IntroductionAlliaria petiolata, an herbaceous plant, has invaded woodlands in North America. Its ecology has been thoroughly studied, but an overlooked aspect of its biology is seed dispersal distances and mechanisms. We measured seed dispersal distances in the field and tested if epizoochory is a potential mechanism for long-distance seed dispersal.MethodsDispersal distances were measured by placing seed traps in a sector design around three seed point sources, which consisted of 15 second-year plants transplanted within a 0.25 m radius circle. Traps were placed at intervals ranging from 0.25–3.25 m from the point source. Traps remained in the field until a majority of seeds were dispersed. Eight probability density functions were fitted to seed trap counts via maximum likelihood. Epizoochory was tested as a potential seed dispersal mechanism for A. petiolata through a combination of field and laboratory experiments. To test if small mammals transport A. petiolata seeds in their fur, experimental blocks were placed around dense A. petiolata patches. Each block contained a mammal inclusion treatment (MIT) and control. The MIT consisted of a wood-frame (31 × 61× 31 cm) covered in wire mesh, except for the two 31 × 31 cm ends, placed over a germination tray filled with potting soil. A pan filled with bait was placed in the center of the tray. The control frame (11 × 31 × 61 cm) was placed over a germination tray and completely covered in wire mesh to exclude animal activity. Treatments were in the field for peak seed dispersal. In March, trays were moved to a greenhouse and A. petiolata seedlings were counted and then compared between treatments. To determine if A. petiolata seeds attach to raccoon (Procyon lotor) and white-tailed deer (Odocoileus virginianus) fur, wet and dry seeds were dropped onto wet and dry fur. Furs were rotated 180 degrees and the seeds that remained attached were counted. To measure seed retention, seeds were dropped on furs and rotated as before, then the furs were agitated for one hour. The seeds retained in the fur were counted.ResultsFor the seed dispersal experiment, the 2Dt function provided the best fit and was the most biologically meaningful. It predicted that seed density rapidly declined with distance from the point source. Mean dispersal distance was 0.52 m and 95% of seeds dispersed within 1.14 m. The epizoochory field experiment showed increased mammal activity and A. petiolata seedlings in germination trays of the MIT compared to control. Laboratory studies showed 3–26% of seeds were attached and retained by raccoon and deer fur. Retention significantly increased if either seed or fur were wet (57–98%).DiscussionWithout animal seed vectors, most seeds fall within a short distance of the seed source; however, long distance dispersal may be accomplished by epizoochory. Our data are consistent with A. petiolata’s widespread distribution and development of dense clusters of the species in invaded areas.

Data is used to generate Fig. S1, which includes densities of rosettes and mature plants from 2004-2014 /*Data are rosettes, plotid (plot identification), counts, and quadrats. There are two woods each with two blocks. Quadno are quadrat numbers, numbers 1-11 indicate sample years from 2004-2014. Codes are SAS for PROC GLIMMIX.*/

Alliaria petiolata, a strict biennial in North America, can have an annual alternating high abundance of rosettes and flowering plants. We monitored changes in abundance of rosettes and flowering plants in permanent plots (2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014). Three times during our study, the alternating yearly cycle was not

Alliaria petiolata, an herbaceous biennial plant, has aggressively invaded North American woodlands. It has been extensively studied to understand why it is a successful invader, but certain aspects of its biology have been understudied such as seed dispersal distances and long distance dispersal mechanisms. We experimentally measured A. petiolata seed dispersal distances and determined if epizoochory (external animal transport) is a dispersal mechanism. To measure dispersal distances, seed traps were placed around three A. petiolata seed point sources to capture dispersed seeds at increasing distances away from the point sources. Eight mathematical functions describing dispersal distances were fitted to seed counts in traps via maximum likelihood.The lognormal and 2Dt functions were selected for analyses and both predicted that seed density rapidly declined as distance increased with mean dispersal distances of 0.56 and 0.52m and 95% of seeds dispersed within 1.22 and 1.14m, respectively.To determine if epizoochory is a dispersal mechanism, experimental blocks were placed around seven dense A. petiolata patches in summers 2013-2014. Each block contained a mammal inclusion treatment (MIT), which increased small mammal activity over a germination tray filled with potting soil, and a control, which excluded mammal activity. Seeds dispersed into trays were germinated and the seedlings counted. The increased mammal activity in the MIT resulted in significantly more A. petiolata seedlings than the control.Laboratory studies determined if A. petiolata seeds can attach and be retained by raccoon (Procyon lotor) and white-tailed deer (Odocoileus virginianus) fur, common woodland mammals. A small proportion (3-26%) of seeds attached and was retained by raccoon and deer fur. Attachment and retention significantly increased if either the seed or fur was wet (57-98%). These results are the first to experimentally determine that epizoochory is a seed dispersal mechanism of A. petiolata with raccoon and deer as likely dispersal agents.