Biology Reference
In-Depth Information
(a)
(b)
9
1350
Fig. 12.4
Concealed helper
effects in the
superb fairy-wren
(
Malurus cyaneus
).
(a) The presence of
helpers had no
influence on the
size of chicks
reared, but (b) led
to the dominant
female laying
smaller eggs. (c) In
a cross-fostering
experiment, where
groups with same
size eggs could be
compared, the
presence of helpers
led to an increase in
the size of chicks.
(d) The probability
of a breeding
female surviving to
breed in the next
year was greater
when she had
received help. From
Russell
et al
. (2007).
Reprinted with
permission from
AAAS. Photograph
of a male. Photo
© Geoffrey Dabb.
8
1300
1250
7
6
1200
5
1150
Pair only
Plus helpers
Pair only
Plus helpers
(c)
(d)
10
1.0
9
0.9
8
0.8
7
0.7
6
0.6
5
0.5
Pair only
Plus helpers
Pair only
Plus helpers
equates to four units of energy, which is divided equally, giving each player two units. In
this case, the hunter would get a pay-off of 2
−
1
=
1 (the minus one is the cost of
hunting) and the free rider would get a pay-off of 2
2 (no cost of hunting). If both
players take part, the synergistic benefit of cooperative hunting makes the hunt a huge
success, such that the food returned equates to ten units of energy, which is divided
−
0
=
