Regional Trends of Biological Resources — Grasslands
Prairie Insects and Animals
Invertebrates
A wide diversity of terrestrial insects exists on grasslands. For example, in two years of sampling on a 1,400-hectare area of tall-grass prairie in northeastern Oklahoma, 16 orders, 131 families, and more than 3,000 insect species were noted (Risser et al. 1981). More than 1,600 insect species are known from a short-grass prairie in Colorado (Kumar et al. 1976), and this list is incomplete. Inventories are rarely representative; some taxa are present in hot, dry years, others in wet years, and no single sampling method is adequate.
Other terrestrial invertebrates are also abundant. Smolik (1974) found 2 to 6 million soil nematodes per square meter to the depth of 60 centimeters in South Dakota mixed-grass prairie soil. Terrestrial invertebrates are important to the prairie community: they feed on plant tissue, pollen, nectar, and seeds; regulate numbers of other insects and plants; and recycle energy and nutrients (Risser et al. 1981). Underground, earthworms accelerate the decomposition and mineralization of soil organic matter and affect soil structure through burrowing and casting. The soil formation activities of native and nonindigenous earthworms vary considerably; the latter have a negative effect on soil turnover, at least in tall-grass prairie soils (James 1991). Nevertheless, in short-grass prairie soils, 90% of invertebrate energy cycling occurs belowground, less in tall-grass and mixed-grass prairies.
Preliminary lists of Lepidoptera (butterflies and moths) are available for Montana, North Dakota, Wyoming, Colorado, and New Mexico and are in progress in Texas (Powell 1995). Species numbers in a few selected Lepidoptera families vary from 181 in North Dakota to 520 in Texas, and numbers in Nebraska (254) and Oklahoma (228) rank high (Opler 1995). Several prairie butterflies—the Dakota skipper (Fig. 11), regal fritillary, tawny crescent, and maculated manfreda skipper—and two moths—the rattlesnake-master borer moth and phlox moth—are federal species of concern. An additional six insects—the persius duskywing, poweshiek skipperling, ottoe skipper, byssus skipper, silver-bordered fritillary, and Ozark emerald—are considered species of concern by The Nature Conservancy, and another six are endemic to the prairie (Royer 1992).
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| Fig. 11. The Dakota skipper, a rare prairie butterfly. | Fig. 12. The prairie mole cricket, an unusual
and rare prairie species. |
Adequate inventory and distribution information is unavailable for predicting status and trends for most invertebrates. Ranges of a number of grasshopper species seem focused specifically on short-grass, a combination of shortgrass and mixed-grass, and tall-grass prairies (Otte 1981). Ranges of many other grasshopper species center on grasslands but extend into adjacent forested and scrub habitats. The prairie mole cricket, a strikingly large insect (Fig. 12), and the superb spharagemon grasshopper are federal species of concern. Additional species of concern are the Ozark snaketail dragonfly, a true bug, a fly, six amphipods, nine cave spiders, two cave beetles, a cave amphipod, a cave shrimp, and a number of beetles, including the widely distributed sixbanded longhorn beetle.
Leafhoppers are among the most diverse and well-studied terrestrial insects on the grasslands (Whitcomb et al. 1994). The ranges of some species span considerable distances across the prairie, whereas other species are more restricted in distribution. Most are highly specialized, often endemic, and good indicators of grassland condition. On the short-grass prairie, 20 leafhopper species may colonize a single host, such as blue grama, which indicates a long record of coevolution. There is, however, a rather spectacular partitioning of resources: no more than 10 leafhopper species occur on the blue grama host at a given site. The "invisible wall" partitioning resources is climate, with each taxon showing singular limits to humidity, cold, and heat. Understanding any single assemblage of leafhoppers (and perhaps most other insects) requires knowledge of the communities in which they and their relatives reside and of the past structure and conditions of these communities.
Around 1889 abundant mussel populations of the Great Plains were recognized as an economic resource, particularly as the materials for button production. One example of the abundancy of this resource was a single mussel bed that covered an area of 2.4 kilometers by 288 meters in the Mississippi River near New Boston, Illinois (Carlander et al. 1986). The mussel bed was depleted by 1898, and large-scale propagation to restore the resource failed. No federal regulations restrict the harvest of mussels unless they are federally listed as endangered or threatened. Many states (Illinois, Iowa, Kansas, Minnesota, Missouri, Montana, Nebraska, North Dakota, Oklahoma, South Dakota, and Texas), however, have instituted harvest regulations.
