The cladoceran Daphnia lumholtzi has invaded many US rivers and lakes. To better understand the ecological factors and consequences associated with D. lumholtzi invasion, we carried out a microcosm experiment evaluating competition of D. lumholtzi with a widespread native daphnid, D. pulex. We applied two light treatments to these two different microcosms and found strong context-dependent comp...

We show that loyalty discounts create an externality among buyers even without economies of scale or downstream competition, and whether or not buyers make any commitment. Each buyer who signs a loyalty discount contract softens competition and raises prices for all buyers. We prove that, provided the entrant’s cost advantage is not too large, with enough buyers, this externality implies that i...

Microbial metabolism drives our planet's biogeochemistry and plays a central role in industrial processes. Molecular profiling in bioreactors has revealed that microbial community composition can be highly variable while maintaining constant functional performance. Furthermore, following perturbation bioreactor performance typically recovers rapidly, while community composition slowly returns t...

The microbial population of the intestinal tract is a complex natural resource that can be utilized in an effort to reduce the impact of pathogenic bacteria that affect animal production and efficiency, as well as the safety of food products. Strategies have been devised to reduce the populations of food-borne pathogenic bacteria in animals at the on-farm stage. Many of these techniques rely on...

Chicken and human isolates of Campylobacter jejuni were used to provide oral challenge of day-old broiler chicks. The isolation ratio of the competing challenge strains was monitored and varied, depending upon the isolates used. A PCR-restriction fragment length polymorphism assay of the flagellin gene (flaA) was used to discriminate between the chick-colonizing isolates. Our observations indic...

A heterosexually active population is exposed to two competing strains or two distinct sexually-transmitted pathogens. It is assumed that a host cannot be invaded simultaneously by both disease agents and that when symptoms appear, a function of the pathogen or strain virulence, individuals recover. We conclude that in a behaviorally and genetically homogeneous population coexistence is not pos...

Salmonella Enteritidis emerged as a major egg-associated pathogen in the late 20th century. Epidemiologic data from England, Wales, and the United States indicate that S. Enteritidis filled the ecologic niche vacated by eradication of S. Gallinarum from poultry, leading to an epidemic increase in human infections. We tested this hypothesis by retrospective analysis of epidemiologic surveys in G...

Biodiversity conservation becoming increasingly urgent. It is important to find mechanisms of competitive coexistence of species with different fitness in especially difficult circumstances on one limiting resource, in isolated stable uniform habitat, without any trade-offs and cooperative interactions. Here we show a mechanism of competitive coexistence based on a soliton-like behaviour of pop...

The competitive exclusion principle (CEP) states that no equilibrium is possible if n species exploit fewer than n resources. This principle does not appear to hold in nature, where high biodiversity is commonly observed, even in seemingly homeogenous habitats. Although various mechanisms, such as spatial heterogeneity or chaotic fluctuations, have been proposed to explain this coexistence, non...

Competitive exclusion is proved for a discrete-time, size-structured, nonlinear matrix model of m-species competition in the chemostat. The winner is the population able to grow at the lowest nutrient concentration. This extends the results of earlier work of the first author [11] where the case m = 2 was treated.