Biogeographic Cycles

Phosphorus Cycle

 


Nitrogen Cycle




Limiting Factors

Density Dependent Factors: Density Dependent factors are characteristics that are influenced by the size of a population. Density-dependence generally regulates populations within ecosystems that have many species, if they are not stressed by physical conditions. This is not typically true of the tundra. Its extreme climate reduces the number of species that successfully survive there. Even though this is true, species are still affected by predation and competition in the Tundra. Musk Oxen and Caribou can compete for sedges and grasses. Also, when the population of arctic hares increases the population of artic foxes will go up due to increases predation.

Density Independent Factors: Density Independent Factors affect populations by the same percentage, regardless of density.Temperature is a major factor in the Tundra because most species aren't able to tolerate the cold temperature and harsh winds. Trees and other tall plants cannot survive in the Tundra. Another density independent factor is the amount of sunlight. Depending on the latitude, the Sun can remain below the horizon for up to 2 months, leaving the Arctic tundra in darkness. Although the sun remains in the sky 24 hours a day during the summer, it stays close to the horizon and provides only low intensity sunlight. This is another reason why trees cannot survive in the tundra; they require an ample amount of sunlight.

Introduced Species

Felis catus, the common house cat, was domesticated in the eastern Mediterranean c. 3000 years ago. It was brought to the tundra by people from all around the world who wanted pets. It has threatened native bird species, especially on islands where native species have evolved in relative isolation from predators.

  

Symbiotic Relationships

Mutualism- Lichen is a composite organism that is usually made up of a fungus and a green alga or cyanobacterium. The alga is photosynthetic in nature and so, reduces carbon dioxide into sugars that feeds the fungus as well. The fungal counterpart in the meantime, helps provide protection to the alga by retaining water and helping in obtaining minerals from substrate. Thus, both the fungus and the green alga benefit from this relation.

Commensalism- The caribou or reindeers tend to feed on lichens when the weather is at its worst and coldest, as more often than not, this is the only food available to them which can provide them with carbohydrates and can give them energy and heat. So, when the caribou is on the lookout for food, the arctic fox follows it. Then, when the caribou digs the ground snow in a quest to find food, it digs up the soil and slightly exposes, or at least brings closer to the surface some of the subnivean mammals, with whom the arctic fox shares a predator prey relationships in the tundra. So, once the caribou is done with its hunting, the arctic fox then follows and digs further deep and gets its food in the form of the mammals. Hence, this is one of the best examples of commensalism in the tundra region, wherein the caribou remains unaffected but the arctic fox manages to get its food with some help from the caribou.

Parasitism-  One of the lesser known tundra facts is that even parasitism is seen in the tundra region. This is usually seen in cases of liver tapeworm cysts. The liver tapeworm cysts tend to stay and grow in the body of various animals like moose, caribou and even wolves. These tapeworms then feed on the food that is eaten by these animals, which leads to malnutrition in the host body, that is, in the animal.

Competition- Caribou and Musk Ox can compete for food if the supply is low. Both eat plants and may compete for sedges and grasses. For the most part, animals in the Tundra do not have to compete for resources since the Tundra is only inhabited by a select number of species who can survive the harsh conditions.

Coevolution Mechanisms

Camouflage- Many animals in the tundra are snow white, which allows them to blend in to their environment- Snowy Owls, Arctic Foxes, Arctic Hares, and Polar Bears are some examples.

  

Secondary Compound: Arctic Willow- During its best growing season, the Arctic Willow produces a pesticide so antagonists like insects, for example the Arctic Wholly Bear, cannot eat them.

Predator-prey relationship

Polar bear eating a seal

Snowy owl chasing a lemming

Arctic fox eating a lemming