Transcript Document

Types of mating systems:
Monogamy: 1 male, 1 female
Polygamy:
Polygyny: 1 male, >1 female
or
> 1 male, >1 female
Polyandry: 1 female, >1 male
Factors affecting the type of mating
system:
• Need for male parental care
• Distribution of females in space and
time
Distribution of resources
Distribution of females
Distribution of males
Factors influencing monogamy:
•Need for male parental care
•Paternity certainty
•Spatial and temporal distribution of females
Both influenced by:
Distribution of resources
Predation pressure
•Female-female competition
Types of Polygyny:
• Resource defense polygyny
Male (or males) defends an area to which
females are attracted
• Leks
Loose aggregations of males to which
females are attracted
• Female defense polygyny
Male (or males) defends a group of females
that are already social for other ecological
reasons
Polygyny threshold model
1st female
2nd female
Polygyny threshold
Fitness cost
y
x
x
Territory quality
y
Problems with models of resource
defense polygyny:
• Male genetic quality not considered
• Male parental contribution not considered
• Polygyny might not be costly to females
Marmots
Yearlings per individual
3
Male
2
1
Female
0
0
1
2
3
4
Number of females on territory
5
Why do males congregate at leks?
• Because females are attracted to nearby
resources?
• Because leks reduce the costs of predation?
• Because leks allow females to compare males?
(based on their quality alone, because
there is no male PI)
Monkeys
Selective factors favoring female sociality:
• Defense against predation
• Defense of resources
Consequences:
• Close bonds among female kin
• Strong between-group competition
• (Often) strong within-group
competition, resulting in a
female dominance hierarchy
Why are groups multi-male?
1. Female group size or
range may be too big for a
male to defend alone (e.g.
baboons, vervets)
2. Males may benefit by
cooperating (e.g. chimps,
lions)
Multi-male groups can arise through
either resource-defense or
female-defense polygyny
Chimpanzees: Resource defense
polygyny
Many related males defend an
area
Females are often unrelated,
less social than males.
Baboons: Female defense polygyny
Many unrelated male migrants
Females are resident, often
related, and very social
Evolutionary paths to polyandry:
• Female lays a clutch, male incubates;
female lays another clutch, she incubates.
Female may not be ‘faithful’ to first male
• Monogamous pair accepts a ‘helper’
‘Cooperative’ polyandrous breeding
• Mammalian groups with competition and
reproductive suppression
Effectively polyandrous breeding
Dunnocks
Polygyny: High food density
Monogamy: Medium food density
Polyandry: Low food density