On page 41 of the novel, Shubin gives an in-depth description on what life probably was like in the time of Tiktaalik. He says "the most common fish species we find alongside Tiktaalik is seven feet long and has a head as wide as a basketball" (p. 41), in addition to mentioning sixteen-foot-long predators. Although Tiktaalik was probably 'jacked' (seeing as he was the only creature around with the ability to perform push-ups), this fish was definitely 'the prey' in these predator-prey relationship. (See Campbell p. 1201 for more information on predation.)
This interdependence of predator-prey in nature eventually caused some creatures to avoid the hunt and, as according to Shubin, "get out of the water" (p. 41). What other examples can you think of a prey developing special skills/features to avoid being hunted? Additionally, if fish like Tiktaalik had not been in danger of predators, would limbs ever have arisen?
(Jackie Edelson; jedelson92@gmail.com)
There are millions of examples of prey having special skills/features to avoid being hunted including something as simple as camouflage. According to Campbell, “Cryptic coloration makes prey difficult to spot” (Campbell 1201). This is because animals that exhibit this type of behavior, like chameleons or Canyon tree frogs blend into the environment so the predator (hopefully) passes by them not noticing their prey is sitting right there. Cryptic coloration isn’t always ideal, however. Other methods of avoiding getting eaten are certain defense mechanisms like that of which the skunk does when it feels threatened -- it sprays; the Turkey Vulture is capable of projectile vomiting onto another organism if it feels threatened; porcupines can release their quills if a predator gets too close, etc.
ReplyDeleteAlthough obviously the answer to whether or not limbs could have arisen if fish had not been in danger of predators is unknown, my best guess is yes, they still would have. Perhaps there was something in the water that was killing off the other animals. If that was the case, eventually the fish would need to get out of the water and limbs would be the only way to do so. Furthermore, perhaps there wasn’t even smaller prey left to eat and many of the fish were going hungry. They too, might see that after many years, having limbs serves as a selective advantage for climbing out of the water and onto land. Eventually, the fish would have to differ somehow that would leave some to stay in the water and others to get out. “An individual has a probability of adopting the opposite behaviour from the one used by its most successful neighbour” (Alonso, J, Fernández,
A, & Fort, H;June 2006). Eventually one of the fish species would be under the threat of being hunted and that fish species, through generations, would through some sort of genetic mutation form limbs, and would find that having limbs is a selective advantage and is also, opposite from its most successful neighbors (the fish hunting that species).
Michelle Layvant, mlayvan2@students.d125.org
While animals try to escape predation by blending in with their surroundings, plants have other methods to prevent themselves from becoming dinner. Plants appear seemingly primitive and well… “dumb”. However, plants have adapted very intricate and fascinating methods of protection against predators. One very common method used to fight predation is physical defense (ex. Spikes and thorns). A cactus has thorns, which are its leaves, to prevent many herbivores from eating it. Cacti are usually found in dry environments like deserts, and water is very precious in such environments. The loss of water poses a very large threat to cacti, so cacti embellish their bodies with super-sharp thorns to protect its succulent, water-rich flesh from predators. One plant, Amorphophallus titanium, has a very un-plantlike defense mechanism: stink. This gigantic flower was given the nickname “The Corpse Flower” because the odor it emits is similar to a rotting corpse. The flower “invests a lot of energy during blooming to heat up the sulfur-based compound in the flower stalk so the carrion-like odor will spread several feet away from the plant” (Virginia Polytechnic Institute and State University). The plant gives off such an odor to repel predators.
ReplyDeleteI actually don’t think Tiktaalik would have “sprouted” limbs, as opposed to what Michelle thinks. One major factor that drives the evolutionary process is an environmental pressure (In the Evolutionary Flow Chart). This environmental pressure either favors certain animals that are physical fit to survive or kills off other animals that simply don’t have what it takes to survive and reproduce. If Tiktaalik had no natural predators, not to forget unnatural predators, then there technically isn’t an environmental pressure! There wouldn’t be any natural selection for the radical Tiktaaliks that were able to “do push-ups” and live on land (Shubin 39). The Tiktaaliks with no effective land-dwelling-limbs would not be outbred because they were just as physically fit as those with limbs. If anything, the Tiktaalik population would proliferate as a whole because nothing would cause death except for time itself, and the population would keep increasing until it reached its habit’s carrying capacity, “the maximum population size that can be supported by the available resources” (Campbell G-6).
Mikey Ling (mikeyling@ymail.com)
Organisms are constantly changing as they try to outdo the other organisms around them in order to become more successful and survive. Prey often have adaptations to avoid predators because, "a mutation may
ReplyDeleteconfer a secondary defensive trait of arbitrary value, in which case individuals may be characterised
by the presence/absence of a defence" (http://www.maths.sussex.ac.uk/Reports/SMRR/SMRR-2004-07.pdf). This allows for organisms to be able to avoid more predators at an earlier stage in the hunting stage. One of the main ways that organisms avoid predators is Batesian and Mullerian mimicry. This allows organisms to change their outward appearance (usually but sometimes sound, behavior, etc) in order to trick organisms that will eat it. Mullerian mimicry allows harmful organisms to look alike in order to make their shared predator confused as to who to eat. In Batesian mimicry, only one of the organisms changes in order to protect itself.
I agree with Michelle that if Tiktaalik had not been hunted, then limbs still would have developed even if they developed in a slightly different way. Considering there are two main keys to survival and although one is the avoidance of predators, the other is the capture of prey. Limbs allow Tiktaalik to have an advantage over many smaller creatures that allowed him to gain sufficient nutrients. Without these limbs, he would be unable to capture food and therefore become extinct. Also, if there was a lack of food in the water, the answer was either to get onto land or die.
Jackie James (jackie.james@comcast.net)