where
lx = probability
of
survival from birth to age x (cumulative)
[cf. survivorship =
probability
of survival to age x+1 from age x ]
mx = fecundity
(# offspring) at age x
Roerat
low population density
Assumptions:
Maximum life
span is 4 years.
Iteroparity
& semelparity are alternative phenotypes:
fecundity
for each phenotype is genetically determined.
Survivorship
patterns are the same for both phenotypes:
these
are determined by the environment
Table records
total ## offspring (male & female) born to each female.
50% survivorship 75% survivorship 25% survivorship
lx
* mx = lxmx
lx * mx
= lxmx
lx * mx
= lxmx
0 1.00
0
0
1.00 0
0.00
1.00 0 0.00
1 0.50
2
1.00
0.75 2
1.50
0.25 2 0.50
2 0.25
3
0.75
0.56 3
1.68
0.063 3 0.19
3 0.125
2
0.25 0.42
2
0.84 0.016
2
0.03
4
0
0
0
0 0
0
0 0 0
Ro
=
2.00
=
4.02
= 0.72
Semelparous strategy: reproduction is entirely in the first year.
50% survivorship 75% survivorship 25% survivorship
lx
* mx = lxmx
lx * mx
= lxmx
lx * mx
= lxmx
0 1.00
0
0
1.00 0
0
1.00 0 0
1 0.50
4
2.00
0.75 4
3.00
0.25 4 1.00
2 0.25
0
0
0.56 0
0
0.063 0 0
3 0.125
0
0
0.42
0
0
0.016 0 0
4
0
0
0
0 0
0
0 0 0
Ro
=
2.00
=
3.00
= 1.00