Chapter 10: Life History Patterns

Question 1

What are some possible advantages to larger body size?

Answer 1

better competitive ability, ability to find mates, success as a predator or decreased vulnerability to predation

Question 2

Why will rapid development normally be favored by natural selection?

Answer 2

Shortened generation time greatly increases reproductive rates

Question 3

Under what circumstances might arrested development be favored?

Answer 3

if an organism has to pass through highly unfavorable period of its lifetime

Question 4

What are the advantages and disadvantages of asexual?

Answer 4

+ 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

Question 5

What are the advantages and disadvantages of sexual reproduction?

Answer 5

+ 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

Question 6

List some organisms that switch between asexual and sexual reproduction.

Answer 6

daphnia, rotifers, water fleas

Question 7

Under what circumstances do such organisms switch from asexual to sexual reproduction?

Answer 7

unfavorable times like crowding, dying, freezing

Question 8

Describe the pattern of reproduction seen in Daphnia during favorable and unfavorable conditions.

Answer 8

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

Question 9

Give two major determinants of the nature and evolution of male-female relationships in nature.

Answer 9

• availability and distribution of resources

- ability of individuals to control access to mates or resources

Question 10

Under what circumstances in nature do females gain no advantage by remaining with a male?

Answer 10

if the male has no role in feeding and protection of the young and defends no resources available to them

Question 11

What is monogamy and under what conditions is it likely to be seen?

Answer 11

formation of a pair bond between one male and one female

-cooperation by parents is needed to rear young successfully

Question 12

Why are so few birds but so many male mammals promiscuous?

Answer 12

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

Question 13

Distinguish between polygyny and polyandry.

Answer 13

Polygyny: one male with several females
Polyandry: one female with several males

Question 14

what factors dictate the number of females a male can monopolize?

Answer 14

• 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

Question 15

Under what circumstances might it be preferable to produce fewer, larger young than many smaller ones?

Answer 15

when offspring fitness is related to offspring size

Question 16

What kinds of measurements are used to assess reproductive allocation?

Answer 16

• relative clutch mass ratios
• gonad weight to body weight ratios
• seed crop weight to plant weight ratios

Question 17

Define reproductive value.

Answer 17

measure of the combined effects of fecundity and survivorship

Question 18

On what does expected (residual reproductive output depend?

Answer 18

expected future survivorship and expected future fecundity

Question 19

How is reproductive value calculated for an individual in a population that is staying the same?

Answer 19

its total lifetime expectation of reproductive output from its current age-class

Question 20

Is the reproductive value of an individual in a population that is increasing lower or higher? why?

Answer 20

lower because an individual’s proportionate contribution of genes will be smaller

Question 21

is the reproductive value of an individual in a population that is decreasing lower or higher? why?

Answer 21

higher because the individual’s proportionate contribution of genes will be larger

Question 22

What is the “cost of reproduction” and how is it measured?

Answer 22

• it is the reduction in survivorship or rate of growth

- measured in the reduction of survivorship and/or rate of growth

Question 23

Give two reasons why there may be a “cost of reproduction”.

Answer 23

• loss of energy spend on reproduction takes away from other life sustaining activities
• risks like increased vulnerability to predation

Question 24

What is meant by “trade-offs” in life history patterns?

Answer 24

compromises in the way available resources are allocated, benefits of one process will always be bought at the expense of another

Question 25

Why do such “trade-offs” occur?

Answer 25

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

Question 26

In terms of life histories, what will be maximized by natural selection?

Answer 26

life histories with the greatest reproductive value

Question 27

Distinguish between size-beneficial and size-neutral habitats.

Answer 27

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

Question 28

Give some examples of habitats that might be classified as size-neutral.

Answer 28

temporary ponds that dry up or freeze

footpaths

Question 29

Why did the dandelion variety inhabiting the footpath in Gadgil and Solbrig’s study (1972) produce the greatest number of flower heads?

Answer 29

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

Question 30

Why did the dandelion variety inhabiting the undisturbed pasture in Gadgil and Solbrig’s study (1972) produce the fewest number of flower heads?

Answer 30

it is a size beneficial habitat favoring lower current reproductive allocation with the expectation of increasing future reproductive value

Question 31

How might the allocation of energy and resources to eggs rather than to growth reduce the residual reproductive value of a lizard?

Answer 31

because fecundity is related to body size, if you put more energy into reproduction this year, it will reduce next years fecundity

Question 32

What reproductive strategy was seen in Texas fence lizards by Tinkle and Ballinger (1972)?

Answer 32

highest mortality so they matured the earliest and produced the greatest number of eggs per season

Question 33

How do you account for the observed reproductive traits in the Texas lizards?

Answer 33

they didn’t know if they would survive to the next year so they put all of their energy into reproducing right away

Question 34

What reproductive strategy was seen in Ohio fence lizards by Tinkle and Ballinger (1972)?

Answer 34

eggs were produced at the end of the year and they only produced a few each season

Question 35

How do you account for the observed reproductive traits in the Ohio lizards?

Answer 35

low mortality

Question 36

What did Baker’s study of seed size in California show?

Answer 36

there is an inverse relationship between seed weight and soil moisture

Question 37

How would you interpret his results?

Answer 37

smaller seeds had higher mortality during drought, so seeds in drier climates are larger while seeds in more moist climates were smaller