Fast–slow traits predict competition network structure and its response to resources and enemies

Plants interact in complex networks but how network structure depends on resources, natural enemies and species resource‐use strategy remains poorly understood. Here, we quantified competition networks among 18 plants varying in fast–slow strategy, by testing how increased nutrient availability and reduced foliar pathogens affected intra‐ and inter‐specific interactions. Our results show that nitrogen and pathogens altered several aspects of network structure, often in unexpected ways due to fast and slow growing species responding differently. Nitrogen addition increased competition asymmetry in slow growing networks, as expected, but decreased it in fast growing networks. Pathogen reduction made networks more even and less skewed because pathogens targeted weaker competitors. Surprisingly, pathogens and nitrogen dampened each other's effect. Our results show that plant growth strategy is key to understand how competition respond to resources and enemies, a prediction from classic theories which has rarely been tested by linking functional traits to competition networks

Redes de asociación planta-planta: Organización de las especies y la comunidad vegetal, y adaptación del sistema a factores de estrés en ecosistemas semiáridos

El objetivo general de la presente tesis es profundizar en el análisis de las interacciones bióticas a nivel de comunidad vegetal empleando redes topológicas. Las comunidades vegetales están formadas por distintas especies de plantas cuyas interacciones pueden aproximarse a partir del análisis de su patrón espacial. Cuando dos especies de plantas aparecen asociadas en el espacio se puede deducir un beneficio de dicha asociación y, por tanto, una interacción positiva entre ambas especies. Sin embargo, cuando dos plantas aparecen segregadas en el espacio se puede deducir un perjuicio de dicha asociación y como resultado, una interacción negativa entre ambas especies. De este modo es posible construir una red donde los nodos son las especies vegetales y las conexiones son las interacciones que establecen entre ellas. Es la primera vez que se analiza en ecología una red que considera simultáneamente conexiones positivas y negativas. Las redes espaciales se construyeron para las comunidades vegetales de dos regiones semiáridas de la Península Ibérica: las comunidades vegetales de yesos y arcillas del sector central del valle del Ebro y las comunidades de matorral y alfa-estepa del Parque Natural de Cabo de Gata-Níjar. A partir del análisis de las redes espaciales de estas comunidades vegetales se evaluaron diferentes hipótesis ecológicas. Se comprobó que la estructura de las redes de asociación planta-planta en zonas áridas es similar a la de las redes ecológicas mutualistas, y que esta estructura se ve modificada por el efecto de diferentes factores de estrés como son la aridez, la dominancia de una especie competitiva y el pastoreo. También se encontró que la organización espacial en manchas de vegetación típica de las zonas semiáridas está determinada por las interacciones que establecen entre sí las especies, y que la estrategia de vida de las plantas determina sus propiedades dentro de la red. Además, por primera vez se evaluó la hipótesis del gradiente de estrés (la intensidad de estrés determina la importancia de las interacciones positivas y negativas de una comunidad) para una comunidad vegetal completa, teniendo en cuenta las interacciones positivas y negativas simultáneamente y verificando la hipótesis de que las interacciones positivas presentan su máxima importancia a niveles de estrés intermedios. Aunque el patrón espacial presenta limitaciones como aproximación de las interacciones entre especies, las redes de asociación espacial parecen una buena herramienta para evaluar las interacciones a nivel de comunidades vegetal. Su análisis nos proporciona información valiosa acerca de la importancia de las especies de plantas en la comunidad así como de la estructura de la comunidad vegetal. Los futuros objetivos derivados de esta tesis incluyen perfeccionar el método, ponderando las conexiones de la red, y extender el análisis a otras comunidades vegetales no áridas para confirmar la validez del método a nivel general

Redes de Interacción Ecológicas: Balance y Frustración en Redes Complejas con Signo.

