Download Ecology Lecture 11

Ecology Lecture 11
Life History Patterns 2
Overview
A mating system includes
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Types of mating systems
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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.
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
Key principles
The system that evolves depends upon
the individual interests of each gender
Male and female interests are often in
conflict. Why?
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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.
Polygyny
 Resource defense polygyny
 Example: African cichlid fish, Lamprologus
callipterus
 Defended resource = shells in which females lay
eggs
Polygyny
 Female defense polygyny
 Example: Elephant seals (females aggregate)
Photo: www.driftersister.com
Polygyny
 Female defense polygyny
 Example: Elephant seals (males compete for
beachmaster status)
Photo: www.wetasschronicles.com
Male-male competition and sexual
dimorphism (seals)
NOTE: Each point represents a species
Polygyny
 Lek polygyny
 Males clump, but not due to another resource
 Males become the clumped resource!
 Example 1: satin bowerbirds
Satin Bowerbirds: multiple signals of
health and fitness (and good genes?)
Polygyny
 Lek polygyny
 Example 2: bullfrogs
 Females choose males with longest, loudest and deepest
calls
 But don’t forget the sneaky f--kers
www.tc.umn.edu
Polygyny: benefits/costs
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Male
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number of offspring likely to correlate with
number of mates (+)
Female:
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gets a high-quality male (+)
gets less of the male’s time and attention for
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raising young
being defended against predators
Monogamy
 Common or
rare?
 In which group
of animals is it
most common?
www.magicmud.com
Monogamy: alternate
hypotheses
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Mate assistance: it
takes two parents
to raise the
offspring
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Example: Adelie
penguins
Both parents needed
for chick survival
Monogamy: alternate
hypotheses
Mate guarding: guarding assures
paternity; not guarding jeopardizes it
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Especially critical if females are rare or receptive for
a limited time
Example: many crab species (see sexual selection
lecture)
Monogamy: alternate
hypotheses
Female-enforced
monogamy
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Similar to mateguarding, 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
Monogamy: alternate
hypotheses
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Danger “theory”
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Leaving  increases
chance of dying if
predation rates are
high.
Example: The
mantis shrimp
Lysiosquilla sulcata
Lysiosquilla sp. Opencage.info
Mantis shrimp (another type)
Monogamy: alternate
hypotheses
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Pop ‘em out
“theory”
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Highly fertile mate
Not worth
time/energy to seek
another.
Example: Djungarian
hamsters
bbs.petsky.com.cn
Social Monogamy and extrapair copulations
Extra-pair copulations can increase
fitness of participants
Males: More mates  more offspring
possible.
Females:
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Historical (not current) ideas: no advantage for
females
Observational/experimental evidence: clear fitness
benefits documented for some species
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Example: Yellow-toothed cavy
Yellow-toothed cavy: Offspring survival as a
function of multiple mates for females
Social Monogamy and extrapair copulations
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Direct fitness benefits: genetically
based
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Good genes
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Genetic compatibility
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What does this mean?
What does this mean?
Genetic variability among offspring
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Why important?
Social Monogamy and extrapair copulations
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Other benefits that may improve
fitness for females
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More resources hypothesis
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Example: Orange-rumped honeyguides
swap food for sex.
Better protection/care hypothesis
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Example: Dunnocks (European song bird)
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Mate with two males  both care for young
Infanticide reduction hypothesis
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Example: chimpanzees (who’s dad?)
Polyandry (w/o polygyny)
Spotted sandpipers: near-complete sexrole reversal
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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.
What circumstances
promote polyandry?
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Female: only lays 4 eggs at once
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Add eggs (experimentally)  decrease the
total young successfully raised
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Female can  reproductive success by laying
a second brood
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Related to incubation effort and protection
Needs second mate
Reproductive success limited by
mates rather than gametes in this
case
What circumstances
promote polyandry?
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Why would males “comply?”
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Operational sex ratio biased toward males
(related to absolute ratio for this species)
She abandons 
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Male 1: Certain of paternity for clutch 1;
possibility of paternity for clutch 2
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He stays  offspring survive
He leaves  offspring die
How is this possible?
Male 2: Later arrivals less dominant, but still
have a chance of paternity if they stay.
What circumstances
promote polyandry?
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Food fluctuation hypothesis
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In food-poor years, females put all energy
into eggs and have no energy left for care of
eggs/young.
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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
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Monogamy  Polyandry
What circumstances
promote polyandry?
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Heavy predation pressure on nests
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Multiple nests assure that at least some
young will survive.
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Male is needed to prevent predation
Young will all be lost if he doesn’t stay.
Patterns of reproductive effort
Variations
Numbers of young produced at a
time
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More young = less parental
investment/individual high mortality
among young
Care of eggs/larvae
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Variability in parental investment
Type of young produced
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Precocial vs. altricial offspring (What is the
difference?)
Patterns of reproductive effort
Variations (cont.)
Number of reproductive events in a
lifetime
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Semelparous: one big reproductive event in
lifetime/many offspring
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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:
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begin early  materials/energy into reproduction,
Begin later  materials/energy into survival and
growth
“r” vs. “K” strategists
“r”-strategists
Semelparous
Many offspring
Little/no parental investment
per individual offspring
Relatively short lifespan
Begin to reproduce relatively
early in life
Good colonizers of newly
available habitat, but often
not effective competitors
“K”-strategists
Itoparous
Few offspring
High levels of investment per
individual offspring
Relatively long lifespan
Begin to reproduce relatively
later in life
Not usually colonizers, but
arrive later in succession,
compete successfully