i 



54 



8. Population ecxalogy of taxcn. 



A- General sunnaxy: In general, Howell ia aquatilis was observed to 

 ocaxpy less densely vegetated areas within the wetleinds where it 

 occaors. Ihis suggests that it cainnot conpete vigorously with 

 other aquatic plant species. In areas of more open water, the 

 species Ccin grew very densely, forming mats in seme ceises. No 

 specific obligate relationships are known. 



B. Positive emd neutral interactions: The submersed stems euid 

 leaves of H. acpjatilis were frequently observed to have egg 

 roeisses attached to them, as well as caddis fly cases. None of 

 these were observed to have a negative effect on the plants. 



C. Negative interactions. 



1. Herbivores, predators, pests, parasites and diseases: None 

 directly observed; it is likely that some pleuits are 

 ingested by browsing auiimals, euid/oi^ disturbed by movements 

 of the latter in the associated wetlands. 



2. OcBDpetition. 



a. Intraspecific: In several Montana populations (i.e., 

 Lindbergh lake (044)), H. aquatilis was observed to 

 grow very densely in open water. No adverse effects 

 were observed in such sites. 



b. Interspecific: TVro patterns were observed in Montana: 

 1.) in many ponds, the greatest densities of Ij. 

 aquatilis were found 2unound the pond margins, under the 

 cxjver of surrounding overhanging shrubs (Salbc spp. , 

 Alnus incana . Comus stolonifera ) . In this zone, other 

 emergent aquatic species do not occur in abundance, and 

 H. aquatilis is able to ^read throu^out such open 

 areas, often growing in thick mats; 2.) in pcaids 

 dominated throughout by Carex vesicaria and/or 

 Equisetum fluviatile, tJ. aquatilis was frequently 

 observed to oocx?3y openings among such vegetation. 

 Sijtiilcurly, in pcxids with open water in the center, H. 

 aquatilis was observed to be most dense in suoh areas. 

 While the species was found to occur amongst the stems 

 of other emergent plants, it was often not as abundant 

 in suoh situations. These observations suggest that H. 

 aquatilis may prefer more open micrc*iabitats within the 

 ponds it oocL^jies, and that it cannot conpete 

 vigorously with other aquatic plcint species. In Idaho, 

 Howell ia aquatilis does occur within the moderately 

 dense matrix of associated submergent species. 



3. Toodc and allelopathic interactions: None known or 

 observed. 



