What characteristic contributes to high populations of rats and mice?

High reproductive potential is the characteristic that significantly contributes to the establishment of large populations of rats and mice. These species are known for their ability to reproduce quickly and in large numbers, which allows their populations to grow rapidly in favorable environments. For instance, a single pair of rats can produce several litters within a year, leading to hundreds of offspring if conditions are suitable, such as the availability of food, shelter, and absence of predators.

The other factors might play a role in the lifestyle and behavior of these rodents but do not independently drive population growth to the same extent as high reproductive potential. Nocturnal activity allows them to exploit resources during night hours but does not inherently enhance population numbers. Strong territorial instincts may limit their range or interactions with other groups but do not significantly influence reproduction rates. Climbing ability enables them to access various habitats or food sources but again does not directly affect their reproductive output. Therefore, reproductive potential is the key factor in understanding why populations of rats and mice can reach such high numbers.