Life history traits

Question 1

What are life history traits?

Answer 1

lifetime pattern or growth, development and reproduction. = adaptions that evolved through natural selection.

Question 2

What is maximum fitness?

Answer 2

number of offspring that live to reproductive age.

Question 3

What are the aspects of life history traits?

Answer 3

1. mode of reproduction
2. age at first reproduction
3. energy allocation to reproduction
4. number and size of egg/young/seeds
5. timing of reproduction.

individuals have limited resources to allocate aspects of life history - an allocation to one spect reduces the resources available for others.

Question 4

The evolution of life history traits involves trade-off and can be divided into 2 groups. What are the 2 groups?

The evolution of life histories involves trade-
offs

Answer 4

Intrinsic and extrinsic

Question 5

What intrinsic factors impose contraints?

The evolution of life histories involves trade-
offs

Answer 5

▪ the evolutionary history of the species
▪ developmental patterns
▪ genetics
▪ physiology

Barnecle - only hermaphoroditic arthropod.

Question 6

What extrinsic factors directly influencing survivorship and mortality?

The evolution of life histories involves trade-
offs

Answer 6

▪ the physical environment
▪ the presence of predators
▪ the presence of competitors
▪ Availability of food

Question 7

What is asexual reproduction?

Mode of reproduction may be sexual or
asexual

Answer 7

– NO involvement of egg AND sperm
▪ Rhizomes—strawberry plants
▪ Splitting in two—Paramecium single celled animal like organisms.
▪ Budding—hydra (jellyfish)
▪ Parthenogenesis—aphids = prent produces egg but eggs hatch into individuals without sperm being used.

Question 8

What is sexual reproduction?

Mode of reproduction may be sexual or
asexual

Answer 8

– fusion of haploid egg and sperm to form a diploid zygote

Can either be:
▪ Gonochorism – separate sexes

• Hermaphroditism
  – Simultaneous
  ▪ Could produce twice as many offspring
  ▪ Earthworms
  – Sequential
  ▪ sex change – why?
  ▪ Maturation & growth, M:F
  ▪ Coral reef fish, gastropods, bivalves

when eggs and sperm are involved even tho its in a lab or water column.
NB slide costs and benefits between asex and sex reproduction Lec 9 slide 7

Question 9

How does age and size @ 1st reproduction influences fecundity?

Answer 9

▪ Fecundity frequently depends on size (number of offspring)
▪ Size frequently depends on age
▪ Indeterminate growth
▪ Delaying reproduction in animals

Question 10

What is indeterminate growth?

age and size @ 1st reproduction influences fecundity

Answer 10

– no characteristic adult size
– Fecundity directly proportional to size & age
▪ Giant clams
▪ Many trees

Question 11

Delaying reproduction in animals?

age and size @ 1st reproduction influences fecundity

Answer 11

– Gizzard shad
@ 2 yr = 59K eggs;
@ 3 yr = 379K eggs
- by delaying reproduction you reduce the possibility of the animal dying after giving birth, and increasing the body size and potential for viable offspring production.

– Ragworm Nereis
– Red squirrels

Question 12

Delaying reproduction in plants

age and size @ 1st reproduction influences fecundity

Answer 12

▪ Delay flowering until big enough or favourable conditions.
– Perennials
▪ sufficiently large size
– Biennial plants
▪ favourable environmental conditions

Question 13

What is reproductive effort?

Allocation of time & energy to reproduction
carefully budgeted

Answer 13

– time and energy
– production + care + nourishment of offspring
▪ Trade-off between reproduction and growth and
maintenance
– Perennials: 15 – 20%
– Annuals: up to 40%

Question 14

How does parental investment depend on the
number and size of young?

Answer 14

▪ # offspring inversely proportional to parental
investment per offspring

▪ Many small offspring
– Parental care: impossible
– Environment: unpredictable/ unstable
– External food availability for offspring: guaranteed.

▪ Few large offspring
– Parental care: High
▪ Brooded; protected during most vulnerable stage of life
– Environment: Stable/ predictable
– External food availability for offspring: not always
guaranteed

Question 15

What is semelparity?

Species differ in the frequency/timing of
reproduction

Answer 15

– One suicidalact of reproduction
– The life span varies
▪ several days to months (many invertebrates, annual
plants )
– Inhabit unstable/disturbed habitats
▪ years (salmon) to decades (bamboo)
– High ‘once-off’ fitneness compensates for loss of repeated
reproduction.

Question 16

What is Iteroparity?

Species differ in the frequency/timing of
reproduction

Answer 16

– Repeated reproduction
– Fewer young at one time
▪ Live for months to years
▪ Total reproductive output spread over longer lifetime
– Mammals, birds, perennial plants, shrubs, and trees
▪ inhabit stable, predictable environments (usually)
– trade-off betw early versus late reproduction

Question 17

How do environmental conditions influence the evolution of life history characteristics?

Answer 17

▪ Life history characteristics are the product of
evolution and reflect adaptations to the prevailing environmental conditions
– species that exhibit similar life history patterns tend
to inhabit similar environments

▪ r - and K -selection (R. MacArthur,
E.O. Wilson, and E. Pianka)
– ris the intrinsic rate of natural increase
– Kis equilibrium density or number of
individuals under constant conditions
▪ Two broad habitat types
– Variable in time and short-lived, vs
– Relatively stable in time, long-lived,
and constant
▪ Species occupying them will differ in
life history traits

▪ J.P. Grime developed a life history classification
for plants
– R(ruderal) rapidly colonize disturbed sites
– C(competitive) predictable habitats with abundant
resources
– S(stress-tolerant) habitats where resources are
limited