Extinction in a field of bullets: a search for causes in the decline of the world's freshwater fishes

Because human actions alter the physical nature of aquatic ecosystems similarly worldwide, the extinction risk among many freshwater fishes that share particular life-history traits may also be similar. Determining whether taxonomic selectivity, the preferential loss (or persistence) of certain species groups, exists among the world's freshwater fish families is then a key step in predicting future species declines and triaging future conservation efforts. We use binomial statistics to look for taxonomic patterns among the world's freshwater fish families currently at risk of extinction. Families are identified as being at risk of extinction if at least one species within a given family is classified as either extinct or at risk of extinction by the International Union for the Conservation of Nature's Redlist of Threatened Animals [Groombridge, B., Baillie, J., 1997. 1996 IUCN Red list of Threatened Animals. IUCN Gland, Switzerland and Cambridge, UK]. Eighteen freshwater families have more threatened species than expected if extinction risk was evenly distributed across all families. Next, we use a series of chi-squared analyses to determine if various family-level characteristics (e.g. geographic distribution, body length, habitat preference, etc.) produce this taxonomic pattern. We find that families that inhabit well-studied regions of the world contain more threatened species. However, we find no indication of a unifying set of extinction-promoting biological or ecological traits that contribute to extinction risk among freshwater families. A possible explanation for this discrepancy is that aquatic alterations worldwide are so severe that extinction is being driven by extrinsic rather than intrinsic factors. (C) 2001 Elsevier Science Ltd. All rights reserved.