Yesterday`s blog on Batesian mimicry got me started thinking (thus the big tank of air, brain activity requires oxygen!). Batesian mimicry was about “parasitizing” on the true signal of something sending out an honest warning. This is a very special type of mimicry. Camouflage, where animals try to look like something more or less inedible, either some dead object or something alive far less nutritious than the camouflaged species, is essentially a form of mimicry (not Batesian though). There can be different reasons for camouflage, but in this post I will concentrate on the camouflage used to evade predation by fooling a potential predator.
First of all, there are advantages to mimic something dead and widely available. In a forest, bark on tree trunks would be a great thing to mimic, as bark is widely available. In shallow marine areas, sand serve the same purpose. A significant amount of marine animals live on sandy bottoms and are perfectly coloured and often even structured to blend in.
Other common areas in marine habitats are algae covered rocks. Many animals camouflage themselves as such a small rock, with octopus the masters of algae covered rock resemblance.
Obviously, camouflaging one self as a dead object carries some costs. First of all, you are limited to live on the substrate you are adapted to, and migration over other areas might be hard. Second, and maybe most problematic, is that you are more or less forced to live life slowly. Quick movements from a camouflaged prey will quickly alert a predator to the presence of the prey, thus negating the advantage of the camouflage.
Some animals camouflage them selves as live animals with little nutritional value. The advantage is obvious, as you actually can move somewhat with out being called on the bluff, while the disadvantages probably in many cases will be the scarcity of proper models to imitate. One of the most striking examples would be the ghost pipefishes were the ornate ghost pipefish resembles crinoids, and its close relative, the Halimeda ghost pipefish looks like Halimeda algae.
One more example struck me this morning. One of the guest was for some reason taking pictures of an upside-down jelly. I went over to look, but didn´t really get what I saw to fit. Tentacles ok, groups of zooxanthellae ok, but there was some asymmetry to the whole thing that didn´t feel quite right. Suddenly, the big catch mask from a Melibe shot out, and it turned out that the jellyfish in question was a Melibe, which is a large nudibranch. So, gliding around slowly, the Melibe could mind its own business as very few animals seem to be interested in eating the upside-down jellyfish.