Mating Systems Causes Types and distribution Ecological factors –Polygyny threshold –Polyandry
Causes of spacing patterns Males disperse in space to maximize mating opportunities with females
Parental care and female dispersion influence mating system
Monogamy Lar gibbon Silver-backed jackal
Social monogamy > 90% of all birds, most biparental care < 10% of all mammals –males help provision young canids, marmosets,carnivorous bats –males defend single female dik-dik, some rodents Rare in –insects (carrion beetles) –Fishes, reptiles, amphibians
Mate assistance in Peromyscus californicus
Mate assistance monogamy in snow buntings
Social monogamy ≠ genetic monogamy
Polygyny (> 90% of mammals)
Ecological correlates of polygyny Females solitary, but ranges defensible by male –prosimian primates Females solitary, range not defensible –Moose, orangutan Females social, range defensible –Seasonal harems - elephant seals, red deer –Permanent harems - baboons, zebra, spear-nosed bats Females social, range not defensible –Female movements unpredictable males follow females, e.g. elephants –Female movements predictable - males display on leks
Polygyny (< 10% of birds) Males defend food or nesting sites –Blackbirds –Grouse –Cotingas
Ecological factors affecting polygyny Female sociality Female movement predictability Habitat heterogeneity
If there is spatial habitat heterogeneity And fixed territory size Then females will have to choose between unmated males on poor territories or mated males on rich territories or If territory size is related to size or age Then females should choose largest territory
Resource defense polygyny
Polygyny threshold model
Polygyny threshold predictions Polygyny should be most common in patchy habitats Male territory quality influences # of females Females mating to already mated males should have RS comparable to females pairing with unmated males
Polygyny in pied flycatchers
Polygyny in anolis lizards depends on size
Polyandry Rare in birds –Sequential - sanderling, stint –Simultaneous - phalarope, jacana –Cooperative - pukeko Very rare in mammals –Tamarins Common in fish
Ecological reasons for polyandry Rich resource, eggs are cheap Short breeding season Male biased sex ratio
Why should females multiple mate?
Pseudoscorpions gain fertility benefit
Human mating systems