Life-History theory

Question 1

what life history trade offs do animals face?

Answer 1

• energy vs. risk of being killed
• maintenance & repair vs. reproduction
• number vs. quality of offspring
• current vs. future reproduction.

Question 2

when are optimisation decisions static/dynamic?

Answer 2

STATIC: single decision
[which might be repeated]
doesn’t change over time
eg when to leave a patch (MVT)
which prey item to eat.
DYNAMIC: Series of state-dependent decisions
‘state’ could be size, energy reserves, health…
Animal’s decisions now affects the future

Question 3

define fitness - how can fitness be calculated?

Answer 3

Fitness ― long-term number of descendants, looking far into future
tricky to calc if pop is growing
if pop not growing, can use lifetime reproduction success of offspring.

Question 4

what does adult size determine?

Answer 4

metabolic rate
	survival
	intake rate
	rate of reproduction
however, may have a low chance of surviving to an adult size.

Question 5

why is fat beneficial, and what limits fat extent

Answer 5

If big enough, can get through winter on body fat
- Polar bear: pregnant female may fast for eight months
loses 43% body mass.
- buffer against starvation.

Question 6

in what way is fat regulated in small birds?

Answer 6

• limited in amount of excess weight they can carry around
  in winter - longcold nights, spend more energy and also days short so limits foraging time. therefore, roost in groups to allow a lower body temp at night and store more fat.
• Fat levels not limited by food availability, and not at the max value in midwinter. higher right before migration where will be using more energy.

Question 7

what costs of being fat to small birds?

Answer 7

Wittler and Cuthill, 1993
harder to take off
less agile in air
higher energy costs of flight.

Question 8

demonstration of costs of fat to small birds.

Answer 8

Wittler, cuthill and bonser, 1994
starlings trained to fly through maze of padded poles. when mass added, performance worse.
therefore predation likely to increase with fat.

Question 9

what trade off in fat level

Answer 9

Trade-off between two sources of mortality
increased fat: ▼starvation, ▲ predation
best long term strategy minimises starvation and predation and maximises survival.

Question 10

how has dynamic -programming been used

Answer 10

McNamara, Houston
- sequence of decisions, eg forage vs rest.
- decisions are state dependent, eg based on mass at that time.
- foraging is stochastic - random due to environment but obeys rules.
predation risk increases with mass.
- optimal decision depends on time of day, state.
- easiest to work back from time where relationship between currency and state is known.

Question 11

what s the optimal foraging strategy found by dynamic programming of small birds?

Answer 11

maximises long term survival

• forage when resources low to avoid starvation
• build up resources to get through night
• must cope with interruptions (e.g. bad weather when they can’t forage).

Question 12

at a given time of day, how does fat level change?

Answer 12

• if +food, - fat
• if +interruptions, + fat
• if +overnight energy expense, +fat
• if +predator abundance, - fat

Question 13

study of mass change under different pred conditions.

Answer 13

Gosler et al, 1995
wytham woods, oxford
primary pred - Sparrowhawk
long-term data on great tit population
sparrowhawks declined in ’70s (organophosphate pesticides) then recovered
looked at changes in great tit mass.
- great tits heavier when sparrow hawks are rare. Wrens rarely killed by sparrowhawks, displayed no change in mass.

Question 14

what trade off does rep face?

Answer 14

Williams - trade off between

current & future reproductive success.

Question 15

external costs of reproduction

Answer 15

• attracts predators
• male comp = deaths and injuries
• pred risk for parent feeding young

Question 16

internal costs of reproduction

Answer 16

• hard work attracting mates/ caring for young reduces condition → increased mortality
• costs are typically long-lasting

Question 17

what is non annual breeding

example

Answer 17

cycle takes over 1 year, environmental, and animal conditions affect breeding decision.

Question 18

example of non annual breeding decisions based on animals condition

Answer 18

Albatross
Ticknell.
smaller albatrosses cycle less than 1 year.
- Black browed: 4kg, breeds at 10 years, then every year.
- Grey headed: 4kg, first breeds at 12/13 years, then biennial, skips the year after a successful attempt.
in a failed attempt, the later in the year it is, more likely to skip breeding. (higher cost of rep, more likely to skip next year).
- wandering albatross
9.5kg
breeds every other year

Question 19

example of non annual breeding decisions based on environmental condition

Answer 19

eg Ural owl. prey, vole, abundance follows 3 year cycle. in good years, 75% breed, in bad years, 21%.

Question 20

is measuring phenotypic correlation a good way to measure costs of reproduction?

Answer 20

measure current reproduction and future success in natural population. usually neg correlation. not clear evidence of costs of rep.
- problems: may see no variation, every animal at optimum, cant see costs of deviating from this.
pattern may reflect adaptive variation (unmeasurable), good quality animals survive better and reproduce better.

Question 21

what is better than measuring phenotypic correlation for measuring costs of reproduction

Answer 21

must see what happens when animal does something different, so experimental manipulation.

Question 22

experimental manipulation example for measuring costs of reproduction.

Answer 22

Wernham and Bryant 1988
group 1:
gave extra food to young, caused parents reduced effort
Control: no extra food.
After 1 year, no difference in propn parents returning
exp. group had greater fledgling success (68% vs 24%)
exp. young in better condition.
in these years, condition for puffins generally were not very good. agrees with the idea that that costs may only be revealed in bad years.

Question 23

what was lack’s idea about clutch size?

why is it wrong?

Answer 23

Lack, 1947
trade off no. offspring /their success, to maximise productivity
too many young → do badly, fewer survive
this is an influential idea, although typically the clutch size is smaller than predicted by Lack.
ignored future rep. success.
eg Large clutch, parent works more causing cost. parent may reduce clutch to avoid cost.

