Social Systems

What are the advantages and disadvantages of group living?

advantages:

• decrease predation risk

• increase prey detection and capture (find food easier)

• can take down larger prey

• reduce calve mortality → reproduction increases

• decrease harassment from males

disadvantages:

• more mouths to feed = increase food sharing

• increase competition for mates (reduce individual fitness)

• increase the risk of infection (disease transmission)

• increase of predator attraction (big group attracts predators)

What factors within the environment can affect the evolution of social systems and in what ways? (e.g. Behavior and availability of prey, exposure to predators)

if you hunt solitary prey = being in small groups or solitary groups

• prey must be big like tuna

large groups favor widely dispersed, clumped prey

small predator & big prey = can hunt in groups

big predator group hunting needs multiple prey

When predators school:

• her and corral prey

• easier to find prey patch

• reduces the advantage of schooling prey

How does the exposure to predators relate to social system evolution?

• if you are offshore, more exposed to predators than coastal (more directions predators can come from

  • use the “dilution effect” of schooling to lower risk

• How can reproduction affect the evolution of social systems / group behavior?

• if offspring are dependent on their mothers for longer, they tend to be more social

• social grouping offers protection from predators

• the stability of breeding and accessibility of food influences sociality

• Within groups, what factors shape social structures?

• predator and prey distributions

• home-range overlap

• affinity for kin

• sex and age-structure of a population

• Describe the general social tendencies of odontocetes.

Odontocetes then to be highly social with relationships that range from highly stable (for life) to unstable (short term associations)

• often in societies with fission fusion dynamics

• Group structure influenced majorly by

  • predator avoidance

  • habitat type

• promiscious mating systems

• Male-male competition and cooperative behavior among male coalitions (in order to coerce or corral females)

• How does the environment affect the social tendencies of odontocetes?

Coastal and inshore = tend to be resident (stay year round

• smaller, fluid schools because lower predation risk

Pelagic/offshore

• cover extensive areas

• large schools with many subunits (100-1000s)

• can even be mixed species

• What are fission-fusion systems? What species are known to exist in fission-fusion societies?

Groupsings that fluctuate in size and membership over time

fusion:

• small stable groups that join for feeding or reproduction (2,3 10 individuals with long term association)

• herds

• larger groups increase safety

fission:

• large group splits into stable sub-units

• stable, can associate for decades

• pods

spinner dolphins have pods that rest in coastal bays

• form herd to feed pelagically

• spinning behavior might maintain bonds(?)

• Describe the three general ecotypes of killer whales including group size, diet, vocal behavior, and echolocation tendencies.

Residents

• large and stable size

• fish

• group specific vocalizations

• frequently echolocate

Transients

• small, fluid group size

  • within group competition limits group size

  • peak at intake with 3 individuals, drop off at 9

• eat marine mammals

• population specific vocalization

• rarely echolocate

Offshore

• large, possibly fluid

• squid, sharks, and fish

• unsure about vocalization

• very frequently echolocate

• How does social care in odontocetes affect social patterns?

• there is high juvenile mortality and low adult mortality

• females are mostly responsible for care and protection of young

• groups protect offsrping which increases reproductive success

• Alloparental care = taking care of offspring other than ypour own

  • teacup formation: vunerable animals in middle, dominant adults outside

• Name and describe the three main groupings observed within bottlenose dolphin populations.

• male alliances

  • 1st order alliance

    • strong, stable (2-3 individuals)

    • long term (10+ years) could be life

    • cooperate for mating

  • 2nd order alliance

    • short term groupings of 2+ smaller alliances

      • maybe to drive off mutally hated group

    • take females from other alliances or guard against this behavior

    • aggressively separate females from groups

    • reciprocal altruism

• juvenile groups (“bachelor groups”

  • not prime reproductive age

  • forming groups to increase foraging success

• reproductive groups (females and calves)

  • less strong than male pairing

  • Mom-calf to mom-calf

  • more fluid

• What is the social structure of sperm whales?

matrilineal groups

• interact with other groups in short term = brief, transiting or foraging

Females

• bond based on cooperative care of young

• calves are too young to accom mom on deep foraging dive

Males

• disperse at ~6 yrs old in search of female in estrus

• increasingly solitary

• roam between female groups

• What are the social structures of killer whales and pilot whales?

• matrilineal groups

• kin based coop care: older females may nurse and defend related young

  • two nursing females may share nursing obligation

• older females are bank of cultural knowledge

• both sexes remain in pod for life

• males do not mate with closely related pod members

• interpod mating can occur when pods encouter each other in foraging and resting areas; males may leave group to mate then return

• Describe the general social tendencies of mysticetes. How does the environment affect the social tendencies of mysticetes?

