Competition is defined as a rivalry or a battle of wills and opposing sides, and brings to mind the classic image of sports teams going head to head on the gridiron. But competition between species in the animal world takes on a different meaning, especially when the subjects in question are mule deer and elk.
Competition occurs when two species use the same limited resource, and one of the two suffers in some way because of that use. But for true competition to take place, the suffering must occur at the population level, where one of the two species has lower survival rates or fewer young that survive to adulthood. Merely viewing mule deer and elk in the same valley foraging on similar plants is not true species competition.
Given the definition of competition in wildlife, do elk, whose numbers have been increasing in the West over the past several decades, compete with mule deer, and if so, in what way does that competition affect mule deer populations? Looking at adaptations mule deer and elk have developed over time can provide clues that may help answer the question.
1. Energy - Summer heat and severe winter conditions place the greatest stress on mule deer and elk. Mule deer movements and foraging become restricted in snow depths of 10 inches or more, whereas elk are not adversely affected until snow depths reach 18 inches. If mule deer and elk are using the same resources in severe weather, elk will have the advantage.
2. Digestion - Mule deer have smaller stomachs than elk and forage on shrubs and forbs, compared to the grass-dominated diet of elk. Mule deer need better quality plants with greater digestibility than elk. If resources are restricted because of habitat or weather, elk would have the survival advantage.
3. Changes in habitat – Landscape changes across the west have created habitats that may be better suited for elk than mule deer.
4. Livestock - In some cases, deer and elk may completely leave an area that is heavily grazed by cattle. Competition between mule deer and elk may increase if these species are forced to move from preferred habitats to less suitable habitat types.
5. The Human Factor - Development in winter range affects mule deer more than elk because elk are capable of wintering in higher elevations than mule deer. Elk hunting seasons can cause elk to move into dense cover and forage in areas used by deer.
6. Parasites - Biting flies affect elk more than mule deer, and horseflies carry a disease called elaeophorosis, an arterial worm that causes blindness, malformed antlers, loss of muzzle and ear tissue, and death in elk. Mule deer are unaffected by the disease, but are hosts for the worm.
7. Predation - The effects predators such as mountain lions, black bears, coyotes, grizzly bears and wolves have on prey populations are dependent upon habitat conditions, the numbers of predators and prey, and the sex and age ratios of predator and prey populations.
8. Population Dynamics - Elk are longer lived, produce fewer young during their life, and are found in fairly stable habitats. Mule deer have shorter lives, produce more young during their life, and live in unstable habitats, or habitats that change over time.
Tom Keegan, Wildlife Manager with the Idaho Department of Fish and Game, said that making a statement that elk are responsible for mule deer declines would not be accurate because some mule deer populations have declined in the absence of elk. And Keegan said, "Other deer populations have grown and responded well in conjunction with growing elk herds.
“The problem I see is half the people wanting more elk and half the people wanting more deer,” said Keegan. “One piece of land won’t fit their expectations. And what people want quickly changes all the time. At some point, state agency managers are going to get stuck between a rock and a hard place every time they go down a management road.”
Fred Lindzey, Assistant Wildlife Cooperative Unit Leader and Professor at University of Wyoming, said habitat and weather are driving forces for mule deer.
“A lot of livestock management practices create grasses that benefit elk more than mule deer,” said Lindzey. “Elk can physiologically handle more roughage. So you end up with competition for the food resources. Habitat manipulations that we have brought about have largely favored elk over mule deer.”
Lindzey said weather increases the potential for competition between mule deer and elk. “There were very few historic records where we lost large numbers of elk to bad weather,” he said. “At the same time, we really lost a lot of mule deer during the severe weather of the 80s. Mule deer are extremely sensitive to severe weather patterns. The mule deer population is being knocked back in local areas, and elk are increasing, and weather has exacerbated the situation.”
Lindzey said interactions between mule deer and elk generally don’t occur long-term. “I think these interactions occur periodically,” said Lindzey. “You’ve got mule deer on that human-agriculture edge with the elk above them and people below them, and they can no longer drift further down into these valleys - it’s the old winter range problem. Elk are separated from mule deer by vegetation, but in a bad year, they fall down on top of the mule deer. Elk can physically displace mule deer or keep them from using the resources. This may happen one year out of six.” But that one bad year can hurt a mule deer population, especially when winter range and transition ranges are being lost to development.
“Mule deer are driven by environmental factors,” said Lindzey. “We’ve lost critical and valuable mule deer winter range. Most of these winter ranges just sustained mule deer through the winter. They don’t get fat on winter ranges – they just expect to break even. If you shorten those opportunities where they can move to secure the greatest reduction in energy – and that’s what is happening with all this oil and gas development - then in a bad winter, you lose the fawns. If you can’t access those resources to mediate the effects of weather, then you have adult survival problems. These guys are engineered to handle the weather that is dumped on them. But now we’ve started to muck up the good stuff.”
Lindzey stressed the importance of long-term research to give biologists the tools they need to make management decisions, respond to development issues and answer questions about mule deer and elk interactions.
“If there’s anything biologists are lacking as a group, it’s long-term research that elucidates the influence of potential impacts on populations. Without those data, we’ll always be sticking our thumbs in the dike.”
