[Paleopsych] SW: On Optimization

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Evolution: On Optimization

    The following points are made by William J. Sutherland (Nature 2005
    1) The essence of optimization is to calculate the most efficient
    solution to a given problem, and then to test the prediction. The
    concept has already revolutionized some aspects of biology, but it has
    the potential for much wider application. Of course, optimization has
    long been employed effectively in subjects other than biology.
    Economists have traditionally calculated the options that result in
    the greatest profit, and engineers routinely calculate the best design
    solution, such as the strongest bridge of a given weight.
    2) Darwin's theory of natural selection provided an obvious mechanism
    for explaining optimization in biology: more efficiently designed
    individuals will leave more offspring. But it was another century
    before biologists calculated optimal solutions. David Lack pioneered
    its use in biology with his concept of the optimal clutch size the
    number of eggs that would produce the greatest number of offspring.
    The use of optimization has allowed biologists to move from merely
    describing patterns or mechanisms to being able to predict, from first
    principles, how organisms should be designed. Optimality models are
    based on three elements: the choices available; what is being
    optimized; and the constraints.
    3) Physiologists have used optimization to answer a wide range of
    questions about animal morphology. For example, optimization has been
    invoked to predict the design of a bone of given weight that minimizes
    the risk of breaking or buckling; the speed at which it is most
    efficient to switch from running to walking; and the gut design that
    provides the highest energy gain from a given diet. The prediction of
    the triplet code as the most parsimonious means of coding 20 amino
    acids using the four bases of DNA is another successful example of
    this methodology.
    4) But optimization has its critics. The most common objection centers
    on the mistaken belief that the aim of this method is to test whether
    organisms are optimal. Actually, it is the assumptions of optimality
    that are tested. The failure to find support for a prediction can be
    used to determine whether an assumption is wrong. For example, if
    animals do not select the diet that maximizes energy intake, it may be
    because they are choosing a diet that optimizes a balance of different
    components, or that avoids the costs associated with obtaining larger
    prey. Once such possibilities have been identified, a new theory can
    be devised and its predictions tested. It has been argued that this
    process is circular but in practice it is no different from the
    successive predicting and testing that underlies most science.[1-3]
    References (abridged):
    1. Alexander, R. M. Optima for Animals (Princeton Univ. Press,
    Princeton, 1996)
    2. Lucas, P. W. Dental Functional Morphology (Cambridge Univ. Press,
    Cambridge, 2004)
    3. Sutherland, W. J. From Individual Behavior to Population Ecology
    (Oxford Univ. Press, Oxford, 1996)
    Nature http://www.nature.com/nature
    Related Material:
    The following points are made by Steven Buskirk (Science 2004
    1) For decades ecologists have sought to understand the principles
    underlying how mammals optimize their space requirements. It is
    intuitive that mammals need home ranges, areas they routinely traverse
    that are large enough to meet their energy needs, but small enough to
    be protected from intrusions by same-species neighbors that occupy
    adjacent home ranges. Early attempts to understand the relation
    between body mass and home-range area suggested that home-range area
    increases at the same rate as metabolism (1). As metabolic rate is
    proportional to body mass raised to the 3/4 power, then home-range
    size should also have the same proportion to body mass (2).
    2) However, abundant data on the home ranges of mammals, primarily
    derived from wildlife telemetry studies, suggest that this is not the
    case. Indeed, the home-range area increases at a higher rate than
    metabolic rate and, in fact, scales almost linearly with body mass
    (3,4). Yet parallel evidence from mammalian population density studies
    is consistent with a metabolic explanation of individual spatial
    requirements in that the reciprocal of population density (area per
    animal) appears to scale to the 3/4 power of body mass (5). As large
    mammals have home ranges bigger than would be predicted from their
    energetic needs, this implies a maintenance cost that goes beyond the
    acquisition of essential resources.
    3) Jetz et al (2004) have coalesced all of these findings by deriving
