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At least 613 records · Page 34Linked to original sources
USGS2001

Experimental repatriation of boreal toad (Bufo boreas) eggs, metamorphs, and adults in Rocky Mountain National Park

The boreal toad ( Bufo boreas ) is an endangered species in Colorado and is considered a candidate species for federal listing by the United States Fish and Wildlife Service. Boreal toads are absent from many areas of suitable habitat in the Southern Rocky Mountains of Colorado presumably due to a combination of causes. We moved boreal toads from existing populations and from captive rearing facilities to habitat which was historically, but is not currently, occupied by toads to experimentally examine methods of repatriation for this species. Repatriation is defined as the release of individuals into areas currently of historically occupied by that species (Dodd and Seigel, 1991). This effort was in response to one of the criteria for delisting the boreal toad in Colorado stated in the conservation plan and agreement for the management and recovery of the Southern Rocky Mountain population of the boreal toad (Loeffler, 1998:16); "...there must be at least 2 viable breeding populations of boreal toads in each of at least 9 of 11 mountain ranges of its historic distribution." Without moving eggs from established wild populations, or from captivity to historical localities, it is doubtful whether the recovery team will attain this ambitions goal.

Colorado↗
USGS2001

Implications of seed size for seedling survival in Carnegiea gigantea and Ferocactus wislizeni (Cactaceae)

Larger seeds have been shown to convey benefits for seedling survival but the mechanisms of this process are not well understood. In this study, seed size and seedling survival were compared for 2 sympatric cactus species, Carnegiea gigantea (Engelm.) Britt. & Rose and Ferocactus wislizeni (Engelm.) Britt. & Rose, in laboratory and field experiments in the northern Sonoran Desert. Both species have small seeds, but Ferocactus seeds are nearly twice as long and 3 times as heavy as those of Carnegiea . The difference in size is perpetuated after germination: new Ferocactus seedlings have 4 times the estimated volume of new Carnegiea seedlings. In an outdoor experiment, annual survivorship of both species was low but was 6 times higher for Ferocactus (6 seedlings, 8.1%) than Carnegiea (1 seedling, 1.4%). The pattern of seedling mortality in relation to temperature and rain suggests that, after the initial flush of seed and seedling predation, drought and heat took a greater toll on Carnegiea than Ferocactus seedlings, probably because the larger seedling volume of Ferocactus conferred greater drought tolerance. In addition, F. wislizeni could become established without benefit of nurse plants whereas C. gigantea could not; this might reflect differential tolerance to high soil temperatures.

Arizona↗
USGS2001

Influence of changes in sagebrush on Gunnison sage grouse in Southwestern Colorado

The decline in abundance of the newly recognized Gunnison sage grouse ( Centrocercus minimus ) in southwestern Colorado is thought to be linked to loss and fragmentation of its habitat, sagebrush ( Artemisia ) vegetation. We documented changes in sagebrush-dominated areas between the 1950s and 1990s by comparing low level aerial photographs taken in these time periods. We documented a loss of 20% or 155,673 ha of sagebrush-dominated areas in southwestern Colorado between 1958 and 1993. The amount of sagebrush-dominated area was much higher and loss rates were much lower in the Gunnison Basin. We also found that 37% of plots sampled underwent substantial fragmentation of sagebrush vegetation. If current trends of habitat loss and fragmentation continue, Gunnison sage grouse (and perhaps other sagebrush-steppe obligates) may become extinct. Protecting the remaining habitat from further loss and fragmentation is paramount to the survival of this species.

Colorado↗
USGS2000

Abiotic factors affecting summer distribution and movement of male paddlefish, Polyodon spathula, in a prairie reservoir

Six male paddlefish, Polyodon spathula , were implanted with ultrasonic temperature-sensing transmitters and tracked during June through August 1997 to quantify effects of physicochemical conditions on their distribution and movement in Keystone Reservoir, Oklahoma. Paddlefish moved about twice as much during night than day. Movement rate of paddlefish was related to reservoir water level, inflow, and discharge from the reservoir at night; however, none of these variables was significant during the day. Location in the reservoir (distance from the dam) was negatively related to water level and positively related to inflow during day and night periods. Location in the reservoir was negatively related to discharge during the day. Paddlefish avoided the highest available water temperatures, but did not always avoid low dissolved oxygen concentrations. Paddlefish avoided the Cimarron River arm of the reservoir in summer, possibly because of high salinity. Our study demonstrates that distribution of paddlefish during summer and movement in Keystone Reservoir was influenced by physicochemical and hydrologic conditions in the system. However, biotic factors (e.g., food availability) not measured in this study may have been influenced by abiotic conditions in the reservoir.

