# Variation in Mortality and Ageing Rate in a Fast‐Paced Species: Insights From 24 Years of Hazel Dormouse (Muscardinus avellanarius) Data

## TL;DR

A 24-year study of hazel dormice in Lithuania found that male survival rates exceeded females, and survival changes were linked to environmental factors affecting aging rates, not just early-life mortality.

## Contribution

The study provides new insights into how environmental changes affect aging rates in a fast-paced rodent species.

## Key findings

- Male hazel dormice had higher life expectancy than females across all three population phases.
- Changes in survival were mainly due to age-independent mortality and aging rates, not juvenile mortality.
- Environmental variation can modulate aging rates in species with fast life histories like the Hazel Dormouse.

## Abstract

Recent research has found that, among some mammal species, differences in environmental conditions among populations of the same species drive changes in infant and juvenile mortality, but not in the rate of senescence, also known as the rate of ageing. Although this pattern has been confirmed in primates and some carnivores, it remains untested on other taxonomic groups with faster life histories, such as rodents. Here, we analysed age‐specific survival in Hazel Dormouse, using a 24‐year capture‐mark‐recapture data set from Lithuania. We used Bayesian survival trajectory analysis (BaSTA) and tested different models of age‐specific mortality. The population has experienced three distinct demographic phases—increasing (1999–2006), declining (2007–2014) and stable‐low abundance (2015–2022). We divided the dataset into these three periods to assess changes in survival over time. During all three periods, the life expectancy of males was larger than that of females, contrary to the general mammalian trend of higher female survival. Differences in survival among the three periods were primarily due to changes in age‐independent mortality and ageing rates, but not due to changes in juvenile mortality. Our findings support the notion that the low variance rate of ageing is limited to species with slow life histories. However, they also suggest that rodents, even those like the Hazel Dormouse which can reduce exposure to external threats, can substantially modulate their ageing rates in response to environmental variation.

A Hazel dormouse population in Lithuania has undergone three distinct phases each spanning 7 years across 24 years—increasing (1999–2006), declining (2007–2014) and low abundance (2015–2022). During all three periods, male life expectancy was larger than that of females. These differences in survival were primarily due to changes in age‐independent mortality and, to a lesser degree, changes in aging rates.