Along with siltation and contamination, dams, with their altered flow regimes and accompanying reservoirs, are believed to have caused declines of mussels and other aquatic organisms. Four pearlymussels—the elktoe, spectacle-case, snuffbox, and scaleshell—are federal species of concern. The American Fisheries Society has identified 213 of 297 (71.7%) mussels found in the United States and Canada as threatened, endangered, or of special concern (Williams et al. 1993). Many of these species are endemic; for example, all three endangered and six threatened species, and about one-third (two of seven) of the mussels of special concern recently added by the American Fisheries Society list for Texas are species with restricted ranges. Several nonindigenous species, particularly the Asian clam and the zebra mussel, pose potential threats to the native mussel fauna on the Great Plains.
Across the grasslands, a number of snails, including both land and aquatic species, are federal species of concern: 10 are found in Texas, at least 8 in the upper Midwest (Illinois, Iowa, Minnesota), 5 in the central plains (Missouri and Oklahoma), and 3 in the West (Wyoming and the Dakotas). One snail, the Iowa Pleistocene snail, is listed as endangered. The same factors negatively affecting other species—habitat loss, drainage, water pollution, stream desiccation accompanying the lowering of water tables for agriculture and municipalities, and competition with and predation by introduced species—are thought to threaten freshwater native snails, crayfishes, and other aquatic invertebrates.
Sidebar: Tall-grass Prairie Butterflies and Birds
Fishes
In general, drainages east of the Rocky Mountains have a richer fish fauna than those to the west (Brooks and McLennan 1993). The western Mississippi basin occupies much of the grasslands, including the basins of the Missouri, Arkansas, and Red rivers. Geological and presettlement history and current information depict changing fish distributions and abundances across this vast region (Cross et al. 1986). Geological information provides insights into how glacial advances fragmented fish populations into smaller, subregional distributions and transported species to distant and distinct drainages. Government surveys seeking routes for human immigrants to the Southwest and Pacific coast provide important historical information. Recent concern for prairie (and other) fishes has encouraged the continuation of many ongoing surveys.
The western Mississippi basin contains at least 266 species of fishes from the United States, which is slightly more than one-third of the fish species in the United States and Canada (Cross et al. 1986). Thirty-one species were introduced to North America or now exist beyond their past ranges. Two species are diadromous (and thus reside at some time in their life cycles in marine waters), and 34 are endemic to one or more drainages in the vast basin.
Cross et al. (1986) described two physiographic regions that encompass the habitat of most fishes on the grasslands: the Great Plains, from eastern Montana south to western Texas, and the Central Lowlands, from North Dakota south to eastern Texas. Thirteen fishes are endemic to the two physiographic regions: 2 to the Central Lowlands, and 11 to the Great Plains. The Great Plains province has 77 fish species (86 including introduced species), that, with the exception of 5 species, are a subset of the Central Lowlands fish assemblage. The Central Lowlands has 139 native species with over 24 species introduced into the region, most intentionally as sport fish or forage for sport fish. Eleven grassland fishes are large-river species that have centers of origin in one or two adjacent physiographic regions but are shared among the Central Lowlands and Great Plains physiographic regions. Overall, the species inhabiting small streams and rivers outnumber those in large rivers about ten to one.
Decades of intensive agricultural development and modified flow regimes are held responsible for declines in the fishes endemic to the small streams and turbid rivers of the Great Plains (Cross and Moss 1987). Nevertheless, the first declines noted in regional endemic fishes were in those species in small, clear, spring-fed streams, particularly streams that were home to the Topeka shiner and Arkansas darter. Although agriculture and altered flow regimes may explain declines, patterns in decline differ among species, with colonization of suitable habitat of restricted stream and river reaches exceptionally rare. Several fish species of shifting-sand bottom streams in the Great Plains are considered federal species of concern, including the sicklefin chub, the sturgeon chub, the Arkansas River speckled chub (a subspecies of the speckled chub), and the Arkansas River shiner. The Topeka shiner, the plains topminnow, and the Arkansas darter, which occur in clear streams fed by springs and seeps, and the lake sturgeon are also candidates for species of concern (Echelle et al. 1995).
Overall, 9 of 10 species and subspecies of broad, shallow, and sandy-bottom streams seem to be in serious decline. Two additional species, the plains minnow and flathead chub, seem to be drastically declining (V. M. Tabor, U.S. Fish and Wildlife Service, Manhattan, Kansas, unpublished manuscript) and are candidates for federal listing. Marked increases are known in some fishes in the natural prairie community. Clear-water fishes, particularly sunfish, perch, and introduced species such as carps, replace species native to turbid conditions and tend to be increasing. Within the Missouri River drainage, the upper Missouri and Yellowstone rivers provide the best remaining habitat for the large-river natives. About 20% of the native large-river fish species are declining.
