F. POPULATION DEMOGRAPHY AND BIOLOGY 



46 



€ 



1. PHENOLOGY: Collection dates in Montana range from May 10 to 

 August 1. The indeterminate infloresence can have prolonged 

 flowering well beyond the May-June period of peak flowering. 



■ It is easiest to spot when in flower but cannot be 

 identified with certainty unless fruits are present. 



2. POPULATION SIZE AND CONDITION: The two recent collections 

 in Montana represent small populations or population waifs. 

 The two sets of label information noted the number of plants 

 observed as "one" and "few"; these populations are possibly 

 extirpated. 



3. REPRODUCTIVE BIOLOGY: Rorippa calycina has two reproductive 

 adaptations as a colonizing species: it is self-compatible, 

 and has strong vegetative reproduction (Mulligan and Porsild 

 1966; cited in Lichvar 1981). 



The restriction of this species to old shoreline zones 

 suggest that its seeds are disseminated by water. The 

 "migrant" population in the Northwest Territories is thought 

 to have been dispersed by waterfowl (Rollins 1993) . 



POPULATION ECOLOGY 



1. BIOLOGICAL INTERACTIONS 



a. COMPETITION: As a colonizing species, it is likely to be a 

 poor competitor. 



b. HERBIVORY: It is reported as a decreaser under livestock 

 grazing (Lichvar 1981) • 



LAND OWNERSHIP: The McCone County population (EG #001) is on 

 private land, though BLM administers subsurface mineral rights. 

 The recent collection in Choteau County along the Missouri River 

 (EG #005) was probably within the highwater mark and would 

 therefore be administered by the Montana Department of State 

 Lands. 



I. ASSESSMENT AND MANAGEMENT RECOMMENDATIONS 



1. THREATS TO CURRENTLY KNOWN POPULATIONS: In Wyoming, it has 

 been noted as susceptible to grazing, vulnerable to 

 trampling where it occurs in heavily-used recreation areas, 

 and potentially impacted by increases in reservoir size ^ 

 (Lichvar 1981) . Some of its Wyoming sites are also invaded^ 

 by noxious weeds. Nevertheless, it appears that the 