En ecología se han estudiado las interacciones entre los miembros de un ecosistema estableciendo las relaciones entre las especies que lo forman. El conjunto de relaciones se codifica en una red compleja donde los nodos son las especies y los links entre los nodos codifican diferentes tipos de interacción. En este trabajo consideramos especies vegetales cuyas interacciones pueden ser positivas (favorecedoras), negativas (competitivas) o neutras. Nuestro interés radica en estudiar el balance estructural de estas redes comparándolo con el balance estructural de redes equivalentes generadas al azar. El objetivo es entender y cuantificar cómo las redes observadas han evolucionado hacia estructuras con un balance casi óptimo lo cual las convierte en sistemas robustos y adaptables

The BIODESERT survey: assessing the impacts of grazing on the structure and functioning of global drylands

Grazing by domestic livestock is both the main land use across drylands worldwide and a major desertification and global change driver. The ecological consequences of this key human activity have been studied for decades, and there is a wealth of information on its impacts on biodiversity and ecosystem processes. However, most field assessments of the ecological impacts of grazing on drylands conducted to date have been carried out at local or regional scales and have focused on single ecosystem attributes (e.g., plant productivity) or particular taxa (mainly aboveground, e.g., plants). Here we introduce the BIODESERT survey, the first systematic field survey devoted to evaluating the joint impacts of grazing by domestic livestock and climate on the structure and functioning of dryland ecosystems worldwide. This collaborative global survey was carried out between 2016 and 2019 and has involved the collection of field data and plant, biocrust, and soil samples from a total of 326 45 m × 45 m plots from 98 sites located in 25 countries from 6 continents. Here we describe the major characteristics and the field protocols used in this survey. We also introduce the organizational aspects followed, as these can be helpful to everyone wishing to establish a global collaborative network of researchers. The BIODESERT survey provides baseline data to assess the current status of dryland rangelands worldwide and the impacts of grazing on these key ecosystems, and it constitutes a good example of the power of collaborative research networks to study the ecology of our planet using much-needed field data.This research has been supported by the European Research Council (ERC grant agreement no. 647038 – BIODESERT) and the Conselleria de Innovación, Universidades, Ciencia y Sociedad Digital, Generalitat Valenciana (grant no. CIDEGENT/2018/041). Nicolas Gross was supported by CAP 20-25 (16-IDEX-0001) and the AgreenSkills+ fellowship program which has received funding from the EU's Seventh Framework Programme under grant agreement no. 996 FP7-609398 (AgreenSkills+ contract). Hugo Saiz is supported by a María Zambrano fellowship funded by the Ministry of Universities and European Union Next Generation plan

Global ecosystem thresholds driven by aridity

Aridity, which is increasing worldwide because of climate change, affects the structure and functioning of dryland ecosystems. Whether aridification leads to gradual (versus abrupt) and systemic (versus specific) ecosystem changes is largely unknown. We investigated how 20 structural and functional ecosystem attributes respond to aridity in global drylands. Aridification led to systemic and abrupt changes in multiple ecosystem attributes. These changes occurred sequentially in three phases characterized by abrupt decays in plant productivity, soil fertility, and plant cover and richness at aridity values of 0.54, 0.7, and 0.8, respectively. More than 20% of the terrestrial surface will cross one or several of these thresholds by 2100, which calls for immediate actions to minimize the negative impacts of aridification on essential ecosystem services for the more than 2 billion people living in drylands.This research was supported by the European Research Council [ERC grant nos. 242658 (BIOCOM) and 647038 (BIODESERT) awarded to F.T.M.]. M.B. acknowledges support from a Juan de la Cierva Formación grant from the Spanish Ministry of Economy and Competitiveness (FJCI-2018-036520-I). F.T.M. acknowledges support from Generalitat Valenciana (CIDEGENT/2018/041), the Alexander von Humboldt Foundation, and the Synthesis Centre for Biodiversity Sciences (sDiv) of the German Centre for Integrative Biodiversity Research (iDiv). M.D.-B. acknowledges support from the Marie Sklodowska-Curie Actions of the Horizon 2020 Framework Program H2020-MSCA-IF-2016 under REA grant no. 702057. S.S. was supported by the Spanish Government under a Ramón y Cajal contract (RYC-2016- 20604). N.G. was supported by the AgreenSkills+ fellowship program, which has received funding from the EU’s Seventh Framework Programme under grant no. FP7-609398 (AgreenSkills+ contract). V.M. was supported by FRQNT-2017-NC-198009 and NSERC Discovery 2016-05716 grants from the government of Canada. H.S. was supported by a Juan de la Cierva Formación grant from the Spanish Ministry of Economy and Competitiveness (FJCI-2015-26782). A.L. and M.C.R. were supported by an ERC Advanced Grant (Gradual Change grant no. 694368) and by the Deutsche Forschungsgesellschaft (grant no. RI 1815/16-1). Y.Z. was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (grant no. XDA19030500)