Reptiles and Amphibians
Most grassland reptiles and amphibians are widely distributed. Half of the species (6 of 12) found in Alberta also occur several hundred kilometers to the south in northern Mexico (N. J. Scott, Jr., U.S. Geological Survey, San Simeon, California, unpublished manuscript). More than 40 reptiles and amphibians are characteristic of prairie habitat (Table 2). The number of local species is influenced by the presence of water (which amphibians need to complete their life cycle), complex habitats, and sandy or loose soils needed for concealment by some species.
| Table 2. Reptiles and amphibians of the North American prairie by habitat association (N.J. Scott, Jr., U.S. Geological Survey, San Simeon, California, unpublished manuscript). |
| Habitat | Species |
| Grassland | Ornate box turtle |
| Great Plains skink | |
| Prairie skink | |
| Western slender glass lizard | |
| Racer | |
| Western rattlesnake | |
| Night snake | |
| Prairie kingsnake | |
| Texas slender blind snake | |
| Massasauga (rattlesnake) | |
| Lined snake | |
| Temporary water | Wyoming toad |
| Great Plains narrow-mouthed red toad | |
| Spotted chorus frog | |
| Plains leopard frog | |
| Yellow mud turtle | |
| Plains garter snake | |
| Common garter snake | |
| Checkered garter snake | |
| Bare ground | Lesser earless lizard |
| Texas horned lizard | |
| Coachwhip | |
| Six-lined racerunner | |
| Bare ground and water | Great Plains toad |
| Green toad | |
| Plains spadefoot toad | |
| Black-spotted newt | |
| Sandy soils | Glossy snake |
| Wester hog-nosed snake | |
| Sandy soils and water | Woodhouse's toad |
| Trees or rocks | Reticulate collared lizard |
| Spot-tailed earless lizard | |
| Collared lizard | |
| Eastern fence lizard | |
| Great Plains rat snake | |
| Plains black-headed snake | |
| Milk snake | |
| Rocky canyons and water | Red-spotted toad |
| Spiny softshell | |
| Plain-bellied water snake | |
| Diamondback water snake | |
| Slider |
Loss of small water areas, nonindigenous terrestrial and aquatic predators, grazing, exotic plantings, and prairie dog control are believed to contribute to reptile and amphibian declines. Most reptiles and amphibians rely on temporary ponds rather than streams or rivers. Permanent water provides habitat for the especially predatory bullfrog, catfish, and sunfish. Woody vegetation near permanent water favors mammalian predators such as the Virginia opossum, raccoon, and skunk (Schwalbe and Rosen 1989). Moderate grazing increases habitat structure and patchiness important to reptile and amphibian abundance, but overgrazing reduces needed habitats, as does planting of nonindigenous species such as buffelgrass (Scott 1997). Prairie dog burrows provide winter retreats and summer nesting sites for reptiles and amphibians, thus their destruction may cause local reptile and amphibian declines.
Most grassland reptiles and amphibians seem widespread and secure. Several, however, particularly those with very restricted ranges, are thought to be declining. Habitat for the reticulate collared lizard and spot-tailed earless lizard, species restricted to south Texas, is threatened by exotic buffel grass (Scott 1997). Agriculture in the Lower Rio Grande valley in Texas has reduced the number of temporary ponds, which are needed by the black-spotted newt. Pesticides may negatively affect the Wyoming toad, an endangered species, but conclusive evidence is lacking. Across its range, the yellow mud turtle, a federal species of concern, is restricted to a few widely distributed ponds (Dodd 1983).
Sidebar: Amphibians of the Northern Grassland
Birds
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| Fig. 13. A mountain plover,
an endemic bird species of the short-grass prairie that evolved with intensive grazing pressure from bison, pronghorn, and prairie dogs in Colorado. |
Of the 435 bird species that breed in the United States, 330 breed on the Great Plains (Knopf and Samson 1995). Nevertheless, few North American bird species are believed to have evolved within the Great Plains. Mengel (1970) suggested that only 12 bird species are endemic to the grasslands. An additional 25 species are believed to have evolved on the grassland, though they range widely into adjoining vegetation provinces. Five of these 25 species are specifically associates of sagebrush landscapes of the Great Basin (Knopf and Samson 1995).
As a group, the endemic grassland bird species have shown more consistent, widespread, and steeper declines (Table 3) than any other guild of North American bird species (Knopf 1992, 1996). Individually, populations of the mountain plover (Figs. 13 and 14a), Cassin's sparrow (Fig. 14b), and clay-colored sparrow (Fig. 14c) are declining throughout their breeding ranges. Breeding habitats are disappearing locally for the Franklin's gull (Fig. 14d), the dickcissel (Fig. l4e), the Henslow's sparrow (Fig. 14f), the grasshopper sparrow (Fig. 14g), and the western meadowlark (Fig. 14h). Breeding ranges are shifting for the ferruginous hawk (Fig. 14i), the Mississippi kite (Fig. 14j), the upland sandpiper (Fig. l4k), the homed lark, the vesper sparrow, the savannah sparrow, and the Henslow's sparrow. Populations of the wetland-associated marbled godwit and Wilson's phalarope seem stable, and populations of the upland sandpiper and McCown's longspur (Fig. 14l) have increased markedly.
