Fundamentals of Conservation Biology. Malcolm L. Hunter, Jr.. Читать онлайн. Newlib. NEWLIB.NET

Автор: Malcolm L. Hunter, Jr.
Издательство: John Wiley & Sons Limited
Серия:
Жанр произведения: Биология
Год издания: 0
isbn: 9781119144175
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appetite for variety. The explosion of color and form in flower gardens and love of different types of hot peppers in cooking are strong testament to the saying, “variety is the spice of life.”

Photos depict ankole watusi cattle that is raised as beef on a dry pasture in Malawi versus Holstein Friesian cattle on lush pasture of a dairy farm in Belgium cannot effectively cannot trade places or purpose.

      (Matthew Bellemare/Flickr/CC BY 2.0 [top] and Tobias Nordhausen/Flickr/CC BY 2.0 [bottom])

      The genetic diversity of some wild populations is also important to plant and animal breeders because wild relatives of domestic species are a significant source of genetic material. For example, when scientists at the International Rice Research Institute in the Philippines set out to develop a variety of rice that would be resistant to a major disease, grassy stunt virus, they screened over 6000 varieties of rice and found only one variety that was resistant to the disease. That variety, a wild species of rice called Oryza nivara, was represented in their collection by only 30 kernels, of which only three showed resistance (Hoyt 1988). Returning to the area in north‐central India where the rice sample had been collected, they could find no new material; the original collection site had been inundated by a dam. Fortunately, this story still had a happy ending because they were able to use the genetic information in these three kernels to develop a new variety of rice, IR36, that is resistant to this virus and is planted across millions of hectares in Asia (Ma et al. 2016).

       Postscript

      Careful readers may wonder why we have departed from the taxonomy of values used for species and ecosystems: intrinsic, instrumental, and uniqueness. We could squeeze genes into this classification, but it seems a bit contrived to talk about intrinsic value and uniqueness of molecules. Although a DNA helix is conceptually a beautiful and inherently intriguing structure, the value of genes lies in what they do, rather than what they are, and in this sense all of their value is instrumental. The classification used here distinguishes between values that are important to the species itself (evolutionary potential and loss of fitness) versus those that are important to people and other species (utilitarian values).

      To better understand the relationship between reduction in genetic diversity and loss of fitness, we will now consider the processes that diminish genetic diversity, especially in small populations: genetic bottlenecks, random genetic drift, and inbreeding.

      Bottlenecks and Drift

      Some populations are quite large: thousands of individuals are loosely connected through a web of interbreeding that ensures gene flow throughout the population. On the other hand, some populations are quite small, perhaps because they are confined to tiny, isolated patches of habitat and have limited dispersal abilities. In this section we are primarily concerned with what can happen to the genetic diversity of small populations, especially among species that typically occur in large populations but have been forced into small numbers. Profound changes occur in reduced populations and thus management of small‐population phenomena is a major focus for conservation biology.

      Based on Frankel and Soulé 1981

Average number of alleles retained from an original set (m) of 4
Sample size (N) after bottleneck Proportion of heterozygosity retained p 1 = 0.70, p2 = p 3 = p 4 = 0.10 p 1 = 0.94, p 2 = p 3 = p 4 = 0.02
1 0.50 1.48 1.12
2 0.75 2.02 1.23
6 0.917 3.15 1.64
10 0.95*

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