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Unformatted text preview: Mating Systems- Introduction- General definitions- Classification of mating systems- Mating systems and ecology Introduction- Recall that parental investment is not the same for both sexes o In males Sperm represents a small investment 5% of the body weight throughout an entire breeding season o In females Eggs are big investments In some species, an egg can be 30% of an animals body weight- Since female investment > male investment o This leads to: Female choice and male-male competition for access to females This should favor polygyny But other mating systems exist: Monogamy Polyandry Promiscuity o Why? Some Basic Definitions to Know:- Monoga my: one m ale m at es with one fem ale during a single breeding season- Polygyny: one m ale m at es with m ore than one fem ale during a single breeding se ason- Polyandry: one fem ale m at es with m ore than one m ale during a single breeding season- Promiscuity: m ultiple partnering between m ales and fem ales during a single breeding se aso Emlen and Oring- Mating syste m s tend to differ between m a m m als and birds o Birds tend to be socially monoga mous o Mam m als tend to be polygynus- Why?- Mam m als vs Birds o Among birds, they observed that 90% of all species are socially monoga mous and Nest sites and resources tend to be scattered and not defendable Breeding se asons can be short Both sexes can care for young and young ne ed a lot of care to fledge o So for m ales, the greatest chance for enhanced RS is to help raise their own young o By contrast, m a m m als tend to practice polygyny As in birds, fem ales m ake an extre m e reproductive invest m ent Fertilization and developm ent is internal Only fem ales lactate o How can these differences be explained?- Monoga my should be favored where feeding or nesting resources cannot be defended so ne sex is able to m onopolize more than one m e m b er of the opposite sex- Basic observation resulted in Classification of Mating Systems- Mating Syste ms o Monogamy: Why does it exist? (Tinbergens 3 rd question) HYP I: Mate-Assistance hypothesis HYP II: Mate-Guarding hypothesis HYP III: Female-Enforced hypothesis o Mating systems reflect the ability of one sex to monopolize mates or resources Resources = clumped Polygyny or polyandry...
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- Spring '09