Ecology Lecture 11 Ecology Lecture 11 Life History Patterns 2
Dec 20, 2015
Ecology Lecture 11Ecology Lecture 11
Life History Patterns 2
OverviewOverview
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
Key principlesKey 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.
PolygynyPolygyny
Resource defense polygyny Example: African cichlid fish,
Lamprologus callipterus Defended resource = shells in which females
lay eggs
PolygynyPolygyny
Female defense polygyny Example: Elephant seals (females
aggregate)
Photo: www.driftersister.com
PolygynyPolygyny
Female defense polygyny Example: Elephant seals (males compete for
beachmaster status)
Photo: www.wetasschronicles.com
Male-male competition and sexual Male-male competition and sexual dimorphism (seals)dimorphism (seals)
NOTE: Each point represents a NOTE: Each point represents a speciesspecies
PolygynyPolygyny
Lek polygyny Males clump, but not due to another resource
Males become the clumped resource! Example 1: satin bowerbirds
Satin Bowerbirds: multiple signals Satin Bowerbirds: multiple signals of health and fitness (and good of health and fitness (and good
genes?)genes?)
PolygynyPolygyny
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/costsPolygyny: benefits/costs
Male number of offspring likely to correlate
with number of mates (+) Female:
gets a high-quality male (+) gets less of the male’s time and
attention for raising young being defended against predators
MonogamyMonogamy
Common or rare?
In which group of animals is it most common?
www.magicmud.com
Monogamy: alternate Monogamy: alternate hypotheseshypotheses
Mate assistance: it takes two parents to raise the offspring
Example: Adelie penguins
Both parents needed for chick survival
Monogamy: alternate Monogamy: alternate hypotheseshypotheses
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)
Monogamy: alternate Monogamy: alternate hypotheseshypotheses
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
Monogamy: alternate Monogamy: alternate hypotheseshypotheses
Danger “theory” Leaving
increases chance of dying if predation rates are high.
Example: The mantis shrimp Lysiosquilla sulcata
Lysiosquilla sp. Opencage.info
Mantis shrimp (another Mantis shrimp (another type)type)
Monogamy: alternate Monogamy: alternate hypotheseshypotheses
Pop ‘em out “theory”
Highly fertile mate Not worth
time/energy to seek another.
Example: Djungarian hamsters
bbs.petsky.com.cn
Social Monogamy and Social Monogamy and extra-pair copulationsextra-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
Yellow-toothed cavy: Offspring survival Yellow-toothed cavy: Offspring survival as a function of multiple mates for as a function of multiple mates for
femalesfemales
Social Monogamy and Social Monogamy and extra-pair copulationsextra-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?
Social Monogamy and Social Monogamy and extra-pair copulationsextra-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 (who’s dad?)
Polyandry (w/o polygyny)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.
What circumstances What circumstances promote polyandry?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
What circumstances What circumstances promote polyandry?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.
What circumstances What circumstances promote polyandry?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
What circumstances What circumstances promote polyandry?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 doesn’t stay.
Patterns of reproductive Patterns of reproductive efforteffort
VariationsVariations 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?)
Patterns of reproductive Patterns of reproductive efforteffort
Variations (cont.)Variations (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
““r”-strategistsr”-strategists ““K”-strategistsK”-strategists
Semelparous Itoparous
Many offspring Few offspring
Little/no parental investment per individual offspring
High levels of investment per individual offspring
Relatively short lifespan Relatively long lifespan
Begin to reproduce relatively early in life
Begin to reproduce relatively later in life
Good colonizers of newly available habitat, but often not effective competitors
Not usually colonizers, but arrive later in succession, compete successfully
““r” vs. “K” strategistsr” vs. “K” strategists