Biology Reference
In-Depth Information
(a)
(b)
Producer side
Uncovered
Covered
0.4
0.4
0.3
0.3
P
P
0.2
0.2
0.1
0.1
S
S
0
1
2
3
4
5
6
0
1
2
3
4
5
6
Barrier
Scrounger side
Number of scroungers
(c)
5
4
3
2
1
0
2
4
6
8
10
12
14
16
Days
Fig. 5.10
Mottley and Giraldeau's (2000) experiment with spice finches to test the model in Fig. 5.9b.
(a) Experimental aviary. On the producer side, birds can sit on little perches (the T shapes) and pull a string to
release food into a dish. On the scrounger side, birds have to wait for producers to make food available (see text
for details). (b) Results from one flock, showing how foraging rate of producers (p - solid dots) and scroungers
(s - open circles) varies with the number of birds in the scrounger compartment. There are six birds in total in
the flock. In the graph on the left, the feeding dishes were uncovered and scrounger
=
producer feeding rate
when 2-3 birds of the flock are scroungers. In the right-hand graph, the dishes were covered, which reduced
scrounger (but not producer) food access; here equal success occurs when 0-1 birds are scroungers. (c) When
all six birds have free access to either side, the numbers converge on the predicted stable equilibrium (shaded
areas) over successive days of the experiment. On days 1-8, dishes were covered and on days 9-16 they were
uncovered.
Strategy
. This is a genetically based decision rule, so differences between strategies are
due to differences in genes. For example one strategy might be 'always fight' and another
strategy might be 'always sneak'. Strategies might also be
conditional strategies
, where
individuals vary their competitive behaviour depending on their body size ('fight if
larger than size x, sneak if smaller than x'), or depending on the environment ('fight
above threshold cue y, sneak below threshold cue y'). Here, the genetic variation
between strategies would involve differences in response thresholds.
Tactic
. This is a behaviour pattern played as part of a strategy. For example, if the
strategy is 'fight above threshold x, sneak below x', then 'fight' and 'sneak' are now
alternative tactics within the same overall genetic strategy.
Strategy
differences reflect
genetic
differences
