulation represents a fundamental lateral transport mechanism to be integrated into gas budgets. Cooling-induced horizontal circulation redistributes gases daily between littoral and pelagic lake waters under calm conditions

Can we detect ecosystem critical transitions and signals of changing resilience from paleo-ecological records?

Nonlinear responses to changing external pressures are increasingly studied in real-world ecosystems. However, as many of the changes observed by ecologists extend beyond the monitoring record, the occurrence of critical transitions, where the system is pushed from one equilibrium state to another, remains difficult to detect. Paleo-ecological records thus represent a unique opportunity to expand our temporal perspective to consider regime shifts and critical transitions, and whether such events are the exception rather than the rule. Yet, sediment core records can be affected by their own biases, such as sediment mixing or compression, with unknown consequences for the statistics commonly used to assess regime shifts, resilience, or critical transitions. To address this shortcoming, we developed a protocol to simulate paleolimnological records undergoing regime shifts or critical transitions to alternate states and tested, using both simulated and real core records, how mixing and compression affected our ability to detect past abrupt shifts. The smoothing that is built into paleolimnological data sets apparently interfered with the signal of rolling window indicators, especially autocorrelation. We thus turned to time-varying autoregressions (online dynamic linear models, DLMs; and time-varying autoregressive state-space models, TVARSS) to evaluate the possibility of detecting regime shifts and critical transitions in simulated and real core records. For the real cores, we examined both varved (annually laminated sediments) and non-varved cores, as the former have limited mixing issues. Our results show that state-space models can be used to detect regime shifts and critical transitions in some paleolimnological data, especially when the signal-to-noise ratio is strong. However, if the records are noisy, the online DLM and TVARSS have limitations for detecting critical transitions in sediment records

Designing Inter- and Transdisciplinary Research on Mountains: What Place for the Unexpected?

In recent decades, research on mountains has become more inter- and transdisciplinary, but a greater effort is needed if such research is to contribute to a societal transformation toward sustainability. Mountain research centers are a crucial actor in this endeavor. Yet, the literature has not paid sufficient attention to how these centers should (re-)design inter- and transdisciplinary research. In this study, we explored this question with a self-reflexive approach. We analyzed the first 15 months of the Interdisciplinary Centre for Mountain Research (CIRM) of the University of Lausanne (Switzerland) through qualitative data collected via interviews and observation. We used a simple model of inter- and transdisciplinarity at the organizational level of a research center. Special attention was devoted to the individual and collective ability to exploit the unexpected (serendipity). Our results indicate an interdependency between the coconstruction of research objects and the creation of integrative partnerships. They also shed light on the types of institutional resources and integrative methodologies that enhance inter- and transdisciplinary research, as well as their challenges. Our experience shows that implementing inter- and transdisciplinarity requires deep changes in research evaluation procedures, research funding policies, and researchers themselves. Serendipity is in turn shown to play an important role in inter- and transdisciplinarity due to its potential to change the research process in creative ways. We speculate that serendipity offers unique opportunities to capitalize on hidden resources that can catalyze a radical transformation of mountain researchers, research organizations, and society in the face of unprecedented global change