^ 



» 



52 



b. J^ecific agents: Another possible means of seed 

 dispersal for H. aquatilis is by wildlife 

 disseminaticxi. Waterfcwl were frequently observed in 

 the pothole ponds; it is likely that, when feeding on 

 aquatic vegetation, these birds cxjuld ingest H. 

 aquatilis and distribute the seeds later in other 

 ponds. 



In addition, seed movement by manmals (i.e., deer, 

 bears, moose) eilso appears to be pxjssible. Deer and 

 moose brcwse in such ponds, and could thus ingest and 

 transport seeds. In Montana, signs of becu: foraging 

 were noted at the Lost Creek-Cilly Creek site (008) 

 late in the sunmer, after all water had dried from the 

 pond; dispersal between pods could perhaps also occur 

 in this way. 



Seed movement between pcHids, in sediments lodged in 

 the feet of these bird and mamnal species, may also be 

 possible. 



c. vulnerability of dispersal agents and mochanisns: To 

 the extent that habitat alteration might cause 

 permanent drying of its habitat, or inpacts on the 

 putative wildife di^iersers, the dispersal of B. 

 aquatilis could be influenced by disturbance. 



d. Kittems of propagule dispersal: Seed di^^ersed by 

 waterfcwl could peurtially explain the scattered 

 distributioi of ij. a quatilis in the Pacific Northwest; 

 in Moitana, di^jersal by waterfowl and maimals between 

 adjacent ponds could produce the clustered arrangement 

 of adjacent populations at the Lost Creek-Cilly Creek 

 Ponds (008-017), Dxf Creek (018, 019), Condon Creek 

 (020-031), Elk Creek (054, 055) and Lindbergh Lake 

 (001-004, 032-051) sites. Meinke (1982) also 

 suggested that H. aquatilis may be "...randomly 

 dispersed through the wanderings of migratory 

 waterfcwl," and that this could pnxJuce the wide, 

 patchy distributic»i pattern. In Idaho, H. aquatilis 

 has been present on the CVTibey property for at least 20 

 years, but has never occurred in more than one pond 

 (Ruth CXd/nbey, pers. comm.). This suggests that 

 dispersal mechanisms eure limited at this site. 



4. Seed biology. 



a. Amount amd variation of annual seed production: 



Evidence for the presence of a seed bank is reported by 

 Lesica et al. (1987) . At the Swan River OidxM (005) 

 site, examination of the surface 3 cm of soil from 

 three 2.25 dm^ quadrats in 1986 yielded an estimate of 

 approximately 200 seeds/m^. The presence of such a 

 seed bank should help buffer the occurrences from 