| Table 3. Birds of the North American grassland with annual rates of change in populations. U.S. Geological Survey (Breeding Bird Survey data 1966-1993; Knopf 1986). |
| Species | Rate of change |
| Endemic species | |
| Ferruginous hawk | +1.6% |
| Mountain plover | -3.7% |
| Long-billed curlew | -1.7% |
| Marbled godwit | +0.8% |
| Wilson's phalarope | -0.1% |
| Franklin's gull | -0.9% |
| Sprague's pipit | -3.6% |
| Lark bunting | -2.1% |
| Baird's sparrow | -1.8% |
| Cassin's sparrow | -2.5% |
| McCown's longspur | +7.3% |
| Chestnut-collared longspur | +0.4% |
| Secondary species | |
| Mississippi kite | +0.9% |
| Swainson's hawk | +1.4% |
| Northern harrier | -0.4% |
| Prairie falcon | +0.3% |
| Greater prairie-chicken | -6.9% |
| Lesser prairie-chicken | N/Aa |
| Sharp-tailed grouse | +1.1% |
| Upland sandpiper | +2.7% |
| Burrowing owl | -0.2% |
| Short-eared owl | -0.6% |
| Horned lark | -0.7% |
| Eastern meadowlark | -2.3% |
| Western meadowlark | -0.5% |
| Dickcissel | -1.6% |
| Savannah sparrow | -0.5% |
| Grasshopper sparrow | -4.1% |
| Henslow's sparrow | -5.0% |
| Vesper sparrow | -0.3% |
| Lark sparrow | -3.5% |
| Clay-colored sparrow | -1.2% |
| a N/A means sampling effort was inadequate. | |
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| Fig. 15. A bison herd in southwestern South Dakota. |
The prairie pothole region is a key breeding area for species such as the mallard, blue-winged teal, and northern pintail. Researchers believe that preserving native grassland and wetlands is essential for slowing declines in duck numbers, including the mallard, American widgeon, and northern pintail (Canadian Wildlife Service and U.S. Fish and Wildlife Service 1994). Predation on eggs and hatchlings by red foxes, striped skunks, raccoons, and other species substantially reduces the abundances of ducks (Ball et al. 1994).
Sidebar: Wetland Birds in the
Northern Great Plains
Sidebar: Waterfowl in the Prairie
Pothole Region
Sidebar: Duck Plague: Emergence
of a New Cause of Waterfowl Mortality
Mammals
The grasslands have a fertile history of plant- and seed-eating mammals (Hall and Kelson 1959). A rich array of large herbivores, including camels, rhinoceroses, mammoths, mastodons, and bison, evolved on the North American grasslands only to disappear during the last Ice Age (Van Valkenburgh and Janis 1993). The surviving large grassland herbivore, the plains bison, evokes a mystique not shared by any other North American mammal and which is largely derived from Native American and frontier heritages (Meagher 1978). In the past, bison (Fig. 15) numbered from about 60 to 70 million and roamed in large herds that, in the 1860's, often required horseback riders several days to successfully penetrate and cross.
As many as 5 billion prairie dogs may have been in North America before European settlement. An estimated 98% decline in prairie dog numbers has occurred since European settlement (Summers and Linder 1978). The black-tailed prairie dog may occupy less than 0.5% of its original range, the short-grass and mixed-grass prairies. As a result, a variety of species closely associated with the prairie dog are either federally listed as endangered or are being considered for listing as threatened or endangered. These include the black-footed ferret, the swift fox, and the mountain plover.
The ranges of more than 100 native mammals extend into the prairie; nearly half of these occur in the forest—grassland ecotone and others in diverse habitat types (Risser et al. 1981). Nevertheless, surveys of eastern and western species whose ranges stop short of the Great Plains support the effectiveness of the grassland as an evolutionary barrier to dispersal (Hall and Kelson 1959). Estimates of Great Plains-restricted mammals range from as few as 10 (Risser et al. 1981) to as many as 18 (Jones et al. 1985). These species include one lagomorph (the white-tailed jack rabbit), eight rodents (thirteen-lined ground squirrel, Franklin's ground squirrel, black-tailed prairie dog, plains pocket gopher, olive-backed pocket mouse, plains pocket mouse, plains harvest mouse, and prairie vole), and two carnivores (swift fox and black-footed ferret).
One recent extinction, the Audubon bighorn sheep, was a subspecies found along the upper Missouri River, including North Dakota, South Dakota, Wyoming, and Nebraska. Populations of the caribou, a species once common across northern North Dakota but which is now extirpated, are still common in Canada. Similarly, the gray wolf and elk, once common on the grasslands, and the less common mountain lion and wolverine are found elsewhere.
Sidebar: Population Trends for Prairie Pothole Carnivores
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