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Federal Register / Vol. 86, No. 103 / Tuesday, June 1, 2021 / Proposed Rules Distinct Population Segment Evaluation Under the Act, the term species includes any subspecies of fish or wildlife or plants, and any distinct population segment of any species of vertebrate fish or wildlife which interbreeds when mature. 16 U.S.C.
153216. To guide the implementation of the distinct population segment DPS
provisions of the Act, we and the National Marine Fisheries Service National Oceanic and Atmospheric AdministrationFisheries, published the Policy Regarding the Recognition of Distinct Vertebrate Population Segments Under the Endangered Species Act DPS
Policy in the Federal Register on February 7, 1996 61 FR 4722. Under our DPS Policy, we use two elements to assess whether a population segment under consideration for listing may be recognized as a DPS: 1 The population segments discreteness from the remainder of the species to which it belongs, and 2 the significance of the population segment to the species to which it belongs. If we determine that a population segment being considered for listing is a DPS, then the population segments conservation status is evaluated based on the five listing factors established by the Act to determine if listing it as either endangered or threatened is warranted.
As described in Previous Federal Actions, we were petitioned to list the lesser prairie-chicken either rangewide or in three distinct population segments.
The petition suggested three DPS
configurations: 1 Shinnery Oak Ecoregion, 2 the Sand Sagebrush Ecoregion, and 3 a segment including the Mixed-Grass Ecoregion and the Short-Grass/CRP Ecoregion. The petition also combined the Sand Sagebrush Ecoregion, the Mixed-Grass Ecoregion, and the Short-Grass/CRP
Ecoregion due to evidence they are linked genetically and geographically Molver 2016, p. 18. Genetic studies indicate that lesser prairie-chicken from the Mixed-Grass Ecoregion are similar in genetic variation with the ShortGrass/CRP Ecoregion, with individuals likely dispersing from the Mixed-Grass Ecoregion to the Short-Grass/CRP
Ecoregion Oyler-McCance et al. 2016, p. 653. Other genetic data indicate that lesser prairie-chicken from the Sand Sagebrush Ecoregion and lesser prairiechicken from the Mixed-Grass and Short-Grass/CRP Ecoregion also share genetic traits. Genetic studies of neutral markers indicate that, although lesser prairie-chicken from the Sand Sagebrush Ecoregion form a distinct genetic cluster from other ecoregions, they have also likely contributed some
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individuals to the Short-Grass/CRP
Ecoregion through dispersal OylerMcCance et al. 2016, p. 653.
Additionally, these three ecoregions are not geographically isolated from one another Figure 3. As a result of the shared genetic characteristics and the geographic connections, we have concluded the Sand Sagebrush Ecoregion, the Mixed-Grass Ecoregion, and the Short-Grass/CRP Ecoregion are appropriately considered as one potential DPS configuration.
Under the Act, we have the authority to consider for listing any species, subspecies, or, for vertebrates, any distinct population segment DPS of these taxa if there is sufficient information to indicate that such action may be warranted. We considered whether two segments meet the DPS
criteria under the Act: The southernmost ecoregion Shinnery Oak and a segment containing the three northernmost ecoregions Mixed-Grass, Short-Grass/CRP, and Sand Sagebrush.
Discreteness Under our DPS Policy, a population segment of a vertebrate taxon may be considered discrete if it satisfies either of the following conditions: 1 It is markedly separated from other populations of the same taxon as a consequence of physical, physiological, ecological, or behavioral factors.
Quantitative measures of genetic or morphological discontinuity may provide evidence of this separation; or 2 it is delimited by international governmental boundaries within which differences in control of exploitation, management of habitat, conservation status, or regulatory mechanisms exist that are significant in light of section 4a1D of the Act.
We conclude the two segments satisfy the markedly separate conditions.
The two groups of ecoregions are not separated from each other by international governmental boundaries.
The southernmost ecoregion Shinnery Oak is separated from the three northern ecoregions by approximately 95 mi 153 km, much of which is developed or otherwise unsuitable habitat. There has been no recorded movement of lesser prairie-chickens between the Shinnery Oak Ecoregion and the three northern ecoregions over the past several decades. Because there is no connection between the two parts of the range, there is subsequently no gene flow between them OylerMcCance et al. 2016, entire.
Therefore, we have determined that both the southern ecoregion and the northern three ecoregions of the lesser prairie-chicken range both individually
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meet the condition for discreteness under our DPS Policy.
Significance Under our DPS Policy, once we have determined that a population segment is discrete, we consider its biological and ecological significance to the larger taxon to which it belongs. This consideration may include, but is not limited to: 1 Evidence of the persistence of the discrete population segment in an ecological setting that is unusual or unique for the taxon, 2
evidence that loss of the population segment would result in a significant gap in the range of the taxon, 3
evidence that the population segment represents the only surviving natural occurrence of a taxon that may be more abundant elsewhere as an introduced population outside its historical range, or 4 evidence that the discrete population segment differs markedly from other populations of the species in its genetic characteristics.
For the lesser prairie-chicken, we first considered evidence that the discrete population segment differs markedly from other populations of the species in its genetic characteristics. The most recent rangewide genetic study examined neutral markers in the four ecoregions where the lesser prairiechicken occurs. It concluded that there is significant genetic variation across the lesser prairie-chicken range. The study also concluded that although there is genetic exchange between the three northern ecoregions particularly movement of birds northward from the Mixed-Grass Ecoregion to the ShortGrass/CRP Ecoregion, and, to a lesser extent, from the Sand Sagebrush Ecoregion into the Short-Grass/CRP
Ecoregion, lesser prairie-chicken from the Shinnery Oak Ecoregion in the southwestern part of the range are a group that is genetically distinct from the remainder of the range OylerMcCance et al. 2016, p. 653. The Shinnery Oak Ecoregion is more distinct from all three ecoregions in the Northern DPS than those ecoregions are from each other Oyler-McCance et al.
2016, Table 4. The Shinnery Oak Ecoregion was likely historically connected to the remainder of the range, but the two parts have been separated since approximately the time of European settlement. Therefore, the two segments of the range are genetically distinct from each other.
We next considered evidence that loss of the population segment would result in a significant gap in the range of the taxon. As discussed above, the southwestern and northeastern parts of the range are separated by
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