Interspecific competition occurs when different species such as deer and domestic livestock compete for resources that are in short supply. Competition does not occur simply because two species are consuming the same types of food plants. It is possible for sheep, goats, cattle and deer to occupy the same range without competition if the animals are present in low numbers and there is a diversity and abundance of forage plants. Even when grazing animals are present in moderate numbers, competition is usually minimal. Competition becomes severe only when livestock numbers exceed the forage supply or deer numbers exceed the carrying capacity of the habitat. Several years after overstocking results in decreased plant vigor, forage production and livestock production potential. Range overutilization has a direct impact on deer habitat and the nutritional quality of deer diets.
Certain kinds of livestock are preferable to others when competition with deer for forage is a concern. Under similar stocking rates, competition between deer and sheep or goats. Because goat and deer diets are similar, they have a greater diet overlap than deep and other domestic species. However, competition will be minimal if deer and goat numbers are relatively low and forage is abundant. Sheep tend to eat mostly forbs and grass thus will often compete with deer for forbs, especially when they are scarce. Cattle compete the least with deer since they eat primarily grass, although they will consume some forbs and browse . On an overgrazed range, cattle will compete with deer for remaining forbs and browse. During a drought, when herbaceous plants have deteriorated or have been consumed, cattle will shift their diet to browse and may compete with deer.
Exotic species are significant competitors with white-tailed deer in some area of South Texas and in the Edwards Plateau. Some large species (for example, nilgai and eland) have diets similar to cattle, but most of the smaller deer species (for example axis, sika and fallow) have diets similar to white-tails. They prefer forbs and succulent browse tips, but unlike white-tails, they have the physiological capacity to effectively utilize grasses to obtain nutrients. Exotic deer do very well on Texas rangelands and can increase herd size rapidly. They compete directly with white-tailed deer, and because of their superior digestive capabilities, they can out-compete native deer in over populated habitats.
Intraspecific competition (competition among the individuals of the same species) is common among herds in many areas of Texas where the carrying capacity has been exceeded. This competition among deer can become significant in areas where predators have been eliminated, especially if there is little hunting pressure. Another factor that can contribute to overpopulation is a hunting policy of harvesting only bucks. The usual result is a high doe to buck sex ratio, low harvest rate compared to fawn survival, overpopulation and declining body condition.
Increasing Forage for Deer
Some ranchers feel uncomfortable about increasing their deer harvest and choose to artificially increase the carrying capacity of their ranch. One way is by providing supplemental feed. Feeding a deer herd is extremely expensive, and generally the costs of maintaining the additional deer far outweigh the financial returns. In addition, the extra nutrition provided by feeding will magnify the problem, resulting in increased reproduction. Fawning rates will increase and herd size will expand until it is once again above carrying capacity. Therefore, if the manager is not willing to increase harvest to compensate for herd growth, the strategy of supplemental feeding will not reduce forage competition. With a few possible exceptions, supplemental feeding is not financially profitable.
Another method to increase a habitat’s carrying capacity is the establishment of food plots. Food plots are sometimes irrigated to provide nutrient-rich green forage to deer diets that are seasonally deficient in quality and quantity of food plant. This method can be used to maintain higher deer numbers, but overpopulation can also occur if herd growth is not checked through harvest. Food plots have been successful in many areas of Texas in improving individual deer performance when used with a proper deer harvest program to keep deer numbers balanced with forage.
A third method for minimizing intraspecific competition is managing deer numbers through hunting so that the population is always below carrying capacity. This requires careful monitoring of deer numbers, deer body condition and seasonal habitat conditions. This management strategy is successful if forage availability and quality are adequate within the habitat of the deer herd. Improved deer herd nutrition should not be expected if livestock numbers are increased to take advantage of the additional high quality forage.