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Taxonomic and Geographic Patterns of Decline for Threatened and Endangered Species in the United States

机译：美国受威胁和濒危物种下降的分类和地理模式

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摘要

Species listed under the U.S. Endangered Species Act (i.e., listed species) have declined to the point that the probability of their extinction is high. The decline of these species, however, may manifest itself in different ways, including reductions in geographic range, number of populations, or overall abundance. Understanding the pattern of decline can help managers assess extinction probability and define recovery objectives. Although quantitative data on changes in geographic range, number of populations, and abundance usually do not exist for listed species, more often qualitative data can be obtained. We used qualitative data in recovery plans for federally listed species to determine whether each listed species declined in range size, number of populations, or abundance relative to historical levels. We calculated the proportion of listed species in each state (or equivalent) that declined in each of those ways. Nearly all listed species declined in abundance, and range size or number of populations declined in approximately 80% of species for which those data were available. Patterns of decline, however, differed taxonomically and geographically. Declines in range were more common among vertebrates than plants, whereas population extirpations were more common among plants. Invertebrates had high incidence of range and population declines. Narrowly distributed plants and invertebrates may be subject to acute threats that may result in population extirpations, whereas vertebrates may be affected by chronic threats that reduce the extent and size of populations. Additionally, in the eastern United States and U.S. coastal areas, where the level of land conversion is high, a greater percentage of species' ranges declined and more populations were extirpated than in other areas. Species in the Southwest, especially plants, had fewer range and population declines than other areas. Such relations may help in the selection of species' recovery criteria.
机译：根据《美国濒危物种法》列出的物种（即所列物种）已经下降到灭绝的可能性很高的地步。但是，这些物种的减少可能以不同的方式表现出来，包括地理范围，人口数量或总体丰度的减小。了解下降的模式可以帮助管理人员评估灭绝的可能性并确定恢复目标。尽管通常对于所列物种不存在有关地理范围，种群数量和丰度变化的定量数据，但更经常可以获得定性数据。我们在联邦计划列出的物种的恢复计划中使用了定性数据，以确定每种列出的物种的范围大小，种群数量或相对于历史水平的丰度是否下降。我们计算了每种州（或同等州）以每种方式下降的所列物种的比例。几乎所有列出的物种都大量减少，而拥有这些数据的物种中，大约80％的物种的范围大小或种群数量下降。然而，下降的模式在分类和地理上有所不同。脊椎动物的范围下降比植物更普遍，而种群灭绝在植物中更普遍。无脊椎动物的范围和种群数量下降的发生率很高。狭窄分布的植物和无脊椎动物可能会遭受可能导致种群灭绝的急性威胁，而脊椎动物可能会受到减少种群数量和规模的慢性威胁的影响。此外，与其他地区相比，在美国东部和美国沿海地区，土地转换的水平很高，物种分布范围的下降幅度更大，并且灭绝了更多的种群。西南地区的物种，特别是植物，其分布范围和种群数量减少的幅度小于其他地区。这种关系可能有助于选择物种的恢复标准。

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