File:Various population bottlenecks.PNG

English: The mechanisms underlying bottlenecks shape the relationship between inoculum size and founding population size. Five conceptual examples of how the relationship between the inoculum size and founding population size changes with different types of bottlenecks. (A) An “absolute” bottleneck allows the unobstructed passage of organisms until its capacity is exhausted, thereby defining an upper limit on the number organisms that can pass. (B) During passage through a “fractional” bottleneck, a proportion of the inoculum does not survive. In this scenario, low inoculum sizes can occasionally give rise to infection, even if the expected bottleneck size is below one; however, for simplicity, in the graph, low inocula are set to a founding population size of zero. (C) With a “limited” bottleneck, a fixed amount of the inoculum is killed. (D) With a “cooperative” bottleneck, a population cannot pass through the bottleneck unless a sufficient number of organisms are present in the inoculum. Once the population size crosses this threshold, all organisms become competent for bottleneck passage. (E) In more realistic scenarios, diverse mechanisms of host defense collectively limit the founding population size.