Oklahoma↗
USGS2000

The swift fox in rangeland and cropland in western Kansas: Relative abundance, mortality, and body size

We assessed suitability of cropland and shortgrass rangeland for swift foxes ( Vulpes velox ) in western Kansas. Relative abundance and survival were similar for foxes in rangeland and cropland. Mortality resulting from non-traumatic causes, coyotes, and motor vehicles differed significantly between habitats. Predation by coyotes, motor vehicles, and non-traumatic causes were responsible for 45%, 36%, and 18%, respectively, of 11 deaths in rangeland and 20%, 10%, and 70%, respectively, of 10 deaths in cropland. Swift foxes in rangeland were larger and in better condition than those in cropland. Males were larger than females based on mass, standardized mass (mass/body length), body length, hindfoot length, and ear length.

Kansas↗
USGS2002

Taxonomic assessment of the black bear (Ursus americanus) in the eastern United States

The subspecific status of the Louisiana black bear ( Ursus americanus luteolus ) and Florida black bear ( U. a. floridanus ) were assessed using morphologic features to determine their distinctness in relation to one another and to the black bear ( U. a. americanus ). Forty-four dimensions were recorded from skulls of 125 male and 127 female adult (4.5 years or older) bears. Results showed skulls of U. a. luteolus, U. a. floridanus , and U. a. americanus to be similar in morphology. However, features of U. a. luteolus , and U. a. floridanus tended, in general, to be larger and shaped differently than those of U. a. americanus . Differences between measurements of U. a. luteolus and U. a. floridanus were less apparent than those between either of these taxa and U. a. americanus . For U. a. luteolus and U. a. floridanus , means of most characters differed only slightly, and ranges of all measurements overlapped to some degree. Yet, small numbers of characters that reflected molar tooth measurements or features relating to dentition, height of frontal region, and skull length and width appeared to correctly classify these taxa in most cases. Results were interpreted to support the subspecific recognition of U. a. luteolus, U. a. floridanus , and U. a. americanus .

Southwestern Naturalist↗
USGS2000

Predation on Corynorhinus townsendii by Rattus rattus

Corynorhinus townsendii (Townsend's big- eared bat) is a rare and declining species. Ex- tensive surveys for the coastal subspecies, C. t. townsendii, in California indicate that only 50% of historic maternity colonies are occu- pied currently (Pierson and Rainey, 1996). Three of the largest maternity colonies occur in Marin Co. Two of these have been moni- tored with evening exit counts on a regular basis since their discovery (1987-Randall House; 1990-Jerrys) through 1996. From 1987 through 1993, the Randall House colony slowly increased from 123 to 215 bats as the colony was afforded greater protection from disturbance once the bats were discovered. Since 1990, both colonies have been com- posed of ca. 200 adult bats in the spring, and ca. 300 adults and young through the summer and early fall.

Southwestern Naturalist↗
USGS2000

Status of translocated sea otters at San Nicolas Island, California

In the 1970s about 1,650 southern sea otters (Enhydra lutris nereis) were restricted to the central California coast (Riedman and Estes, 1990), and a high volume of oil was being shipped through the region. Because of the vulnerability of sea otters to contamination from oil (Costa and Kooyman, 1982; Williams and Davis, 1995) that would likely spread wide- ly along the shore after a large spill (Van- Blaricom and Jameson, 1982), the subspecies was listed as threatened in 1977 under the United States Endangered Species Act.

Southwestern Naturalist↗
USGS2002

Geographic variation in the black bear (Ursus americanus) in the eastern United States and Canada

The pattern of geographic variation in morphologic characters of the black bear ( Ursus americanus ) was assessed at 13 sites in the eastern United States and Canada. Thirty measurements from 206 males and 207 females were recorded to the nearest 0.01 mm using digital calipers and subjected to principal components analysis. A matrix of correlations among skull characters was computed, and the first 3 principal components were extracted. These accounted for 90.5% of the variation in the character set for males and 87.1% for females. Three-dimensional projection of localities onto principal components showed that, for males and females, largest individuals occurred in the more southern localities (e.g., males--Louisiana-Mississippi, eastern Texas; females--Louisiana-eastern Texas) and the smallest animals occurred in the northernmost locality (Quebec). Generally, bears were similar morphologically to those in nearby geographic areas. For males, correlations between morphologic variation and environmental factors indicated a significant relationship between size variation and mean January temperature, mean July temperature, mean annual precipitation, latitude, and actual evapotranspiration; for females, a significant relationship was observed between morphologic variation and mean annual temperature, mean January temperature, mean July temperature, latitude, and actual evapotranspiration. There was no significant correlation for either sex between environmental factors and projections onto components II and III.

