18 COMMENTS

  1. So as I understand it the fishers are positive frequency dependently selected while the pirates are negative frequency dependently selected for a balancing selection overall.

    Fishers do better when there are more of them ( to a point ) and pirates do worse when there are too many of them.

    All in all though I would rather be a pirate!

  2. Why isn’t it the case that predatory birds would be both fishers and pirates depending on circumstances? A range of opportunistic behavior including hunting, scavenging, and stealing would seem likely to confer greater survival advantage on a predator.

  3. Analogously would a hard working stiff of a human pull off armed robberies on his off time?

    The mix of strategies could exist on some level but the energy expended and repercussions to pirates might help to keep this strategy at a frequency far below the fisher strategy.

  4. Neodarwinian
    Aug 2, 2015 at 2:59 pm

    The mix of strategies could exist on some level but the energy expended and repercussions to pirates might help to keep this strategy at a frequency far below the fisher strategy.

    I think the classic dichotomy is the star avian pirate robber of sea-birds,, the Frigate Bird.

    http://www.tropicalbirds.com/frigatebird.php

    Frigate birds canvas the sky looking for the foodstuffs of other birds or unintelligent fish swimming close to the water surface, yet curiously frigate birds lack waterproof feathers.

    The hooked bill of the frigate bird means business. The frigate bird perches less, hunts more than many in its family. Bills dip inside and under the water for marine life including crustaceans and jellyfish. But frigate birds also feed by dive bombing other birds and capturing their prey. Thus the pirate bird appellation is explained. Boobies and pelicans must clutch their supper carefully when flying through frigate bird territories.

  5. Analogously would a hard working stiff of a human pull off armed robberies on his off time?

    Birds are not analogous to humans. They are not governed by morality, criminal statutes or maritime law. As for the expenditure of energy, that would be contingent on circumstances. Opportunities for stealing fish could present themselves with very low energy requirements.

    Alan4″s reference to the Frigate Bird is captivating. The species has a specialized beak for skimming water to snatch surface fish while also equipped with vital skills for “dive bombing other birds and capturing their prey.” Lacking waterproof feathers, this species would perish if soaked in water very often. Dr. Dawkins appears to be describing either-or behavior developing in the same species: either fisher or pirate. Why not both? Probably just an oversight he failed to mention or clarify because it would distract from his central narrative.

  6. ” Frigatebirds are referred to as kleptoparasites as they occasionally rob other seabirds for food, ”

    The operative word is occasionally. If this were a great strategy it would be used more than occasionally. Google kleptoparasite.

    The analogy to humans is true enough without all of those provisos you put in because some humans are not governed by any of those things as many prisons can show you. Would Somalis rather be farmers, factory workers or pirates?

    Fishers are the dominant strategy for a reason as too many pirates is unsupportable in any population and we are discussing one population of birds.

    Boobies and pelicans must clutch their supper carefully when flying through frigate bird territories.

    He who does not ” score ” does not eat, so most of the time and, possible, most of the Frigate birds are ” honest ” birdies!

  7. Neodarwinian
    Aug 2, 2015 at 6:14 pm

    The cost of this strategy must be extremely high as the parasitism only nets a 1% catch rate.

    I think this is 1% of passing traffic from large sea-bird colonies.

    http://www.bbc.co.uk/programmes/p0050h5j

    Finding the prey isn’t the problem for the red-billed tropicbirds of Little Tobago, however. Of more concern is how they get the food back to their hungry chicks when they have to run the gauntlet of waiting magnificent frigatebirds on their way back to the cliffs. The frigates aren’t out to kill the tropicbirds, they’re just trying to steal an easy meal by wresting the catch off the smaller birds.

  8. Aerial dogfights ensue with a favourite attack from behind. The tropicbirds’ narrow wings allow them to turn more quickly, and if they stay near to the waves they have a chance of escaping the clutches of the much larger frigate birds. The lack of oil in the frigate birds’ feathers means they can’t risk ditching into the water. Back on shore, the chicks hungrily await their parent’s return, but will there be anything left to give it?

    I am will to bet good money that the little tropicbirds get a lot back to the chicks. I wonder how many Frigate birds are forced to ditch in their pirating attempt? That last question looks rhetorical to me.

    By the way the video is no longer available.

    http://onlinelibrary.wiley.com/doi/10.1046/j.1420-9101.1999.00078.x/full

    More on the subject plus the costs of the strategy.

