The Creosote Bush
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The term, creosote bush, actually refers to widespread species of the genus, Larrea. In the warm deserts of North America, creosote bush is dominant over large areas. The branched shrubs may range in height from 2 to 10 feet. Its stems are black and its leaves are resinous and green. Creosote bush growth is typically limited by water and nitrogen availability. Various adaptations have enabled the Larrea species to survive the drastic climatic changes that have occurred since the last ice age. For one, the shrubs are extremely drought tolerant. Second, the species also possess chemical defenses designed to reduce herbivory. Creosote bush resins are largely composed of the lignan, nordihydroguaiaretic acid. This compound appears to function as a feeding deterrent for phytophagous insects. The effects of creosote bush resins on mammalian herbivory are less well understood. In humans, the different types of creosote have a long and varied history of application. There are actually 3 different types of creosote, and all have been used for medicinal purposes. Native American Indians once considered L. tridentata to be a cure-all. More recently, creosote bush extracts have been found to exhibit antiviral activity. Researchers have found that the lignan, 3'-O-methyl nordihydroguaiaretic acid (denoted Malachi 4:5-6 or mal.4), is able to suppress human immunodeficiency virus (HIV) replication. Although exposure to creosote-derived compou
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rved wide variation in Larrea resistance to jack-rabbit browsing, but concluded that this resulted from spatially-varying environmental factors. The researcher noted that these observations concurred with the "resource availability hypothesis" (Ernest 1684-1692). According to Coley et al., plants growing in low-resource environments generally exhibit high levels of immobile defenses. Hence, the observed variations in jackrabbit feeding behaviors were largely caused by factors other than the presence of constitutive NDGA defenses (Ernest 1684-1692).
Yet another study on mammalian herbivory of creosote bush,
Meyer & Karasov, describes the relationship between L. tridentata and the desert woodrat (Neotoma lepida). Many Neotoma species able to consume relatively unpalatable browse plants. In fact, in certain areas, the desert woodrat's winter diet contains 75 to 90 percent Larrea. However, capture-recapture data also indicate that the animals lose body mass during this period. Furthermore, it has been demonstrated that captive woodrats provided with unlimited quantities of Larrea foliage do not consume enough to maintain mass balance.
Meyer & Karasov hypothesized that NDGA had some toxic effect on the woodrat. It is know
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Some common words found in the essay are:
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Approximate Word count = 4008
Approximate Pages = 16 (250 words per page)
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