Risk assessment

On a practical level, it is difficult to assess which species are most at risk. Because biodiversity encompasses the range of variation, from individuals to populations to habitats themselves, it is virtually impossible to enumerate and quantify. Nevertheless, it is precisely that complexity that is worth conserving. In the absence of long-term data and exact numbers for such ecological parameters as abundance and diversity, conservation efforts usually focus on surrogate species and assume that the protection of some species will include others. Generally, surrogate species fall under three categories: flagship species, umbrella species, and biodiversity indicators. The first group includes well-known or well-publicized species that appeal to the general public. Umbrella species are those that require such large tracts of habitat that their protection envelops other species; for example, large mammalian carnivores. The third surrogate category includes sets of species or taxa whose presence indicates a rich variety of other species. For example, a species of bee may indicate several species of plants it pollinates and they, in turn, may provide habitat to a number of species of birds, invertebrates or mammals. In this particular example, the bee functions as a "keystone" species, since its activities support the well-being of others.

Species are often interdependent in ways that are less apparent. For example, white wartyback mussels (Plethobasus ci-catricosus) are dependent on a fish host in their larval phase. When rivers in which the mussels and fishes lived were dammed, the fishes could not survive in the colder river water released from those dams and died out. Thus, although white wartyback mussels can still be found, the population cannot reproduce and is functionally extinct, a "living ghost." Such rare species as white wartyback mussels run a higher risk of extinction than common species.

Endemic species are restricted to a given area and are rare by definition; that is, they are found nowhere else. Endemism is common among island flora and fauna because they have evolved more or less in isolation from other populations. Over time, natural selection acts to mold such species into what are often very specific niches; they adapt themselves to very narrowly defined habitats. The many shapes of bills found on the finches of the Galapagos Islands may serve as a common example. Endemic species are commonly used surrogates in conservation strategies.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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