The frecjuency of bolting was much higher at Vipond Park, and this is 

 likely the source of much of the difference between Arabis fecunda life 

 histories at the two sites. Bolting plants have higher annual fecundity and 

 much higher mortality than axillary flowering plants. Axillary flowering 

 plants are iteroparous (perennial or polycarpic), while bolting plants 

 approach the semelparous (annual or monocarpic) life history. 



Discussion of the environmental characters that cause these differences 

 in Arabis fecunda life history can only be speculative. Charleys Gulch is 

 warmer and likely has lower precipitation. Bare soil was more common and 

 vegetation cover was lower. The bleached color of the mineral soil at 

 Charleys Gulch may indicate a more extreme edaphic environment. These 

 conditions may result in slower growth but lower density-dependent mortality 

 which, in turn, should provide more stable population sizes and favor the 

 iteroparous habit. The high elevation of the Vipond Park site may provide an 

 more unstable habitat in which the semelparous habit and a long-term seed bank 

 are favored (van Groenendael and Slim 1988). 



The differences in life history traits exhibited among the populations 

 studied could be the result of genetic differentiation, phenotypic plasticity 

 (one genotype that produces different phenotypes under different conditions) 

 or both. Quantitative genetics studies are required to determine the basis of 

 the variation. Leeper et al. (in press) used starch gel electrophoresis to 

 investigate apportionment of genetic variation in Arabis fecunda populations, 

 including the three that we studied. Of 18 putative loci scored, 17 were 

 invariant; however, the one polymorphic locus had different frequencies among 

 the populations, suggesting a fair degree of differentiation. Results of the 

 germination studies indicate that there is genetic differentiation between the 

 Charleys Gulch and Vipond Park populations. Furthermore, they suggest that 

 there is a genetic difference between plants that bolt and those that do not. 



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