Southwestern Naturalist↗
USGS1999

Mortality of unionid bivalves (Mollusca) associated with Dreissenid mussels (Dreissena polymorpha and D. bugensis) in Presque Isle Bay, Lake Erie

Two exotic species of dreissenid mussels (Dreissena polymorpha and D. bugensis) began to colonize bottom substrates in Presque Isle Bay, Lake Erie in 1990. By 1991, all native unionid (Unionidae) shells were infested by dreissenids. In 1990 and 1991, about 500 individual unionids of 15 species were collected: in 1992, 246 individuals of 12 species were collected; in 1993, 64 individuals of 6 species; in 1994, three individuals of three species; and in 1995, no unionids were found. In general, infestation indices of unionids were relatively low in 1990 and 1991, increased in 1992, and decreased in 1993. Mortality of unionids associated with infestation in the bay occurred in a shorter period of time (ca. two to three years) than has been documented in other water bodies. Observations in an area of Presque Isle not included in the present study, indicate that a small remnant population of unionids exists in the presence of heavily-colonized substrates by dreissenid mussels. Since other shallow-water areas of Lake Erie support infestation-free unionids in the presence of dreissenid mussels, it is hoped that some unionids will survive in Presque Isle Bay of Lake Erie.

Northeastern Naturalist↗
USGS2011

Bats of Mesa Verde National Park, Colorado: Composition, reproduction, and roosting habits

We determined the bat fauna at Mesa Verde National Park (Mesa Verde) in 2006 and 2007, characterized bat elevational distribution and reproduction, and investigated roosting habits of selected species. We captured 1996 bats of 15 species in mist nets set over water during 120 nights of sampling and recorded echolocation calls of an additional species. The bat fauna at Mesa Verde included every species of bat known west of the Great Plains in Colorado, except the little brown bat ( Myotis lucifugus ). Some species showed skewed sex ratios, primarily due to a preponderance of males. Thirteen species of bats reproduced at Mesa Verde. Major differences in spring precipitation between the 2 years of our study were associated with differences in reproductive rates and, in some species, with numbers of juveniles captured. Reduced reproductive effort during spring drought will have a greater impact on bat populations with the forecasted increase in aridity in much of western North America by models of global climate change. We radiotracked 46 bats of 5 species to roosts and describe the first-known maternity colonies of spotted bats ( Euderma maculatum ) in Colorado. All 5 species that we tracked to diurnal roosts relied almost exclusively on rock crevices rather than trees or snags, despite the presence of mature forests at Mesa Verde and the use of trees for roosts in similar forests elsewhere by some of these species. Comparisons with past bat surveys at Mesa Verde and in surrounding areas suggest no dramatic evidence for effects of recent stand-replacing fires on the composition of the bat community.

Colorado↗
USGS2014

Evidence of repeated wildfires prior to human occupation on San Nicolas Island, California

Understanding how early humans on the California Channel Islands might have changed local fire regimes requires a baseline knowledge of the frequency of natural wildfires on the islands prior to human occupation. A sedimentary sequence that was recently discovered in a small canyon on San Nicolas Island contains evidence of at least 24 burn events that date to between ∼37 and 25 ka (thousands of calibrated 14 C years before present), well before humans entered North America. The evidence includes abundant macroscopic charcoal, blackened sediments, and discrete packages of oxidized, reddish-brown sediments that are similar in appearance to sedimentary features called “fire areas” on Santa Rosa Island and elsewhere. Massive fine-grained sediments that contain the burn evidence are interpreted as sheetwash deposits and are interbedded with coarse-grained, clast-supported alluvial sediments and matrix-supported sands, pebbles, and cobbles that represent localized debris flows. These sedimentary sequences suggest that the catchment area above our study site underwent multiple cycles of relative quiescence that were interrupted by fire and followed by slope instability and mass wasting events. Our 14 C-based chronology dates these cycles to well before the arrival of humans on the Channel Islands and shows that natural wildfires occurred here, at a minimum, every 300–500 years prior to human occupation.

