What is Competition?
  Competition between 2 species is a situation in which the 2 species use the same limited resource and 1 or both species suffer because of the interaction between them.  In addition, one or both species may have decreased survival or productivity leading to decreased population growth.

Energetics
  Deer and elk usually select habitats and behave so that they conserve energy. They must continually make choices to maintain a positive energy balance.

Snow and Winter Severity  
   Winter weather can be very bad for mule deer.  Snow depth, cold temperatures and wind all contribute to reduced mule deer survival and productivity in following years. Elk can use areas with higher snow depths than deer.

Digestive Physiology
  Although deer and elk can and do eat the same types of food at times, there are physical differences that give elk an advantage over deer. Stomach size and body size require deer to eat higher quality foods to survive. In general, elk are able to eat prefered deer foods, but deer rarely eat common elk foods. Also, elk eat much more than deer, therefore it is more likely that foraging elk will impact deer more likely than deer will impact elk.

Digestion and Chemicals in Plants
  Many plants contain chemicals that affect digestion.  Because deer depend on more rapid digestion than elk, chemicals that slow digestion many be more likely to affect deer.

Habitat and Diet
  Deer tend to eat shrubs and forbs while elk eat more grasses and some forbs. Further, elk usually eat more plant species than deer and are less selective in which plant parts are eaten. Even with this natural separation, some conditions such as snow depth, can lead to greater diet similarity and competition for limited food sources.

Succession and Habitat Change
  Habitat disturbances in the 1900s started a process that increased shubs in areas that were previously mostly grasses or dense forests. Those changes provided good to excellent deer habitat temporarily.  Plant succession, however is a continuous process and in many places these shrub communities have grown into woodlands or have been converted back to grasslands. This change favors elk over deer.

Livestock
  Diet overlaps occur between sheep, cattle and deer.  Livestock use of browse tends to be highest when ranges are overgrazed. For example, cattle prefer to feed on grasses but switch to bitterbrush when grass is depleted or becomes overgrown and coarse. In addition, deer and elk tend to shy away from cattle. The effect between them is not known, however, if deer and elk do not look for food around livestock grazing areas, then less area is available to them which may increase the competition between them.

Effects of Human Activites
   Human development on big game habitat is a serious problem for mule deer and elk. In most areas, development on winter range causes the most problems because the animals are most stressed in the winter. These activites affect both species, but seem to have more affect on deer because development tends to concentrate on lower elevation winter range. Elk normally winter at higher elevations than deer. In addition, human transportation systems are normally at lower elevations and will tend to affect deer more than elk.

Parasites
  Biting flies, particularly horseflies, may cause greater harassment for elk than deer in some areas. Some even speculate that elk may migrate to higher elevations to evade horseflies as much as search for high quality foods. Another negative effect of horseflies is the transmission of disease, which can limit elk populations but does not affect mule deer.

Population Dynamics
  The two species have different life structures. Elk generally live longer than deer. Mule deer generally have greater reproductive potential because yearling does are twice as likely to breed as yearling cows. Also, adult does typically produce twins, but adult cows generally have a single calf.
   The survival of young is affected mostly by winter conditions, however weather conditions in other seasons also produce an effect. In general, deer are more affected by poor weather conditions than elk. This is shown by the fact that deer populations tend to be more variable than elk populations.