Rock Lobsters And Whelks Around Two Islands example essay topic

Our categorizations of nature are based on domination. The world is divided ecologically into predator and prey, or bigger more advanced animals versus smaller simpler creatures. One category is superior which dominates the second category which is inferior. But this dualism based on dominance represented by the demand of a preferred human order upon nature is in fact contradictory. As an obvious example, carnivorous plants like the Venus flytrap consumes insects, and the bigger and more taxonomically advanced the prey, the more mysterious nature becomes. The following examples demonstrate the reversal of the food chain.

Frogs eat flies. But one day in August 1982, at a small pond in Arizona, thousands of spade foot toads were emerging to adulthood from their tadpole stage. Among them were toads that were dead or dying. The predator was a large insect larva identified as that of the horsefly Tab anus punctifer.

The enormous larvae are bigger than toads and to think that flies can eat toads is amazing. The fly larvae force themselves into the mud, rear end first, until their front end, bearing the mouthparts, lies flush with the surface. The larvae then catch the toads by hooking their pointed mandibles into the hind legs or belly, and them dragging the toad part way into the mud. The larvae then suck the toad dry by ingesting blood and body fluid only. Unusually large insects like the praying mantis fee on small invertebrates like frogs, small birds, and mice. Decapod crustaceans like lobsters, crabs, and shrimp eat snails.

Two scientists, Amos Bar kai and Christopher Mc Quaid, did research on rock lobsters and whelks (snails of middling size) around two islands, Marcus and Malgas, off the coast of South Africa. On Malgas Island, the rock lobsters ate mollusks, mostly mussels, and several species of whelks. Twenty years ago rock lobster was common on both islands. During the 1970's, lobster started disappearing from Marcus Island, this was probably due to periods of low levels of oxygen. Since lobster, the top predator, was absent, extensive mussel beds were established and the whelk population increased dramatically. The scientists questioned the recolonization of Marcus Island despite the high availability of food.

The answer and astonishing discovery was that the food had become the feeder. The whelks, which are much smaller than the lobsters, outnumbered the lobsters. Their experiment consisted of one thousand rock lobsters from Malgas Island transferred to Marcus Island. The result was immediate.

The lobsters were outnumbered by the whelks. Hundreds were attacked instantly and in a week no lobster could be found on the island. On average each rock lobster was killed within fifteen minutes by more than three hundred whelks that removed all the flesh in less than an hour. Fish do not generally eat dinoflagellates and in return dinoflagellates certainly do not eat fish for the fact that dinoflagellates are microscopic and it would be crazy to even think that. However, dinoflagellates do kill fish.

Studies show that under favorable conditions, dinoflagellate population can increase to sixty million organisms per liter of water. These so-called blooms discolor and poison the waters leading to massive deaths of fish and marine organisms. Red tide is the most familiar example of these blooms. The largest of these blooms resulted in nearly one million Atlantic menhaden dead in the estuary of North Carolina's Pamilco River. These deaths are a common consequence of dinoflagellate bloom, but the oddity of this case lies in that supposedly dinoflagellates might actively kill fish as an evolved response for their own advantage, including a potential nutritional benefit.

And it does seem that dinoflagellates are killing and eating fish in a manner suggesting active evolution. The dinoflagellates lives in a dormant state, lying on the sea floor within a protective cyst. When approached by a fish, the cyst breaks and releases a mobile cell that swims, grows, and secretes a powerful, water-soluble neurotoxin, killing the fish. The main evidence for active evolution in predation on fish is both anatomical and behavioral. The swimming cell grows a projection called a peduncle from its lower surface.

The cells seem to move actively toward dead or dying fish. Tissue from the fish gets attached to the peduncle and gets digested. As bizarre as a fish-eating dinoflagellate, scientists J. Vacelet and N. Bury-Esn ault, have found a killer sponge. Relatives of this sponge, members of the genus Asbestopluma, have only been known to live in very deep waters where behavioral and food preferences could not be observed. But this new species was found in a shallow-water Mediterranean cave, where scuba divers can watch directly.

Asbestopluma has lost both filtering channels through the body and the specialized cells, choanocytes, that pump the water through. Instead of filter feeding, this new species grows long filaments extending from the upper end of the body. The surface of the filaments is covered by a blanket or tiny spicules. The spicules give the filaments a Velcro-like adhesiveness which is the key to its feeding. The sponge captures small crustaceans on the filaments. Because of the adhesiveness, prey can not escape.

After one day thin filaments completely cover the prey and within a few days, the prey is digested. This sponge has become a carnivore. These four stories refute this dualism based on domination of one category over another. The little guys turn the tables and have proved their superiority in these examples, which brings the method of categorization into question.