Transcript Predation
Predation Psychology 3106 Introduction You hear quite a bit about foraging Foraging is a two way street There has to be a ‘foragee’ as well Just as foragers have evolved strategies, so have prey Possible Strategies Live in a group Camouflage Armour Fight back Don’t taste good! Aposematism Some insects taste bad and are obvious about it Usually have a diet of plants that does not taste good to the predator The Monarch butterfly is great example Questions, Questions, Questions….. Two evolutionary questions can be asked 1) How did distastefulness evolve? 2) Why are distasteful prey so obvious about it? Question 1 Well, it should increase the probability of the prey surviving But, the predator has to sample a prey item in order to learn that it will get sick How does the fitness of the prey item increase if it has been eaten? Species level? Not a chance in hell….. So How then? Well, here’s a hint: Usually aposematic bugs are gregarious Usually they are surrounded by siblings If only a few of the brood are eaten then the frequency of the distasteful gene will spread (Fisher, 1958) one of the first kin selection models Why be so obvious then? First off, not all distasteful prey are obvious Most are though Two possible explanations Contrast with the background makes learning easier than learning about cryptic prey Gibson (1974) Blue, green or red millet on a green dot background Gibson (1974) Feeding platform dropped when red ‘aposematic’ grain was eaten The birds stopped eating red seeds, still ate the blue and green Can’t be the background then, as the cryptic ones were still eaten Gittleman and Harvey (1980) Chicks fed two grain types Colour did not matter on its own Distastefulness and colour are the key Shettleworth (1972) Chicks learned to avoid unpalatable water if it was a novel colour (other than what they were raised on) Novelty is the key, not contrast So, could be that the prey evolved a strategy of being different as possible Kin Selection Aposematism must have evolved through kin selection Aposematic butterflies are gregarious Cryptic butterflies are not! Aposematic live longer than cryptic They could still ‘teach a lesson’ Other characteristics They have smaller territories They roost communally They have delayed sexual maturity So, because they live longer they can teach the lesson more easily Mimicry Some insects are aposematic and successful, why not copy? Batesian mimicry Colouration is similar to toxic species, but the prey item is not toxic Mullerian Mimicry In Mullerian mimicry, all species that share a colouration are dangerous Many snakes use this Also may have characteristics that make prey look like a predator! Conclusions Evolution is basically an arms race As fast as aposematism or crytic colouration evolve, species learn to detect the prey Learn evolutionarily or in the real sense