Final answer:
Nonrandom mating, also known as assortative mating, occurs when individuals select partners based on phenotypic similarity, physical location, or other traits favored by natural selection. Environmental factors can also affect these choices, as seen with temperature-dependent sex determination in reptiles.
Step-by-step explanation:
Another term used to describe nonrandom mating is assortative mating. This type of mating occurs when individuals prefer to mate with partners who are phenotypically similar to themselves. An example of this can be seen in peahens selecting peacocks with larger and brighter tails, which is indicative of mate choice dictated by natural selection. Apart from mate choice, another factor that influences nonrandom mating is physical location; individuals in large populations may have limited access to potential mates based on geographic distance and environmental barriers.
Environmental factors also play a role in phenotypic variance within a population. For instance, temperature-dependent sex determination (TSD) in reptiles is influenced by the temperature at which eggs are incubated, which is an environmental variable.
Different mating systems such as monogamous, polygynous, and polyandrous, further illustrate the variety of innate behaviors that lead to nonrandom mating within animal populations.