• solitary

• brought together by breeding habitat

• exception with humpback whales mapping to same location foraging

• reversed sexual dimorphism (females larger)

• tend to calve in warm waters with less predators, and migrate north to feed

Humpback whale; feed in alaska, calve hawaii

Grey: feed in bering sea, calve in baja

• Describe the main mating strategies of mysticetes (e.g. direct competition, sperm competition).

In humpack whales they do direct competition

• display of older males

  • territory sorts

• escort females for long pds

• potential for sneaker males to come in and copulate without display

• female tend to mate 1 male a season

Bowhead, Right and gray whales

• large testes (tend to have sperm competition)

• multiple copulations = increase ratio of their sperm

• few male-male interactions: males don’t compete with one antoher, just pump sperm

  • no big driver for big males

• females mate with multiple whales

• What are the main drivers of social and mating systems in pinnipeds? Compare and contrast males and females.

• females are the limiting sex

  • limited by time and resources needed for pregancy laxctation and post reproductive recovery

  • selected for effecient energy acquistion

  • 1 pup at a time, not multiple opportunites to mate

• males only need time to mate

  • females limiting resource for them

  • selected for increasing ability to access and breed females

  • lead to sexual dimorphism

• Define the various breeding/mating strategies: polygamy, polygyny, polyandry, monogamy, and serial monogamy.

polygamy

• polygyny = one male, many females

• polyandry = one female, many males (not typical with MMs)

monogamy

• does not rule out “cheating”
  <5% of MMs (true monogamy)

serial monogamy

• one male, one female

• many mates over course of one season

• stay with female for exgtened period and then move onto someone else

• How does the environment (e.g. stability of breeding substrate) affect pinniped mating systems?

land and islands

• stable sites to give birth

• protection from predators

• proximity to food (otariids)

• clumping of females and synch estrous

• males can control access to females = extreme polygyny = extreme sexual dimorphism

  • except harbor and monk seals

• all otariids, some phocids exhibit extreme polygny

• Sexual dimorphism

  • northern fur seals, aus fur seals, guadulupe fur seals

  • aus sea liobs, steller sea lions

  • elephant seals and gray seals

• How does the fast ice affect pinniped mating systems?

• females are well separated (reduce predation pressure)

  • near cracks and holes

  • predation presusre (hide from polar bears)

  • males defend ice holes (from other males)

  • breeding happens in the water

• makes have limited control over access to females

  • slight polygyny

  • reverse sexual dimorphism (larger females, larger pups, higher success to weaning)

• some phocids (ice seals)

  • ringed seals

• How does the pack ice affect pinniped mating systems?

• females are well separated and mobile

• vast amt of space

• unstable env

• quick lactation

• breed in water after weaning

• males have no control over access to females

  • serial monogamy

  • males mate guard until copulation then seek new female

• most arctic and some Antarctic phocids

  • hooded seals (hang out until pup is weaned)

  • bearded seals

  • crabeater seals

  • harp seals

  • leopard seals

• How does the environment affect the evolution of sexual dimorphism?

Stable environments lead to controlling access of females and drives sexual dimorphism. Unstable environments cant control females not as much sexual dimorphism and can even be the reverse.

• How are monk seals, harbor seals, and walruses different in their breeding strategies than other pinnipeds? Be able to describe their breeding strategies.

monk seals

• mating happens in water and cannot defend access to females

• mobbing of females (males outnumber females 3:1) or scramble competition

  • can be killed in process

• harbor seals and walruses exhibit lekking

  • a number of males group together and display vocalizations

• mating happens in water where males cannot defend access

• male defender underwater territories

• Describe the breeding behavior and social tendencies of polar bears.

• solitary predators, rare grouping

• will associate with members of other sex wehn courting and mating (april may)

• mothers asso with cubs 2 yrs

• many individuals may forage on same prey resource but not social

• physical competition for females

• induced ovluation: must mate to ovulate

  • serial monogamy bc females hard to find

• Describe the breeding behavior and social tendencies of sea otters.

• spatial dispersion related to location of coastal invertebrate prey

• may “raft” in groups near feeding areas (not sure if social)

• breeding males establish terretories that include multiple female home ranges

• males often harass females with large pups to force separation and induce estrous (shortly after weaning)

  • trauma to females nose (not seen in alaska)

• Describe the breeding behavior and social tendencies of sirenians. Compare and contrast manatees and dugongs.

Manatees

• disperse to food and warm fresh water

• asocial, with only strong bond between mom and calf

• estorus may unduce male scramble competition

• form amtting herd (1 fem, 2-22 males)

  • can follow for weeks

  • sperm competition may occur

dugongs

• food and warm water

• asocial, mom calf

• mating herds (100s)

• lasts for <1day

• promiscuous intense mating

• more aggressive competition, could lead to lekking