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a Alabama and a neighboring state b Considered extinct, endangered, threatened, or of special concern a Alabama and a neighboring state b Considered extinct, endangered, threatened, or of special concern

Other groups of vertebrates also are highly imperiled. The global decline of amphibians, attributed to climate change, disease, and habitat loss amongst other causes, threatens an estimated one third of all species worldwide (Stuart et al. 2004). Dudgeon et al. (2006) summarize evidence for the imperiled status of crocodilians, turtles, and other reptiles, particularly in tropical rivers. The freshwater dolphins, arguably the most endangered mammals still alive, number fewer than 100 individuals in the case of the Yangtse Dolphin. Because recent surveys of this species, also known as the Baiji, have failed to record any sightings, it may have recently become extinct; if confirmed, this represents the loss of an entire family (the Lipotidae).

Finally, although much attention rightfully focuses on rarity and extinction, many species within modern-day assemblages frequently have restricted ranges and reduced abundances relative to their historical condition. Using historical records to establish the original ranges of 25 fish species native to the lower basin of the Colorado River, Fagan et al. (2005) found that on average, species ranges had diminished >45% relative to their historical distribution, and fully one third of species had lost at least half of their occurrences. Of the 15 species, one is extinct (Cyprinodon arcuatus), and of the remaining 14, eight are considered endangered, two are vulnerable, and four are at lower risk. As this example illustrates, even when the majority of the original fauna still survives, their restricted and fragmented distributions are evidence of a functionally altered biological community.

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