Life history strategies in a North American red squirrels population Sébastien Descamps PhD...
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Transcript of Life history strategies in a North American red squirrels population Sébastien Descamps PhD...
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-offYear 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
Age (years)0 1 2 3 4 5 6 7 8 9
Su
rviv
al
0.0
0.2
0.4
0.6
0.8
1.0
Full-age dependant model : (a) p
FemalesModel Dev np AIC
(j; ]1 yr, 5yr[ ; >5 yr) p 2319 40 2399
(j; >1 yr) p 2349 30 2409
Females’ survival3 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.
-------------------------
29.521 7 0.0001
=> Senescence
Females’ survival
=> 2 stages for adults
Females’ survival
1986 1988 1990 1992 1994 1996 1998 2000 2002
Sur
viva
l
0.0
0.2
0.4
0.6
0.8
1.0
Prime age FemalesSenescent Females
Males’ survival
Age (years)0 2 4 6 8 10
Su
rviv
al
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Model with 1 juvenile class and 1 adult class
(j; >1 yr) p(t)
=0.690.21
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. 1998 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 projectRed 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
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 projectRed 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-offAge
Survival
Reproduction
Population Dynamic
Conclusion