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Federal Register / Vol. 86, No. 103 / Tuesday, June 1, 2021 / Proposed Rules prairie-chicken, has been much reduced and fragmented compared to historical conditions across its range.
Habitat impacts occur in three general categories that often work synergistically at the landscape scale:
Degradation, loss, and fragmentation.
Habitat degradation results in changes to a species habitat that reduces its suitability to the species, but without making the habitat entirely unsuitable.
Degradation may result in lower carrying capacity, lower reproductive potential, higher predation rates, or other effects. Habitat loss may result from the same anthropogenic sources that cause degradation, but the habitat has been altered to the point where it has no suitability for the species at all.
Habitat fragmentation occurs when habitat loss is patchy and leaves a matrix of grassland habitat behind.
While habitat degradation continues to be a concern, we focus our analysis on habitat loss and fragmentation from the cumulative effects of multiple sources of activities as the long-term drivers of the species viability.
Initially, reduction in the total area of available habitat may be more significant than fragmentation and can exert a much greater effect on populations Fahrig 1997, pp. 607, 609.
However, as habitat loss continues, the effects of fragmentation often compound effects of habitat loss and produce even greater population declines than habitat loss alone Bender et al. 1998, pp. 517
518, 525. Spatial habitat fragmentation occurs when some form of disturbance, usually habitat degradation or loss, results in the separation or splitting apart of larger, previously contiguous, functional components of habitat into smaller, often less valuable, noncontiguous patches Wilcove et al.
1986, p. 237; Johnson and Igl 2001, p.
25; Franklin et al. 2002, entire. Habitat loss and fragmentation influence habitat availability and quality in three primary ways: 1 Total area of available habitat constrains the maximum population size for an area; 2 the size of habitat patches within a larger habitat area, including edge effects changes in population or community structures that occur at the boundary of two habitats, influences habitat quality and size of local populations; and 3 patch isolation influences the amount of species movement between patches, which constrains demographic and genetic exchange and ability to recolonize local areas where the species might be extirpated Johnson and Igl 2001, p. 25; Stephens et al. 2003, p.
101.
Habitat loss, fragmentation, and degradation correlate with the
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ecological concept of carrying capacity.
Within any given block or patch of lesser prairie-chicken habitat, carrying capacity is the maximum number of birds that can be supported indefinitely by the resources available within that area, that is, sufficient food, shelter, and lekking, nesting, brood-rearing, and wintering areas. As habitat loss increases and the size of an area decreases, the maximum number of birds that can inhabit that particular habitat patch also decreases.
Consequently, a reduction in the total area of available habitat can negatively influence biologically important characteristics such as the amount of space available for establishing territories and nest sites Fahrig 1997, p.
603. Over time, the continued conversion and loss of habitat will reduce the capacity of the landscape to support historical population levels, causing a decline in population sizes.
Habitat loss not only contributes to overall declines in usable area for a species but also causes a reduction in the size of individual habitat patches and influences the proximity and connectivity of these patches to other patches of similar habitat Stephens et al. 2003, p. 101; Fletcher 2005, p. 342, reducing rates of movement between habitat patches until, eventually, complete isolation results. Habitat quality for many species is, in part, a function of patch size and declines as the size of the patch decreases Franklin et al. 2002, p. 23. Both the size and shape of the habitat patch have been shown to influence population persistence in many species Fahrig and Merriam 1994, p. 53. The size of the fragment can influence reproductive success, survival, and movements. As the distances between habitat fragments increase, the rate of dispersal between the habitat patches may decrease and ultimately cease, reducing the likelihood of population persistence and potentially leading to both localized and regional extinctions Harrison and Bruna 1999, p. 226; With et al. 2008, p.
3153. In highly fragmented landscapes, once a species becomes extirpated from an area, the probability of recolonization is greatly reduced Fahrig and Merriam 1994, p. 52.
For the lesser prairie-chicken, habitat loss can occur due to either direct or indirect habitat impacts. Direct habitat loss is the result of the removal or alteration of grasslands, making that space no longer available for use by the lesser prairie-chicken. Indirect habitat loss and degradation is when the vegetation still exists, but the areas adjacent to a disturbance the disturbance can be natural or manmade
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are no longer used by lesser prairiechicken, are used at reduced rates, or the disturbance negatively alters demographic rates or behavior in the affected area. In many cases, as discussed in detail below for specific disturbances, the indirect habitat loss can greatly exceed the direct habitat loss.
Primarily due to their site fidelity and the need for large, ecologically diverse landscapes, lesser prairie-chickens appear to be relatively intolerant to habitat alteration, particularly for activities that fragment habitat into smaller patches. The birds require habitat patches with large expanses of vegetative structure in different successional stages to complete different phases in their life cycle, and the loss or partial loss of even one of these structural components can significantly reduce the overall value of that habitat to lesser prairie-chickens Elmore et al.
2013, p. 4. In addition to the impacts on the individual patches, as habitat loss and fragmentation increases on the landscape, the juxtaposition of habitat patches to each other and to non-habitat areas will change. This changing pattern on the landscape can be complex and difficult to predict, but the results, in many cases, are increased isolation of individual patches either due to physical separation or barriers preventing or limiting movement between patches and direct impacts to metapopulation structure, which could be important for population persistence DeYoung and Williford 2016, pp. 88
91.
The following sections provide a discussion and quantification of the influence of habitat loss and fragmentation on the grasslands of the Great Plains within the lesser prairiechicken analysis area and more specifically allow us to characterize the current condition of lesser prairiechicken habitat.
Conversion of Grassland to Cropland Historical conversion of grassland to cultivated agricultural lands in the late 19th century and throughout the 20th century has been regularly cited as an important cause in the rangewide decline in abundance and distribution of lesser prairie-chicken populations Copelin 1963, p. 8; Jackson and DeArment 1963, p. 733; Crawford and Bolen 1976a, p. 102; Crawford 1980, p.
2; Taylor and Guthery 1980b, p. 2;
Braun et al. 1994, pp. 429, 432433;
Mote et al. 1999, p. 3. Because cultivated grain crops may have provided increased or more dependable winter food supplies for lesser prairiechickens Braun et al. 1994, p. 429, the
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