Document Detail

Variation in litter size: a test of hypotheses in Richardson's ground squirrels.
MedLine Citation:
PMID:  17479749     Owner:  NLM     Status:  MEDLINE    
We studied litter size variation in a population of Richardson's ground squirrels (Spermophilus richardsonii) in Alberta, Canada, from 1987 to 2004. Litter size at first emergence of juveniles from the natal burrow ranged from 1 to 14; the most common litter sizes, collectively accounting for 41.0% of 999 litters, were 6 and 7. The number of offspring surviving to adulthood (attained on emergence from hibernation as yearlings) increased with increasing litter size, a result that was not predicted by Lack's "optimal litter size" hypothesis, Mountford's "cliff-edge" effect, or the "bad-years" effect. Contrary to the negative effects predicted by the "cost of reproduction" hypothesis, litter size had no significant influence on survival of mothers to the subsequent year or on the size of the subsequent litter. Rather, our results best fit the predictions of the "individual optimization" hypothesis, which suggests that litter size is determined by the body condition and environmental circumstances of each mother. Supporting this hypothesis, survival of individual offspring was not significantly associated with litter size. Additionally, year-to-year changes in maternal body mass at mating were positively associated with concurrent changes in litter size (r = 0.56), suggesting that litter size depends on the body condition of the mother. Because the mean number of recruits to adulthood increased as litter size increased (r2 = 0.96) and litter size increased with maternal condition, offspring productivity was greater for mothers in better body condition.
Thomas S Risch; Gail R Michener; F Stephen Dobson
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  Ecology     Volume:  88     ISSN:  0012-9658     ISO Abbreviation:  Ecology     Publication Date:  2007 Feb 
Date Detail:
Created Date:  2007-05-07     Completed Date:  2007-06-19     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0043541     Medline TA:  Ecology     Country:  United States    
Other Details:
Languages:  eng     Pagination:  306-14     Citation Subset:  IM    
Department of Biological Sciences, P.O. Box 599, Arkansas State University, State University, Arkansas 72467-0599, USA.
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MeSH Terms
Litter Size / physiology*
Sciuridae / physiology*
Survival Rate

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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