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

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

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

Questions: 1- Senescence Age Survival Reproduction

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

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

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

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

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

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

Females ModelDev np AIC  (j; ]1 yr, 5yr[ ; >5 yr) p  (j; >1 yr) p Females’ survival 3 age classes: 1 juvenile stage, 1 prime-age stage, 1 senescent stage 2 age classes: 1 juvenile stage, 1 adult stage

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 => Senescence Females’ survival => 2 stages for adults

Females’ survival

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

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

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

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

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

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

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

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