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Federal Register / Vol. 86, No. 103 / Tuesday, June 1, 2021 / Proposed Rules Summary of Biological Status and Threats In this discussion, we review the biological condition of the species and its resources, and the threats that influence the species current and future condition, in order to assess the species overall viability and the risks to that viability.
We note that, by using the SSA
framework to guide our analysis of the scientific information documented in the SSA report, we have not only analyzed individual effects on the species, but we have also analyzed their potential cumulative effects. We incorporate the cumulative effects into our SSA analysis when we characterize the current and future condition of the species. To assess the current and future condition of the species, we undertake an iterative analysis that encompasses and incorporates the threats individually and then accumulates and evaluates the effects of all the factors that may be influencing the species, including threats and conservation efforts. Because the SSA framework considers not just the presence of the factors, but to what degree they collectively influence risk to the entire species, our assessment integrates the cumulative effects of the factors and replaces a standalone cumulative effects analysis.

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Representation To evaluate representation as a component of lesser prairie-chicken viability, we considered the need for multiple healthy lesser prairie-chicken populations within each of the four ecoregions to conserve the genetic and ecological diversity of the lesser prairiechicken. Each of the four ecoregions varies in terms of vegetative communities and environmental conditions, resulting in differences in abundance and distribution and management strategies Boal and Haukos 2016, p. 5. Despite reduced range and population size, most lesser prairie-chicken populations appear to have maintained comparatively high levels of neutral genetic variation DeYoung and Williford 2016, p. 86. As discussed in Significance above, recent genetic studies also show significant genetic variation across the lesser prairie-chicken range based on neutral markers Service 2021, Figure 2.4, which supports management separation of these four ecoregions and highlights important genetic differences between them Oyler-McCance et al. 2016, p.
653. While it is unknown how this genetic variation relates to differences in adaptive capacity between the
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ecoregions, maintaining healthy lesser prairie-chicken populations across this range of diversity increases the likelihood of conserving inherent ecological and genetic variation within the species to enhance its ability for adaptation to future changes in environmental conditions.
Resiliency In the case of the lesser prairiechicken, we considered the primary indicators of resiliency to be habitat availability, population abundance, growth rates, and quasi-extinction risk.
Lesser prairie-chicken populations within ecoregions must have sufficient habitat and population growth potential to recover from natural disturbance events such as extensive wildfires, extreme hot or cold events, extreme precipitation events, or extended local periods of below-average rainfall. These events can be particularly devastating to populations when they occur during the late spring or summer when nesting and brood rearing are occurring and individuals are more susceptible to mortality.
The lesser prairie-chicken is considered a boom-bust species based on its high reproductive potential with a high degree of annual variation in rates of successful reproduction and recruitment. These variations are largely driven by the influence of seasonal precipitation patterns Grisham et al.
2013, pp. 67, which impact the population through effects on the quality of habitat. Periods of belowaverage precipitation and higher spring/
summer temperatures result in less appropriate grassland vegetation cover and less food available, resulting in decreased reproductive output bust periods. Periods with above-normal precipitation and cooler spring/summer temperatures will support favorable lesser prairie-chicken habitat conditions and result in high reproductive success boom periods. In years with particularly poor weather conditions, individual female lesser prairie-chicken may forgo nesting for the year. This population characteristic highlights the need for habitat conditions to support large population growth events during favorable climatic conditions so they can withstand the declines during poor climatic conditions without a high risk of extirpation.
Historically, the lesser prairie-chicken had large expanses of grassland habitat to maintain populations. Early European settlement and development of the Southern Great Plains for agriculture initially, and for energy extraction later, substantially reduced the amount and connectivity of the grasslands of this
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region. Additionally, if historically some parts of the range were drastically impacted or eliminated due to a stochastic event, that area could be reestablished from other populations.
Today, those characteristics of the grasslands have been degraded, resulting in the loss and fragmentation of grasslands in the Southern Great Plains. Under present conditions, the potential lesser prairie-chicken habitat is limited to small, fragmented grassland patches relative to historical conditions Service 2021, pp. 6478.
The larger and more intact the remaining grassland patches are, with appropriate vegetation structure, the larger, healthier, and more resilient the lesser prairie-chicken populations will be. Exactly how large habitat patches should be to support healthy populations depends on the quality and intactness of the patches. Recommended total space needed for persistence of lesser prairie-chicken populations ranges from a minimum of about 12,000
ac 4,900 ha Davis 2005, p. 3 up to more than 50,000 ac 20,000 ha to support single leks, depending on the quality and intactness of the area Applegate and Riley 1998, p. 14;
Haufler et al. 2012, pp. 78; Haukos and Zavaleta 2016, p. 107.
A single lesser prairie-chicken lek is not considered a population that can persist on its own. Instead, complexes of multiple leks that interact with each other are required for a lesser prairiechicken population to be persistent over time. These metapopulation dynamics, in which individuals interact on the landscape to form larger populations, are dependent upon the specific biotic and abiotic landscape characteristics of the site and how those characteristics influence space use, movement, patch size, and fragmentation DeYoung and Williford 2016, pp. 8991. Maintaining multiple, highly resilient populations complexes of leks within the four ecoregions that have the ability to interact with each other will increase the probability of persistence in the face of environmental fluctuations and stochastic events. Because of this concept of metapopulations and their influence on long-term persistence, when evaluating lesser prairie-chicken populations, site-specific information can be informative. However, many of the factors affecting lesser prairiechicken populations should be analyzed at larger spatial scales Fuhlendorf et al.
2002, entire.
Redundancy Redundancy describes the ability of a species to withstand catastrophic events. Catastrophes are stochastic
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