TOPIC 12: LIFE HISTORIES

Question 1

What is often limited?

Answer 1

Resources are often limited…
* organisms must decide how to allocate time/energy to different activities
throughout lifespan

Question 2

allocation decisions

Answer 2

will affect an individual’s fitness – by influencing growth, reproduction and survival

• Therefore, organisms will develop allocation strategies over evolutionary
  time to adapt to abiotic and biotic conditions in their environment

Question 3

Trade-of

Answer 3

increased allocation of time/energy to some activities results in a decreased
allocation to other activities
* increase in one thing means a decrease in something else

Question 4

Life History Trade-off:

Answer 4

Growth & Survival VS. Reproduction

Question 5

Reproductive effort

Answer 5

the proportion of available resources that an individual allocates to
reproduction throughout its lifespan
= current + future reproductive output

Question 6

future reproductive output

Answer 6

survival + fecundity in the future

Question 7

fecundity

Answer 7

number of offspring produced/event

Question 8

Lifetime Reproductive Success (LRS)

Answer 8

the number of offspring produced
throughout the lifespan of an individual
~ similar to fitness… but not does not involve the offspring surviving to reproductive age

Question 9

Life History Strategy

Answer 9

set of choices and decisions resulting in an individual’s allocation to
reproductive effort through its lifespan

Question 10

example

Answer 10

1. Invest heavily in current reproduction
   – may drain a parent’s energy reserves
   reduce ability to grow → lower probability of survival
   If survive, may produce fewer offspring in the future
2. Invest heavily in current growth/survival (delay reproduction):
   faster growth → higher probability of survival
   larger size – more resources available for future reproduction

Answer 11

The optimal strategy will be a compromise between the allocation of time/energy to
growth/survival versus reproduction..

Question 12

Life History Traits

Answer 12

1) Body size / growth
2) Age at sexual maturity
3) Number of reproductive events
4) Number of offspring produced per event
5) Offspring size
6) Amount of parental care
7) Senescence, programmed death

Question 13

Body Size/Growth

Answer 13

• General Pattern: Fecundity increases with body size
• Larger individuals have more resources to devote to offspring.
• But how much to invest in growth before reproducing?; females are generally larger
• Body size will affect aspects of survival as well

Question 14

Maturity

Answer 14

General pattern: Age of maturity increases as adult lifespan or annual survival rate
increases; longer you live the later your reproduce

Question 15

Long lifespan

Answer 15

high annual survival rate):
* current fecundity should not jeopardize future growth, survival and
reproduction
* favour growth in 1st few years to increase fecundity
* favour reproduction over lifespan (~ breed older)

Question 16

Short lifespan

Answer 16

(low annual survival rate):
* current fecundity at the expense of adult survival
* do not favour growth – may die before breeding
* favour current reproduction (~ breed younger)

Question 17

E.g. Bird

Answer 17

Low annual survival – breed younger
High annual survival – breed older

Question 18

Parity

Answer 18

number of breeding events

Question 19

Semelparity

Answer 19

reproduce once and die

Question 20

iteroparity

Answer 20

reproduce repeatedly throughout life span

Question 21

General pattern

Answer 21

semelparity occurs more for organisms living under variable
environmental conditions

Question 22

When is semelparity favoured?

Answer 22

Adult survival is low (lifespan < 1-2 years)
– Adult survival is high – but long intervals between years with
conditions suitable for high offspring survival
» Organisms store resources and reproduce when conditions
are favourable and most offspring are likely to survive
(Carpe diem! Seize the day

Question 23

Fecundity General pattern

Answer 23

as more offspring are produced – the survival of each offspring decreases
Fewer offspring:
* allocate more resources per offspring
More offspring:
* allocate less resources per offspring

Question 24

Oviparous

Answer 24

eggs provided with yolk hatch externally

Question 25

Ovoviviparous

Answer 25

eggs provided with yolk hatch internally

Question 26

Viviparous

Answer 26

nutrition provided directly by mother; live birth

Question 27

Resource-based

Answer 27

different life history strategies are favoured under varying abundances of
resources

Question 28

1. If resources are abundant

Answer 28

• Low competition among individuals within a population
• Population growth (“intrinsic rate of increase”, r) is at its maximum
• adaptations will enhance (selection will favour) rapid population growth
  Reproduction&raquo_space; Growth/Survival = r-selected
  large reproductive allocation but invest little in survival

Question 29

If resources are limited

Answer 29

• High competition among individuals within a population
• Population growth is low - population is at “Carrying Capacity”, K
• adaptations will enhance (selection will favour) competitive ability
  Growth/Survival&raquo_space; Reproduction = K-selected
• large allocation to survival but little in reproduction