Biology Reference
In-Depth Information
strategy (ESS). Animals may compete by exploitation or by resource defence, or by a
mixture of both. A simple model of exploitation is the 'ideal free' distribution, which
predicts the stable distribution of individuals across good and poor habitats. Experiments
reveal that sticklebacks and ducks distribute in an ideal free manner between foraging
sites of different profitability. Observations show that male dung flies, waiting for
females at cowpats, also adopt a stable distribution across different waiting times.
Resource defence is influenced by both benefits and costs. The idea of economic
defendability can predict territory defence in sunbirds and territory sharing in pied
wagtails.
Competition can lead to variable foraging behaviour within a population, for example
a mixture of producers and scroungers. Producers may be better competitors with
scroungers 'making the best of a bad job', or the two may coexist in a stable mixture
with equal pay-offs. These same two alternatives apply to variable mating behaviour
within a population. This may result from alternative tactics within one conditional
strategy; for example, poorer competitors sneak matings while better competitors
display or fight for females (natterjack toads). Conditional strategies may involve
morphological switches at threshold body sizes (horns in dung beetles, long
forceps in earwigs). Variable mating behaviour can also reflect alternative
genetic strategies within a population (ruffs, isopods). At equilibrium, we would expect
equal average success of the alternative strategies. However, in side-blotched lizards
there is no stable equilibrium; three colour morphs of males show cycles in frequency
because each morph has an advantage over one morph but is vulnerable to exploitation
by another morph.
Many of the examples discussed in this chapter involve discrete traits (sneaker versus
fighter, horned versus hornless). Recent studies have recognized individual differences
in continuous traits, such as exploratory behaviour or aggression. Consistent differences
in individual behaviour, both over time and across different contexts (and often involving
suites of correlated traits) are referred to as personalities. These may involve differences
in risk taking, aggression or sociality. In great tits, for example, there are genetic
differences in individual exploratory behaviour which are correlated with many other
behavioural traits. In theory, personality variation may be maintained by frequency
dependent selection as an ESS. Or, different personalities may do best under different
social and ecological conditions.
Further reading
Tom Tregenza (1995) discusses the ideal free distribution. Giraldeau and Dubois (2008)
discuss producer-scrounger games in foraging. Jane Brockmann (2001) reviews
alternative strategies and tactics. Gross (1996) and Tomkins and Hazel (2007) consider
models and evidence for condition dependent switches in tactics. Simmons and Emlen
(2006) show how the size threshold for horns in dung beetles also influences investment
in testis mass (sneaks have large testes). Müller
et
al. (2006) describe alternative tactics
in both male (satellite behaviour) and female (brood parasitism) burying beetles, where
there is competition for carcasses, which provide food for their larvae. Hori (1993)
shows how frequency dependent selection leads to a stable frequency of 50% left
'handed' and 50% right 'handed' scale-eating cichlid fish (where 'handedness' refers to
