Ecology Lecture 11

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Ecology Lecture 11

• Life History Patterns 2

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Overview

• A mating system includes
• how members of a particular species (or
  population) choose and bond with mates
• how many mates per individual
• how parental care (if it occurs) takes place.
• Types of mating systems
• Monogamy One male mates with one female
• Polygyny One male mates with several females
• Polyandry One female mates with several males
• Social vs. genetic monogamy

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Key principles

• The system that evolves depends upon the
  individual interests of each gender
• Male and female interests are often in conflict.
  Why?
• Differences in gamete investment and/or total
  parental investment
• Male default ____________. Why?
• Is there a female default?
• Interests/behavior of one gender serve to
  constrain options available to the other gender.

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Polygyny

• Resource defense polygyny
• Example African cichlid fish, Lamprologus
  callipterus
• Defended resource shells in which females lay
  eggs

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Polygyny

• Female defense polygyny
• Example Elephant seals (females aggregate)

Photo www.driftersister.com
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Polygyny

• Female defense polygyny
• Example Elephant seals (males compete for
  beachmaster status)

Photo www.wetasschronicles.com
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Male-male competition and sexual dimorphism
(seals)NOTE Each point represents a species
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Polygyny

• Lek polygyny
• Males clump, but not due to another resource
• Males become the clumped resource!
• Example 1 satin bowerbirds

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Satin Bowerbirds multiple signals of health and
fitness (and good genes?)
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Polygyny

• Lek polygyny
• Example 2 bullfrogs
• Females choose males with longest, loudest and
  deepest calls
• But dont forget the sneaky f--kers

www.tc.umn.edu
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Polygyny benefits/costs

• Male
• number of offspring likely to correlate with
  number of mates ()
• Female
• gets a high-quality male ()
• gets less of the males time and attention for
• raising young
• being defended against predators

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Monogamy

• Common or rare?
• In which group of animals is it most common?

www.magicmud.com
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Monogamy alternate hypotheses

• Mate assistance it takes two parents to raise
  the offspring
• Example Adelie penguins
• Both parents needed for chick survival

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Monogamy alternate hypotheses

• Mate guarding guarding assures paternity not
  guarding jeopardizes it
• Especially critical if females are rare or
  receptive for a limited time
• Example many crab species (see sexual selection
  lecture)

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Monogamy alternate hypotheses

• Female-enforced monogamy
• Similar to mate-guarding, but done by female.
• Example Burying beetles
• A female would lose resources, and possibly her
  offspring if she allows her male to mate again.

www.royalbertmuseum.ca
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Monogamy alternate hypotheses

• Danger theory
• Leaving ? increases chance of dying if predation
  rates are high.
• Example The mantis shrimp Lysiosquilla sulcata

Lysiosquilla sp. Opencage.info
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Mantis shrimp (another type)
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Monogamy alternate hypotheses

• Pop em out theory
• Highly fertile mate
• Not worth time/energy to seek another.
• Example Djungarian hamsters

bbs.petsky.com.cn
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Social Monogamy and extra-pair copulations

• Extra-pair copulations can increase fitness of
  participants
• Males More mates ? more offspring possible.
• Females
• Historical (not current) ideas no advantage for
  females
• Observational/experimental evidence clear
  fitness benefits documented for some species
• Example Yellow-toothed cavy

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Yellow-toothed cavy Offspring survival as a
function of multiple mates for females
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Social Monogamy and extra-pair copulations

• Direct fitness benefits genetically based
• Good genes
• What does this mean?
• Genetic compatibility
• What does this mean?
• Genetic variability among offspring
• Why important?

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Social Monogamy and extra-pair copulations

• Other benefits that may improve fitness for
  females
• More resources hypothesis
• Example Orange-rumped honeyguides swap food for
  sex.
• Better protection/care hypothesis
• Example Dunnocks (European song bird)
• Mate with two males ? both care for young
• Infanticide reduction hypothesis
• Example chimpanzees (whos dad?)

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Polyandry (w/o polygyny)

• Spotted sandpipers near-complete sex-role
  reversal
• Females arrive on breeding grounds compete with
  other females for territories.
• Initial male arrives, mates, cares for her first
  clutch.
• Second male arrives later, mates, and cares for
  her second clutch.

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What circumstances promote polyandry?

• Female only lays 4 eggs at once
• Add eggs (experimentally) ? decrease the total
  young successfully raised
• Related to incubation effort and protection
• Female can ? reproductive success by laying a
  second brood?
• Needs second mate
• Reproductive success limited by mates rather than
  gametes in this case

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What circumstances promote polyandry?

• Why would males comply?
• Operational sex ratio biased toward males
  (related to absolute ratio for this species)
• She abandons ?
• He stays ? offspring survive
• He leaves ? offspring die
• Male 1 Certain of paternity for clutch 1
  possibility of paternity for clutch 2
• How is this possible?
• Male 2 Later arrivals less dominant, but still
  have a chance of paternity if they stay.

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What circumstances promote polyandry?

• Food fluctuation hypothesis
• In food-poor years, females put all energy into
  eggs and have no energy left for care of
  eggs/young.
• Mate assistance (by male) essential ? monogamy
• In food-rich years (i.e. many mayflies), the
  female recovers her body mass and can lay
  another batch
• Monogamy ? Polyandry

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What circumstances promote polyandry?

• Heavy predation pressure on nests
• Multiple nests assure that at least some young
  will survive.
• Male is needed to prevent predation
• Young will all be lost if he doesnt stay.

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Patterns of reproductive effortVariations

• Numbers of young produced at a time
• More young less parental investment/individual?
  high mortality among young
• Care of eggs/larvae
• Variability in parental investment
• Type of young produced
• Precocial vs. altricial offspring (What is the
  difference?)

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Patterns of reproductive effortVariations (cont.)

• Number of reproductive events in a lifetime
• Semelparous one big reproductive event in
  lifetime/many offspring
• Many are relatively short-lived (squid, annual
  plants)
• But some are long-lived (periodical cicadas)
• Itoparous many reproductive events in lifetime/
  fewer offspring per event.
• Common especially birds and mammals
• Timing is an issue
• begin early ? materials/energy into reproduction,
  
• Begin later ? materials/energy into survival and
  growth

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r vs. K strategists