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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essential; they shape the synthesis of the biochemicals that control cellular activity and, ultimately, all biological activity and form. The capacity for genes to encode this information is stupendous; a typical mammal might have 100,000 genetic loci.

      Of course, most of this wealth of genetic diversity is encapsulated in the diversity of species and their interspecific genetic differences. The key issue to address here is the distribution and diversity of alleles that characterize a species. Why is it important to maintain different versions of the same gene and, in many circumstances, to have them well distributed in a population dominated by heterozygotes rather than homozygotes? There are three basic answers: evolutionary potential, loss of fitness, and utilitarian values.

      Evolutionary Potential

      A key requisite for natural selection is genetic‐based variability in the fitness of individuals; that is, some individuals must be more likely to survive and reproduce than others. If every individual were genetically identical and only chance determined which ones left progeny, then populations would change erratically through time, if at all. If they are to persist, however, populations must change as their environment changes, which environments everywhere are now doing rapidly (see Chapter 6). Of course, the physical world has always changed as continents drift around the globe, mountains rise and erode, oceanic currents and jet streams shift paths, and the planet’s orbit around the sun varies. The biological world also changes as species evolve, become extinct, and shift their geographic ranges, coming into contact with new species that may be predators, prey pathogens, or competitors. Changes have been particularly dramatic during the last few decades as human populations and their technological capabilities have grown and profoundly altered the conditions for evolution in most species. To put it more directly: humans are now the central organizing reality around which all nonhuman life will evolve. To some degree, all species must respond to the environmental changes we are wreaking almost everywhere if they are to survive. And they need genetic diversity to do so.

Photos depict (a) the species of snowball plants of the genus Saussurea that are used in traditional Tibetan and Chinese medicine have declined in height based on herbarium specimens and field collections over the past 100 years. (b) Another species that is seldom collected, S. medusa, showed no significant decline.

      (Courtesy of Law and Salick/National Academy of Sciences, USA)

      Environments change through space, as well as time, and a species with greater genetic diversity is more likely to colonize a wider range of environments than a species with limited genetic diversity. For example, a survey of the heterozygosity and polymorphism of 189 species of amphibians indicated that genetic diversity was greatest in amphibians that lived in the most heterogeneous environments (e.g. forests) and least in homogeneous environments (e.g. aquatic ecosystems and underground) (Nevo and Beiles 1991). A similar pattern has been shown for plants (Gray 1996). More disturbed environments also tend to support species with lower genetic diversity (Banks et al. 2013).

      Loss of Fitness

      (Reed and Frankham 2003/John Wiley & Sons)

Graph depicts Juvenile mortality in 44 species of mammals bred in captivity.

      Data from Ralls and Ballou 1983)