Do squirrels shrink?

Senescence, growth rate, selective disappearance.

Miles H. Kent (he/him), Do squirrels shrink?

Senescence is one of the most widely observed traits across taxa. However, not all species exhibit senescence. Incorporating 29 years of lifetime growth and survival data from North American red squirrels, we tested for late life senescence and selective disappearance over the lifespan of red squirrels, and determined what type of growth red squirrels exhibited. We found that red squirrel growth was not captured by any standard growth rate model (Monomolecular, von Bertalanffy, Richards, Gompertz, and Logistic) and instead, could be best modelled with an arctangent growth model. Surprisingly, we also did not find any support for senescence or selective disappearance in red squirrel growth. Red squirrels were able to maintain body mass and growth until their end of life. Accounting for environmental variation did not change these results. Our results suggest that studies may be overestimating the importance of senescence and selective disappearance as a demographic process if they are not testing for them explicitly.