39 



I The characteristic which may be roost ijtportant in 



W maintaining the pothole ponds inhabited by H. aquatilis is 



that they generedly always dry corpletely by the end of the 

 growing seasoi (late August-S^jtember in Montana) . Such 

 drying inhibits the rate of muck aocunulaticMi (Reuter 1986) , 

 and may serve to maintain these ponds in an earlier 

 emergent suooessional stage. 



In pcxris which are more suooessional ly advanced, and which 

 may remain wetter for most of the growing season, Typha 

 lati folia and Nuphcu: veuriegatum are more frequent. In 

 Montana, Howell ia acaiatilis occurs in association with J. 

 lati folia in 12 such ponds or wetlands (Condon Creek (031) , 

 Dog Creek (018), Lindbergh Lake (004, 012, 032, 033, 037, 

 040, 042, 046, 047, 048), and Swan River Oxbow (005)); it is 

 associated with N. varieqatum in three locations (Last 

 Creek-Cilly Creek Ponds (Oil, 012), Lindber^ Lake (047)). 

 In many cases, these ponds support less vigorous populations 

 of IJ. aquatilis . pxassibly owing to the advancing succession 

 and deeper unconsolidated botton sediments of such habitats. 



Suooessional trends at the Idaho site could not be 

 discerned due to the limited nuniber of visits made to the 

 2upea. Vemzd ponds have been present at the site for at 

 leeist 20 yezurs (Ruth O^nbey, pers. conn.) . 



f Despite the fact that H. aquatilis occurs over a large 



geographic area, it is ecologically adapted to a narrcMly 

 defined aquatic habitat. Ihus, any direct inpacts on its 

 habitat may be more li3cely to cause extirpation. Ihe 

 ^lecies does not appear to be capable of colonizing 

 disturbed habitats. 



6. Dependence on dynamic aspects of biotic associaticns and 

 ecosysten features: Howellia acMatilis occurs in shallcw 

 ponds and wetlands which generally contain water from 

 ^ring to mid- or late sutmer, d^sending on climatic 

 conditions. In the majority of cases, at least in Montana, 

 these habitats then dry coirpletely near the end of sunmer 

 (September) ; in seme cases in which tJ. aquatilis occurs near 

 the margins of deeper ponds, these margins may dry out while 

 the center remains filled. Thus, the species appeaurs to be 

 adapted to 'Vernal pool" conditions; substantial seed 

 germination nay require yecurly drying after seed dispersal. 

 This habitat relationship would surely be closely influenced 

 by yeeurly variation in precipitation amounts, e^secially 

 sncw depth and resultant run-off. In Washington, some of 

 the ponds which contain ]i. aquatilis were dry through all of 

 1987; it remains to be seen hew the populations will respond 

 once these sites have water in them again (J. Gamon, pers. 

 comti. ) . 



