Life-History theory Flashcards
(44 cards)
what life history trade offs do animals face?
- energy vs. risk of being killed
- maintenance & repair vs. reproduction
- number vs. quality of offspring
- current vs. future reproduction.
when are optimisation decisions static/dynamic?
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
define fitness - how can fitness be calculated?
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.
what does adult size determine?
metabolic rate survival intake rate rate of reproduction however, may have a low chance of surviving to an adult size.
why is fat beneficial, and what limits fat extent
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.
in what way is fat regulated in small birds?
- 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.
what costs of being fat to small birds?
Wittler and Cuthill, 1993
harder to take off
less agile in air
higher energy costs of flight.
demonstration of costs of fat to small birds.
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.
what trade off in fat level
Trade-off between two sources of mortality
increased fat: ▼starvation, ▲ predation
best long term strategy minimises starvation and predation and maximises survival.
how has dynamic -programming been used
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.
what s the optimal foraging strategy found by dynamic programming of small birds?
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).
at a given time of day, how does fat level change?
- if +food, - fat
- if +interruptions, + fat
- if +overnight energy expense, +fat
- if +predator abundance, - fat
study of mass change under different pred conditions.
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.
what trade off does rep face?
Williams - trade off between
current & future reproductive success.
external costs of reproduction
- attracts predators
- male comp = deaths and injuries
- pred risk for parent feeding young
internal costs of reproduction
- hard work attracting mates/ caring for young reduces condition → increased mortality
- costs are typically long-lasting
what is non annual breeding
example
cycle takes over 1 year, environmental, and animal conditions affect breeding decision.
example of non annual breeding decisions based on animals condition
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
example of non annual breeding decisions based on environmental condition
eg Ural owl. prey, vole, abundance follows 3 year cycle. in good years, 75% breed, in bad years, 21%.
is measuring phenotypic correlation a good way to measure costs of reproduction?
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.
what is better than measuring phenotypic correlation for measuring costs of reproduction
must see what happens when animal does something different, so experimental manipulation.
experimental manipulation example for measuring costs of reproduction.
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.
what was lack’s idea about clutch size?
why is it wrong?
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.
study of kestrel brood size and future RS
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.
