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Return of an Icon: Plains Bison in the Canadian Mixed-grass Prairie Gates et al. IUCN American bison: Status survey and conservation guidelines, 2010 Map from: World Wildlife Fund Terrestrial Ecosystems They classified 116 different Ecoregions Plains Bison occupied at least 46 of these Plains bison were the most widespread of all North American large mammals. NORTHERN SHORT GRASSLAND ECOREGION Grasslands National Park Why did Grasslands National Park re-introduce Plains Bison to this mixed-grass prairie ecosystem? 1. To restore a natural grazing regime using bison as the dominant herbivore. 2. To compliment, not replicate the grazing patterns on surrounding lands. 3. To restore the inter-relationships between bison, wildlife, vegetation and soil disturbance. 4. To provide visitors with the opportunity to bison on the mixed grass prairie. Grazing History There is abundant evidence that this region was heavily used by bison for thousands of years By the 1870’s the last wild bison were gone Grazing History Val Marie was the northern terminus of the Chisholm Trail, which saw cattle from Texas trailed north to markets in Canada Grazing History For over 100 years these ranchers were excellent stewards of the prairie. As local ranchers retired and sold their land to Parks Canada, GNP removed cattle and cross fences. Grasslands National Park Establishment The Larson ranch was purchased in 1987 All cattle were removed and prairie allowed to rest With no grazing, a heavy layer of thatch built up, with a resulting change in diversity of all species. Upland grass is the habitat most impacted by the removal of large herbivores. It is the habitat type where impacts from the return of bison will be most obvious. Bison impact the ecosystem in three principle ways; 1. Disturbance 2. Direct Relationships 3. Indirect Relationships Ecological Relationships Winter Pugging Disturbance Trails Urine Patch Grazing Wallows Manure Ecological Relationships Direct Relationships External Carcasses Parasites Internal Predation Parasites Nitrogen deposition Increased plant growth Ecological Relationships Indirect Relationships White-tailed deer White-tailed Jackrabbit Nuttall’s Cottontail Black-Tailed Prairie Dogs Facilitative Grazing Pronghorn Mule Deer Ecological Relationships 3rd Order Relationships Diverse niches for insects 77 grasshopper species in GNP Shed hair Nesting material for birds Diverse niches for microtines Predators & Scavengers There are 26 species of birds that are “endemic grassland birds”. Nine of these require habitat types that cannot be found in a homogenous landscape. These 9 species are known as “obligate grassland birds”. The mixed grass prairie of GNP has 35 mammal species, but of these, less than a dozen are endemic to the mixed grass prairie. Benefits of Bison Grazing Increases heterogeneity of upland grass community Changes in vegetation create opportunities for other species A study by A.T. Finnamore, showed that there were 65 species of beetles in GNP. The ungrazed prairie had 35 species while the grazed sites had 22 species of beetles. The Return of Bison Enhances Habitat for Wildlife Populations That Are Endemic To The Mixed Grass Prairie Masked Shrew Western Jumping Mouse Northern Pocket Gopher Grasshopper Mouse White-tailed Jackrabbit Swift Fox Black-tailed Prairie Dog Black-footed Ferret Olive-backed Mouse Canadian Toad Great Plains Toad Spade-footed Toad Greater Short-horned Lizard Plains Hog-nosed Snake Prairie Rattlesnake Blotched Tiger Salamander Yellow-bellied Racer Plains Garter Snake Mountain Plover Baird’s Sparrow Lark Bunting McCowan’s Longspur Sprague’s Pipit Long-billed Curlew Ferruginous Hawk Chestnut-collared Longspur Loggerhead Shrike How do bison create, or enhance the niches occupied by these prairie species? Grazing Lawns Grazing lawns are first established during the winter months Bison select for the highest volume forage, and through cratering, create a short grass sward within the tall grasses. When spring arrives, these clipped patches green-up first. Ungrazed Grazed Ungrazed Grazed FACILITATION For other species Average plains bison wallow density in EINP = 4.5 wallows / ha Average ancient wallow density in GNP = > 30 wallows / ha > 12 species of mammals, birds, herptiles observed using wallows Vernal wetlands created by rain-flooded wallows – ideal habitat for many species Prairie Dogs, Bison and the species that depend upon them Bison graze the edges of