Geographic distribution of endangered species in the United States

Science

Volumn 275, Issue 5299, 1997, Pages 550-553

  Dobson, A P ^a   Rodriguez, J P ^a   Roberts, W M ^a   Wilcove, D S ^b  

^a PRINCETON UNIVERSITY   (United States)

^b ENVIRONMENTAL DEFENSE FUND   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ARTICLE; ENVIRONMENTAL MONITORING; GEOGRAPHIC DISTRIBUTION; NONHUMAN; PRIORITY JOURNAL; SPECIES; UNITED STATES;

ENDANGERED SPECIES; GEOGRAPHICAL DISTRIBUTION;

USA;

AVES;

EID: 0030621340     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.275.5299.550     Document Type: Article

References (27)

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14. Half of the currently listed plant species are found in the 13 highest ranked counties in their complementary county subset; the total area of these counties is 1.33% of the U.S. land mass. The equivalent figures for the other groups are as follows: molluscs, 6 counties (0.14%); arthropods, 9 counties (0.46%); fish, 14 counties (2.04%); herptiles, 7 counties (0.34%); birds, 4 counties (0.28%); and mammals, 7 counties (0.40%).
15. Mean values for birds are inflated by the occurrence of peregrine falcons (Falco peregrinus) and bald eagles (Haliaeetus leucocephalus) in a large number of counties throughout the United States. If data for these two species are excluded, the mean number of counties that each endangered bird species was located in would drop to 31.7, with 37% of endangered birds restricted to a single county.
16. U. S. Bureau of the Census, Statistical Abstract of the United States: 1991 (U.S. Government Printing Office, Washington, DC, 1991).
17. The stepwise multiple regression analysis was performed on the entire data set and then on each major taxonomic division. Because complete sets of economic and geographic data are only available at the state level, the analysis was performed at this coarser geographic scale. The density of endangered species was expressed as the total number of endangered species recorded in the state, divided by total area of the state for all terrestrial species. In the case of predominantly aquatic species (fish and clams), only the area of each state classified as water or wetland was used to calculate density. The variables included in the analysis were the annual value of farm products produced in the state, the year in which the state was incorporated into the United States, water use in the state, manufacturing exports, percent of the net state area that is forested, percent of the state that is urban, percent of the state classified as wetlands, percent of the state classified as agricultural land, human population density in the state, percent of the human population living in urban areas, highest point in the state, average annual temperature in the state, and average annual rainfall in the state. The analysis was undertaken twice - once including Hawaii and once for just the mainland states. In both cases there was no substantial difference in the analyses, except for birds, plants, and all species combined. A large proportion of the endangered birds and plants occur only in Hawaii. When Hawaii is included in the analysis, its high density of endangered species and extreme values for several independent variables (such as extreme topography and tropical climate) combine to yield trends that are unrepresentative of the continental United States. For this reason, we have only provided results for the 49 continental states in the main text.
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26. Bringing these species to the point of recovery (by increasing their populations) would involve a greater amount of land than they currently occupy. However, as the geographic distributions of many endangered species do not overlap more than a single county, this is likely to be less of a problem for species groups with restricted ranges (such as plants and arthropods) than it is for birds and mammals.
27. We thank L. Turner and M. Hood at the Environmental Protection Agency for comments on the manuscript and for providing us with the raw data for this analysis; user support services at Golden Software, CO, for providing help in producing the maps in Figs. 1 and 2; and M. Scott, M. Bean, and three anonymous referees for comments on the manuscript. The work was made possible by a grant to the Environmental Defense Fund from the Charles Stewart Mott Foundation.