Chapter 8

Question 1

Life history

Answer 1

the schedule of an organism’s growth, development, reproduction, and survival; represents an allocation of limited time and resources to achieve maximum reproductive success.

Question 2

Fecundity

Answer 2

the number of offspring produced by an organism per reproductive episode.

Question 3

Parity

Answer 3

the number of reproductive episodes an organism experiences.

Question 4

Parental investment

Answer 4

the time and energy given to an offspring by its parents.

Question 5

Longevity (life expectancy)

Answer 5

the life span of an organism.

Question 6

“Slow” life history

Answer 6

• Long time to sexual maturity
• Long life spans
• Low numbers of offspring High parental investment Examples: elephants, oak trees

Question 7

“Fast” life history

Answer 7

• Short time to sexual maturity
• Short life spans
• High numbers of offspring Little parental investment Examples: fruit flies, weeds

Question 8

Plant life history depends on?

Answer 8

stress, competition, and the frequency of disturbances.

Question 9

stress tolerators

Answer 9

potential growth rate: slow

age of sexual maturity: late

proportion of energy being used to make seeds: low

importance of vegetative reproduction: frequently important

Question 10

competitors

Answer 10

potential growth rate: fast

age of sexual maturity: early

proportion of energy being used to make seeds: low

importance of vegetative reproduction: often important

Question 11

ruderals

Answer 11

potential growth rate: fast

age of sexual maturity: early

proportion of energy being used to make seeds: high

importance of vegetative reproduction: rarely important

Question 12

What are stress tolerators?

Answer 12

typically small herbs with a long life span, slow growth, and a long time to sexual maturity.

Many stress tolerators rely on vegetative reproduction (reproducing from roots and stems) instead of producing costly seeds.

Question 13

competitors

Answer 13

(e.g., goldenrod) grow fast, achieve early sexual maturity, and devote little energy to seed production.

Question 14

Ruderals

Answer 14

(e.g., weeds such as Canada thistle) grow fast and devote a high proportion of their energy to reproduction.

Question 15

What are trade-offs?

Answer 15

when one life history trait is favored, it prevents the adoption of other advantageous traits.

Question 16

Principle of allocation

Answer 16

the observation that when resources are devoted to one body structure, physiological function, or behavior, they cannot be allotted to another.

Natural selection will favor individuals that allocate their resources in a way that achieves maximum fitness.

There is a tradeoff between offspring number and offspring survival.

Question 17

Determinate growth

Answer 17

a growth pattern in which an individual does not grow any more once it initiates reproduction; occurs in many species of birds and mammals.

Question 18

Indeterminate growth

Answer 18

a growth pattern in which an individual continues to grow after it initiates reproduction; occurs in many species of plants, invertebrates, fishes, reptiles, and amphibians.

Question 19

Organisms with a long life span favor what type of growth?

Answer 19

determinate growth, which allows them to grow first and reproduce later.

Question 20

Organisms with a short life span favor what type of growth?

Answer 20

indeterminate growth, which allows them to quickly reproduce before death.

Question 21

The age of sexual maturity is __________ associated with the _______________ an animal will survive after reaching maturity.

Answer 21

positively; the number of years

Question 22

What does delaying sexual maturity do?

Answer 22

allows an individual to grow large and produce more offspring per year once reproduction begins.

Question 23

senescence

Answer 23

a gradual decrease in fecundity and an increase in the probability of mortality.

Question 24

Semelparity

Answer 24

when organisms reproduce only once during their life; relatively rare in vertebrates, but common in insects and plants.

Question 25

Iteroparity

Answer 25

when organisms reproduce multiple times during their life; common among birds, reptiles, mammals, and amphibians.

Question 26

Annual

Answer 26

an organism that has a life span of one year.

Question 27

Perennial

Answer 27

an organism that has a life span of more than one year.

Question 28

When does semelparity arise?

Answer 28

when there is a massive amount of energy required for reproduction.

Examples:
Bamboos are semelparous tropical plants that have few opportunities for seed germination.

