The Elements of Evolution (51-1-5) Mammal Predation, Defecation

 Mammal Predation

Most small mammal predators are themselves preyed upon. Hence they evolved a suite of antipredator defenses that tend to sort them into 2 quite different lifestyles.

The solitary ones, such as skunks, are often aposematically colored and armed with noxious anal sprays. Subject to predation by other mammals, they tend to be nocturnal.

Gregarious species, such as mongeese, are socially vigilant. Such creatures tend to be diurnal, and at risk from birds of prey.

 Mammal Defecation

The smell of body waste attracts predators, which is dangerous for animals. ~ American mechanical engineer Patricia Yang

Defecation is not a life-history variable for mammals. From mice to elephants, mammals excrete cylinders of waste like humans, and they all do so in about 12 seconds. This is consistent with the fact that all mammals take the same duration to empty their bladders.

Cylindrical feces are not squeezed through a nozzle (like a toothpaste tube).

It’s more like a plug that just goes through a chute. ~ Patricia Yang

The normal, low level pressure that mammals apply to push through a bowel movement is constant, unrelated to animal size. To achieve this consistency among species, the lubricating mucus in the colon varies in viscosity. Larger animals have longer feces and correspondingly longer rectums, so they produce thicker mucus which accelerates excretion: hence, feces flows a longer distance in the same time.