What is the biological reason as to why “mouth watering occurs?

Explanation:

Enzymes are present in your saliva which break down large molecules of food into smaller molecules so that it is easier to swallow and therefore, digest.

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.