GEOG 235. Biogeography
	Mountain Sheep Biogeography: An Exercise

Below are basic descriptions of six species of mountain sheep found in Eurasia and North America. Maps show the modern distribution of these species and—in the case of O. canadensis—of subspecies. You are asked to reconstruct the historical biogeography of the members of the genus Ovis based on the textual and map information presented herein. Follow the steps outlined below.

Instructions:

1. Prepare a diagram showing the phylogeny of species in the genus Ovis. This may be a cladogram, a phylogenetic tree, or some hybridization of the two.
2. Prepare an area diagram that corresponds to the taxonomic one produced in part 1.
3. Write (in well written, paragraph format) a clear explanation of the evolution of the species and subspecies of Ovis and of the development of their contemporary distribution pattern. Demonstrate your understanding of basic concepts of biogeography (dealing with the origins, dispersal histories, evolution, speciation, environmental change, and extinction processes involved). You will be evaluated on the quality (and not length) of your explanation. My judgment of quality will be based not so much on your accurate unraveling of the historical biogeography of Ovis as on the statements you make that support your contentions and demonstrate your understanding of biogeography. You may use one or more explanatory diagrams or sketch maps as part of this essay.

Mountain Sheep (genus Ovis, Family Bovidae)

Some taxonomists classify mountain sheep into two subgenera, recognizing that two distinct body shapes occur:

• "Eurasian" forms (O. musimum, O. orientalis, and O. ammon) are long-legged and light-bodied. They inhabit open rolling plateau surfaces and foothills and are sympatric with ibex or goats that inhabit steeper slopes and cliffs.

• "American" forms (O. nivicola, O. dalli, and O. canadensis) are short-legged, broad-chested bighorn sheep. They are superb jumpers and climbers and inhabit precipitous terrain. They scramble up rock faces when in danger. "American" sheep evolved in the absence of goats.

Urials (O. orientalis) are most primitive in terms of taxonomic (phenotypic) characters. The subspecies on Cyprus is the smallest of the mountain sheep (80 lbs).

Siberian argali (O. ammon) are the largest of all mountain sheep (450 lbs).

The bighorn sheep (O. canadensis) is considered the most highly evolved of the sheep.
Among its subspecies, O. c. canadensis is largest; O. c. nelsoni is the most primitive—that is, most dalli-like. O. c. nelsoni inhabits the deserts of the Southwest; it is relatively small, and has the largest ears and longest tooth row (snout length) of all members of the species. Subspecies audubonii has become extinct in historic times.

Source: Mountain Sheep; A Study in Behavior and Evolution by Valerius Geist. (Chicago: University of Chicago Press), 1971.