Managing Time and Energy

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Managing Time and Energy

• ??? (Ayo)
• ?????? ???????

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Managing time and energy

1. Introduction
2. The function approach
3. The benefits of energy reserves
4. The costs of energy reserves
5. Relating short-term (??) behaviour to lifetime
   reproductive success
6. Final considerations

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Introduction

• All behaviour takes time and consumes energy.
• (??????????????)
• Feeding strategies?

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The functional approach

• Cost-benefit analysis (????)
• In practice it is often difficult to assess
  future reproductive success, and so attention has
  often been focused on simple currencies which
  have the following properties
• They are easy to measure
• Maximizing them will maximize fitness

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5.3 The benefits of energy reserves

• The value of feeding (?????) is to provide the
  raw material for self-maintenance, growth and
  reproduction.
• ?????????,??????,??????,?????
• ?????????,???????????(??)?

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• ????,?????????,??????????(Ekman Hake, 1990)
• ???????????,great tits ???????(Bednekoff et al.,
  1994)
• Photoperiod is a good predictor of body mass in
  birds (reviewed by Blem, 1990)

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Fig. 5.1 (a) Great tits were switched from a 9-h
feeding day (long days) to a 6-h feeding day
(short days) while holding photoperiod constant.
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Fig. 5.1 (b) starlings were exposed to fixed
length interruptions in their feeding day.
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• Several authors have found differences in mass
  and fat correlated with factors expected to
  affect the predictability (????) of food intake.
• The effects of social dominance on fat-storage.

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5.4 The costs of energy reserves

• Animals with naturally high levels of fat, or
  high mass are considered to be in good
  condition or of high quality.
• However, fat storage must have costs.
• Acquisition costs
• Storage costs
• The cost of being fat

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5.4.1 Acquisition costs (?????)

• There are two types of cost associated with
  feeding
• Acquisition of the food
• Maintenance of the energy reserve once secured.
• ???????,???????,?????????

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5.4.2 Storage costs

• ?????,????,??????,?????,??????
• ??????????????
• ????,??????????
• ?????,???????????
• ???????????

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Fig. 5.2 Hurly (1992) measured seed hoarding (??)
and body mass changes in captive marsh tits.
When an automatic feeder delivered seeds at
highly unpredictable times, the birds hoarded
more seeds per day, but did not increase body
reserves.
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5.4.3 The costs of being fat

• The most obvious costs of fat storage in human
  life are the various pathological conditions
  associated with obesity(??) heart disease, gall
  and kidney stones, diabetes and various forms of
  cancer and arthritis.
• However, there are almost no data on pathological
  effects of fat storage in wild animals.
• If migrating birds have heart attacks, how do we
  find out?

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• ???????,????,?????????????,??????????????
• Mass increases associated with being gravid have
  been shown to impair mobility and reduce escape
  speeds in several species of lizard and snake
  (Madsen, 1987 Siegel et al., 1987 Cooper et
  al., 1990)

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Fig. 5.3 (a) adding artificial masses to
starlings resulted in a shallower angle of ascent
(?????) when escaping from a simulated predator
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Fig. 5.3 (b) reduction of natural body mass by
means of short-term food deprivation, also showed
that heavier birds had lower take-off angles.
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Fig. 5.3 ( c) The natural daily variation in body
mass of zebra finches is correlated with the time
they take to ascend a given vertical height.
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Fig. 5.4 (a) In years when sparrowhawks were
absent, the resident great tits maintained higher
body mass than when the predators were present.
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Fig. 5.4 (b) Starlings were assigned randomly to
experimental aviaries differing in the amount of
protective cover they contained.
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5.5 Relating short-term behaviour to lifetime
reproductive success

• The costs and benefits of energy acquisition and
  storage
• ????????????
• ???????????????
• ???????,???????
• ?????????,???????

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Fig. 5.5 The optimal policy for an animal over a
season, where the decision whether to feed or
rest depends on both energetic state and time. If
reserves are less than some critical level Xc,
the future reproductive success is 0.
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Stochastic dynamic programming (SDP)

• SDP is a numerical technique for finding the
  optimal behavioural decision as a function of
  state and time (?????).
• The animal is characterized by one or more state
  variables and a set of possible behavioural
  options.
• For technical details see Mangel and Clark (1988)
  Dynamic Modelling in Behavioural Ecology.
  Princeton University Press.

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Fig. 5.6 When food availability is low, birds
forage at a high level for most of the day (open
circles). When food availability is higher, the
overall level of foraging is lower.
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5.6 Final considerations

• Is the dynamic programme really necessary?
• Dynamic programming is a particular technique for
  finding optimal solutions. But it is not always
  necessary to use this technique just because a
  simple rate-maximizing approach is inadequate.
• Stochasticity can be analyzed without using
  dynamic programming.

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