A community of microorganisms is demonstrating a shift in overall composition as the abiotic factors of the immediate area change. The pH of the water in which the organisms live is rising because a nearby stream has started to erode a layer of newly exposed limestone. The shift happens slowly. Organism A, which started off with about 10^9 individuals is dying off faster than it reproduces, so that the population shrinks by about 1000=10^3 individuals for every month of time, m. Meanwhile, Organism B is growing from a population of about 10^4, adding a net growth of 100=10^2 individuals every month.