Summary• Ecological network theory predicts that in mutualistic systems specialists tend to interact with a subset of species with which generalists interact (i.e. nestedness). Approaching plantarbuscular mycorrhizal fungi (AMF) association using network analyses will allow the generality of this pattern to be expanded to the ubiquitous plant-AMF mutualism.• Based on certain plant-AMF specificity recently suggested, networks are expected to be nested as a result of their mutualistic nature, and modular, with certain species interacting more tightly than others. Network analyses were used to test for nestedness and modularity and to compare the different contribution of plant and AMF to the overall nestedness.• Plant-AMF networks share general network properties with other mutualisms. Plant species with few AMFs in their roots tend to associate with those AMFs recorded in most plant species. AMFs present in a few plant species occur in plant species sheltering most AMF (i.e. nestedness). This plant-AMF network presents weakly interlinked subsets of species, strongly connected internally (i.e. modularity). Both plants and AMF show a nested structure, although AMFs have lower nestedness than plants.• The plant-AMF interaction pattern is interpreted in the context of how plant-AMF associations can be underlying mechanisms shaping plant community assemblages.
Summary• Understanding the adaptive basis of life history variation is a central goal in evolutionary ecology. The use of model species enables the combination of molecular mechanistic knowledge with ecological and evolutionary questions, but the study of life history variation in natural environments is required to merge these disciplines.• Here, we tested for clinal variation in life history and associated traits along an environmental and altitudinal gradient in the model species Arabidopsis thaliana. Seventeen natural populations of A. thaliana were geo-referenced in northeastern Spain on a gradient in which precipitation increases but maximum spring temperature and minimum winter temperature decrease with altitude.• One hundred and eighty-nine genotypes from the 17 populations were grown under uniform controlled conditions. Variations in traits related to biomass allocation, fecundity, phenology and vegetative growth were tested for relationships with the altitude and climatic variables associated with the home sites. Aboveground mass, number of rosette leaves at bolting, developmental time and seed weight increased with the home site's altitude. Root allocation, vegetative growth during winter and number of seeds decreased with altitude.• We suggest that the differences among home sites provide clues to the variation in adaptive strategies associated with the climatic gradient. We compared these results with adaptations and clinal relationships reported for other species and with molecular mechanisms described in Arabidopsis.
Theory predicts that contrasting properties of mutualistic and antagonistic networks differentially promote community resilience to species loss. However, the outcome of most ecological interactions falls within a continuum between mutualism and antagonism, and we ignore the extent to which this interactions' continuum might influence community stability. Using a large data set of interactions, we compared co-extinction cascades that either consider or ignore the mix of beneficial and detrimental actions that parrots exert on plants. When the antagonism-mutualism continuum was considered, a combination of the properties that separately enhance community stability in ecological networks emerged. This combination of properties led to an overall increase of the parrot community robustness to face plant species loss. Our results highlight that the conditional outcomes of interactions can influence the structure of ecological networks, thus affecting our predictions of community stability against eventual changes.
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