Investigating Seed Dispersal Distances And Long Distance Dispersal Mechanisms Of The Invasive Plant, Alliaria Petiolata

Abstract

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.