Variability in life histories 



Life history theory predicts tradeoffs between traits that will maximize 

 fitness for a particular environment. In particular, there is thought to be a 

 negative relationship between reproduction and growth and survival. Some 

 environments favor slower growth, greater age at first reproduction, smaller 

 output per reproductive bout, and greater longevity. Other environments 

 select for shorter lifespan, early maturity and larger reproductive output per 

 bout. Early maturing, highly fecund populations have a higher intrinsic 

 population growth rate. Early maturity is favored in environments where adult 

 mortality is relatively high or highly variable (Stearns 1992). In plants, 

 the extreme case is the annual habit. 



There was great variation in life history traits among the three 

 populations studied. In most cases, the Charleys Gulch and Vipond Park 

 populations occupied the two extremes of life history trait continua with the 

 Lime Gulch population intermediate. For the purpose of this discussion, we 

 will compare the former two populations, bearing in mind that the Lime Gulch 

 population was similar to Charleys Gulch for some traits but more similar to 

 Vipond Park for most. 



The Arabis fecunda population at Charleys Gulch had a lower recruitment 

 rate but higher overall as well as new recruit survivorship. On average, 

 plants grew more slowly, were older at first reproduction, and had lower 

 annual fecundity as a result of producing fewer seeds per fruit. The Vipond 

 Park population had higher recruitment, faster growth, and higher mortality. 

 Annual fecundity was higher and plants became fecund at an earlier age. 

 Population size was more stable at Charleys Gulch than at Vipond Park. The 

 Vipond Park population demonstrated germination traits that make a long-term 

 seed bank more likely than at Charleys Gulch. 



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