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THE EFFECTS OF WHITE-TAILED DEER POPUTALTION ON PLANT DIVERSITY AND VEGATAION DENSITY July 6, 2010 INTRODUCTION Population ecology is the study of how a group of organisms relate to each other and their environment. The carrying capacity is the maximum sustainable population for an area, and is determined by a set of limiting factors, such as low food supply, disease, predators, and limited space. Mortality, the death rate, and natality, the birth rate, affect the growth of populations. When natality is slightly higher than White-tailed deer (Odocoileus virginianus) gets their name from the underside of their tail being covered in white hair, and when running holds it up so that the underside is visible. The white-tailed deer is an herbivore and eats both woody and herbaceous plant species. The normal habitat of the white-tailed deer is heavily wooded forests across the continent of North America. Their mating season begins in September and lasts into late January. When Europeans first came to America, white-tailed deer populations were free and uncontrolled. They were a primary choice for hunters for their meat and fur. Trees were also heavily cut down for lumber, and took away habitats for deer. Eventually, they were hunted so much that there were fewer than 150,000 white-tailed deer across the country. With the realization that the deer were dying out, hunting regulations were established, trees were replanted and being conserved and local housing developments away from cites called suburbs were created, giving white-tailed deer more habitat and protection from hunters. Also, major predators of the deer were hunted and removed in order to increase the natality rate of deer and decrease the mortality. Today, deer populations are higher than ever. In some places, there are more than 140 per mile². There are more habitats for deer, like national parks, where hunting is not allowed. 1 P:\RMSC\RMS\Group Papers\Deer Populations- 2010.docx Save: 10/2/2015 10:09 AM Printed: October 2, 2015 Food selection by white-tailed deer is mainly a function of seasonal availability, palatability, and nutritional factors. Palatability is distinction between food choices based on taste. The white-tailed deer eat many herbaceous and woody stem species of plants, such as clovers, berries, nuts, evergreen stems and leaves, and fruit. Besides palatability, white-tailed deer choose food based on nutritional value as well. Sources of minerals like calcium, protein, and energy. Protein is essential for proper growth, weight gain, appetite, and milk secretions. Without proper protein intake, does run the risk of giving birth to an unhealthy fawn or not being able to support the fawn once born, decreasing natality. Deer have a special need for high energy foods during the breeding season and in cold weather. Many deer, especially fawns, die as a result of energy deficiencies, increasing mortality. High white-tailed deer populations cause depletion of favored vegetation and therefore affect the diversity of ecosystems. Many forests have become overwhelmed with plants like heyscented fern and black cherry trees because they are the few plants that deer do not find palatable. Hey-scented fern used to cover less than three percent of Pennsylvania forest floors. Now, because deer devour its competition, this fern dominates more than a third of the forested area in Pennsylvania and throughout the northern United States. The higher the deer populations, the more of a competition for food there is between themselves and other wild animals. Bear and squirrels are threatened by the white-tailed deer’s devouring of wild berries and nuts, along with other plants that provided shelter for them. Not only do they affect other populations, but themselves as well. The less food there is to eat, the more malnourished the white-tailed deer become, increasing mortality. This also decreases natality because the does do not have enough nutrients to support both a fetus and themselves, and have miscarriages. 2 P:\RMSC\RMS\Group Papers\Deer Populations- 2010.docx Save: 10/2/2015 10:09 AM Printed: October 2, 2015 METHODS Two sites were used to conduct the experiment: Catoctin mountain national park and Frederick municipal forest. Both sites were located just outside of Frederick, Maryland. Catoctin Mountain Park was our experimental site because of its high deer densities. Being a national park, there is no hunting allowed at Catoctin national park. Also, its close proximity to Camp David caused issues and a permit was needed in order to conduct the experiment. Frederick municipal forest was used as our control site since it was especially set aside for environmental reasons. Hunting is aloud there. Data was collected on July 7, 2010. We measured the total stem abundance for groundcover and understory levels. Plants that qualified as ground cover had to be less than 30cm tall. We counted all the plants that were inside our 1m² quadrats. All different species of plants were recorded and then individually counted the number of stems for each species. Grass species were counted in clumps instead of by stems because grass is a clumping species. Any plants that were not identified during testing were brought back to the lab for further research into their identification. Plants that qualified for understory had to be greater than 30cm tall but less than 5cm in diameter at breast height (about 1.37m). We counted the understory in 4m² quadrats. All species found were identified and recorded. Plants that were preferred by deer were picked out and tested between the two study sites. 