L11 Flashcards
What does mating system classification encompass?
- Copulation behaviour
- Social organisation
- Parental care system
- Competition for mates
Monogamy
- Pair bond
- Short or long time scale
- Often both sexes care for young
- Mostly birds
- Rare in mammals
Anenome fish
- No need for males to be larger to compete
- No costs of large body size
- All start off male
Monogamy across Birds
- Variable rates of extra pair mating’s across birds
- <25% of socially monogamous birds are also genetically monogamous
Polygyny
- One male associates with several females
- Few birds, most mammals
- Essentially means males sequentially moves on to different mates
Polyandry
- One female associates with several males
- Same time or in succession
Promiscuity (polyandry)
- Multiple females and males
- Less common in birds and mammals
- Some have no set paternity
Does the mating system often vary within a species?
Yes
- Eg extra pair paternity in monogamous species
- Eg dunnocks
- Exhibit a variable mating system
- eg some humans, are man and wife and some are eg two brothers and one wife
Reproductive potential and a general model
- Based on gametes males have a greater reproductive potential than females
- Males are limited by access to females, females are limited primarily by access to resources
General model
Expect female dispersion to be determined by the distribution of resources (Ecology)
- Male distribution is determined by female distribution (this is a mating system)
Ecology and mating systems, what does a mating system depend on?
- Comparative study of mammalian mating systems
- In mammals, male parental care is rare
- Female monopolisation by males and hence mating system depends on:
- Female group size
- Female range size
Solitary females
- Females with small ranges, are defendable by males
- When range is larger, male can only defend a single female not multiple (monogamy emerges)
- Range must be full of resources enough to survive
Orangutans
- To gain enough food female needs to travel large distances
- No single male can defend such a large area
- Scramble competition occurs : males wander looking for fertile females they can associate with and mate during her fertile period
Social females
- May confer defence benefits
- Easier to find resources
- Defendable by one male which can monopolise a large group of females
- Pride of lions requires multiple males for defence
- Sometimes single male defends small pride
- Sometimes multiple males defend a larger pride
Large range not defendable
- Females live in large unstable groups - Males lek - Females visit leks and then return after copulation
Lek polygyny
- Females with large ranges cannot be defended by males
- When female ranges are smaller, males can defend so have a larger range
- Ecological factors determine range size
Male dispersion is dependent on female dispersion
Does food distribution determine female dispersion? Experiment
- Range collapses when food provided as no need for it
- Yes, but males also converged on food, this could be because they were after females or after food
Experiment 2
- When females were clumped into small ranges, male ranges clumped around these
- When females clumped into large ranges, male ranges were larger
Experiment 3
- No effect of male dispersion on females
Resource defence by males
- Tent-making bat
- Females roost in tent
- Small tent = few females to roost in
- Resource opens opportunity to breed with roosting females
- Once males provide paternal care, males become critical for females
Is reproductive potential of males limited by care?
- Male reproductive rate
Sex role depends on potential reproductive rate, which in turn depends on relative provision of parental care
- Comparison of species with male-only care - Females grow ornaments and become aggressive - Sometimes males provide so much parental care, males have a lower reproductive rate, but sometimes not
In 13 species, where males have a higher reproductive rate there was conventional roles
When females had a higher reproductive rate a sex role reversal ensued
Sexual conflict over mating systems
- Extreme sexual selection
- Males prefer polygyny
- Females may prefer polyandry if they get more/ better resources
- In many species, monogamy occurs as a compromise between conflicting interests of the sexes
Females raise more offspring in small groups
Males raise more offspring in large groups
More females = more resources so each female doesn’t do as well
Males do best when there are more females
