, Volume 178, Issue 1, pp 89–101 | Cite as

Covarying variances: more morphologically variable populations also exhibit more diet variation

  • Lisa K. SnowbergEmail author
  • Kimberly M. Hendrix
  • Daniel I. Bolnick
Special Topic: Individual-level niche specialization


Many ecologically generalized populations are composed of relatively specialized individuals that selectively consume a subset of their population’s diet, a phenomenon known as ‘individual specialization’. The Niche Variation Hypothesis posits that this individual specialization can arise during ecological release if niche expansion occurs mainly through diet divergence among individuals, leading to greater morphological variation. Most tests of this hypothesis have searched for correlations between niche width and morphological variance, but this approach rests on the untested assumption that within-population morphological diversity is highly correlated with ecological diversity. Here, we test whether intrapopulation diet variation is correlated with intrapopulation morphological variation, across 12 lacustrine populations of three-spine stickleback. First, we use behavioral observations, isotopes, and gut contents to show that, within populations, individuals differ in microhabitat use and diet. Second, we show that some populations exhibit more diet variation than others, as evidenced by differences in both isotopic and gut content variation among individuals. Finally, we confirm that populations with greater dietary variation are more morphologically variable. However, this relationship is only significant when total morphological variance is examined, not for individual morphological traits. This discordance may reflect among-population differences in the relationship between individual morphology and diet. Because morphology–diet relationships can differ among populations, morphological variance may be a poor predictor of actual diet variation when diverse populations are being compared.


Ecomorphology Individual specialization Niche variation hypothesis Microhabitat preference Stable isotopes 



We thank Tania Tasneem and On Lee Lau for help in collecting survey fish. Chris Harrison and Bob Rodbumrung assisted with the setup of the microhabitat enclosure. Rose Carlson assisted with the functional morphology measurements on recaptured enclosure fish. This work was funded by National Science Foundation DEB-0412808 and a David and Lucille Packard Foundation fellowship to DIB. LKS was supported by a National Science Foundation Graduate Research Fellowship.

Conflict of interest

The authors declare no conflict of interest.

Supplementary material

442_2014_3200_MOESM1_ESM.docx (31 kb)
Supplementary material 1 (DOCX 30 kb)


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Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  • Lisa K. Snowberg
    • 1
    Email author
  • Kimberly M. Hendrix
    • 2
  • Daniel I. Bolnick
    • 3
  1. 1.Department of Ecology, Evolution and BehaviorUniversity of Texas at AustinAustinUSA
  2. 2.LubbockUSA
  3. 3.Section of Integrative Biology, Howard Hughes Medical InstituteUniversity of Texas at AustinAustinUSA

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