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Biodiversity
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Biodiversity loss is a normal aspect of nature. Nature is a dynamic, complex process; ecosystems are in a constant state of agitation and transformation (Merchant, 1995). The planet has cooled from its molten beginnings; meteors and asteroids have hit the planet; ice ages come and go. Habitats are always changing; species are constantly evolving, interacting and migrating. Although there have been several prehistoric periods of dramatic species loss, most likely due to catastrophic external events, even between these events, species extinction occurs on a regular basis. In the normal eco-churn, species extinction is such a ongoing process that biologists have developed a "background rate of extinction" measurement of 0.1 - 1.0 extinctions per millions of species per year that estimates a normal rate of extinctions in the pre-human environment (MEA). Because species extinction is an easily quantifiable dimension of biodiversity, the background rate of extinction can serve as a useful baseline for measuring the human impact on biodiversity.
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Biodiversity is being threatened at an unprecedented scale by global environmental change brought about by human societies. In addition to the many moral reasons to preserve it for its own sake, biodiversity provides numerous ecosystem services that are crucial to human well-being at present and in the future. Ecosystem services (... called environmental services or nature’s services) are benefits provided by ecosystems to humans, that contribute to making human life both possible and worth living. Biodiversity can affect ecosystem services directly. For example, humans derive most of their essential food and fibers from animals and plants. Certain plants and animals are at the core of traditional knowledge systems.
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Biodiversity threats can work in tandem and may escalate problems. For example, habitat loss often results in fragmented habitats scattered over an area. A fragmented habitat can be detrimental to biodiversity because there are more openings allowing invasive and naturally aggressive species to enter and compete with native species. Smaller habitat patches may not be large enough for species requiring large areas and they may disappear. Increased edges in fragmented habitats may ... result in unnaturally high predation. Erosion and water contamination could increase from the removal of vegetation that acts as a soil anchor and water filter.
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Biodiversity found on Earth today is the result of 4 billion years of evolution. The origin of life has not been definitely established by science, though evidence suggests that life may already have been well-established a few hundred million years after the formation of the Earth. Until approximately 600 million years ago, all life consisted of bacteria and similar single-celled organisms.
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Biodiversity in the desert is often measured on a scale that would not be used in the tropical rainforest. Desert ecologists have found twenty kinds of wildflowers growing together in a single square yard (.84 m2), while a single tropical tree might take up the same amount of space. On an acre (.4 ha) of cactus forest in the Tucson Basin, seventy-five to 100 species of native plants share the space that three mangrove shrubs might cover in swamp along a tropical coast. These levels of diversity are a far cry from the "bleak and barren" stereotype, and it may well be that the Sonoran Desert region is more diverse than other arid zones of comparable size.
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Biodiversity was first defined as taxonomic diversity – the number of species. More recently, biodiversity has been broadened to include biological and geographic entities such as genetic diversity (genes, chromosomes), taxonomic diversity (species, genera, families, phyla, etc.) and biogeographic diversity (biogeographic regions, landscapes, ecosystems, habitats). Biodiversity always refers to the genetic, or taxonomic variability, within a specific area or region.
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Biodiversity