The Three-Minute Outdoorsman: Wild Science from Magnetic Deer to Mumbling Carp

11. Deer and Their Subspecies

t h e t h r e e - m i n u t e o u t d o o r s m a n 52 11 deer and their subspecies fact or fiction? Anyone who has looked at more than one white-tailed deer in an area has usually noticed at least subtle differences between them: darker or paler, different patterns of white, different sizes even at the same age and sex. We are very attuned to seeing differences among people, even from the same family. If we were as astute in seeing (and smelling) deer, we would likely think they are just about as different as are kids in a family, and as are you from your aunts, uncles, and grandparents. Such is the nature of heredity— variation is the nature of life, and the closer you are to someone in your genealogy the more similar you tend to look. These sorts of comparisons can be taken a step further by comparing how deer look in one area with those that live elsewhere . Just about any organism that is distributed over a broad area shows some sort of regional differences, a sort of bar code linking them to their specific home area. The phenomenon is called geographic variation. Typically we think that geographic differences are related to how plants and animals adapt to geographically varying environments. Over longer periods of time, we think that geographic differences lead to new species. Another activity that students of geographic variation have engaged in is providing taxonomic names for recognizably different populations in different areas. Most readers know that animals have a genus and a species name in Latin, as part of a system of classification devised by famous eighteenth-century Swedish scientist Carl Linnaeus. Thus, when someone tells you they observed an Odocoileus virginianus, you know that they saw a white-tailed deer. The classification system is designed such that you know that other deer species in the same genus share more features in common than they do with species in other genera. Taxonomists (the namers) have also extended the Linnaean A L L T H I N G S D E E R 53 system below the species level to a category known as subspecies, which correspond to morphologically distinct populations living in different areas. Incidentally, for the record, species and subspecies are both singular and plural; thus, subspecie is not a word. By classifying the population as a subspecies, taxonomists call attention to the observation that these populations differ in some way from geographically more distant populations. For example, within species of warm-blooded vertebrates, individuals living in the north tend to be largest. We think this is because when body size increases, surface area increases as a square, but volume increases as a cube; therefore, as an animal increases in body size, it will lose less heat through its relatively smaller surface area and be better adapted to cold places. White-tailed deer are a good example (think of the pictures of huge-bodied Saskatchewan deer). This general phenomenon is called Bergmann’s rule, although there are exceptions. Back to subspecies. Although the species category is relatively robust, the same cannot be said for the subspecies category. The reason is the lack of consistent criteria for recognizing subspecies . Some confounding factors are the following: How many geographic areas were studied? How many specimens were examined ? How many features were studied? How much do they vary? Is the variation geographically discrete or continuous? Thus, a subspecies of one animal might be an arbitrary grouping based on subtle differences in coat color, whereas another subspecies might be a very clear and geographically distinct division. Some taxonomists adhere to a “75 percent” rule, where 75 percent or more of the individuals must be recognizable as one or another subspecies . However, most subspecies do not match even this goal. The standards are often lax, and it sometimes seems that there were no rules applied at all. To note an extreme example, the subspecies O. v. leucurus, from the Columbia River area, was based on a single individual that was not preserved but eaten; typically all scientific names are traced to a museum specimen so that it can be studied by others and serve as a perpetual reference. The subspecies category can be a total mess depending on T H E T H R E E - M I N U T...