Experimental tests of

food limitation

Larsen et al. 1997. J. Mamm. 78:192-203

Becker et al. 1998. Oikos 81:81-92

Boutin & Larsen 1993 J.Anim.Ecol. 78:192-203

• Individual as the experimental unit

The effects of food supplementation on winter survival…

1989 1990

-C C +C +S C +C +S

Win

ter

Sur

viva

l

0

20

40

60

80

100

p=0.07 p=0.22

…body mass

1989 1990

-C C +C +S C +C +S

Pre

par

tum

Ma

ss (

g)

0

50

100

150

200

250

300

p=0.79 p=0.27

…parturition date

1988 1990

-C C +C +S C +C +S

Par

turit

ion

Dat

e

Apr 2

Apr 12

Apr 22

May 2

May 12

May 22

Jun 1

p=0.003 p=0.73

…litter size

1989 1990

-C C +C +S C +C +S

Litte

r S

ize

0

1

2

3

4

5

p=0.14 p=0.10

1989 1990

-C C +C +S C +C +S

Offs

prin

g W

eane

d

0

1

2

…weaning success

p=0.63 p=0.73

ReproductiveEnergetics

• Natural and experimental variation in litter size

• Short-term energetic and behavioural consequences

• Long-term life history consequences

Humphries & Boutin 2000 Ecology 81:2867-77

Humphries & Boutin. 1996. J. Anim. Ecol. 65:332-338

Humphries & Boutin 1999 Can. J. Zool. 77:171-73

1990 1992 1994 1996 1998 2000

Spr

uce

Con

e In

dex

0

50

100

150

200

250

300 M.Sc.

+/-/ 2 offspring

Weigh and tag

Maternal behaviourand energetics

1994 1995

Aug Con Aug Con

Gro

wth

Rat

e(g

ram

s pe

r da

y)

0.0

0.5

1.0

1.5

2.0

2.5

Juvenile growth

Treatment p=0.009 Year p<0.001

1994 1995

Aug Con Aug Con

% T

ime

For

agin

g

0

10

20

30

40

50

Maternal behaviour

Treatment p=0.54 Year p<0.001

6 7 8 9 10 11 12 13

Dai

ly E

nerg

y E

xpen

ditu

re(k

J / g

/ da

y)

1.20

1.35

1.50

1.65

1.80

1.95

2.10

2.25

Lower Critical Temperature - Ambient Temperature (oC)

Augmented

Control

Donor

Maternal expenditure

Treatment p=0.001 Temperature p<0.001

Ave

rage

Litt

er S

ize

0

1

2

3

4

Gro

wth

Rat

e (g

/day

)

0.0

0.5

1.0

1.5

2.0

Year

1989 1990 1991 1992 1993 1994 1995 1996 1997

Spr

uce

Con

e In

dex

0

50

100

150

200

Litte

r S

urvi

val (

%)

0

20

40

60

80

100

Donor Control Augmented

Nu

mb

er

of

Su

rviv

ing

Off

spri

ng

pe

r F

em

ale

0.0

0.5

1.0

1.5

2.0

2.5

Post-weaning Juvenile Survival

Treatment p=0.04