Chapter 10: Life History Patterns Flashcards
What are some possible advantages to larger body size?
better competitive ability, ability to find mates, success as a predator or decreased vulnerability to predation
Why will rapid development normally be favored by natural selection?
Shortened generation time greatly increases reproductive rates
Under what circumstances might arrested development be favored?
if an organism has to pass through highly unfavorable period of its lifetime
What are the advantages and disadvantages of asexual?
+ quick reproduction of many individuals well adapted to the environment at that time
-low genetic variability; if the environment changes, they will have low fitness
What are the advantages and disadvantages of sexual reproduction?
+ high amount of genetic variability, meets changing selective pressures, prevents accumulation of harmful mutations
- expensive; individual only passes half of its genes; many have poor fitness
List some organisms that switch between asexual and sexual reproduction.
daphnia, rotifers, water fleas
Under what circumstances do such organisms switch from asexual to sexual reproduction?
unfavorable times like crowding, dying, freezing
Describe the pattern of reproduction seen in Daphnia during favorable and unfavorable conditions.
Favorable: asexual parthenogenesis creating many that are identical
Unfavorable: sexual reproduction, produce highly resistant resting eggs with many different genotypes that hatch when conditions improve
Give two major determinants of the nature and evolution of male-female relationships in nature.
- availability and distribution of resources
- ability of individuals to control access to mates or resources
Under what circumstances in nature do females gain no advantage by remaining with a male?
if the male has no role in feeding and protection of the young and defends no resources available to them
What is monogamy and under what conditions is it likely to be seen?
formation of a pair bond between one male and one female
-cooperation by parents is needed to rear young successfully
Why are so few birds but so many male mammals promiscuous?
young birds are helpless when they hatch and need warmth, food and protection. This can increase a males fitness by staying with the female.
In mammals the female lactates, so the male doesn’t contribute much, so it is advantageous to mate with as many females as possible
Distinguish between polygyny and polyandry.
Polygyny: one male with several females
Polyandry: one female with several males
what factors dictate the number of females a male can monopolize?
- degree of synchrony in sexual receptivity
- if that is large then it depends on the availability of females and how many the male can energetically defend
Under what circumstances might it be preferable to produce fewer, larger young than many smaller ones?
when offspring fitness is related to offspring size
What kinds of measurements are used to assess reproductive allocation?
- relative clutch mass ratios
- gonad weight to body weight ratios
- seed crop weight to plant weight ratios
Define reproductive value.
measure of the combined effects of fecundity and survivorship
On what does expected (residual reproductive output depend?
expected future survivorship and expected future fecundity
How is reproductive value calculated for an individual in a population that is staying the same?
its total lifetime expectation of reproductive output from its current age-class
Is the reproductive value of an individual in a population that is increasing lower or higher? why?
lower because an individual’s proportionate contribution of genes will be smaller
is the reproductive value of an individual in a population that is decreasing lower or higher? why?
higher because the individual’s proportionate contribution of genes will be larger
What is the “cost of reproduction” and how is it measured?
- it is the reduction in survivorship or rate of growth
- measured in the reduction of survivorship and/or rate of growth
Give two reasons why there may be a “cost of reproduction”.
- loss of energy spend on reproduction takes away from other life sustaining activities
- risks like increased vulnerability to predation
What is meant by “trade-offs” in life history patterns?
compromises in the way available resources are allocated, benefits of one process will always be bought at the expense of another
Why do such “trade-offs” occur?
because energy is spent in three ways: growth, maintenance and reproduction. An increase in one leads to a decrease in another because there is only so much energy to use
In terms of life histories, what will be maximized by natural selection?
life histories with the greatest reproductive value
Distinguish between size-beneficial and size-neutral habitats.
Size-beneficial: larger individuals may be at an advantage because of competition for mates, resources or reduced predation risk, increased expected future reproductive values
Size-neutral: expected future reproductive value is little affected or actually decreases with size
Give some examples of habitats that might be classified as size-neutral.
temporary ponds that dry up or freeze
footpaths
Why did the dandelion variety inhabiting the footpath in Gadgil and Solbrig’s study (1972) produce the greatest number of flower heads?
because it is in a size-neutral habitat that has indiscriminant mortality which favors early reproduction, semelparity, increasing current reproduction over future output because there is little chance of surviving til next year
Why did the dandelion variety inhabiting the undisturbed pasture in Gadgil and Solbrig’s study (1972) produce the fewest number of flower heads?
it is a size beneficial habitat favoring lower current reproductive allocation with the expectation of increasing future reproductive value
How might the allocation of energy and resources to eggs rather than to growth reduce the residual reproductive value of a lizard?
because fecundity is related to body size, if you put more energy into reproduction this year, it will reduce next years fecundity
What reproductive strategy was seen in Texas fence lizards by Tinkle and Ballinger (1972)?
highest mortality so they matured the earliest and produced the greatest number of eggs per season
How do you account for the observed reproductive traits in the Texas lizards?
they didn’t know if they would survive to the next year so they put all of their energy into reproducing right away
What reproductive strategy was seen in Ohio fence lizards by Tinkle and Ballinger (1972)?
eggs were produced at the end of the year and they only produced a few each season
How do you account for the observed reproductive traits in the Ohio lizards?
low mortality
What did Baker’s study of seed size in California show?
there is an inverse relationship between seed weight and soil moisture
How would you interpret his results?
smaller seeds had higher mortality during drought, so seeds in drier climates are larger while seeds in more moist climates were smaller