Functional rarity and evenness are key facets of biodiversity to boost multifunctionality

The functional traits of organisms within multispecies assemblages regulate biodiversity effects on ecosystem functioning. Yet how traits should assemble to boost multiple ecosystem functions simultaneously (multifunctionality) remains poorly explored. In a multibiome litter experiment covering most of the global variation in leaf trait spectra, we showed that three dimensions of functional diversity (dispersion, rarity, and evenness) explained up to 66% of variations in multifunctionality, although the dominant species and their traits remained an important predictor. While high dispersion impeded multifunctionality, increasing the evenness among functionally dissimilar species was a key dimension to promote higher multifunctionality and to reduce the abundance of plant pathogens. Because too-dissimilar species could have negative effects on ecosystems, our results highlight the need for not only diverse but also functionally even assemblages to promote multifunctionality. The effect of functionally rare species strongly shifted from positive to negative depending on their trait differences with the dominant species. Simultaneously managing the dispersion, evenness, and rarity in multispecies assemblages could be used to design assemblages aimed at maximizing multifunctionality independently of the biome, the identity of dominant species, or the range of trait values considered. Functional evenness and rarity offer promise to improve the management of terrestrial ecosystems and to limit plant disease risks.This work was funded by the British Ecological Society (SR17\1297 grant, PI: P.G.-P.) and by the European Research Council (ERC Grant Agreement #647038, BIODESERT, PI: F.T.M.). Y.L.B.-P. was supported by a Marie Sklodowska-Curie Actions Individual Fellowship within the European Program Horizon 2020 (DRYFUN Project #656035). H.S. was supported by a Juan de la Cierva-Formación grant from the Spanish Ministry of Economy and Competitiveness (FJCI-2015-26782). F.T.M. and S.A. were supported from the Generalitat Valenciana (CIDEGENT/2018/041). M.D. was supported by a Formación del Profesorado Universitario (FPU) fellowship from the Spanish Ministry of Education, Culture and Sports (FPU-15/00392). S.A. was supported by the Spanish MINECO for financial support via the DIGGING_DEEPER project through the 2015 to 2016 BiodivERsA3/FACCE‐JPI joint call for research proposals. B.K.S. research on biodiversity-ecosystem functions was supported by the Australian Research Council (DP170104634 and DP190103714). P.G.-P. was supported by a Ramón y Cajal grant from the Spanish Ministry of Science and Innovation (RYC2018-024766-I). R.M. was supported by MINECO (Grants CGL2014-56567-R and CGL2017-83855-R)

Diffusion-based structural connectivity patterns of multiple sclerosis phenotypes

BACKGROUND: We aimed to describe the severity of the changes in brain diffusion-based connectivity as multiple sclerosis (MS) progresses and the microstructural characteristics of these networks that are associated with distinct MS phenotypes. METHODS: Clinical information and brain MRIs were collected from 221 healthy individuals and 823 people with MS at 8 MAGNIMS centres. The patients were divided into four clinical phenotypes: clinically isolated syndrome, relapsing-remitting, secondary progressive and primary progressive. Advanced tractography methods were used to obtain connectivity matrices. Then, differences in whole-brain and nodal graph-derived measures, and in the fractional anisotropy of connections between groups were analysed. Support vector machine algorithms were used to classify groups. RESULTS: Clinically isolated syndrome and relapsing-remitting patients shared similar network changes relative to controls. However, most global and local network properties differed in secondary progressive patients compared with the other groups, with lower fractional anisotropy in most connections. Primary progressive participants had fewer differences in global and local graph measures compared with clinically isolated syndrome and relapsing-remitting patients, and reductions in fractional anisotropy were only evident for a few connections. The accuracy of support vector machine to discriminate patients from healthy controls based on connection was 81%, and ranged between 64% and 74% in distinguishing among the clinical phenotypes. CONCLUSIONS: In conclusion, brain connectivity is disrupted in MS and has differential patterns according to the phenotype. Secondary progressive is associated with more widespread changes in connectivity. Additionally, classification tasks can distinguish between MS types, with subcortical connections being the most important factor