#1: The populations of Phoca groenlandica and of Paralithodes camtschatica are limited primarily by density dependent factors. They each interact with other organisms in predator-prey and competitive relationships. They are often slightly limited by density independent factors as well, though, such as undesirable weather.

#2: The harp seal is a K-selected species, because its population is greatly influenced by K–the carrying capacity. (The carrying capacity is the maximum stable number of a population that a particular environment can support over an extended period of time.) This carrying capacity varies over time periods and in different locations because of limited resources. Known as K-selected populations, harp seals are also known as equilibrium species. They are said to be equilibrial because they maintain a steady density near the limit set by the carrying capacity.

In an evolutionary thought, the harp seal may have been the first mammal to migrate or "evolve" in the arctic regions. Though harp seals now are not opportunists, they may have been when they first began to occupy the arctic regions–supposedly around the Oligocene period after the Cretaceous extinctions. Harp seals could have been r-selected species if they had little fluctuating densities or little competition. If so, they were likely to have limited homeostatic capability, a short maturation time, a short lifespan, and, often, a high mortality rate. Reproductive characteristics they would have had if they were opportunists are these: they would have usually had only one reproductive episode per lifetime.

Characteristics that the harp seal has now, being an equilibrial, are basically the opposite of those of opportunists.

The king crab is also a K-selected specimen. However, if this crab was ever in an environment where it had very little competition, it would have been considered an r-selected species.

#3. The harp seal’s geographical distribution is limited greatly in that it lives only in icy waters.

The king crab doesn’t appear to be very limited in geographical distribution. It must live in an aquatic environment, which appears to be its only requirement involving location.

#4: Both chosen organisms may live in the arctic regions. These waters are near the poles of the earth, and they generally contain many icebergs in them. The king crab dwells primarily on the bottom of the waters. The harp seal, on the other hand, dwells primarily on the icecaps, though it does dive quite deep. The harp seal must come to the surface about every hour because the seal’s respiratory medium is air.

#5: Phoca groenlandica eats arctic cod and arctic crabs–including the king crab.

The king crab eats sessile bottom feeders in the Palearctic, Nearctic, Oriental, Ethiopian, Neotopical, and Australian waters, as well as all four oceans.

#6: The harp seal is preyed upon by the polar bears of the North Pole and whales such as the killer whale.

Paralithodes camtschatica is eaten by harp seals, walruses, penguins, and sharks.

#7: In most instances, the harp seal is in the trophic level as the tertiary consumer, and the king crab usually plays the role as the secondary consumer.

#8: Food Web of Ecosystem:

#9: The two chosen organisms (the king crab and the harp seal) interact in the described ecosystem in a predator-prey relationship. The harp seal is the predator; the king crab is the prey. (The harp seal preys on the king crab.)

#10: If the harp seal were to become extinct, two main possibilities relating to the king crab would occur. The king crab’s per capita growth rate would either increase or decrease. Because the harp seal limits the population of the king crab by preying upon it, the absence of this predator could increase the per capita growth rate of this animal. However, the other animals that eat crabs and cod, just as the harp seal does, would probably increase their realized niche of food due to the absence of a chief competitor. If this latter case were to occur, there would be no drastic change in the king crab’s per capita growth rate. The same situations that would occur in the king crab would also occur in the crabs and the cod that are eaten by harp seals, sharks, walruses, and penguins. The animals that eat the harp seal, such as killer whales and polar bears, would miss a food source, probably causing them to eat larger quantities of the other organisms that they eat, which then causes these species to have a lower per capita growth rate. This cycle could keep continuing, illustrating how much of a change in the ecosystem one extinction of species would be.

The major effects of extinction of the king crab would be these:

The harp seal would be lacking a good food source, and the sessile bottom feeders upon which this crab feeds would be missing a major predator.

The resources for this report are the following:

Campbell, Neil A. #1

Menlo Park, CA: The Benjamin/Cummings Publishing Co. Inc., 1996

The University of Michigan’s Animal Diversity Web Page #2