adversely affect population persistence if they were coupled with 

 other environmental challenges such as pollinator limitation or 

 climatic stress. 



The strong positive correlation between the proportion of 

 fecund inflorescences and total inflorescences and the strong 

 negative correlation between proportion of aborted inflorescences 

 and total inflorescences suggests two possible hypotheses: 



(1) Pollinator limitation. In years when fewer inflorescences 

 are produced, pollinators are less attracted to A^ scaphoides 

 resulting in lower levels of pollination, a lower proportion of 

 fecund inflorescences, and a higher proportion of aborted 

 inflorescences (Heinrich 1975) . 



(2) Resource limitation. In years with suboptimal growing 

 conditions (e.g., low soil moisture), fewer inflorescences are 

 produced, and a higher proportion of these are arborted (Ehrlen 

 1992, Harper and Wallace 1987, Stephenson 1981). 



The negative correlation between proportion of fecund 

 inflorescences and aborted inflorescences is consistent with both 

 hypotheses. These two hypotheses are not mutually exclusive 

 (Vaughton 1991) . 



Under the pollinator limitation hypothesis, a reduction in 

 total flowering inflorescences decreases pollination, thus 

 increasing the proportion of aborted inflorescences. Predation 

 reduces the number of flowering inflorescences; thus, the 

 pollinator limitation hypothesis predicts a positive correlation 

 between predation and abortion. If abortion is primarily the 

 result of resource limitation, removal of inflorescences by 

 predation should lower abortion levels. Consequently, the 

 resource limitation hypothesis predicts a negative correlation 

 between abortion and predation. 



The observed negative correlation between proportion of 

 aborted and predated inflorescences indicates that abortion is 

 caused primarily by resource limitation. Furthermore, these 

 results and the generally high annual levels of abortion suggest 

 that Astragalus scaphoides plants frequently initiate more 

 inflorescence than they have resources to mature. This behavior 

 may be the result of selection imposed by predation. A plant 

 that initiates more inflorescences than it can mature can loose 

 preflowering inflorescences to predation without sacrificing 

 reproductive output. If predation is low, the surplus 

 inflorescences are aborted. Thus, inflorescence predation can be 

 at least partly compensated for lower levels of abortion. 



Population persistence is determined by an interplay of 

 mortality, reproduction and recruitment. Monitoring Astragalus 

 scaphoides has shown that these critical demographic parameters 



14 



