|Wald, Eric - SDSU, BROOKINGS, SD|
|Larson, Gary - SDSU, BROOKINGS, SD|
|Johnson, W - SDSU, BROOKINGS, SD|
Submitted to: American Midland Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 5, 2005
Publication Date: October 15, 2005
Citation: Wald, E.J., Kronberg, S.L., Larson, G.E., Johnson, W.C. 2005. Dispersal of leafy spurge (Euphorbia esula L.) seeds in the feces of wildlife. Am. Midl. Nat. 154:342-357. Interpretive Summary: Ranchers, farmers and other land managers that have to fight infestations of the noxious weed leafy spurge often suspect that wildlife are transporting leafy spurge seed to new areas and consequently helping to spread leafy spurge to new areas. We investigated the possibility that deer, sharp-tailed grouse and turkeys were moving viable leafy spurge seed by eating it then depositing it on the ground in their feces. With pen trials with these three species of wildlife we determined that small amounts of leafy spurge could pass through the digestive tract of deer, sharp-tailed grouse and turkeys. We also collected feces from wild deer, sharp-tailed grouse and turkeys and determined that wild turkeys probably do not disperse leafy spurge seed in their feces while deer and sharp-tailed grouse may do so on a limited basis.
Technical Abstract: Leafy spurge (Euphorbia esula) was introduced into North America from Europe many years ago and has become a very problematic invasive plant in many areas of western United States and Canada. A number of mechanisms by which leafy spurge is dispersed to new areas are understood, but there are rough areas in pastures and wildlands where individual or small clusters of leafy spurge plants can be found that are a good distance uphill from older and larger patches of leafy spurge. In these situations, wildlife are suspected as possible dispersers of leafy spurge seed. One means that wildlife can disperse seed is by ingesting then excreting it in their feces. Fecal deposits of free-ranging deer (Odocoileus hemionus and virginianus; n=176), sharp-tailed grouse (Tympanuchus phasianellus; n=201) and wild turkeys (Meleagris gallopavo; n=206) were collected during a summer in Theodore Roosevelt National Park (TRNP) in western North Dakota, and for deer only in Medicine Lake National Wildlife Refuge (MLNWR) in northeastern Montana. Feces was evaluated for the presence of leafy spurge seeds and when any were found they were tested for germination. If they did not germinate, their viability was determined with tetrazolium. Only one intact leafy spurge seed was found in one grouse fecal deposit and it was not viable. No leafy spurge seed was found in turkey feces. Two seeds that appeared to be immature leafy spurge seeds were found in one fecal deposit from a deer in TRNP, but neither seed was viable. One leafy spurge seed was found in each of four deer fecal deposits from MLNWR. All of these seeds had seed coat scarification indicating they passed through the digestive system of deer, but only one seed was viable and germinated. Trials with captive deer (n=4), sharp-tailed grouse (n=4) and wild turkeys (n=4) were conducted to determine how leafy spurge seeds interact with the digestive systems of these animals. The only viable seeds defecated by the grouse and turkeys were seeds they excreted one day after ingesting them. No leafy spurge seeds were excreted by two turkeys, and only a few viable seeds were defecated by the other two turkeys. One grouse defecated a larger number of viable seeds but the other three grouse excreted only a few viable seeds. Most seeds did not survive passage through the digestive tracts of grouse and wild turkeys. Deer defecated viable seeds each of four days after ingesting the seed with most viable seed excreted on the first two days. All four deer excreted viable seeds, but as with the birds, most seeds did not survive passage through the digestive tracts of the deer. These findings along with those for the free-ranging animals indicate that wild turkeys probably do not disperse leafy spurge seed while sharp-tailed grouse and deer may do so on a very limited basis.