    a general model of mammalian spatial requirements that incorporates
    body mass, energy requirements, home-range size and, crucially,
    interactions with same-species neighbors. The authors use an equation
    from physics for collisions among gas particles to predict the
    frequency of interactions between home-range owners and intrusive
    neighbors. They demonstrate that large mammals require a home range
    that is larger than predicted by resource needs because they share
    resources with their neighbors to a greater extent than do small
    mammals. This forced sharing is the result of body size-dependent
    processes, such as whether the mammal is able to traverse its home
    range often enough to exclude its neighbors.
    4) The general approach of Jetz et al (2004) falls within the realm of
    allometric macroecology, which attempts to explain biological
    differences among species by examining patterns over a wide range of
    body sizes. For terrestrial mammals, this range is represented by the
    six orders of magnitude that separate the body masses of shrews and
    elephants. Metabolic rate, the most fundamental of physiological
    attributes, was shown by Kleiber (1) to be proportional to the 3/4
    power of body mass in mammals across an entire range of body sizes,
    rather than the 2/3 power predicted by a simple surface area to volume
    relation. Recently the 3/4 exponent was derived from first principles
    by West et al (1997).
    References (abridged):
    1. M. Kleiber, The Fire of Life (Wiley, New York, 1961)
    2. B. K. McNab, Am. Nat. 97, 133 (1963)
    3. A. S. Harestad, F. L. Bunnell, Ecology 60, 389 (1979)
    4. S. L. Lindstedt et al., Ecology 67, 413 (1986)
    5. J. Damuth, Biol. J. Linn. Soc. 31, 193 (1987)
    Science http://www.sciencemag.org
    Related Material:
    The following points are made by G.P. Burness et al (Proc. Nat. Acad.
    Sci. 2001 98:14518):
    1) The size and taxonomic affiliation of the largest locally present
    species ("top species") of terrestrial vertebrate vary greatly among
    faunas, raising many unsolved questions. Why are the top species on
    continents bigger than those on even the largest islands, bigger in
    turn than those on small islands? Why are the top mammals marsupials
    on Australia but placentals on the other continents? Why is the
    world's largest extant lizard (the Komodo dragon) native to a
    modest-sized Indonesian island, of all unlikely places? Why is the top
    herbivore larger than the top carnivore at most sites? Why were the
    largest dinosaurs bigger than any modern terrestrial species?
    2) A useful starting point is the observation of Marquet and Taper
    (1998), based on three data sets (Great Basin mountaintops, Sea of
    Cortez islands, and the continents), that the size of a landmass's top
    mammal increases with the landmass's area. To explain this pattern,
    they noted that populations numbering less than some minimum number of
    individuals are at high risk of extinction, but larger individuals
    require more food and hence larger home ranges, thus only large
    landmasses can support at least the necessary minimum number of
    individuals of larger-bodied species. If this reasoning were correct,
    one might expect body size of the top species also to depend on other
    correlates of food requirements and population densities, such as
    trophic level and metabolic rate. Hence the authors assembled a data
    set consisting of the top terrestrial herbivores and carnivores on 25
    oceanic islands and the 5 continents to test 3 quantitative
    a) Within a trophic level, body mass of the top species will increase
    with land area, with a slope predictable from the slope of the
    relation between body mass and home range area.
    b) For a given land area, the top herbivore will be larger than the
    top carnivore by a factor predictable from the greater amounts of food
    available to herbivores than to carnivores.
    c) Within a trophic level and for a given area of landmass, top
    species that are ectotherms will be larger than ones that are
    endotherms, by a factor predictable from ectotherms' lower food
    3) The authors point out that on reflection, one can think of other
    factors likely to perturb these predictions, such as environmental
    productivity, over-water dispersal, evolutionary times required for
    body size changes, and changing landmass area with geological time.
    Indeed, the database of the authors does suggest effects of these
    other factors. The authors point out they propose their three
    predictions not because they expect them always to be correct, but
    because they expect them to describe broad patterns that must be
    understood in order to be able to detect and interpret deviations from
    those patterns.
    Proc. Nat. Acad. Sci. http://www.pnas.org

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