Indirect effects on fitness between individuals that have never met via an extended phenotype

David N. Fisher* (Corresponding Author), Jessica A. Haines, Stan Boutin, Ben Dantzer, Jeffrey E. Lane, David W. Coltman, Andrew G. McAdam

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)


Interactions between organisms are ubiquitous and have important consequences for phenotypes and fitness. Individuals can even influence those they never meet, if they have extended phenotypes that alter the environments others experience. North American red squirrels (Tamiasciurus hudsonicus) guard food hoards, an extended phenotype that typically outlives the individual and is usually subsequently acquired by non‐relatives. Hoarding by previous owners can, therefore, influence subsequent owners. We found that red squirrels breed earlier and had higher lifetime fitness if the previous hoard owner was a male. This was driven by hoarding behaviour, as males and mid‐aged squirrels had the largest hoards, and these effects persisted across owners, such that if the previous owner was male or died in mid‐age, subsequent occupants had larger hoards. Individuals can, therefore, influence each other's resource‐dependent traits and fitness without ever meeting, such that the past can influence contemporary population dynamics through extended phenotypes.

Original languageEnglish
Pages (from-to)697-706
Number of pages10
JournalEcology Letters
Issue number4
Early online date10 Feb 2019
Publication statusPublished - Apr 2019

Bibliographical note

Funding Information
Natural Sciences and Engineering Research Council
Ontario Ministry for Research and Innovation
National Science Foundation

We thank Agnes MacDonald for long‐term access to her trapline, and to the Champagne and Aishihik First Nations for allowing us to conduct work on their traditional territory. We thank all the volunteers, field assistants and graduate students whose tireless work makes the KRSP possible. We also thank Andrea Wishart for providing helpful comments on a draft of this manuscript. Funding for this work was provided by the Natural Sciences and Engineering Research Council, the Ontario Ministry for Research and Innovation, and the National Science Foundation. We have no conflicts of interest. This is KRSP paper number 96.


  • extended phenotype
  • indirect effect
  • inheritance
  • KRSP
  • quantitative genetics
  • resource hoarding
  • Tamiasciurus
  • territory


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