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The spread of an enteric pathogen in the human gut depends on many interacting factors, including pathogen exposure, diet, host gut environment, and host microbiota, but how these factors jointly influence infection outcomes remains poorly characterized. Here, we develop a model of host-mediated resource-competition between mutualistic and pathogenic taxa in the gut that aims to explain why similar hosts, exposed to the same pathogen, can have such different infection outcomes. Our model successfully reproduces several empirically observed phenomena related to transitions between healthy and infected states, including (1) the nonlinear relationship between pathogen inoculum size and infection persistence, (2) the elevated risk of chronic infection during or after treatment with broad-spectrum antibiotics, (3) the resolution of gut dysbiosis with fecal microbiota transplants, and (4) the potential protection from infection conferred by probiotics. We then use the model to explore how host-mediated interventions, namely shifts in the supply rates of electron donors (e.g., dietary fiber) and respiratory electron acceptors (e.g., oxygen), can potentially be used to direct gut community assembly. Our study demonstrates how resource competition and ecological feedbacks between the host and the gut microbiota can be critical determinants of human health outcomes. We identify several testable model predictions ready for experimental validation. 

Seed dispersal and local filtering interactively govern community membership and scale up to shape regional vegetation patterns, but data revealing how and why particular species are excluded from specific communities in nature are scarce. This lack of data is a missing link between our theoretical understanding of how diversity patterns can form and how they actually form in nature, and it hampers our ability to predict community responses to climate change. Here, we compare seed, seedling, and adult plant communities at 12 grassland sites with different climates in southern Norway to examine how community membership is interactively shaped by seed dispersal and local filtering, and how this process varies with climate across sites. To do this, we divide species at each site into two groups:locally transientspecies, which occur as seeds but are rare or absent as adults (i.e., they arrive but are filtered out), andlocally persistentspecies, which occur consistently as adults in annual vegetation surveys. We then ask how and why locally transient species are disfavored during community assembly. Our results led to four main conclusions: (1) the total numbers of seeds and species that arrived, but failed to establish locally persistent populations, rose with temperature, indicating an increase in the realized effects of local filtering on community assembly, as well as an increase in the number of species poised to rapidly colonize those warmer sites if local conditions change in their favor, (2) locally transient species were selectively filtered out during seedling emergence, but not during seedling establishment, (3) selective filtering was partly driven by species climate preferences, exemplified by the poor performance of seeds dispersing outside of their realized climate niches into colder and drier foreign climates, and (4) locally transient species had traits that likely made them better dispersers (i.e., smaller seeds) but poorer competitors for light (i.e., shorter statures and less persistent clonal connections) than locally persistent species, potentially explaining why these species arrived to new sites but did not establish locally persistent adult populations. Our study is the first to combine seed, seedling, and adult survey data across sites to rigorously characterize how seed dispersal and local filtering govern community membership and shape climate‐associated vegetation patterns.