Direct vs. indirect competition model, Biology

Pikas (component 1), also known as "rock rabbits" or "coneys", are small relatives of rabbits belonging to the genus Ochotona. The 30 species in this genus are confined to high altitudes in Asia, North America, and parts of eastern Europe, where they live in alpine tundra environments. Although most species live in crevices on rocky mountainsides, a few burrowing species are found in open steppe landscapes. One of the latter species is the plateau (or black-lipped) pika (O. curzoniae), which lives on the Tibetan Plateau in the People's Republic of China. In this area, pikas are believed to act as a "keystone species" (one whose presence or absence exerts a disproportionate effect on community diversity).

Pikas feed mostly on grasses (component 2) and to a much lesser extent on other plants (component 3). Similarly to prairie dogs in the American west, pika make burrows that are the primary homes of a variety of small birds and lizards, create soil disturbance (e.g., aeration, mixing) that increases plant species diversity, are the main or major prey species for most of the predatory animals in the area, and engage in other activities (e.g., fertilizing soil with their waste products and burying food stores of seeds that may sprout later on) that increase the growth of other plants and overall ecological productivity.

Lizards (component 4), including: Ching Hai toadhead agamas (Phrynocephalus vlangalii) and multi-ocellated racerunners (Eremias multiocellata) live in pika burrows, but do not benefit (or hinder) the pikas.

Passarine birds (component 5), including: Hume's ground jay (Pseudopodoces humilis), Isabelline wheatears (Oenanthe isabellina), and several species of snowfinches (Pyrgilauda spp.) use the burrows constructed by the pikas for nesting. They likewise also do not benefit or hinder the pikas. They avoid pika burrows that are already occupied by lizards (and lizards avoid burrows once they are occupied by birds).

Small predatory birds (component 6), including: upland buzzards (Buteo hemilasius), black kites (Milvus migrans), and little owls (Athene noctua), and small predatory mammals (component 7) such as steppe polecats (Mustela eversmanni), mountain weasels (M. altaica), Tibetan sand and red foxes (Vulpes ferrilata, V. vulpes), and Pallas's cat (Otocolobus manul) all rely heavily on pikas for food.

Raptors (component 8), including: saker falcons (Falco cherrug), goshawks (Accipiter gentiles), and golden eagles (Aquila chrysaetos), depend upon pikas as a major food source. They also feed on passerine birds and small predatory birds.

Domestic livestock (component 9) including sheep, horses, and yaks are maintained by humans for meat and milk, and also serve as work animals. They graze on grass and other plants. Their feeding activities and trampling the on the soil increases the amount of barren ground, which is good for pikas.

Large carnivores (component 10), including, wolves (Canis lupus), and snow leopards (Uncia uncia) feed on pikas and the young of domestic livestock. They also feed on small predatory mammals or their young.            

Brown bears (component 11) occasionally feed on pikas. More importantly, however, they feed on a wide variety of plants (but not on grasses).

Humans (component 12) in the area depend on their domestic livestock for meat and milk. Their livestock benefit from human protection. Humans shoot golden eagles (even though these have been shown not to eat livestock), snow leopards and wolves (which do prey upon their livestock or their young). Humans hunt brown bears for their skins and some of their other body parts (i.e., claws, bones, and gall bladders that make their way to Chinese cities, where they are sold on the black market for "medicinal" purposes), but they do not eat them. They also poison pikas, believing both that they compete with their livestock for food and that their holes injure livestock that step in them.

1.   Click on the "Prediction" button. You will then be able to simulate the effects of an increase in each species by clicking on its highlighted number at the top of the matrix. What happens to the pika (i.e., does this species increase, decrease, or remain the same) when each of the following: passerine birds, smaller carnivores, larger carnivores, livestock, and humans both increase and decrease? Explain what you think is happening to produce these changes.

2.  What happens to all other species when the pika both increase and decrease (i.e., which species' populations increase, decrease, or remain the same)? Explain what you think is happening to produce these changes.

3.  Which model (direct vs. indirect competition) seems to be more realistic? How could your models better address this question? Explain and give examples.

Posted Date: 2/18/2013 7:57:17 AM | Location : United States

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