Pinniped Social Systems

Transcription

1 Pinniped Social Systems Animal Mating Systems Polygamy Polygyny (one male & many females) Polyandry (one female & many males) Monogamy One male & one female Does not rule out hanky panky Serial Monogamy One male & one female at a time Over the course of season, many mates 1

2 Animal Mating Systems Development of these mating systems occurred because Internal fertilization Males exhibit low parental investment Contribute only sperm Females exhibit high parental investment Fetus Nurse and protect offspring Sexual Dimorphism Female Northern Fur Seal Male Northern Fur Seal 2

3 # of Females in Estrous Development of Polygyny Less than 5% of all mammal species are monogamous Environmental Potential for Polygyny (EPP) EPP is greatest when reproductive duration is moderate and the number of females that enter estrous is moderate EPP Greatest Reproductive Duration 3

4 Why Did Polygyny Evolve in Pinnipeds? Terrestrial Parturition Allowed animals to colonize at a central place and time Ensures synchrony in breeding Harem formation Marine feeding Animals disperse after breeding Difficult for males to maintain harem Island Pack Ice 4

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6 Estrous Synchrony Delayed Implantation or Embryonic Diapause 1) Blastocyst does not implant in uterine wall for 2-3 months 2) Normal gestation of 9 months 3) Progesterone triggers implantation So, why not have a 12-month gestation? - Allows female to recover after provisioning previous pup - Very difficult in Otariids 6

7 Estrous Synchrony Delayed Implantation or Embryonic Diapause 1) Blastocyst does not implant in uterine wall for 2-3 months 2) Normal gestation of 9 months 3) Progesterone triggers implantation So, why not have a 12-month gestation? - Allows female to recover after provisioning previous pup - Very difficult in Otariids 7

8 Female Distribution Main determinant of breeding habitat So, what factors control female distribution? 1) Limiting breeding space 2) Protection from predators - Mostly breed on islands 3) Resource distribution - Particularly important for Otariids The resources that are necessary to females will drive the type of polygyny Resource Defense Polygyny Males defend an important resource or territory for females Weddell Seal (Leptonychotes weddelli) 8

9 Males Defend Ice Holes Resource Defense Polygyny 9

10 Female or Harem Defense Polygyny Males defend a group of females irrespective of the territory (Elephant Seals) 10

11 Male Male Competition Distinct Boundaries 11

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13 Dire Consequences Male Male Competition 13

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15 Lek (Contest Competition) Males display to females to attract a mate Generally, no direct physical contact Harbor Seal Walrus Types of Pinniped Mating Systems Highly polygynous to serial monogamy Variations in sexual dimorphism Most with males larger than females A few with reversed or no sexual dimorphism Three main types of breeding Island (or Land) breeders Fast Ice breeders Pack Ice breeders 15

16 Island (or Land) Breeders Extreme polygyny (all Otariids, some Phocids) Sexually dimorphic Exceptions are Harbor, Monk seals Form rookeries on beaches, rocks, flat areas Island breeding was important for: Parturition sites Lack of predators Proximity of food for Otariids Factors all contribute to Polygyny because males can control access to females 16

17 Fast Ice Breeder 17

18 Fast Ice Breeding Seals are generally found in small wellspaced colonies with females well separated Colony formation is around cracks or holes Predation pressure Breeding is synchronous Males defend ice holes Slight polygyny Reversed sexual dimorphism (agility?) Breeding takes place in water Antarctic Pack Ice Not connected to land 18

19 Pack Ice Breeding Most Arctic species Serial Monogamy Females are widely dispersed Form triads (mother, pup, and male) Females come into estrous upon weaning Although synchronous, difficult for males to mate with many females Desert females after copulation to seek other receptive females Some sexual dimorphism (e.g. Hooded seal) Unstable environment No formation of harems Quick provisioning periods How Is Reproduction & Foraging linked? Capital Breeders: Single long trips Economical foraging strategy Income Breeders: Multiple short trips Expend high energy to obtain high energy 19