Life history strategies in a North American red squirrels population

1. Life history strategies in a North American red squirrels population Sébastien Descamps PhD candidate Under the supervision of Dominique Berteaux and Jean-Michel Gaillard

2. Life history strategies? « Life histories are the probabilities of survival and the rates of reproduction at each age in the life span » Partridge & Harvey 1988 Demographic tactics Co-adaptation of demographic parameters Response to evolution

3. The red squirrel at Kluane • > 15 years of data • > 1200 males and 1200 females of known age • Reproduction (litter size, mass, growth rate…) • Low dispersion • Food availability index

4. 1- Senescence Survival Age Reproduction Questions:

5. Survival Age Reproduction Questions: • 2- Cost(s) of reproduction trade-off

6. Questions: • 3- Cohort effects Survival Year of birth Year of birth trade-off Age Reproduction

7. Questions: • 4- Demographic modelisation Survival Population dynamic Year of birth trade-off Age Reproduction

8. Lots of results with mice in the lab Senescence Small mammals: • Very few results in natural conditions, and with small mammals other than mice or voles

9. Senescence Red squirrel at Kluane > 50 individuals older than 5 years old (without the 2003 dataset!) Preliminary results showing female survival decreasing with age:

10. Females’ survival Full-age dependant model : (a) p

11. 3 age classes: 1 juvenile stage, 1 prime-age stage, 1 senescent stage 2 age classes: 1 juvenile stage, 1 adult stage Females’ survival

12. Females’ survival Likelihood Ratio Test between Model with 2 adult classes: ]1 yr, 5yr[; >5 yr and Model with 1 adult class: >1 yr Chi-sq. df Prob. ------------------------- 29.521 7 0.0001 => 2 stages for adults => Senescence

13. Females’ survival

14.  =0.690.21 Model with 1 juvenile class and 1 adult class  (j; >1 yr) p(t) Males’ survival

15. Males’ survival • No senescence for males? • Senescence later in life? • Strong selection on males => only the best males survive until 5 years and more?

16. Some theories explain the existence of senescence by the existence of reproduction costs => Important to study the reproduction costs to understand the effects of age on reproduction/survival

17. Expression of the costs of reproduction according to food availability ? Previous experimental work: Koskela et al. 1998 on Bank Vole =>Manipulation of reproductive effort =>Manipulation of environmental conditions • Systems allowing such manipulations are rare!!!

18. Food addition Increased +2 No food addition Litter size Food addition Decreased -2 No food addition Experimental project Red squirrel at Kluane: • Litter size manipulation (Humphries and Boutin 2000) • Food addition (seed buckets) 2 treatments experiment:

19. Group 1 Group 2 Group 3 Food add Group 4 increased No food Litter size Food add decreased No food Experimental project Hypotheses: Success Group 1 = Success Group 3 Success Group 2 < Success Group 4 significant cost of reproduction when food scarcity

20. Experimental project Red squirrel at Kluane: Year 2004: low food availability (low cone production since 1999, and very low in 2003) • Red squirrels should respond to experimental food addition • Good opportunity to study the expression of reproductive costs according to food availability

21. Survival Population Dynamic trade-off Year of birth Age Reproduction Conclusion