Biology Reference
In-Depth Information
Taxonomic comparison
Main factors leading to different
mating systems
Table 9.3
A hierarchical
approach to
mating system
diversity (Owens
& Bennett, 1997)
Between orders or families
(e.g. pheasants versus hawks)
Differences in life history constraints (e.g. precocial
versus altricial young)
Between species within a genus
Differences in ecology (e.g. food, breeding sites)
Between individuals within a
population of one species
Social conflicts
Differences
between related
species reflect
differences in
ecology
weaverbird species that exploit insects (harder to exploit, more likely to need both
parents to raise a brood; Chapter 2).
Finally, differences within populations of a species are likely to be explained by social
conflicts (theme (iii) above), for example differences in the success with which individuals
can exploit their mates. A male dunnock or burying beetle that can gain a second mate
despite the attempts of his first female to prevent this will profit, though his first female
will suffer. Different outcomes may occur depending on which individuals can gain
their preferences, despite the conflicting preferences of others.
Unravelling the interactions between these three processes is a challenge for future
studies.
Differences within
species or
populations
reflect social
conflicts
Summary
When males do not provide parental care, the mating system often emerges as the
outcome of a two-step process: (i) females distribute in relation to resources and (ii)
males distribute in relation to female dispersion, either competing for females directly
(female defence) or competing for resource rich sites (resource defence). The economics
of defence by males depends on both the spatial and temporal distribution of females/
resources. These themes are illustrated by experiments with voles and wrasse, and
comparative studies of mammalian mating systems.
In some species, males aggregate on leks. Five hypotheses for these male aggregations
are: settlement on female 'hotspots'; reducing predation; increasing female attraction;
parasitizing 'hotshot' males; and facilitating female choice.
Where males provide care (most birds), males become a resource for females and the
mating system often depend on patterns of desertion by either sex. Monogamy may be
obligate because both male and female need to cooperate for any success, but often
individuals are constrained to be monogamous, either by their partner's behaviour or
competition for mates. Social monogamy often does not lead to genetic monogamy
because of extra-pair matings. Females may choose polygyny on a good quality male
territory rather than monogamy on a poor one (polygyny threshold model, e.g. red-
winged blackbirds).
There are often conflicts between the sexes over the mating system that maximizes an
individual's success (burying beetles, pied flycatcher, dunnock), which may lead to
variable mating systems within a population. In some shorebirds there is sex role
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