Deer, Plants, and Itty Bitty Mammals

It’s November. In Wisconsin, that means that everyone is obsessed with one animal: white-tailed deer (Odocoileus virginianus). If you are not hitting them with your car, you are probably hunting them. If you are not doing either of those, you have at least seen them.

As often overabundant megafauna, they tend to have a large impact on their environment. Deer selectively consume a variety of plants, typically leaving less palatable plants to proliferate, including non-natives. As a result, a habitat that might have once had a high diversity of native plants can become taken over by a diversity of non-native, inedible plants (5). However, in areas where this happens, deer become more willing to munch on some of the less palatable native and non-native plants (5).

While the deer adapt to other foods, their preferred snacks, such as Trillium grandiflorum, can be extirpated after only a few decades of overpopulation. One study found that, in


Trillium grandiflorum. Photograph by Mark A. Wilson.

areas where deer are not hunted, they can consume about half of the reproductive Trillium (1). On the occasions that the seed is ripe, deer are viable seed dispersers and have been found to help the plant migrate (6). That is a rather rare occurance, though. Herbaceous plants like Trillium can be eaten easily with just one bite and often are eaten before a seed is ripe, limiting the ability of the plant to reproduce (1).


Trillium is just one of the many plants that deer love to eat, often leading to limited vegetation cover for small prey mammals, such as mice, voles and shrews. The larger species, such as white-footed mice (Peromyscus leucopus), southern red-backed voles (Myodes gapperi), woodland voles (Microtus pinetorum), and northern short-tailed shrews (Blarina brevicauda) tend to have lower populations in highly browsed habitats (3, 5). This may be due to being more easily seen by predators, but may also have to do with differences in microclimates, in the case of the voles and shrews (3).

The populations’ failure to thrive around deer may also be due to limited food. For


Peromyscus leucopus. Photograph by Shawn P. Carey.

example, white-footed mice rely on acorns for food when acorns are available, but deer will also consume acorns (4). Other food sources, such as arthropods, can be limited by deer as well (2). Deer trample fallen leaves year round, hastening decomposition, and consume them in winter (2). As a result, there are less places for invertebrates to hide (2).

Unfortunately, deer overabundance is fairly common, and the ecological impacts I described are only some of the effects that have been found and there are likely to be some still not discovered. While they were limited by predators such as wolves (Canis lupus) and mountain lions (Puma concolor) in the past, the most limiting factor now is resource availability and hunting.

But what are the impacts of hunting?

  1. Augustine, D. J., L. E. Frelich. 1998. Effects of White-Tailed Deer on Populations of an Understory Forb in Fragmented Deciduous Forests. Conservation Biology 12:955-1004.
  2. Bressette, J. W., H. Beck, and V. B. Beauchamp. 2012. Beyond the browse line: complex cascade effects mediated by white-tailed deer. Oikos 121:1749-1760.
  3. Byman, D. 2011. The Effects Of Deer Exclosures On Voles and Shrews In Two Forest Habitats. Northeastern Naturalist 18:509-520.
  4. Byman, D., S. D. Harding, and F. W. Spear. 2013. Demographic Effects of White-Tailed Deer (Odocoileus virginianus) Exclosures on White-Footed Mice (Peromyscus leucopus). American Midland Naturalist 170:171-183.
  5. Urbank, R. E., C. K. Nielson, G. A. Glowacki, and T. S. Pruess. Effects of White-tailed Deer (Odocoileus virginianus Zimmerman) Herbivory in Restored Forest and Savanna Plant Communities. The American Midland Naturalist 167:240-255.
  6. Vellend, M., J. A. Myers, S. Gardescu, and P.L. Marks. 2003. Dispersal of Trillium Seeds by Deer: Implications for Long-Distance Migration of Forest Herbs. Ecology 84:1067-1072.

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