chapter5lifehistorystrategies

chapter5lifehistorystrategies内容摘要：

28 Chapt. 05 Mating Systems • Why is the sex ratio usually 1:1? – Aren’t males superfluous? – Answer: Selfish genes! 187。 Populations – predominately female 187。 Populations – predominately male 187。 Over time, sex ratio would be kept at 1:1 • Selection would favor sons • Selection would favor daughters 29 Chapt. 05 Mating Systems – Exception to 1:1 • One male dominates in breeding • Occurs in species with – Low powers of dispersal – Inbreeding is frequent 30 Chapt. 05 Mating Systems • Ex. The parasitic Hymenoptera – Females mate once and store sperm – Females control sex ratio 187。 Use sperm to create females 187。 Without sperm to create males – Process termed haplodiploid • Ex. The mite Acarophenox (Figure ) 31 Chapt. 05 Mating Systems • Mating systems in animals – Monogamy • Exclusive mating • Common among birds (~90%) of species 32 Chapt. 05 Mating Systems – Polygamy • Individuals mate with multiple partners • Polygyny – One male mates with multiple females – Females mate with one male 33 Chapt. 05 Mating Systems • Polyandry – One female mates with multiple males – Males mate with one female – Polygyny • Females must care for the young • Mammals tend to be polygynous – Ex. Figure 34 Chapt. 05 Mating Systems – Polygyny (cont.). • Influenced by spatial and temporal distribution of females – Monogamous relationships result from all females being sexually receptive at the same time – Female receptiveness spread over weeks or months – polygyny can result 35 Chapt. 05 Mating Systems • Resourcebased polygyny – Critical resource is patchily distributed or in short supply – Male can dominate resource and breed with more than one visiting female – Disadvantages for the female 187。 Must share resources 187。 More females means less success 187。 Figure 36 Chapt. 05 Number of females per group 1 2 3 4 5 6 1 2 3 4 5 Number of yearlings per male ( ) Number of yearlings per female ( ) 37 Chapt. 05 Mating Systems • Nonresource based polygyny – Harembased 187。 Common in groups or herds 187。 Protection from predators 187。 Harem master does not remain for long – Communal courting areas – leks 187。 Figure 38 Chapt. 05 Mating Systems – Polyandry • Practiced by a few species of birds • Ex. Spotted sandpiper in the Arctic tundra – Reproductive success not limited by food – Limited by the number of males needed to incubate eggs. • Ex. American jacana (Figure )。