Rats live in very diverse environments, and they adapt to this wide range through fast breeding, small size and a diverse diet. Rats are opportunistic feeders, taking advantage of whatever food sources are present, relying on stealth, and, as a species, a high replacement rate that protects against predation. Their large incisors, typical of rodents, allow for efficient access to shelter and food sources.
Rats are relatively intelligent animals with the ability to learn complex behaviors in response to challenges in their environments. They are found in every continent on Earth, particularly in coastal areas, where they were deposited by human shipping vessels. Indeed, rats' ubiquitousness stems in large part from the similarities between their needs and human needs. Rats tolerate similar temperatures well and find most human food to be edible. Rats can dig their way through materials such as drywall. This means that rats can take full advantage of human structures without having to expose themselves, unless foraging for food. They are nocturnal and so avoid human detection well.
There are two major species commonly called rats. These are black rats and the slightly larger brown rats. Black rats are good climbers, while brown rats are better at swimming. Both are highly social, living in groups with established dominance hierarchies.