California↗
USGS2014

Interpreting the paleozoogeography and sea level history of thermally anomalous marine terrace faunas: A case study from the the last interglacial complex of San Clemente Island, California

Marine invertebrate faunas with mixtures of extralimital southern and extralimital northern faunal elements, called thermally anomalous faunas, have been recognized for more than a century in the Quaternary marine terrace record of the Pacific Coast of North America. Although many mechanisms have been proposed to explain this phenomenon, no single explanation seems to be applicable to all localities where thermally anomalous faunas have been observed. Here, we describe one such thermally anomalous fossil fauna that was studied on the second emergent marine terrace at Eel Point on San Clemente Island. The Eel Point terrace complex is a composite feature, consisting of a narrow upper bench (terrace 2a) and a broader lower bench (terrace 2b). Terrace 2b, previously dated from ∼128 ka to ∼114 ka, was thought to date solely to marine isotope stage (MIS) 5.5, representing the peak of the last interglacial period. Nevertheless, the fauna contains an extralimital northern species and several northward-ranging species, as well as an extralimital southern species and several southward-ranging species. Similar faunas with thermally anomalous elements have also been reported from San Nicolas Island, Point Loma (San Diego County), and Cayucos (San Luis Obispo County), California. U-series dating of corals at those localities shows that the thermally anomalous faunas may be the result of mixing of fossils from both the ∼100-ka (cool-water) and the ∼120-ka (warm-water) sea level high stands. Submergence, erosion, and fossil mixing of the ∼120-ka terraces by the ∼100-ka high-sea stand may have been possible due to glacial isostatic adjustment (GIA) effects on North America, which could have resulted in a higher-than-present local sea level stand at ∼100 ka. The terrace elevation spacing on San Clemente Island is very similar to that on San Nicolas Island, and we hypothesize that a similar mixing took place on San Clemente Island. Existing fossil records from older terraces elsewhere in California also show thermally anomalous elements, indicating that the scenario presented here for the last interglacial complex may have applicability to much of the marine Quaternary record for the Pacific Coast.

California↗
USGS2014

Changes in vegetation and biological soil crust communities on sand dunes stabilizing after a century of grazing on San Miguel Island, Channel Island National Park, California

San Miguel Island is the westernmost of the California Channel Islands and one of the windiest areas on the west coast of North America. The majority of the island is covered by coastal sand dunes, which were stripped of vegetation and subsequently mobilized due to droughts and sheep ranching during the late 19th century and early 20th century. Since the removal of grazing animals, vegetation and biological soil crusts have once again stabilized many of the island's dunes. In this study, historical aerial photographs and field surveys were used to develop a chronosequence of the pattern of change in vegetation communities and biological soil crust levels of development (LOD) along a gradient of dune stabilization. Historical aerial photographs from 1929, 1954, 1977, and 2009 were georeferenced and used to delineate changes in vegetation canopy cover and active (unvegetated) dune extent among 5 historical periods (pre-1929, 1929–1954, 1954–1977, 1977–2009, and 2009–2011). During fieldwork, vegetation and biological soil crust communities were mapped along transects distributed throughout San Miguel Island's central dune field on land forms that had stabilized during the 5 time periods of interest. Analyses in a geographic information system (GIS) quantified the pattern of changes that vegetation and biological soil crust communities have exhibited on the San Miguel Island dunes over the past 80 years. Results revealed that a continuing increase in total vegetation cover and a complex pattern of change in vegetation communities have taken place on the San Miguel Island dunes since the removal of grazing animals. The highly specialized native vascular vegetation (sea rocket, dunedelion, beach-bur, and locoweed) are the pioneer stabilizers of the dunes. This pioneer community is replaced in later stages by communities that are dominated by native shrubs (coastal goldenbush, silver lupine, coyote-brush, and giant coreopsis), with apparently overlapping or cyclical succession pathways. Many of the dunes that have been stabilized the longest (since before 1929) are dominated by exotic grasses. Stands of biological soil crusts (cyanobacteria) are found only on dunes where vascular vegetation is already present. Biological soil crusts are not found on dunes exhibiting a closed vascular plant canopy, which may indicate that the role of soil crusts in dune stabilization on the island is transitory. Particle-size analyses of soil samples from the study area reveal that higher biological soil crust LOD is positively correlated with increasing fine grain content. The findings indicate that changes in vegetation communities may be the most rapid at earlier and later stages of dune stabilization and that regular monitoring of dunes may help to identify the interactions between vegetation and soil crusts, as well as the potential transitions between native and exotic plant communities.

California↗