Greg Detre
Wednesday, June 06, 2001
Prof. Marian Dawkins
Animal Behaviour VII
Notes � animal behaviour VII, optimality
Do animals behave optimally?
J.R.Krebs and A.Kacelnik (1991)� Decision-making.� In: 'Behavioural Ecology' ed. J.R.Krebs and N.B.Davies. 3rd ed. p.105-136
Cuthill, I.C. & Houston, A.I. (1997) Managing time and energy. Chapter 5 of Behavioural Ecology (eds J.R. Krebs and N.B. Davies) 3rd ed.
R.Dawkins (1982) 'The Extended Phenotype'� Chapter 3.
G.A.Parker and J.Maynard Smith (1990) Optimality theory in evolutionary biology. Nature 348: p. 27-33.
S.J.Gould and R.C.Lewontin (1979) The spandrels of San Marco and the Panglossian paradigm:� a critique of the adaptationist programme. Proc. Roy. Soc. Lond. B 205: p.581-598.� (Reprinted in 'The Evolution of Adaptation by Natural Selection' edited by J. Maynard Smith and M.Holliday).
M.Dawkins (1986) 'Unravelling Animal Behaviour' Chapter 2.
C.J.Pierce and J.G.Ollason (1987) Eight reasons why optimal foraging theory is a complete waste of time. Oikos 49: p.111-118. (muddles LT + ST optimality)
S.H. Orzack & E.Sober (1994) Optimality modesl and the test of adaptationism. American Naturalist 143: 361-380.
A.I.Houston and J.M.McNamara (1990) Risk-sensitive foraging and temperature.� Trends in Ecology and Evolution 5(5) p.131-2.
A.Kacelnik (1993) Leaf-cutting ants tease optimal foraging theorists. Trends in Ecology & Evolution 8(10): 346-8.
A.Inman (1990) Group foraging in starlings: distribution of unequal competitors. Animal Behaviour 40: 801-810.
J.R.Lucas et al (1993) The effects of time constraints and changes in body mass and saitation on the simultaneous expression of caching and diet-choice decisions. Animal Behaviour 45: 639-658.
S.H. Orzach and E. Sober (1994) Optimality models and the test of adaptationism. American Naturalist. 143: 361-380.
Animals may not just be �well-designed�, but they may even be optimal: optimal foraging, optimal reproductive strategies, optimal times for threatening an opponent before retreating etc.
1. long-term � �leaving the most viable offspring in a lifetime� � concerned with the reproductive success of an animal over its entire life compared to its rivals
2. short-term � the animal appears to be optimising some function in its day-to-day life, e.g. the amount of energy it is collecting in a certain amount of time, e.g. optimal foraging
Some people think that:
the animals we see are the
best of the ones that could ever exist, because given enough time, all possible
mutations which could arise in a population will arise.
This assumes that the environment has been stable long enough. This seems unlikely. Even if the broad, general, physical aspects of an environment, e.g. temperature, rainfall, have stayed relatively constant, environments also consist of other animals (conspecific competitors, predators, parasites, prey), each providing a constantly changing environment with which to interact (e.g. the Red Queen hypothesis (van Valen, 1973; Bell, 1982), evolutionary dance/arms race).
Optimality is a state which
animals are said to approach when natural selection has been in operation for a
certain length of time in the same environment.
OFT: animals should optimise the net amount of energy
they obtain in a certain time
e.g. a bird taking food from
a small tree and gradually eating up all the food tha tis there would eventually
come to a point when it would gain more energy if it left that tree and flew to
another, where the food had not been depleted, even though the flight would
itself use up valuable energy
The bird would then be optimising its net rate of energy gain � if so, it should be possible to predict exactly when the bird should fly to the new tree, provided that the rate of gaining energy in the old tree, energy cost of flight and expected rate of gaining energy in new tree are all known. This is like the Travelling Salesman problem. If we are able to predict the behaviour, this is an indication that we have discovered the basis on which the bird is making its decisions.
Cowie (1977) used this OFT
model to predict how long great tits should spend foraging in a given �patch�,
depending on the quality of the �patch� and the �travel time� between patches.
His reasonably accurate predictions strongly suggest that the birds were optimising net rate of energy intake.
Krebs & Kacelnik (1991):
get sidetracked by the issue
of whether the detailed predictions of OFT are borne out in practice ???
The important question is how short-term optimality is related to long-term optimality � affecting out understanding of how natural selection acted on an animal�s ancestors.
What can we conclude from an animal that is an optimal forager (given its physiology) under a wide range of circumstances?
Just as adaptation may be studied by seeing parallels between the �design features� of an animal and a humanly-constructed design, so optimally foraging animals are like machines �designed� to optimise energy intake. This saves us having to look at the reproductive success of foragers of different degrees of competence. This supposes that there is a direct connection between the short-term and long-term meanings of optimality, i.e. that short-term optimality gives us an insight about why natural selection favoured an animal over its rivals.
surely this distinction between short- and long-term optimality just comes down to how much of the behaviour the animal is optimising???
if we look at its entire life-span as reproduction-optimising (the long-term view), then this necessarily involves optimising all the way down to its day-to-day activities