Once a bamboo germinates, it spreads vegetatively for years.

Question 29

Agaves

Answer 29

semelparous, arid plants that reproduce by growing a giant flowering stalk that produces a large number of seeds.

Stalk growth is so rapid that it must steal water and nutrients from the leaves; the plant dies soon after reproduction.

Question 30

Yuccas

Answer 30

are mostly iteroparous, but some varieties are semelparous.

Semelparous varieties live in regions prone to fire, which may favor a single, large reproduction effort before fires kill adults.

Iteroparous varieties live where there is less precipitation, but less chance of fire.

Differences in breeding patterns lead to tradeoffs in flower and fruit numbers, and in germination rates.

Question 31

Cicadas

Answer 31

spend the first part of their life underground where they obtain nutrients from xylem tissue of plant roots.

Periodical cicadas spend 13 or 17 years underground as nymphs and then emerge from the ground in synchrony to mate.

The long nymphal period gives larvae time to grow to adulthood on a diet of low nutritional quality.

Question 32

Photoperiod

Answer 32

the amount of light that occurs each day; provides a cue for many events in the life histories of virtually all organisms.

Example:
In Michigan, water fleas (Daphnia) enter diapause in mid-September when the photoperiod declines to less than 12 hours of sunlight.

Related species in Alaska enter diapause in August when the photoperiod declines to less than 20 hours of sunlight.

These photo-sensitivities are related to environmental temperature; the photoperiod is related to decline of temperatures below a hospitable threshold.

Question 33

The effect of resources

Answer 33

Fluctuations in resource availability often determine the timing of life history events.

Example:
Metamorphosis occurs when a larva changes into a juvenile or an adult.

Like many amphibians, the barking treefrog undergoes metamorphosis.

Individuals with high food resources can metamorphose at a relatively large mass and early age.

Individuals with low food resources can metamorphose early and small, but this may reduce fecundity and increase predation risk.

Question 34

The effects of predation

Answer 34

Predation can affect many life history traits (e.g., time to and size at hatching, metamorphosis, and sexual maturity).

Example:
Many embryos can detect the presence of an egg predator and respond by speeding up their hatching time to avoid predation.

The red-eyed tree frog of Central America lays eggs on leaves that overhang water.

The embryos can sense the vibrations of a snake predator on the leaf, and hatch earlier than usual.

This makes them hatch at a smaller size, and leaves them more prone to aquatic predators.

Question 35

The effects of global warming

Answer 35

Small changes in temperature can have substantial impacts on an organism’s physiological processes.

The increase in global temperature has changed the breeding times of many animals and plants.

Example:
Between 1959 and 1991, researchers found that an increase in average May temperatures was associated with earlier egg-laying dates of North American tree swallows.

Many organisms (e.g., amphibians) respond to the duration of warm air temperatures, which is also influenced by global warming.

Question 36

The effects of global warming on plants

Answer 36

Changes in temperature can alter the initiation of flower production.

As temperatures get warmer, flowering occurs earlier and earlier.

Question 37

Consequences of altered breeding

Answer 37

Problems can arise when a species depends on the environment to provide the necessary resources with an altered breeding season.

Example:
The pied flycatcher breeds in Europe each spring.

In 1980, the date of egg hatching began a few days before the peak of caterpillar abundance, which is prey for the flycatchers.

Over the next two decades, spring temperatures warmed and peak caterpillar abundance shifted to two weeks earlier.

The pied flycatcher retained its normal breeding time.

As a result, newly hatched chicks no longer have their major source of food and flycatcher populations have declined by 90%.

Question 38

Impact of humans on organisms

Answer 38

In addition to global warming, human activities can impose strong selection and have substantial impacts on organisms’ life histories.

Example:
Commercial fisheries impose selection pressure on fish size by harvesting only the largest individuals.

Between the 1930’s and 1970’s, the average age at maturity of northeast Arctic cod decreased from 9–11 years to 7–9 years.

This shift is likely associated with changes in fecundity and longevity.