Document Detail

Food and predators affect egg production in song sparrows.
MedLine Citation:
PMID:  17089655     Owner:  NLM     Status:  MEDLINE    
Although the possibility that food and predators may interact in limiting avian populations has long been recognized, there have been few attempts to test this experimentally in the field. We conducted a manipulative food addition experiment on the demography of Song Sparrows (Melospiza melodia) across sites that varied in predator abundance, near Victoria, British Columbia, Canada, over three consecutive breeding seasons. We previously showed that food and predators had interactive effects on annual reproductive success (young fledged per female). Here, we report the effects on egg production. Our results show that food limits the total number of eggs laid over the breeding season ("total egg production") and that interactive food and predator effects, including food effects on nest predation, determine how those eggs are "parceled out" into different nests. Food addition alone significantly affected total egg production, and there was no significant interannual variability in this result. At the same time, both food and predators affected the two determinants of total egg production: "clutch number" (total number of clutches laid) and average clutch size. Both clutch number and size were affected by a food x predator x year interaction. Clutch number was lower at low-predator locations because there was less nest predation and thus less renesting. Food addition also significantly reduced nest predation, but there was significant interannual variation in this effect. This interannual variation was responsible for the food x predator x year interactions because the larger the effect of food on nest predation in a given year, the smaller was the effect of food on clutch number; and the smaller the effect of food on clutch number, the larger was the effect of food on clutch size. Potential predator and year effects on total egg production were thus cancelled out by an inverse relationship between clutch number and clutch size. We suggest that combined food and predator effects on demography could be the norm in both birds and mammals.
Liana Zanette; Michael Clinchy; James N M Smith
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Ecology     Volume:  87     ISSN:  0012-9658     ISO Abbreviation:  Ecology     Publication Date:  2006 Oct 
Date Detail:
Created Date:  2006-11-08     Completed Date:  2007-01-11     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0043541     Medline TA:  Ecology     Country:  United States    
Other Details:
Languages:  eng     Pagination:  2459-67     Citation Subset:  IM    
Department of Biology, University of Western Ontario, London, Ontario N6A 5B7, Canada.
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MeSH Terms
Clutch Size / physiology
Eating / physiology*
Oviparity / physiology*
Predatory Behavior / physiology*
Sparrows / physiology*
Time Factors

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