3 P:\RMSC\RMS\Group Papers\Deer Populations- 2010.docx Save: 10/2/2015 10:09 AM Printed: October 2, 2015 We used the Shannon-wiener index to calculate species richness and species evenness. We also used a robel pole to measure the cover density of the vegetation at each site. The robel is 1.5m in length and has 15 tape rings spread 10cm apart. The pole is placed in the middle of the quadrat. While one person holds the pole, another person walks 4m out and crouches to about 1 m in height and counts the number of rings the can see on the pole. This is repeated 3 more times, 1 for each cardinal direction. The four measurements were than averaged together for a mean cover density for each quadrat. RESULTS We found that there was a significant difference in the preferred groundcover stem abundance, cover pole density, preferred understory stem abundance, and understory Shannonwiener index data. At CMP we found that there was a total of 17 different plant species in the groundcover and understory, while at FMF there was 26 different plant species. We found that there was no significant difference in groundcover stem abundance between CMP and FMF. The average stem abundance of each quadrat at CMP was 16.7 and the standard deviation was 14.6. The average stem abundance of each quadrat at FMF was 20.5 and the standard deviation was 8.6. We also found that there was no significant difference between the understories between each of the study sites. The average stem abundance of each quadrat at CMP was 2.3 and the standard deviation was 6.9. The average stem abundance at FMF was 8.2 and the standard deviation of 6.5. 4 P:\RMSC\RMS\Group Papers\Deer Populations- 2010.docx Save: 10/2/2015 10:09 AM Printed: October 2, 2015 We found that there was a significant difference in the preferred stem abundance in groundcover at FMF over CMP with FMF having an average preferred stem abundance of 6.7 and a standard deviation of 6.5, while CMP had an average preferred stem abundance of 1.1 and a standard deviation of 1.3. We also found that there was a significant difference in preferred stem abundance in understory at FMF over CMP with FMF having an average preferred stem abundance of 1.9 and a standard deviation of 2.1, while CMP had an average preferred stem abundance of 0.1 with a standard deviation of 0.3. We found that there was a significant difference in Cover pole density at FMF over CMP with FMF having an average cover pole density of 3.6 and a standard deviation of 3.7, while CMP had an average density of 0.45 and a standard deviation of 1.4. We found that there was no significant difference in the Shannon-wiener diversity in the ground cover. FMF had an average of 1 and a standard deviation of 0.4 and CMP had an average of 0.6 and a standard diversity of 0.5. We found there was a significant difference in understory Shannon-wiener value at FMF over CMP with FMF having an average of 0.6 and a standard deviation of 0.8 and CMP having an average of 0 and a standard deviation of 0. CONCLUSIONS AND DISCUSSION The results of our study show that we can reject our null hypothesis for ground cover preferred stem abundance, understory preferred stem abundance, cover pole vegetation density, and understory Shannon-Wiener diversity. We fail to reject all other of our hypothesis for groundcover and understory preferred abundance, and groundcover Shannon-Wiener index. 5 P:\RMSC\RMS\Group Papers\Deer Populations- 2010.docx Save: 10/2/2015 10:09 AM Printed: October 2, 2015 Therefore, our research shows that the white-tailed deer population does affect vegetation density, preferred stem abundance, and diversity at the understory level, but does not affect the overall stem abundance. We observed a difference in understory stem abundance between CMP and FMF, but our statistical test showed that it was not significant. This might have been caused by outliers in our understory data at CMP. One of the test plots there was overly abundant og blueberry shrubs (Vaccinium ovalifolium) at the understory level compared to the rest of our test plots there. This one plot might have increased the mean stem abundance collected as well as the variance of the data. With a higher mean and variance, the two test sites have a greater chance of not being statistically different in regards to the t test. We found that the preferred abundance was significantly different between our two test sites, but total stem abundance was not. We believe this is because since deer eat palatable food over non-palatable food, the non-palatable food might be taking over the preferred food once was. So, if the white-tailed deer eat all of the palatable food, CMP and FMF will be left with dominantly non-palatable food. Our data also showed that there was a significant difference for Shannon-wiener at the understory level but not at groundcover. This could have been influenced by seeds sprouting in the groundcover that may soon be eaten. Also, the