Today we’ll discuss the 3 types of Mating Systems: Monogamy, Polygamy, and Promiscuity! But first we shall go over sex ratios before getting into the main topic.
Sex Ratios express the relative abundance of each sex in wildlife populations. Sex ratios are expressed as “the number of males: the number of females“
50 : 50 even sex ratio
75 : 25 sex ratio favors males
30 : 70 sex ratio favors females
Sex Ratios within populations may change, either because of unbalanced sex ratios at birth, or, more often, because of sex-specific mortality associated with age. For example, males succumb to death earlier than females due to hunting, reproductive pressures, etc.
Waterfowl and other wildlife follow one of the 3 broad types of mating systems:
- Monogamy: each breeding adult is mated to ONLY ONE member of the opposite sex.
- Seasonal Monogamy: Pair-bonds established for only the current breeding season (most birds and ducks)
- Life-Time Monogamy: Pair-bonds established for as long as both mates remain alive (geese, cranes)
- Polygamy: An individual has 2 or more mates NONE OF WHICH ARE MATED TO OTHER INDIVIDUALS.
- Polygyny: Several females per male (most deer, many game birds)
- Polyandry: Several males per female – fairly rare but does occur in birds (e.g., Wilson’s Phalarope, Jacanas)
- Promiscuity: Males and females copulate with many of the opposite sex – NO PAIR BONDS ARE FORMED.
- System differs from polygamy in that no one individual has exclusive mating rights over any individuals of the opposite sex (e.g., cottontails, most cats).
- Rape: Forceful mating of females by male(s) (occurs in some ducks)
Monogamous species require a balanced sex ratio for the maximum production of offspring. Any deviation favoring either sex reduces production. In polygynous species, an unbalanced sex ratio is needed to maximize reproduction. Females represent a premium for increased production – males are somewhat expendable.
Wildlife species show large variations in reproduction patters. For example,
- Some breed year-round
- Some breed seasonally
- Some do not breed every year
Remember, reproductive patterns determine a species biotic potential, but the environment and predators determine the realized population growth and productivity!