In human microbiota, the prevention or promotion of invasions can be crucial to human health. Invasion outcomes, in turn, are impacted by the composition of resident communities and interactions of resident members with the invader. Here we study how interactions influence invasion outcomes in microbial communities, when interactions are primarily mediated by chemicals that are released into or consumed from the environment. We use a previously developed dynamic model which explicitly includes species abundances and the concentrations of chemicals that mediate species interaction. Using this model, we assessed how species interactions impact invasion by simulating a new species being introduced into an existing resident community. We classified invasion outcomes as resistance, augmentation, displacement, or disruption depending on whether the richness of the resident community was maintained or decreased and whether the invader was maintained in the community or went extinct. We found that as the number of invaders introduced into the resident community increased, disruption rather than augmentation became more prevalent. With more facilitation of the invader by the resident community, resistance outcomes were replaced by displacement and augmentation. By contrast, with more facilitation among residents, displacement outcomes shifted to resistance. When facilitation of the resident community by the invader was eliminated, the majority of augmentation outcomes turned into displacement, while when inhibition of residents by invaders was eliminated, invasion outcomes were largely unaffected. Our results suggest that a better understanding of interactions within resident communities and between residents and invaders is crucial to predicting the success of invasions into microbial communities.
7In human microbiota, the prevention or promotion of invasions can be crucial to human health. 8 Invasion outcomes, in turn, are impacted by the composition of resident communities and 9 interactions among resident microbes. Microbial communities differ from communities composed 10 of other types of organisms in that many microbial interactions are mediated by chemicals that are 11 released into or consumed from the environment. We ask what determines invasion outcomes in 12 such microbial communities. Here, we use a model based on chemical-mediated interactions 13 among microbial species to assess the impact of positive and negative interactions on invasion 14 outcomes. We classified invasion outcomes as resistance, augmentation, displacement, or 15 disruption depending on whether the richness of the resident community was maintained or 16 dropped and whether the invader was maintained in the community or went extinct. We found that 17 as the number of invaders increased relative to size of the resident community, resident 18 communities were increasingly disrupted. As facilitation of the invader by the resident community 19 increased, resistance outcomes were replaced by displacement and augmentation. By contrast, as 20 facilitation increased among residents, displacement outcomes shifted to resistance. When 21 facilitation of the resident community by the invader was eliminated, augmentation outcomes were 22 replaced by displacement outcomes, while when inhibition of residents by invaders was 23 eliminated, there was little change in the frequency of invasion outcomes. These results suggest 24 that a better understanding of the chemical-mediated interactions within resident communities and 25 between residents and invaders is crucial to predicting the success of invasions into microbial 26 communities. 27 28 31 occupying available niches, or interacting with them directly or indirectly via predation, 32 competition, facilitation, or other mechanisms. The relative importance of these factors in 33 determining invasion outcomes varies between communities and ecosystems. Functional 34 composition of resident communities, for example, is an important determinant of invasion success 35 in many grasslands (1), while release from consumer or competitive pressure is an especially 36 important factor in marine invasions (2). Among microbes, interactions often occur via chemical 37 mediators released into the environment (3,4). These mediated interactions are believed to be 38 influential in many microbial communities, but their importance to invasion outcomes remains 39 unexplored. 40In human microbiota, where preventing invasion is a first step in preventing many diseases, this 41 phenomenon is sometimes referred to as colonization resistance. The potential for resident 42 microbes to protect us from pathogens has been observed as early as 1917, by the discovery of 43 Escherichia coli Nissle 1917 that antagonized and blocked enteric pathogens (5). More examples 44 across different microbiota sites abound: nasal mic...
Summary Pre‐dispersal seed predation is sometimes considered unlikely to dramatically affect plant population growth because plants are generally expected to produce more seeds than there are safe sites for germination. Lupinus constancei is a rare herb of limited distribution, with fewer than 400 reproductive individuals restricted to a single square kilometre of north‐western California, USA. In addition to the vulnerability resulting from its extremely small population size, L. constancei faces heavy seed predation by small mammals. As a stop‐gap measure to prevent population decline, managers began covering a large number of the reproductive plants with herbivory exclosures in 2003, but the population‐level effects of seed predation and the effectiveness of this caging treatment were unknown. We used 10 years of demographic data to compare the population dynamics of plants inside herbivory exclosures with those sustaining ambient rodent seed predation. We found that the stochastic population growth rate would be robust without seed predation (λs = 1·17), but without continued human intervention (i.e. use of exclosures), the current rate of predation would result in a decline towards extinction (λs = 0·92). After our study concluded, high mortality due to two extreme winter droughts followed by a wildland fire reduced the number of reproductive plants to ∼103, making extinction of L. constancei more likely. Synthesis and applications. The prevalence of consumer‐driven population decline is largely unknown, but this study demonstrates that pre‐dispersal seed predation by rodents can have powerful population‐level effects, and represents one set of conditions under which consumer pressure has the potential to drive plant extinction. However, with continued management to limit the effects of seed predation in the short‐term and investigation into the ultimate drivers of this high seed predation rate in the long term, the Lassics lupine population could be restored to a robust rate of growth.
Researchers in many subfields of ecology and evolutionary biology test hypotheses relating to metapopulation dynamics and landscape spatial structure. Key aspects of these hypotheses are often (a) large numbers of subpopulations and dispersal corridors and (b) their positions relative to each other. Testing such spatial hypotheses using traditional laboratory equipment and methods can be impractical, unwieldy, expensive, or impossible. The Metapopulation Microcosm Plate (MMP) overcomes many of these difficulties. This device resembles a 96‐well microtitre plate, but contains dispersal corridors between wells that can be modified in their spatial position to create various artificial landscapes, each with up to 96 habitat patches and hundreds of nonintersecting dispersal corridors of varying lengths. The device can be filled with nutrient broth and used to culture microbial metapopulations. Here, I describe how MMPs are designed, assembled, sterilized, and filled and demonstrate that MMPs can remain water tight and sterile with minimal evaporation for 5–7 days. Metapopulation Microcosm Plates (MMPs) can be used to test many spatial hypotheses that have previously been prohibitively difficult to test. Further, by allowing individual behavioural responses to within‐patch conditions, MMPs can incorporate greater realism than directed pipetting or other artificial dispersal methods.
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