Sometimes students get confused between features that are used for the identification of animals or plants and the things that really account for us considering them as separate species. Two of our local kangaroo rats, Merriam's and Ord's, are an example of this. These two species are of similar size and coloration—to the average student, they look pretty much alike. However, we can easily teach students how to tell them apart. Merriam's Kangaroo Rat has a small fifth toe on the side of the hind foot that is absent in Ord's Kangaroo Rat.
Unfortunately some students jump to the conclusion that the two rodents
are different species because one has five toes on the hind foot and one only has four.
In reality, we consider them separate species because, even though they have the
opportunity, they don't interbreed; the genetic material of each is protected from
that of the other species. The difference in toe number is merely an easy way to tell
them apart—a feature having meaning only after we learned that they truly were separate
kinds.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.