Biology Reference
In-Depth Information
Mating systems with male parental care
Where males provide parental care the males themselves become a resource which may
influence female dispersion, so the simple scheme in Fig. 9.1 no longer applies. As we
saw at the beginning of the chapter, male parental care is particularly common in birds,
so we shall mainly use examples from birds to illustrate the ideas in this section.
Monogamy
Obligate monogamy: fidelity and divorce
David Lack (1968) suggested that monogamy is the predominant mating system in birds
(90% of species) because 'each male and each female will, on average, leave most
descendants if they share in raising a brood'. This hypothesis certainly explains obligate
monogamy in many seabirds and birds of prey, where male and female share incubation or
where males feed females on the nest, and where both sexes are essential for chick-feeding.
In these species, the death or removal of one partner leads to complete breeding failure.
In some of these 'obligate monogamous species' males and females form life-long pair
bonds and their annual reproductive success increases with the duration of the pair
bond. Is this because pairs function better the more that a male and female get to know
each other? Or does it result simply from improved individual experience with age?
A long-term study of oystercatchers
Haematopus ostralegus
on the island of
Schiermonnikoog, in the Dutch Wadden Sea, revealed that pair bond duration
influenced reproductive success independently of male and female age and other
confounding factors (e.g. territory quality). This shorebird is socially and genetically
monogamous and pairs often return to the same territories to breed year after year.
Newly-formed pairs have low reproductive success, but success increases with duration
of the pair bond up to 5-7 years (Fig 9.6). With more experience together, pairs breed
Sometimes it pays
both male and
female to breed
as a monogamous
pair
(a)
(b)
0.7
0.4
0.6
0.3
0.5
0.2
0.4
0.1
0
0
2
4
6
8
10
12+
2
4
6
8
10
12+
Pair-bond duration (years)
Pair-bond duration (years)
Fig. 9.6
Effect of pair-bond duration in oystercatchers on: (a) egg survival and (b) annual fledgling production.
These 'adjusted' measures control statistically for other effects, such as male and female age, individual identity
and territory quality. Sample sizes are shown above the x axes. From van de Pol
et al
. (2006).
