A 20.0 gram sample of a certain radioisotope decays over a period of 19.2 hours. After that time, only 2.50 g of the isotope
remains. Calculate the half-life.

quantity of the substance remaining = initial quantity of the substance * (.5)^(time elapsed/half life of the substance)

2.50 = 20 * (.5)^(19.2/x)

they each offer a fresh glut of resources to the organisms that can arrive and exploit them. as individuals and new species continue to appear, they actively and passively alter the environment. competition for shared resources increases, local abiotic and biotic conditions shift, and the relative abundances of species change accordingly. the process is called ecological succession, and it is one of the earliest and most well-known concepts in ecology.