White-tailed deer (Odocoileus virginianus) are herbivores that feed primarily off the plants present within their habitat. Recent studies have been conducted to determine if the abundance of white-tailed deer in a habitat can affect the vegetation growth in that area. Similarly, can climate, which affects the health of plant species, also affect the abundance of white-tailed deer? Collectively, these studies focus on the relationships between biotic (living) and abiotic (non-living) factors and the white-tailed deer.
How does the size of the deer population affect the habitat?
The primary means by which the habitat is impacted is through over-browsing. This overbrowsing leads to soil disturbance, affects interdependent relationships amongst plants, and changes the dynamic of the vegetation.
Deer populations have a large impact on the forest environments they inhabit, including the plants they use as food. Over-browsing by the deer population largely decreases plant cover and diversity in the forest. This occurs as a result of soil disturbance caused by deer browsing. The soil disturbance affects the competition between plants, such as white-birch trees and other browsing-tolerant species. The population of the browsing-tolerant species is much larger than the other populations. The vast abundance of the browsing-tolerant species makes them the dominant species in the forest, thereby reducing the overall diversity.
Plant communities also have very strong interdependent relationships. The interdependent relationships of plants are affected by deer browsing and soil disturbance. This causes strong cascading effects on the entire plant population in the forest, resulting in a positive correlation between the abundance of deer and the cascading effects on the plant population.
By assessing the variation in diet quality, body mass, hind foot length and reproduction rates over the period of 25 years, the relationship between birth and death rates, along with chronic browsing, was revealed. Studies have shown that growing herbivore deer populations have a negative effect on vegetation due to over-browsing, as implied above. White-tailed deer have a high population density leading to a self-provoked reduction in their food source. The quantity of preferred vegetation has been depleted so significantly that the deer have changed their winter diet to now feed on the balsam fir. The abundance of balsam fir has consequently decreased, leading the deer to now rely on leaf litter on the forest floor during the winter months. In this study of diet quality, it was found that nitrogen content was higher in an earlier sample compared to 30 years later. This demonstrates that diet quality declined between the two periods. Poor diet can negatively affect the pregnancy and survival rate of the deer themselves.
The body mass of white-tailed deer was studied during hunting season over three different time periods. It was found that body mass was also negatively affected by food shortage, and males were more severely impacted due to their higher nutrition requirements. Finally, the reproduction rates of female white-tailed deer did not change significantly, nor did the number of ovulations change in a 25-year period, despite the decrease in food quality. Interestingly, the reproductive habitats did change as the size of the litters at ovulation decreased moderately. This was likely in an effort to conserve energy with a smaller litter size. It is clear that the over-browsing of the overabundant deer population is negatively impacting the size of the younger population.
How do the environmental conditions impact the density of the deer population?
The environmental conditions impact the density of the deer population as it causes a decrease in reproduction and birth rates.
While population size can have a large impact on habitat, weather patterns can affect the density of white-tailed deer, or so a study conducted on Articosti Island, Quebec, over a 23 year period, suggests. The study aimed to shed light on which seasons had the greatest effect on reproduction and survival rates. By studying female deer specifically, findings suggested that autumn and spring seasons had the greatest effect on reproduction rates. Young female deer were constricted the most in autumn, when compact, deep snow became a debilitating factor with respect to food foraging and lactation. These lower reproduction and birth rates lead to a lower abundance of white-tailed deer in the population. Reproduction was found to be at the highest point in the spring months, where a vast amount of high-quality plant material was available. In addition, an abundance of rainfall appeared to positively affect the lactation rates of female white-tails 10 years or older. In comparison, winter was found to have a far less effect on survival than most would assume. Essentially, it is population density, along with the spring and autumn seasons, that has a great impact on deer abundance.
In conclusion...
White-tailed deer, like most species, do best in optimal conditions. When weather conditions are not optimal, deer population can be affected. The relationship between weather and population density can, in turn, affect the surrounding habit in which the deer occupy. This relationship is not uncommon in the animal kingdom, where environment and species go hand in hand. In the end, both the environment and the abundance of deer end up affecting each other, as a large population of deer can over-browse impacting their environment, while the environmental conditions can increase or decrease reproduction and birth rates of the deer.
