The principal hormone secreted by the corpus luteum, which prepares the uterus for pregnancy,

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.