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Ecology and Global Change

Global change is a complex phenomenon induced by humans through activities such as land use changes, redistribution of earth's species or greenhouse gases release. Therefore, adaptation to Global Change will prompt land managers to adapt land uses and resource exploitation to novel scenarios where new species, recurrent climatic extreme events or fertility losses might suddenly change structure and functioning of ecosystems and the ensuing energy/mass exchanges.

Topics

Climate Change
Community Ecology
Biological Invasions

Selected publications

Forest productivity in southwestern Europe is driven by coupled North Atlantic and Atlantic Multidecadal Oscillations.

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The North Atlantic Oscillation (NAO) depicts annual and decadal oscillatory modes of variability responsible of dry spells over the European continent. The NAO therefore holds a great potential to evaluate the role, as carbon sinks, of water-limited forests under climate change. However, uncertainties related to inconsistent responses of long-term forest productivity to NAO have so far hampered firm conclusions on its impacts. We hypothesize that, in part, such inconsistencies might have their origin in periodical sea surface temperature anomalies in the Atlantic Ocean (i.e. Atlantic Multidecadal Oscillation, AMO). In this study, we show strong empirical evidence in support of this hypothesis using 120 years of periodical inventory data from Iberian pine forests. Our results point to AMO+ NAO+ and AMO- NAO- phases as being critical for forest productivity, likely due to decreased winter water balance and abnormally low winter temperatures, respectively. Our findings could be essential for the evaluation of ecosystem functioning vulnerabilities associated with increased climatic anomalies under unprecedented warming conditions in the Mediterranean. (see Madrigal-González et al 2017, Nature Communications)

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Climate reverses directionality in the richness–abundance relationship across the World’s main forest biomes

 

More tree species can increase the carbon storage capacity of forests (here referred to as the more species hypothesis) through increased tree productivity and tree abundance resulting from complementarity, but they can also be the consequence of increased tree abundance through increased available energy (more individuals hypothesis). To test these two contrasting hypotheses, we analyse the most plausible pathways in the richness-abundance relationship and its stability along global climatic gradients. We show that positive effect of species richness on tree abundance only prevails in eight of the twenty-three forest regions considered in this study. In the other forest regions, any benefit from having more species is just as likely (9 regions) or even less likely (6 regions) than the effects of having more individuals. We demonstrate that diversity effects prevail in the most productive environments, and abundance effects become dominant towards the most limiting conditions. These findings can contribute to refining cost-effective mitigation strategies based on fostering carbon storage through increased tree diversity. Specifically, in less productive environments, mitigation measures should promote abundance of locally adapted and stress tolerant tree species instead of increasing species richness. (see Madrigal-González et al 2020, Nature Communications)

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Positive associations among rare species drive their persistence in ecological assemblages

 

How rare species persist in highly competitive environments remains a central but unanswered question in ecology. According to the competitive exclusion principle6, species with low competitive abilities should be excluded by more efficient competitors, and yet, inexplicably, they remain as rare species. Explanations for this diversity paradox include the differential roles of competition, indirect facilitation and neutral interactions, but so far, no single hypothesis satisfactorily explains rare species persistence across taxa and environmental conditions. Here, we report a general spatial organisation of ecological assemblages that, while consistent with the competitive exclusion principle, supports a novel hypothesis of rare species persistence. We analyse 362 assemblages encompassing data from a variety of biomes and taxa and describe their aggregation and segregation patterns by positive and negative association networks. According to the prevalent role of competitive interactions, species show more negative than positive associations and, dominant species monopolise negative associations in c. 90% of the assemblages. Interestingly and in marked contrast, rare species are mostly involved in positive associations, forming small network modules. This spatial pattern suggests that positive interactions among rare species are crucial to overcoming the pressure exerted by superior competitors, contributing to explain the diversity paradox. Indeed, numerical simulations confirm that cooperation among weak competitors would more likely result in the reported empirical patterns and promote species coexistence, even in the presence of habitat heterogeneity. The consistent results across taxa and geography open the door to a unified coexistence theory where positive interactions would be critical to maintaining biodiversity in competitive environments. (see Calatayud et al 2019, Nature Ecology and Evolution)

Bottom-up control of consumers leads to top-down indirect facilitation of invasive annual herbs in semi-arid coastal Chile

 

The abundance of exotic plants is thought to be limited by competition with resident species (including plants and generalist herbivores). In contrast, observations in semiarid Chile suggest that a native generalist rodent, the degu (Octodon degus), may be facilitating the expansion of exotic annual plants. We tested this hypothesis with a 20-year data set from a World Biosphere Reserve in mediterranean Chile. In this semiarid environment, rainfall varies annually and dramatically influences cover by both native and exotic annual plants; degu population density affects the composition and cover of exotic and native annual plants. In low-rainfall years, cover of both native and exotic herbs is extremely low. Higher levels of precipitation result in proportional increases in cover of all annual plants (exotic and native species), leading in turn to increases in degu population densities, at which point they impact native herbs in proportion to their greater cover, indirectly favoring the expansion of exotic plants. We propose that bottom-up control of consumers at our site results in top-down indirect facilitation of invasive annual herbs, and that this pattern may be general to other semiarid ecosystems (see Madrigal et al. 2011, Ecology)

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