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SUMMARY:Fledging mass and survival in a wild bird population: contribution
 s of multi-level processes and selection by a top predator - Sandra Bouwhu
 is and Oscar Vedder - University of Oxford\, UK
DTSTART:20130115T160000Z
DTEND:20130115T170000Z
UID:TALK42124@talks.cam.ac.uk
CONTACT:Oskar Brattstrom
DESCRIPTION:Estimates of the direction\, strength and shape of selection i
 n natural populations are increasingly frequent\, but we generally have li
 mited knowledge about the ecological processes that underlie them. Here\, 
 we present a multi-level analysis of selection on offspring fledging mass 
 over 51 years from a population of great tits _Parus major_\, with the aim
  of identifying environmental modulators of the mass-fitness relationship 
 within this multi-level framework. We show that the trait-fitness covarian
 ce depends on the level at which it is estimated\, with the between-year c
 ovariance being 3 times as large as the between-brood covariance\, which i
 tself is 2.6 times larger than the within-brood covariance. We identify fo
 od availability during\, and following\, reproduction as an environmental 
 factor underlying part of the non-causal covariance between fledging mass 
 and recruitment probability\, and explain variation in within-brood select
 ion with the density of conspecifics and the presence/absence of a princip
 le predator of tits (the Eurasian sparrowhawk _Accipiter nisus_). We show 
 that\, at the individual level\, sparrowhawks indeed selectively prey on g
 reat tit fledglings with low mass\, providing compelling evidence for a pr
 edator to act as a causal agent of selection. Estimates of directional sel
 ection on fledging mass differ by 67% when calculated on the different lev
 els\, while estimates of stabilising selection differ by 30%. These analys
 es therefore provide an example of how correlations between traits\, fitne
 ss and the environment can influence estimates of selection\, pinpoint asp
 ects of the environment that explain covariance between traits and fitness
  at different levels\, and show how partitioning covariance between levels
  of selection and environmental factors is a promising approach to identif
 y causal agents of selection.
LOCATION:Part II Lecture Theatre\, Department of Zoology
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