prairie dog towns, keeping the grass short. Short grass allows the dog town to expand in size Prairie dogs are a Keystone Species; they provide habitat essential to the survival of other species, such as; Photo by Wendy Michael Photo by R. Postma Burrowing owls and bison dung The dung serves several purposes; It masks the smell of the owls, and in doing so protects them from predation. This is known as “Olfactory camouflage”. The presence of dung at a prairie dog burrow, serves to attract potential mates. The dung regulates the humidity inside the burrow, releasing moisture in hot periods, and absorbing it during wet periods. Dung in the burrow reduces the level of carbon dioxide. In one survey of 71 owl pellets, they found the remains of 2484 beetles, 7 sagebrush voles, 3 deer mice and 11 unknown mircrotines; 19 grasshoppers, 2 bees, 1 brown thrasher and 1 horned lark (Holroyd and Trefry 2000). It attracts dung beetles and other insects, which the owls prey upon. A higher density of beetles, at the tunnel entrance, allows chicks the ability to hunt near safety. Burrows with dung have over 75% more insect biomass than those without dung. Dung in and around the burrow informs other owls that this tunnel is occupied – go somewhere else. There are 3 behavioral types of dung beetles; 1. The “Rollers” a male – female pair who collect a wad of dung, then roll it to a place where they bury it. 2. The “Tunnelers” take a chunk and bury it in a tunnel they make close to the manure pat. These two are known as “nesters” because they prepare a home for their young, then bring food to them. 3. The third group are known as the “Dwellers” – they live within the manure patty and raise their young right there (Thomas 2009). Bison Patties An essential part of a healthy prairie Bison defecate, on average, about 12 times per day A herd of 150 bison creates about 1800 patties per day Each bison patty covers about 0.422 square meters Each patty weighs an average of about 1 kilogram Each year about 28 hectares of prairie is covered by bison dung. Each year about 657,000 kilograms of bison manure is deposited on the prairie With the removal of bison from the landscape, the relationships between bison, owls and beetles halted, and dung beetle populations must have crashed. Under ideal conditions, dung beetles can bury all of the dung from a patty in less than one week. Some historical accounts from the 1800’s indicate that a summer bison patty would disappear within three days. Winter patties supplied the bulk of the fuel used by First Nations and early European explorers. As the bison vanished from the prairie, so to did a host of species that depended upon them, and the materials they left behind. Mountain Plovers are an obligate grassland bird They require heavily grazed, short grass to hunt for insects and to build their nests Sharp-tailed Grouse Prairie dog Predators Johane Janelle Many other species use dog towns The Northern Pocket Gopher – An Ecological Engineer The Northern Pocket Gopher Grazed prairie= increased forb diversity = increased Northern Pocket Gopher density = - new tunnels for species such as salamanders, snakes toads, microtines - more prey for avian and mammalian predators - greater turn-over of soil nutrients - improved aeration of soil - improved subsurface movement of water - seed bed for native plant establishment - increased density and diversity of insects - improved grazing for a variety of prairie herbivores Ferruginous hawks are more specialized to hunt pocket gophers than other hawks, due to their habit of stalking their prey, crouching or waiting at burrow entrances, or where pocket gophers are actively moving soil to the surface. An aspen parkland example of inter-species dependence on bison Bison often deposit their patties near the forest / meadow edge Ant queens prefer bison patties when establishing new colonies Northern flickers often create nest cavities close to the forest edge. A large part of the diet of northern flickers are ground insects. In particular, they search for and consume a large quantity of ants, along the forest edge. The Northern Flying Squirrel (Glaucomy sabrinus) Flying squirrels use abandoned northern flicker cavities These squirrels use; “refugia nests” – for shelter or resting “Natal nests” for rearing their young “Toilet nests” in abandoned woodpecker holes. These holes are used exclusively for defecation The dung beetle, Aphodius badiceps only lives on flying squirrel dung Aphodius badiceps Questions ?