  9. Fishers are the dominant strategy for a reason as too many pirates is unsupportable in any population and we are discussing one population of birds.

    Exactly. Dawkins implies the conclusion by saying (paraphrase) that… evolutionary stable might be some kind of ratio -say 80% fishers to 20% pirates. The definition of stability in this case is that both fishers and pirates are doing equally well (presumably to maintain the stable ratio). I think the illustration, however, is a cartoon which serves a purpose unrelated to any reference to any species of seabirds that shares along with their offspring any actual environment. Simply put it does not seem plausible that a species of seabird which had evolved to fish would split off a genetic mutant in the same environment genetically programmed to survive through piracy. There would be occasional incidents of aerial robbery of course, contingent on random rare opportunities but there would be no fisher and pirate variants of the same species. Everyone would fish. I could be wrong and certainly individual specimens could learn variant behavior through operant conditioning. If anyone knows about a species of seabird with such a fisher-pirate mutant ratio within its ranks, I would appreciate a reference. The cartoon and the story illustrate the concept of Evolutionary Stable Strategies in an entertaining form. But unless I learn otherwise, it’s just a cartoon and a story. A parable.

  10. Simply put it does not seem plausible that a species of seabird which had evolved to fish would split off a genetic mutant in the same environment genetically programmed to survive through piracy.

    Why not? Mutation is random. That is the point of evolutionary stable strategies. Cheaters ( pirates ) can maintain a small percentage of the population ( and I suppose the strategy could be switched fisher/pirate-wise ) because cheating here is held less frequent that fishing because if too many birds start pirating the strategy balance is unstable and nobody does very well.

    Read some of the links Alan and I have left and Google kleptoparasite.

  11. Thanks, Neodarwinian. I read your articles but we seem to be talking past each other about the way Dr. Dawkins presents the topic. The cartoon shows two fisher seabird parents standing over an egg. The egg cracks and, because of a mutation, the offspring behaves differently by resorting to piracy, forcibly stealing fish caught by other members of his species. Both the fisher parents and the mutant “pirate” offspring must be the same species which has evolved over eons to become skillful fisher-predators. Granting a genetic tendency for some individuals to be more aggressive than others when engaging in rare attempts to steal from another “handler,” it makes no sense for a segment of this skilled fisher species to resort to piracy as a primary strategy for feeding for the reasons you cite.

    Desiring to illustrate a core concept simply and swiftly, perhaps Dawkins elided the digressive evolutionary story more consistent with Alan’s description of two different species of seabird : the tropicbird, a fisher and the frigate bird, “a kleptoparasite that occasionally robs other seabirds for food.”

  12. Frustrating ,ESS Something I have always been interested in since reading the selfish gene and I can’t access the video!

    I have the comments with interest though and tried to follow some of the thread

    On the piracy issue there is an explanation of learned behaviour regarding Bears fishing in one of RDs books.

    Not a mutation but a chance happening, technique or serendipitous event which resulted in a better catch (If anyone has the book ref I would be grateful)

    If this is fully explained in the Video I apologise then I will nip the library and open it there.

  13. Neodarwinian
    Aug 2, 2015 at 8:02 pm

    By the way the video is no longer available.

    It was available to me when I liked it, and is when I load it now, – but some BBC videos are blocked in some countries for marketing reasons.

  14. Granting a genetic tendency for some individuals to be more aggressive than others when engaging in rare attempts to steal from another “handler,” it makes no sense for a segment of this skilled fisher species to resort to piracy as a primary strategy for feeding for the reasons you cite.

    The pirate strategy is under negative frequency dependent selection and comprises only about 10-20% of the total population of this example bird. So it is not the primary strategy for the population, which is the thing that evolves. If the number of pirates stays low enough this strategy works very well with the fisher strategy and balancing selection is in place then.

    http://www.nature.com/scitable/knowledge/library/game-theory-evolutionary-stable-strategies-and-the-25953132

    More on the ESS models. When I have the time I will send more to this thread.

  15. To illustrate an [evolutionary stable strategy], let us consider a payoff matrix between two organisms each with an aggressive strategy and a passive strategy: the classic ‘hawk vs. dove’ game (From your link).

    I confess I do not have the time to study this payoff matrix. I got lost when the payoff matrix is said to measure
    two different strategies (aggressive and passive) practiced variously by two different species (hawk vs. dove). The cartoon-story inexplicably implies by analogy that two dove parents hatch out a hawk. I look forward to how you sort this out. I’m speculating were talking about different aspects of the topic.

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