Question: What Bison heard is a herd of 250–400 American bison in Wind Cave National Park, South Dakota, USA, that  is one of two subspecies/ecotypes of the American bison?

Context paragraphs:
Henry Mountains bison herd: The Henry Mountains bison herd, numbering 250 to 400 bison, is one of only four free roaming and genetically pure herds on public lands in North America.  The other three herds are the Yellowstone Park bison herd which was the ancestral herd for the Henry Mountains animals, the Wind Cave bison herd in South Dakota and the herd on Elk Island in Alberta, Canada.

National Bison Range: The National Bison Range (NBR) is a National Wildlife Refuge located in western Montana established in 1908 to provide a sanctuary for the American bison.  The NBR is one of the oldest National Wildlife Refuges in the United States.  The size of the bison herd at the NBR is relatively small, numbering between 350 and 500 individuals.  The initial herd of American bison was provided by organizations such as the American Bison Society, and today the refuge serves as the central point for bison research in the United States.

Plains bison: The Plains bison ("Bison bison bison") is one of two subspecies/ecotypes of the American bison, the other being the wood bison ("B. b. athabascae").  Furthermore, it has been suggested that the Plains bison consists of a northern ("B. b. montanae") and a southern subspecies, bringing the total to three.  However, this is generally not supported.  A natural population of Plains bison survives in Yellowstone National Park (the Yellowstone Park bison herd consisting of about 3,000 bison) and multiple smaller reintroduced herds of bison in many places in Canada and the United States.

Lamar Buffalo Ranch: The Lamar Buffalo Ranch was created to preserve one of the last free-roaming bison (buffalo) herds in the United States.  The ranch was established in 1907 when 28 bison were moved from Fort Yellowstone to the Lamar Valley in the northeast portion of the park.  The herd was maintained as a semi-domesticated source of additional bison to enhance the park's natural herd.  The ranch supported bison ranching till the 1950s.  As the ranched herd increased in size, it was released to the open range and it interbred with the wild herd.  The ranch continued to be used to produce hay to feed the bison in the winter until the 1950s.  Because the winter feeding program maintained the herd at artificially high levels and distorted the herd's distribution in the park, it fell from favor as the National Park Service adopted wildlife management policies that interfered as little as possible with each species' natural ecology.

Tallgrass Prairie bison herd: The Tallgrass Prairie bison herd is a population of genetically pure American bison ("Bison bison") inhabiting the Tallgrass Prairie National Preserve in central Kansas.

Yellowstone Park bison herd: The Yellowstone Park bison herd in Yellowstone National Park is probably the oldest and largest public bison herd in the United States.  Yellowstone is known for its geothermal activity and large mammals, especially elk, wolves, American bison, bears, pronghorns, moose and bighorn sheep.  The Yellowstone Park bison herd was estimated in 2015 to be 4,900 bison

Wind Cave bison herd: The Wind Cave bison herd is a herd of 250–400 American bison in Wind Cave National Park, South Dakota, USA.  It is believed to be one of only four free roaming and genetically pure herds on public lands in North America.  The other three herds are the Yellowstone Park bison herd, the Henry Mountains bison herd in Central Utah, and at Elk Island National Park in Alberta, Canada.  The Wind Cave herd are of the Plains bison subspecies ("Bison bison bison").

European bison: The European bison ("Bison bonasus"), also known as wisent ( or ) or the European wood bison, is a Eurasian species of bison.  It is one of two extant species of bison, alongside the American bison.  Three subspecies existed in the recent past, but only one survives today.  The species is, theoretically, descended from a hybrid, a cross between a female aurochs, the extinct wild ancestor of modern cattle, and a male Steppe bison; the possible hybrid is referred to informally as the Higgs bison.  Alternatively, the Pleistocene woodland bison has been suggested as the ancestor to the species.

Antelope Island bison herd: Antelope Island in Great Salt Lake, Utah, is part of Antelope Island State Park.  On the island, a semi–free-ranging population of American bison ("Bison bison, "buffalo) has been in existence since 1893.  Though the island was named for the pronghorn antelope that John C. Frémont and Kit Carson found there when they explored the Great Salt Lake, bison were later introduced and the island is now perhaps most famous for its bison herd.

Wind Cave National Park: Wind Cave National Park is a United States national park 10 mi north of the town of Hot Springs in western South Dakota.  Established in 1903 by President Theodore Roosevelt, it was the seventh U.S. National Park and the first cave to be designated a national park anywhere in the world.  The cave is notable for its displays of the calcite formation known as boxwork.  Approximately 95 percent of the world's discovered boxwork formations are found in Wind Cave.  Wind Cave is also known for its frostwork.  The cave is also considered a three-dimensional "maze cave", recognized as the densest (greatest passage volume per cubic mile) cave system in the world.  The cave is currently the sixth-longest in the world with 140.47 mi of explored cave passageways.  Above ground, the park includes the largest remaining natural mixed-grass prairie in the United States.

Supporting paragraphs: Wind Cave bison herd Plains bison
Answer: The Plains bison