| We're looking at animal behaviour this week, |
| and let's turn now, class, to one of its most dramatic manifestations, animal mimicry. |
| Organisms that are good to eat, or that are attacked for other reasons, |
| often develop devices, through evolution, of course, |
| techniques and devices to protect themselves from their attackers, |
| in order to survive, and in order to reproduce and pass their genes on to the next generation. |
| And one of these techniques, one of these strategies, |
| is to look like something else, to look like something that is not good to eat, |
| or something that is otherwise of no interest to the predator. |
| An organism that does this, that resembles something else, is called a 'mimic', |
| and the thing that it has evolved to resemble is called the 'model', |
| while the predator that it is trying to mislead is called the 'recipient', |
| the one that receives the misleading image. |
| Some mimics do this by adopting camouflage, which is a cryptic resemblance to something of no interest to its enemy, |
| and by doing this, they become invisible, they are hidden. |
| Many animals, insects, lizards, amphibians, mimic the abundant plant life in the habitat around them. |
| I'm sure that you've seen green grasshoppers and brown moths |
| that seem to be well-hidden on grass stems and tree trunks when they're motionless. |
| But the Leaf-tailed Gecko, a small lizard in Madagascar, is a master at this. |
| It avoids its enemies by looking exactly like a cluster of old dead leaves. |
| And there are various species of katydids, grasshopper-like insects, that have managed to duplicate the appearance of leaves with startling accuracy, |
| in all stages of growth, some species looking like fresh green leaves |
| and others looking like old decaying leaves, complete with leaf veins, weathered edges and mildew spots! |
| These adaptations make these animals difficult or impossible for a predator to identify or even notice, |
| and so these otherwise defenseless creatures are overlooked or passed by. |
| Other organisms defend themselves directly with stings or bites, or with poisons or other noxious chemicals, |
| and such organisms often assume bold, characteristic colors and markings, called warning coloration, |
| that warns a predator, reminds it, that this creature can inflict pain or discomfort, |
| or that it tastes very bad. |
| The bold orange-and-black pattern of the common Monarch Butterfly, |
| or the black-and-yellow bands on a bumblebee, are such warning colorations. |
| And sometimes, this warning coloration is so effective |
| that another species, a species that doesn't have any of the protective devices of sting or poison or whatever, |
| will adopt the same warning colors and pattern. |
| This sort of mimicry is called 'Batesian mimicry'. |
| The name comes from the early zoologist, HW Bates, |
| who, back in 1862, first suggested an explanation for the origins of mimicry |
| based on Charles Darwin's new Theory of Natural Selection. |
| This was one of the earliest applications of Darwin's ideas to an unknown biological phenomenon. |
| Now, Viceroy Butterflies taste good to many birds, |
| but because they mimic the Monarch Butterflies model's color pattern, |
| because Viceroy Butterflies look like Monarch Butterflies, |
| they are avoided, just like the Monarch is. |
| In the same way, many harmless fly species resemble the bumblebee model, |
| and also in this way they avoid being eaten by the recipients, birds. |
| So these are Batesian mimics. |
| There are several conditions that must be fulfilled, though, for a Batesian mimic to be successful, |
| the mimic must of course share the same general region and habitat as its model, |
| but the mimic must also be less numerous than its model, |
| which must be relatively abundant. |
| That way, the odds are that the recipient predator will sample an unpalatable model first, |
| which is very important for keeping the trick effective. |
| A similar kind of mimicry is 'Muellerian mimicry', |
| named after another early biologist, |
| and in this sort of mimicry, both the model and the mimic are dangerous or taste bad. |
| A very obvious example is the way that so many unrelated species of bees, wasps, and ants |
| have assumed similar, bold, black-and-yellow or black-and-orange banded patterns. |
| By doing this, Müllerian mimics present a united image that predators soon learn to be wary of. |
| There's also another aspect of mimicry that I'd like to mention, too, |
| and that's the mimicry used by predators. |
| This is called 'aggressive mimicry', |
| and it is used to conceal or misrepresent a predator until its prey comes near enough to capture. |
| Many mantids, for example, are green or brown, |
| so that they blend in with their plant surroundings, |
| but some tropical mantids are fantastically shaped and colored, |
| like the beautiful Orchid Mantis, which resembles a petal of one of those tropical flowers, |
| and it hides motionless next to one of these orchids until an insect comes within its reach. |
| There are also several green-colored vine and grass snakes of various families, |
| which lie invisible among the tangled vines and branches of the jungle |
| until they suddenly lash out to grab their prey. |
| Actually, there are an endless number of ingenious mimics in the natural world, |
| and I recommend that you all try a Google Images search tonight for some more interesting examples of this fascinating behaviour. |