understory shows the effect over time, meaning that it takes longer for understory plants to grow than groundcover. So if the groundcover plants are eaten before they have the possibility to grow into understory plants, then there will not be an understory. These results can help show how deer are impacting the ecosystem. High deer densities might change the composition of future forests by over eating groundcover plants that would normally mature into shrubs and trees. The over story at each of our sites is mainly made up of 6 P:\RMSC\RMS\Group Papers\Deer Populations- 2010.docx Save: 10/2/2015 10:09 AM Printed: October 2, 2015 oak trees, but while testing, we saw many maple tree saplings, showing that in the next fifty to eighty years, we might expect a change in the over story at CMP and FMF, or lose it all together. In order for there to be a change in understory, white-tailed deer densities will need to be reduced. This will give plants and trees a better chance of surviving to adulthood. This would also help restore plant species that have been extirpated by the deer. Extirpated means that a plant species would be almost completely removed from one area. Plants like blueberry shrubs and hay-scented fern are becoming more abundance because the deer do not eat them as much because they do not find them palatable. With less plant sources available for deer and other herbivores, there will in effect be less herbivores overall. Having a small herbivore population will cause there to be a smaller carnivore population, since they will have limited food supplies. Less plants sources will also cause there to be less cover for birds and squirrels, increasing their own mortality. The high white-tailed deer populations will eventually affect themselves. Their mortality will increase because less food sources will lead to starvation. Natality will decrease because of malnutrition for does. Also, a lack of understory vegetation will lead to less cover for fawns, increasing their likelihood of being killed by predators. The white-tailed deer might start emigrating in order to find better food resources. There are many problems and improvements that can be made for future studies. Some plants found at CMP were not found at FMF and vice versa. This could have been caused by the way the experiment was conducted and not actually on the composition of the forests. Ways to improve future studies might be to enlarge the sample size and quadrat size, and to do more transects in different directions. The greater the area tested, the more accurate our results will be and the more representative of the entire forest it will be. Also, if there were twice as many observers and recorders, there would be less of a probability for human error. Further questions 7 P:\RMSC\RMS\Group Papers\Deer Populations- 2010.docx Save: 10/2/2015 10:09 AM Printed: October 2, 2015 regarding our research and related studies might be are the deer leaving permanently or just for dinner? Are other herbivore populations affecting vegetation as well? Did the time of our study affect our results? TABLES AND GRAPHS Understory Stem Abundance 20 15 10 5 Mean 0 CMP FMF -5 -10 Test sites Understory Preferred Stem Abundance 5 Axis Title 4 3 2 Mean 1 0 -1 Cmp FMF Study sites 8 P:\RMSC\RMS\Group Papers\Deer Populations- 2010.docx Save: 10/2/2015 10:09 AM Printed: October 2, 2015 Understory Shannon-Wiener Diversity 1.5 Axis Title 1 0.5 Mean 0 CMP -0.5 FMF Study Sites 9 P:\RMSC\RMS\Group Papers\Deer Populations- 2010.docx Save: 10/2/2015 10:09 AM Printed: October 2, 2015 REFERENCES Carson, W., Banta, J., Royo, A., Kirschbaum, C. (2005). Plant Communities Growing on Boulders in the Allegheny National Forest: Evidence for Boulders as Refugia from Deer and as a Bioassay of Overbrowsing. Natural Areas Journal, 25(1). 10-16. Enger, E., Ross, F., Bailey, D. (2007). Concepts in Biology: Twelfth Edition. Boston: McGraw Hill. Fergus, C., Shope, Bill. (2007). White-tailed Deer. Wildlife Notes. 10 P:\RMSC\RMS\Group Papers\Deer Populations- 2010.docx Save: 10/2/2015 10:09 AM Printed: October 2, 2015 Halls, L. (1984). What Do Deer Eat and Why. Wildlife Management Handbook. 11-16. http://cnrit.tamu.edu/crgm/IRR2/1984/What%20Do%20Deer%20Eat%20And%20Why.p df Levy, Sharon. (2006). A Plague of Deer. BioScience, 56 (9). 718-721. Liscinsky, Stephen A., et al. (2001). What Do Deer Eat? Pennsylvania Game News. Miller, Scott G., Bratton, Susan P. (1992). Impacts of White-tailed Deer on Endangered and Threatened Vascular Plants. Natural Areas Journal, 12(2). 67-74. Porter, William F., Underwood, Brian H. (1999). Of Elephants and Blind Men: Deer Management in the U.S. National Parks. Ecological Applications, 9(1). 3-9. Sandt, Joshua L. 1997. A Brief History of Deer in Maryland and the Northeast. In Deer as Public Goods and Public Nuisance: Issues and Policy Options in Maryland, ed. Bruce L. Gardner, pp. 1-3. College Park, MD: Center for Agricultural and Natural Resource Policy, October 27. Toops, Coonie. (1999). By Leaps and Bounds. National Parks, 73(9). 30-33. Waller, Donald M., Alverson, William S. (1997). The white-tailed deer: a keystone herbivore. Wildlife Society Bulletin, 25(2). 217-226. 11 P:\RMSC\RMS\Group Papers\Deer Populations- 2010.docx Save: 10/2/2015 10:09 AM Printed: October 2, 2015