Question 24

study of kestrel brood size and future RS

Answer 24

Daan et al 1996
manipulated brood sizes of 39 kestrels.
studied time of death, based on return of dead individuals by public
Found reduced clutch size, parent kestrel had less hours of flight per day than control, and vice versa for enlarged clutch.
increased effort = greater winter mortality, not due to predation. physiological cost of higher reproduction eg disease/parasites.

Question 25

what is another thing Lack got wrong?

Answer 25

an animal should breed when foodis most abundant.
however, young born earlier in the year do better as they have more time to grow before winter. seen that early clutches are larger

Question 26

why don’t all parents breed earlier?

Answer 26

need time to get into good condition for breeding.

trade off as waiting to get more reserves (bigger clutch) means a delay which reduces success of offspring.

Question 27

experimental manipulation showing the importance of breeding timing.
5 outcomes

Answer 27

Nilsson & Svensson (1996)
Blue tits moult once a year, immediately after breeding
- experimentally delayed breeding by removing 1st clutch (2nd: 6-7 days later).
- costs of this to great tits were: second clutch to lay, have to feed young later than the best time.
- resulted in:
1. moult delay.
2. higher energy expese in winter than control,
3. higher mass loss in winter
4. lower survival to next year.
5. Females laid later in the following year.
suggets trade off btw rep effort and moulting effort, as poor feathers = poor insulation.

Question 28

there is variation between individuals

Answer 28

means there is diff optimum for each parent in laying date and clutch size.
noise around the mean optimum

Question 29

what is a physiological theory as to why senescence occurs?

Answer 29

inevitable wear and tear cant be repaired.

however some organisms dont age, eg Crosate bust in Mojave desert, >11000 years old. shows scenescence is avoidable.

Question 30

what is an evolutionary theory as to why senescence occurs?

Answer 30

NOT: Die for good of the species - Group selection argument.
Accumulation of mutations
result of trade offs

Question 31

senescence is an accumulation of late acting mutations

Answer 31

Sir Medawar 1952

force of NS declines with age, so discrimination btw individuals is less strong.

Question 32

who described the theory of senescence due to trade offs and why

Answer 32

Williams 1957
antagonistic pleiotropy
small positive effect early in life can counter big negative effect late in life
small chance of paying this cost.

Question 33

who said senescence was due to a disposable soma?

Answer 33

Kirkwood 1977
without senescence body will eventually succumb to predation/accident, so the huge investment in care will eventually be lost.
there must be an optimal level of investment in repair.

Question 34

what is the optimal level of repair?

examples 3

Answer 34

if pop size stable, can predict.
if high extrinsic mortality, independent of condition, low optimal level of maintenance.
eg. Opossums on predator free islands age more slowly than same species on mainland
eg2. Queen ants, low pred rates, and low mortality eg 10 years compared to solitary ants 0.1yr.
eg3. weaver ant large workers mainly outside nest have shorterlife. small workers inside, longer life.

Question 35

what is a physiological explanation of menopause?

Answer 35

depletion of oocytes.
adaptive - based on costs and benefits of rep after 45-50 years. if adaptive, medical interference is bad.
non adaptive - side effect of aging.

Question 36

why may menopause be adaptive?

Answer 36

1. advantage of stopping outweighs cost
   large brain → baby has long period of dependence
   if older, more risk mother dies in childbirth
2. switch to more useful activities: look after dependent children,
   helping grown daughters enhances own RS.
   look after grandchildren.
3. Early models suggest that benefits of stopping do not outweigh costs
   - Mace (2000): models treat female as though she could reproduce at same rate as young woman
   ignores age-related decline in female survival and reproduction.

Question 37

what evidence is there that menopause might be adaptive? 2007

Answer 37

shanley et al 2007
Model: two effects
1. Risk from death in childbirth increases with age
2. Benefit of care by grandmothers (this benefit is not as big as she would get from just reproducing)
Long-term study in The Gambia, measure effects
Not supported
Evidence, but effect not large compared to benefit of reproduction.

Question 38

what is a more recent theory that menopause is adaptive?

Answer 38

Cant and Johnstone 2008
Reduces conflict within group over breeding.
: In humans, females disperse
New younger female joins group & marries son of older resident female
which female should breed?
new female is not related to offspring of old female whereas the old female will be related to new female offspring. therefore new female breeds and old helps.

Question 39

what is an non adaptive explanation for the evo of menopause

Answer 39

Side-effect of living for longer than we did in ‘evolutionary’ environment
for modern hunter gatherers - first reproduction at 15years, half live till 45. quite likely to live until menopause.
Prehistoric populations - maybe didnt survive long enough.
unclear conclusion

Question 40

what is semelparity?

Answer 40

single all-out bout of reproduction, followed by death eg. marsupial mouse, pacific salmon

death itself is not selected for, it is a consequence of high reproductive effort.

Question 41

what is iteroparity?

Answer 41

several bouts of reproduction (most mammals and birds).

Question 42

when is semelparity favoured

Answer 42

if increasing returns from more effort, and low probability of future rep.
however very hard to test empirically.

Question 43

describe life history of 2 lobelia species

Answer 43

Young 1990

1. Lobelia telekii - dry habitat, semelparous, low prob of future rep, greater rep output per flowering episode
2. Lobelia keniensis - wetter habitat, iteroparous, low rep per flowering episode

Question 44

how can life history differ in the same species

Answer 44

Schneider & Lubin 1997
Spider (Stegodyphus lineatus)
mating starts in April, females dead by end of summer.
mother feeds young and later young eat mother.
if brood die, mother breeds again
experimentally removed females from brood. measured value of care and success of 2nd brood.
found semelarity better, as risk of predation lowers chance of 2nd brood.